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Efficient bifunctional electrocatalysts towards oxygen evolution reaction (OER) and urea electrooxidation reaction (UOR) are urgently needed for hydrogen production from urea-containing wastewater electrolysis. The main challenge lies in the sluggish UOR kinetics and the stability of catalyst under practical high current density. Here, a vanadium doped heterostructure of Ni(PO 3 ) 2 /Ni 2 P with shaggy nanosheet morphology was successfully synthesized. The doping of V atoms promotes the formation of Ni(PO 3 ) 2 /Ni 2 P heterojunction in phosphating process. It is demonstrated that V-doped Ni(PO 3 ) 2 /Ni 2 P accelerates the generation of real active site V@NiOOH in OER and UOR processes, which can also be stabilized by the PO 3 - ions. The in-situ formed V@NiOOH increases the adsorption energy of urea molecule, and reduces the adsorption energy of key intermediates *COO, thus facilitating the release of CO 2 product from the catalyst surface. The energy barrier of *HNCON to *NCON is also reduced dramatically, promoting the kinetics of UOR. In addition, the shaggy nanosheets morphology provides large number of catalytic sites and transport channels, which are conducive to mass transfer under high current density. As a result, the V-Ni(PO 3 ) 2 /Ni 2 P electrode based anion-exchange membrane (AEM) electrolyzer needs only 1.61 V to drive the total urea electrolysis at an industrial grade current density of 550 mA cm -2 with an outstanding durability of 700 h. This work paves the way for designing practical efficient and stable electrocatalyst for urea contained wastewater electrolysis to produce hydrogen., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Exploring highly effective nickel-based catalytic materials for urea oxidation reaction (UOR) at high current density remains a challenging task for urea electrolysis. Herein, the vanadium-doped Ni 4 N@CuCoN 0.6 heterostructure with brush shape structure supported on copper foam (denoted as V-doped-Ni 4 N@CuCoN 0.6 /CF) is prepared to serve as a highly-performing UOR electrocatalyst at high current density (E 10/500/1000  = 1.26/1.40/1.45 V). Thanks to the construction of heterojunction, the local charge density undergoes redistribution at the V-doped-Ni 4 N@CuCoN 0.6 /CF interface between Ni 4 N and CuCoN 0.6 , thereby significantly enriching the active site and facilitating the adsorption process of urea molecules in a 1.0 M KOH + 0.5 M urea solution. Notably, V-doping exerts an additional influence by modulating the electronic structure of the catalyst, potentially optimizing the urea adsorption/CO 2 desorption process and reducing the energy barrier for the rate-determining step. Operando electrochemical impedance spectroscopy results show direct oxidation for urea molecules on the surface of V-doped-Ni 4 N@CuCoN 0.6 /CF, indicating that V-doping and heterostructure can effectively improve electron transfer. Furthermore, because the brush shape structure can be beneficial for bubble release and liquid transport on the catalyst's surface, for UOR stability, V-doped-Ni 4 N@CuCoN 0.6 /CF  can maintain at 500 mA cm -2 for 80 h. Overall, this work suggests a highly-performing UOR electrocatalyst and provides a promising strategy for developing highly-efficient catalysts for UOR applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Designing inexpensive, high-efficiency and durable bifunctional catalysts for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is an encouraging tactic to produce hydrogen with reduced energy expenditure. Herein, oxygen vacancy-rich cobalt hydroxide/aluminum oxyhydroxide heterostructure on nickel foam (denoted as Co(OH) 2 /AlOOH/NF-100) has been fabricated using one step hydrothermal process. Theoretical calculation and experimental results indicate the electrons transfer from Co(OH) 2 to highly active AlOOH results in the interfacial charge redistribution and optimization of electronic structure. Abundant oxygen vacancies in the heterostructure could improve the conductivity and simultaneously serve as the active sites for catalytic reaction. Consequently, the optimal Co(OH) 2 /AlOOH/NF-100 demonstrates excellent electrocatalytic performance for HER (62.9 mV@10 mA cm -2 ) and UOR (1.36 V@10 mA cm -2 ) due to the synergy between heterointerface and oxygen vacancies. Additionally, the in situ electrochemical impedance spectrum (EIS) for UOR suggests that the heterostructured catalyst exhibits rapid reaction kinetics, mass transfer and current response. Importantly, the urea-assisted electrolysis composed of the Co(OH) 2 /AlOOH/NF-100 manifests a low cell voltage (1.48 V @ 10 mA cm -2 ) in 1 M KOH containing 0.5 M urea. This work presents a promising avenue to the development of HER/UOR bifunctional electrocatalysts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Combining the urea oxidation reaction (UOR) with the hydrogen evolution reaction (HER) is an effective technology for energy-saving hydrogen production. Herein, a bifunctional electrocatalyst with CoNiP nanosheet coating on P-doped MoO 2 nanorods (P-MoO 2 @CoNiP) is obtained via a two-step hydrothermal followed a phosphorization process. The catalyst demonstrates exceptional alkaline HER performance due to the formation of MoO 2 and the dissolution/absorption of Mo. Meanwhile, the inclusion of Co and P in the P-MoO 2 @CoNiP catalyst facilitated the formation of NiOOH, enhancing UOR performance. Density functional theory calculations reveal that the hydrogen adsorption Gibbs free energy (ΔG H* ) of P-MoO 2 @CoNiP is closer to 0 eV than CoNiP, favoring the HER. The catalyst only needs -0.08 and 1.38 V to reach 100 mA cm -2 for catalyzing the HER and UOR, respectively. The full urea electrolysis system driven by P-MoO 2 @CoNiP requires 1.51 V to achieve 100 mA cm -2 , 120 mV lower than the traditional water electrolysis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Interface engineering and electronic modulation enable precise tuning of the electronic structure, thereby maximizing the efficacy of active sites and significantly enhancing the activity and stability of the electrocatalyst. Herein, a hybrid material composed of Ni-modified Co 9 S 8 nanoparticles ((Co, Ni) 9 S 8 ) encapsulated within an N, S co-doped carbon matrix (SNC) and anchored onto S-doped carbonized wood fibers (SCWF) is synthesized using a straightforward simultaneous carbonization and sulfidation approach. Density functional theory (DFT) calculations reveal that the highly electronegative Ni element promotes electron cloud migration from Co to Ni, shifting the d-band center of Co closer to the Fermi level. This Ni modification induces a synergistic effect, optimizing the internal electronic structure of the central Co metal site and enhancing intermediate adsorption. Additionally, the N, S co-doped carbon encapsulation structure and the anchoring effect of SCWF protect (Co, Ni) 9 S 8 nanoparticles from agglomeration during the catalytic process, resulting in excellent long-term operational stability. Consequently, an ultralow potential of 1.34 V (vs reversible hydrogen electrode, RHE) is sufficient to achieve a current density of 50 mA cm -2 with remarkable stability. The (Co, Ni) 9 S 8 @SNC/SCWF material exhibits superior urea oxidation reaction (UOR) activity and long-term stability compared to recently reported electrocatalysts. For overall urea splitting, an electrolyzed utilizing UOR instead of oxygen evolution reaction (OER) requires only 1.47 V to reach 50 mA cm -2 with excellent stability, which is 220 mV less than the HER||OER system. This research sets the foundation for developing highly efficient UOR electrocatalysts, offering significant potential for advancing energy-efficient hydrogen generation from renewable sources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Inc. All rights reserved.)

Discovering a valid approach to achieve a novel and efficient water splitting catalyst is essential for the development of hydrogen energy technology. Herein, unique hollow-structured ruthenium (Ru)-doped nickel-cobalt oxide (Ru-NiO/Co 3 O 4 /NF) nanocube arrays are fabricated as high-efficiency bifunctional electrocatalysts for hydrogen evolution reaction (HER)/urea oxidation reaction (UOR) through combined electronic and vacancy engineering. The structural characterization and experimental results indicate that the doping of Ru can not only effectively modulate the electronic structure of Ru-NiO/Co 3 O 4 /NF, but also increase the content of oxygen vacancies in the structure of Ru-NiO/Co 3 O 4 /NF to stabilize the existence of oxygen vacancies during the catalytic process. This can optimize the adsorption and desorption of the reactive intermediates on the surface of Ru-NiO/Co 3 O 4 /NF and dramatically accelerate the HER and UOR kinetics. As a result, the Ru-NiO/Co 3 O 4 /NF hollow structure nanocube arrays exhibit overpotentials of 21 and 60 mV for HER, as well as potentials of 1.36 and 1.42 V for UOR at 10 and 100 mA cm -2 , respectively. Furthermore, the coupled HER and UOR system requires only 1.59 V of cell voltage to drive a current density of 100 mA cm -2 , which is approximately 240 mV lower than conventional water electrolysis. This work provides a tremendous promise for the development of novel and high-activity electrocatalysts in future energy conversion applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Coupling the hydrogen evolution reaction (HER) with the urea oxidation reaction (UOR) represents a highly promising energy-saving strategy for hydrogen production. However, the development of cost-effective and high-performance bifunctional electrocatalysts remains a challenge. In this study, a Ni 0.85 Se/CoSe 2 heterojunction was constructed via electrodeposition, leveraging interfacial synergy to significantly enhance catalytic performance. Experimental results demonstrated that the heterojunction interface between N i0.85 Se and CoSe 2 greatly improved charge transfer efficiency, optimized the adsorption free energy of H* during HER, and accelerated water dissociation. In situ characterizations and theoretical calculations further revealed that the formation of CoSe 2 facilitated the reconstruction of Ni 0.85 Se, generating more active sites, lowering the kinetic barriers of UOR, and optimizing the adsorption of reaction intermediates on Ni sites. The Ni 0.85 Se/CoSe 2 catalyst exhibited HER and UOR overpotentials of 102 mV and 1.292 V at 10 mA·cm -2 , respectively, with a urea-assisted electrolytic hydrogen production voltage of only 1.348 V at 10 mA·cm -2 . This study provides an innovative strategy for designing high-efficiency bifunctional electrocatalysts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Inc. All rights reserved.)

Investigating efficient non-precious metal-based catalysts for water electrolysis to produce hydrogen is a significant and urgent need in the field of clean energy technologies. Moreover, utilizing transition metal dichalcogenides (TMDs) to replace the oxygen evolution reaction (OER) with the urea oxidation reaction (UOR), coupled with the hydrogen evolution reaction (HER), is an effective energy-saving hydrogen production method. A heterostructure NiS x /MoO 2 catalyst was prepared by a simple method, which exhibits excellent activity for UOR, requiring only 1.4 V to reach 100 mA cm -2 . The high performance is attributed to the presence of the heterostructure, which effectively promotes charge redistribution and optimizes the electronic structure of the catalyst, thereby enhancing its adsorption capacity for intermediates. As a result, an electrolyzer assembled with NiS x /MoO 2 as a bifunctional catalyst demonstrates excellent catalytic activity, ensures stability for over 200 h at a current density of 10 mA cm -2 , and achieves a hydrogen production rate of 0.402 mmol h -1 at a potential of 1.8 V., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The slow kinetics of the oxygen evolution reaction (OER) present a major obstacle for efficient hydrogen production via water electrolysis. In contrast, the urea oxidation reaction (UOR), with its lower thermodynamic barrier, presents a promising alternative to OER. In this study, we designed and synthesized hierarchical CoFe- PBA@S/NiFe-LDH nanoboxes. Sulfur doping in nickel-iron layered double hydroxides (S/NiFe-LDH) introduces a weak built-in electric field (BIEF), which is further strengthened when combined with cobalt-iron Prussian blue analogue (CoFe-PBA) to form a heterojunction. This heterojunction created localized charge polarization at the interface, facilitating efficient electron transfer and reducing the adsorption energy of reaction intermediates, thereby significantly improving intrinsic catalytic activity. Under conditions of 1 M KOH and 0.33 M urea, the CoFe-PBA@S/NiFe-LDH catalyst achieved a current density of 50 mA cm -2 at a relatively low potential of 1.321 V, accompanied by a low Tafel slope (53 mV dec -1 ). Additionally, it maintained stability at 30 mA cm -2 for 40 h. This work provides vital insights for the strategic design of highly effective heterojunction catalysts for the UOR., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The construction of binder-free electrodes with well-defined three-dimensional (3D) morphology and optimized electronic structure represents an efficient strategy for the design of high-performance electrocatalysts for the development of efficient green hydrogen technologies. Herein, Ru nanocrystals were modified on 3D interconnected porous FeOOH nanostructures with open network-like frameworks on NiFe foam (Ru/FeOOH@NFF), which were used as an efficient electrocatalyst. In this study, a 3D interconnected porous FeOOH with an open network structure was first electrodeposited on NiFe foam and served as the support for the in-situ modification of Ru nanocrystals. Subsequently, the Ru nanocrystals and abundant oxygen vacancies were simultaneously incorporated into the FeOOH matrix via the adsorption-reduction method, which involved NaBH 4 reduction. The Ru/FeOOH@NFF electrocatalyst shows a large specific surface area, abundant oxygen vacancies, and modulated electronic structure, which collectively result in a significant enhancement of catalytic properties with respect to the oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The Ru/FeOOH@NFF catalyst exhibits an outstanding OER performance, requiring a low overpotential (360 mV) at 200 mA cm -2 with a small Tafel slope (58 mV dec -1 ). Meanwhile, the Ru/FeOOH@NFF catalyst demonstrates more efficient UOR activity for achieving 200 mA cm -2 at a lower overpotential of 272 mV. Furthermore, an overall urea electrolysis cell using the Ru/FeOOH@NFF as the anode and Pt as the cathode (Ru/FeOOH@NFF||Pt) reveals a cell voltage of 1.478 V at 10 mA cm -2 and a prominent durability (120 h at 50 mA cm -2 ). This work will provide a valuable understanding of the construction of high-performance electrocatalysts with 3D microstructure for promoting urea-assisted water electrolysis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Efficient production of green hydrogen energy is crucial in addressing the energy crisis and environmental concerns. The oxygen evolution reaction (OER) poses a challenge in conventional overall water electrolysis due to its slow thermodynamically process. Urea oxidation reaction (UOR) offers an alternative anodic oxidation method that is highly efficient and cost-effective, with favorable thermodynamics and sustainability. Recently, there has been limited research on bifunctional catalysts that exhibit excellent activity for both OER and UOR reactions. In this study, we developed a selenium and iron co-doped nickel sulfide (SeFe-Ni 3 S 2 ) catalyst that demonstrated excellent Tafel slopes of 53.9 mV dec -1 and 16.4 mV dec -1 for OER and UOR, respectively. Density Functional Theory (DFT) calculations revealed that the introduction of metal (iron) and nonmetallic elements (selenium) was found to coordinate the d-band center, resulting in improved adsorption/desorption energies of the catalysts and reduced the overpotentials and limiting potentials for OER and UOR, respectively. This activity enhancement can be attributed to the altered electronic coordination structure after the introduction of selenium (Se) and iron (Fe), leading to an increase in the intrinsic activity of the catalyst. This work offers a new strategy for bifunctional catalysts for OER and UOR, presenting new possibilities for the future development of hydrogen production and novel energy conversion technologies. It contributes towards the urgent search for technologies that efficiently produce green hydrogen energy, providing potential solutions to mitigate the energy crisis and protect the environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The production of hydrogen through seawater electrolysis has recently garnered increasing concern. However, hydrogen evolution reaction (HER) by alkaline seawater electrocatalysis is severely impeded by the slow H 2 O adsorption and H* binding kinetics at industrial current densities. Herein, a face-centered cubic/hexagonal close packed (fcc/hcp) NiRu alloy heterojunction was fabricated on Ni foam (N doped NiRu-inf/NF) by a low-temperature nitrogen plasma activation. Simultaneously, nitrogen atoms are introduced into the alloy to facilitate d-p hybridization. When N doped NiRu-inf/NF is integrated into a dual-electrode cell for urea-assisted seawater electrolysis, it achieves 100 mA cm -2 with an ultra-low voltage of 1.36 V and excellent stability. Density functional theory (DFT) verifies that the robust d-p hybridization among Ni, Ru and N exhibits more energy level matching for H 2 O molecule adsorption at the Ru sites, while simultaneously reducing the interaction between H* and Ni sites in N-doped NiRu-inf., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Utilizing the thermodynamically favorable urea oxidation reaction instead of the anodic oxygen precipitation reaction is an alternative pathway for the energy-saving hydrogen production. Therefore, it is significant to explore advanced electrocatalysts for both HER and UOR. In this work, a dendritic heteroarchitectures of 2D CoMoO 4 nanosheets deposited on 1D CoP nanoneedles (CoP/CoMoO 4 -CC) was fabricated as bifunctional electrocatalyst. 1D CoP nanostructure with fast charge transport pathways and 2D CoMoO 4 nanostructure with large specific surface area and short paths for electron/mass transport. The unique morphology endows the superhydrophilic and superaerophobic properties, allowing for the rapid contact with the reactants and rapid removal of surface-generated gases. As a result, the CoP/CoMoO 4 -CC shows efficient bifunctional activity. This work offers a new avenue to rationally design bifunctional electrocatalysts for large-scale practical hydrogen production., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jingwen Ma reports financial support was provided by State Key Laboratory of Low-carbon Smart Coal-fired Power Generation and Ultra-clean Emission. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The electrocatalytic production of "green hydrogen", such as through the electrolysis of water or urea has been vigorously advocated to alleviate the energy crisis. However, their electrode reactions including oxygen evolution reaction (OER), urea oxidation reaction (UOR), and hydrogen evolution reaction (HER) all suffer from sluggish kinetics, which urgently need catalysts to accelerate the processes. Herein, we design and prepare an OER/UOR/HER trifunctional catalyst by transforming the homemade CoO nanorod into a two-dimensional (2D) ultrathin heterojunction nickel-iron-cobalt hybrid phosphides nanosheet (NiFeP/CoP) via a hydrothermal-phosphorization method. Consequently, a strong electronic interaction was found among the Ni 2 P/FeP 4 /CoP heterogeneous interfaces, which regulates the electronic structure. Besides the high mass transfer property of 2D nanosheet, Ni 2 P/FeP 4 /CoP displays improved OER/UOR/HER performance. At 10 mA cm - 2 , the OER overpotential reaches 274 mV in 1.0 M KOH, and the potential of UOR is only 1.389 V in 1.0 M KOH and 0.33 M urea. More strikingly, the two-electrode systems for electrolysis water and urea-assisted electrolysis water assembled by NiFeP/CoP could maintain long-term stability for 35 h and 12 h, respectively. This work may help to pave the way for upcoming research horizons of multifunctional electrocatalysts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Alloys with bimetallic electron modulation effect are promising catalysts for the electrooxidation of urea. However, the side reaction oxygen evolution reaction (OER) originating from the competitive adsorption of OH - and urea severely limited the urea oxidation reaction (UOR) activity on the alloy catalysts. This work successfully constructs the defect-rich NiCo alloy with lattice strain (PMo-NiCo/NF) by rapid pyrolysis and co-doping. By taking advantage of the compressive strain, the d-band center of NiCo is shifted downward, inhibiting OH - from adsorbing on the NiCo site and avoiding the detrimental OER. Meanwhile, the oxygenophilic P/Mo tailored specific adsorption sites to adsorb OH - preferentially, which further released the NiCo sites to ensure the enriched adsorption of urea, thus improving the UOR efficiency. As a result, PMo-NiCo/NF only requires 1.27 V and -57 mV to drive a current density of ±10 mA cm -2 for UOR and hydrogen evolution reaction (HER), respectively. With the guidance of this work, reactant competing adsorption sites could be tailored for effective electrocatalytic performance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Designing efficient non-precious metal-based catalysts for urea oxidation reaction (UOR) is essential for achieving energy-saving hydrogen production and the treatment of wastewater containing ammonia. In this study, sodium dodecyl sulfate (SDS) is employed as a sacrificial template to synthesize NiCo alloy nanowires (NiCo(SDS)/CC), and the instinct formation mechanism is investigated. It is found that SDS can inhibit the Ostwald ripening during hydrothermal and calcination processes, which could release abundant active cobalt, thereby modulating the electronic structure to promote the catalytic reaction. Moreover, SDS as a sacrificial template can induce the deposition of metal atoms and increase the specific surface area of the catalyst, providing abundant active sites to accelerate the reaction kinetics. As expected, the NiCo(SDS)/CC exhibits good activity for both UOR and hydrogen evolution reactions (HER) and it requires only 1.31 V and -86 mV to obtain a current density of ±10 mA cm -2 , respectively. This work provides a new strategy for reducing the agglomeration of transition metals to design high-performance composite catalysts for urea oxidation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

When the anodic oxygen evolution reaction (OER) of water splitting is replaced by the urea oxidation reaction (UOR), the electrolyzer can fulfill hydrogen generation in an energy-economic manner for urea electrolysis as well as sewage purification. However, owing to the sluggish kinetics from a six-electron process for UOR, it is in great demand to design and fabricate high-performance and affordable electrocatalysts. Over the past years, numerous non-precious materials (especially nickel-involved samples) have offered huge potential as catalysts for urea electrolysis under alkaline conditions, even in comparison with frequently used noble-metal ones. In this review, recent efforts and progress in these high-efficiency noble-metal-free electrocatalysts are comprehensively summarized. The fundamentals and principles of UOR are first described, followed by highlighting UOR mechanism progress, and then some discussion about density functional theory (DFT) calculations and operando investigations is given to disclose the real reaction mechanism. Afterward, aiming to improve or optimize UOR electrocatalytic properties, various noble-metal-free catalytic materials are introduced in detail and classified into different classes, highlighting the underlying activity-structure relationships. Furthermore, new design trends are also discussed, including targetedly designing nanostructured materials, manipulating anodic products, combining theory and in situ experiments, and constructing bifunctional catalysts. Ultimately, we point out the outlook and explore the possible future opportunities by analyzing the remaining challenges in this booming field., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Bimetallic phosphides exhibit superior electrocatalytic activities and synergistic effects that make them ideal electrocatalysts for the urea oxidation reaction (UOR). Herein, P, N-codoped carbon-encapsulated cobalt/nickel phosphides derived from NiCo-MOF-74 (NiCoP@PNC) and anchored on P-doped carbonized wood fiber (PCWF) for UOR were prepared through synchronous carbonization and phosphorization. By benefiting from the synergistic effect of structural and electronic modulation, NiCoP@PNC/PCWF exhibits excellent UOR electrocatalytic performance under alkaline conditions, achieving a current density of 50 mA cm -2 with a potential of only 1.34 V (vs reversible hydrogen electrode, RHE) and continuous operation for more than 72 h. In addition, for the overall urea splitting, an electrolyzer using UOR replaced OER, which required only 1.50 V to achieve a current density of 50 mA cm -2 with excellent stability, 230 mV less than that required for the HER||OER system. In-depth theoretical analysis further proves that the strong synergistic effect between Co and Ni optimizes electronic structures, yielding excellent UOR properties. The synergistic strategy of structural and electrical modulation provides broad prospects for the design and synthesis of excellent UOR electrocatalysts for energy-saving hydrogen production by using renewable resources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The exploitation of cost-effective and abundant non-noble metal electrocatalysts holds great significances in enhancing the efficiency of oxygen evolution reaction (OER) and/or urea oxidation reaction (UOR). Herein, we report an electrocatalyst with co-existing V-dopants and Ni(OH) 2 /FeOOH interfaces (referred to as A-NiFeV/NF, with "A" indicating "activated"). The electron coupling between Ni, Fe and V, analyzed through X-ray photoelectron spectroscopy, indicates that Ni and Fe both receive electrons from the V. Additionally, the Fe can also lead to a bias toward a lower valence of the Ni centers in Ni(OH) 2 . Further in situ Raman spectroscopy reveals that Ni 2+ (OH) 2 inevitably undergoes transformation into amorphous Ni 3+ OOH during the activation process, however, the synergistic effects of V-dopants and Ni(OH) 2 /FeOOH interfaces keep the Ni centers mostly in a lower oxidation state of +2 even at high potential ranges. These low-valence Ni centers are proposed to be positively correlated with the optimized OER activity of the Ni-based electrocatalysts. As a result, the designed A-NiFeV/NF electrocatalyst exhibits low overpotentials of 234 and 313 mV to propel current densities of 10 and 100 mA/cm 2 , and a small Tafel slope of 37.8 mV/dec for OER in 1.0 M KOH. The catalyst demonstrates a stable OER activity for over 100 h at 100 mA/cm 2 . Additionally, it can be integrated with a solar cell to construct a solar-driven electrolytic OER device without additional electric input. Similarly, for the small molecule oxidation, UOR, only ∼1.33 and ∼1.39 V vs. RHE (RHE: reversible hydrogen electrode) are required to achieve 10 and 100 mA/cm 2 , respectively, in an electrolyte composed of 1.0 M KOH with 0.33 M urea., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

In this work, we report a robust bifunctional electrocatalyst composed of 2D Ni- organic frameworks (Ni-MOF) and nitrogen doped carbon nanotubes encapsulated Ni nanoparticles (Ni-MOF@Ni-NCNT) for CN and HO bonds dissociation. Due to the presence of Ni-NCNT, adsorption of OH - species is enhanced and CO 2 binding strength is simultaneously weakened leading to a boosted urea oxidation reaction performance reflected by decrement in potential at 100 mA cm -2 by 69 mV. The loosened binding strength with CO 2 specie is highlighted by in-situ electrochemical impedance spectroscopy (EIS) test and DFT calculation. Moreover, the alkaline hydrogen evolution reaction (HER) performance of Ni-MOF@Ni-NCNT is better than Ni-MOF and Ni-NCNT evidenced by the overpotential at 50 mA cm -2 decreased by 224 mV and 900 mV ascribed to the synergistic effect, in which Ni-MOF, Ni nanoparticles and Ni-Nx-C facilitates water adsorption, dissociation and adsorption/combination of hydrogen ions, respectively. The assembled HER- urea oxidation reaction (UOR) system requires only 1.33 V to reach 10 mA cm -2 , 70 mV lower than water splitting driven by Pt/C-IrO 2 ., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The development of efficient bifunctional electrocatalysts for oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is critical for hydrogen production and wastewater purification. In this work, we propose a facile synthetic method for Co and N dual-doped Ni 2 P directly grown on Ni foam (Co-Ni 2 P-N/NF) using hydrothermal and annealing process. Simultaneous Co and N dual-doping into Ni 2 P not only modifies the surface electronic structure, but also generates a multitude of active sites with high valence states, which are beneficial for improving electrocatalytic kinetics for both OER and UOR. As a result, the Co-Ni 2 P-N/NF catalyst exhibits a low overpotential of 329 mV to deliver a current density of 100 mA cm -2 for OER in alkaline solution, which is much lower than that of the state-of-the-art RuO 2 electrocatalyst. In addition, the urea-assisted water oxidation process exhibits a significant reduction of approximately 163 mV in the required potential at 100 mA cm -2 compared to that of the OER, which highlights the remarkable potential of the prepared Co-Ni 2 P-N/NF electrocatalyst in facilitating the purification of wastewater and hydrogen production with significantly lower energy consumption., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The process of electrocatalytic water splitting for hydrogen generation is significantly limited by sluggish kinetics of the anodic oxygen evolution reaction (OER). The efficiency of H 2 electrocatalytic generation can be improved by reducing the anode potential or substituting urea oxidation reaction (UOR) for oxygen evolution process. Here, we report a robust catalyst based on Co 2 P/NiMoO 4 heterojunction arrays supported on nickel foam (NF) for water splitting and urea oxidation. In the hydrogen evolution reaction in alkaline media, the optimized catalyst Co 2 P/NiMoO 4 /NF displayed a lower overpotential (169 mV) at a large current density (150 mA cm -2 ) compared to 20 wt% Pt/C/NF (295 mV@150 mA cm -2 ). In the OER and UOR, the potentials were as low as 1.45 and 1.34 V. These values surpass (for OER), or compare favorably to (for UOR), the most advanced commercial catalyst RuO 2 /NF (at 10 mA cm -2 ). This outstanding performance was attributed to the addition of Co 2 P, which has a significant effect on the chemical environment and electron structure of NiMoO 4 , while increasing the number of active sites and promoting charge transfer across the Co 2 P/NiMoO 4 interface. This work proposes a high-performance and cost-effective electrocatalyst for water splitting and urea oxidation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Multiple-principal-element alloys (MPEAs) with maximized configurational entropy show high catalytic activities for oxygen evolution reaction (OER) and urea oxidation reaction (UOR). However, the accurate relationship between their complex components (i.e., elements, phase structure, grain boundary density) and intrinsic catalytic activity is still unclear. Herein, a series of bulk MPEAs with face-centered cubic (FCC) phase structures were fabricated by the arc-melting method under an argon atmosphere. Compared to the CrCoNi and CrCoNiFeMn, the CrCoNiFe affords a higher UOR performance with the lowest overpotential of 331 mV at 10 mA·cm -2 in 1 M KOH with 0.33 M urea, due to excellent conductivity and high density of grain boundaries. The urea electrolyzer using CrCoNiFe as anode and Pt as cathode shows a low voltage of 1.622 V at 10 mA cm -2 and long-term stability of 60 h at 20 mA cm -2 (4.08% decrease). These findings offer a facile strategy for designing bulk MPEAs electrodes for energy conversion., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Developing multifunctional all-in-one electrocatalysts for energy-saving hydrogen generation remains a challenge. In this study, a simple and feasible thermal phosphorization strategy is explored to rationally construct P-doped MoO 2 -NiMoO 4 heterostructure on nickel foam (NF). The heterointerfaced P-MoO 2 -NiMoO 4 /NF can simultaneously realize the integrated all-in-one functionalities, innovatively introducing superwettable surfaces, photothermal conversion capabilities and electrocatalytic functions. The superwettability gives P-MoO 2 -NiMoO 4 /NF sufficient electrolyte permeation and smooth bubble detachment. The plasmonic MoO 2 with photothermal performance greatly elevates the local surface temperature of in P-MoO 2 -NiMoO 4 /NF, which is conducive to improve the electrocatalytic efficiency. The favorable in-situ surface reconstruction brings abundant active sites for electrocatalytic reactions. As an advanced multifunctional electrocatalyst, the superwettable and photothermal P-MoO 2 -NiMoO 4 /NF exhibits significantly improved performances in oxygen evolution reaction (OER) and urea oxidation reaction (UOR). More importantly, the highly efficient and stable overall water-urea electrolysis assisted by photothermal fields can be simply achieved by exposing P-MoO 2 -NiMoO 4 /NF to near-infrared (NIR) light., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Inorganic-organic hybrids are promising anode catalysts to realize high activity and stability. Herein, an amorphous-dominated transition metal hydroxide-organic framework (MHOF) with isostructural mixed-linker was successfully synthesized on nickel foam (NF) substrate. The designed IML 24 -MHOF/NF exhibited remarkable electrocatalytic activity with an ultralow overpotential of 271 mV for oxygen evolution reaction (OER) and a potential of 1.29 V vs. reversible hydrogen electrode for urea oxidation reaction (UOR) at 10 mA·cm -2 . Furthermore, the IML 24 -MHOF/NF||Pt-C cell required only 1.31 V for urea electrolysis at 10 mA·cm -2 , which was much smaller than traditional water splitting (1.50 V). When coupled with UOR, the hydrogen yield rate was faster (1.04 mmol·h -1 ) than with OER (0.32 mmol·h -1 ) at 1.6 V. The structure characterizations, together with operando monitoring, including operando Raman, Fourier transform infrared, electrochemical impedance spectroscopy, and alcohol molecules probe, revealed that: (1) amorphous IML 24 -MHOF/NF prefers self-adaptive reconstruction into active intermediate species against the external stimulus; (2) pyridine-3,5-dicarboxylate-incorporation into parent framework reconfigures electronic structure of system, thus mediating the absorption of oxygen-containing reactants during anodic oxidation reactions, such as O* and COO*. This work provides a new approach for boosting the catalytic activity of anodic electro-oxidation reactions by trimming the structure of MHOF-based catalysts., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Electrochemical oxidation of urea is of great importance in the removal and energy exchange and storage of urea from wastewater as well as of potential applications in potable dialysis of end-stage renal disease. However, the lack of economical electrocatalysts hinders its widespread application. In this study, we successfully fabricated ZnCo 2 O 4 nanospheres with bifunctional catalysis on nickel foam (NF). The catalytic system has high catalytic activity and durability for urea overall electrolysis. The urea oxidation and hydrogen evolution reactions required only 1.32 V and -80.91 mV to obtain ± 10 mA cm -2 . Only 1.39 V was needed to obtain 10 mA cm -2 for 40 h without noticeably declining activity. The excellent performance could be attributed to the fact that the material can provide multiple redox couplings and a three-dimensional porous structure to facilitate the release of gases from the surface., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Designing efficient electrocatalysts to improve the overall water splitting and urea electrolysis efficiency for hydrogen generation can greatly solve the dilemma of energy shortage and environmental pollution. In this work, Co 8 FeS 8 @CoFe-MOF/NF heterojunction arrays were fabricated by embedding sulfides into the surface of metal-organic frameworks (MOFs) nanosheets as multifunctional electrocatalyst. The introduction of sulfide on CoFe-MOF/NF can not only adjust the electronic structure (electron-rich state) and change the surface properties (more hydrophilic), but also increase the active area to enhance the catalytic activity. The in situ Raman shows Co 8 FeS 8 @CoFe-MOF/NF is more easily to generate active species at low potentials and generates a higher content of active β-MOOH phase than CoFe-MOF/NF. Therefore, the Co 8 FeS 8 @CoFe-MOF/NF exhibits excellent oxygen evolution reaction (OER) performance with an overpotential of 213 mV at 10 mA cm -2 . Furthermore, when used as a urea oxidation reaction (UOR), only an ultralow potential of 1.311 V at 10 mA cm -2 . More importantly, the assembled two-electrode drives overall water splitting and urea electrolysis with cell voltages of 1.62 V and 1.55 V at 10 mA cm -2 , respectively. This work provides insights into the preparation of electrocatalysts with multifunctional heterostructure arrays for hydrogen production., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Synthesis of regular morphology catalysts with self-growing substrates is one of the effective methods to solve the problem of easy shedding of heterogeneous catalysts. In this study, Fe-doped Ni 12 P 5 nanorods were prepared by depositing 1,1' -bis (diphenylphosphine) ferrocene (DPPF) on N-doped C/NF. The bottom-up growth of the nanorod is ascribed to the preferential adsorption of DPPF with a P site to NF that is surface-doped with the solid-solving C, and the length of nanorods can reach tens of microns and has good robustness. The N-doped carbon-constrained rod-shaped Fe-doped Ni 12 P 5 catalyst (Fe-Ni 12 P 5 /N d C/NF-800) that grows on NF has excellent catalytic performance for the urea oxidation reaction. In addition, the current density can be maintained as high as 100 mA cm -2 and the current attenuation is weak for 12 h, and the rod shape remains good. This work provides a new idea for synthesizing self-growing catalysts with regular morphology to improve the performance of heterogeneous catalysts., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Hydrogen production by electrocatalytic water splitting is considered to be an effective and environmental method, and the design of an electrocatalyst with high efficiency, low cost, and multifunction is of great importance. Herein, we developed a crystalline NiFe phosphide (NiFeP)/amorphous P-doped FeOOH (P-FeOOH) heterostructure (defined as P-NiFeO x H y ) as a high-efficiency multifunctional electrocatalyst for water electrolysis. The NiFeP nanocrystals provide remarkable electronic conductivity and plenty of active sites, the amorphous P-FeOOH improves the adsorption energy of oxygen-containing species, and the crystalline/amorphous heterostructure with superhydrophilic and superaerophobic surface generates synergistic effects, providing plentiful active sites and efficient charge/mass transfer. Benefiting from this, the designed P-NiFeO x H y displays ultralow overpotentials of 159.2 and 20.8 mV to achieve 10 mA cm -2 for oxygen evolution reaction and hydrogen evolution reaction, and also shows the superior performance of urea oxidation reaction with a low voltage of 1.37 V at 10 mA cm -2 in 1 M KOH with 0.33 M urea. In-situ Raman spectra and ex-situ XPS analysis were also used to investigate the catalytic process and reveal the surface structure evolution of P-NiFeO x H y under electrochemical oxidation. Accordingly, the designed P-NiFeO x H y is employed as both cathode and anode to assemble into the urea-assisted water electrolysis device, which can reach 10 mA cm -2 with a low 1.36 V and could be further driven by a solar cell. The work reveals a design of superior activity, cost-effective and multifunctional electrocatalysts for water splitting., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Electrocatalytic water splitting has become one of the most promising and effective ways to solve energy crises and environmental pollution.In this work, a series of M-doped Co 3 O 4 materials with foreign ions (M = Ce, Ni and Fe) were grown on a Ni foam substrate through classical hydrothermal and calcination methods.It is worth noting that not all doping of foreign ions can promote the electrocatalytic performance of intrinsic materials.The Ce-doped Co 3 O 4 material shows excellent oxidation properties of water (overpotential of 320 mV at 50 mA cm -2 ) and urea (potential of 1.39 V at 50 mA cm -2 ).However, the doping of Ni reduces the water oxidation performance of the intrinsic material (overpotential of 410 mV@ 50 mA cm -2 ), and the doping of Fe reduces the urea oxidation performance of the inherent material (potential of 1.45 V@ 50 mA cm -2 ).A series of experimental results indicate that the improved activity of the Ce-Co 3 O 4 electrode is attributed to faster electron transport capacity, higher exposure to active sites, and improved conductivity due to doping of Ce. It is noteworthy that the doping of these ions does alter the rate-determination step for the water oxidation reaction. The stability test demonstrated that the current density of water oxidation and urea oxidation of the catalyst had no significant attenuation after a long electrocatalytic activity test. This work provides a new idea for improving the electrocatalytic activity of catalysts by a doping strategy., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Seawater electrolysis is considered to be very challenging owing to competitive reaction kinetics in between oxygen evolution reaction and corrosive chlorine evolution reaction mechanism at anode, especially towards higher current density. The present work, proposes a promising and energy efficient strategy by coupling seawater splitting with urea decomposition lowering oxidation potential and thereby avoiding hypochlorite formation even at high current density. The rational design of Mott-Schottky heterojunction of Se/NiSe 2 as electrocatalyst is considered to be highly effective in this regard. The developed Se/NiSe 2 exhibits extraordinary energy saving for alkaline seawater splitting in presence of urea. The Se/NiSe 2 /NF || Se/NiSe 2 /NF electrolyser configuration achieved 10 and 50 mAcm -2 current densities with cell voltage of 1.59 and 1.70 V along with outstanding operational durability over 50 h. The large number of carrier density generates by synergistic self-driven electron transfer from Se to NiSe 2 at the heterojunction, unique metallic properties of selenium (Se), and also abundance accessible reactive edges on the porous channel of Ni foam are believed to be the reason behind such enhanced electrocatalytic activities towards urea oxidation reaction and hydrogen evolution reaction offering unique and much energy saving approach for alkaline-urea-seawater electrolysis avoiding hypochlorite formation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

NiOOH has been considered as the active center for urea oxidation reaction (UOR), but it remains challenging to synthesize high-performance NiOOH-based catalysts. Herein, we realize the synthesis of a high-performance NiOOH-based catalyst through in-situ transformation from the NiMn-based metal-organic framework to NiMnOOH. X-ray photoelectron spectroscopy characterization shows that the Ni 3+ /Ni 2+ ratio in the NiMnOOH is 3.9 times as big as that in the Ni(OH) 2 , and in-situ Raman characterization further consolidates the presence of the NiOOH species in the NiMnOOH and as well unveils the faciliated Ni 2+ /Ni 3+  redox reaction. The abundant NiOOH species, the markedly facilitated Ni 2+ /Ni 3+ redox reaction and the Ni-Mn synergy contribute to the high intrinsic activity of the NiMnOOH towards UOR. The NiMnOOH exhibits an impressively low onset potential of 1.305 V vs reversible hydrogen electrode (RHE) and requires only a small potential of 1.34 V vs RHE to deliver a current density of 100 mA cm -2 in 1.0 M KOH + 0.33 M urea. In addition, the NiMnOOH catalyst possesses good long-term working stability., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Applications of urea oxidation reaction (UOR) in various sustainable energy-conversion systems are greatly hindered by its slow kinetics. Herein, we demonstrate an in-situ confined synthesis method that produces amorphous chromium oxide confined Ni/NiO nanoparticles-assembled nanosheets (Ni/NiO@CrO x ) with fast reaction kinetics towards UOR. The confinement effect of the in-situ generated CrO x overlay contributes to ultrafine Ni/NiO nanoparticles, bringing about rich Ni/NiO and NiO/CrO x interfaces. In-situ Raman and electrochemical characterization show that both CrO x and metallic Ni can promote the formation of the NiOOH species and the electron transfer, leading to high intrinsic activity and fast reaction kinetics. At 1.40 V vs. reversible hydrogen electrode, the Ni/NiO@CrO x delivers a current density of 275 mA cm -2 , which is about 2.6 and 6.1 times as large as those of the NiO@CrO x and NiO, respectively. In addition, the protective effect of the CrO x overlay leads to robust working stability towards UOR. Further, the Ni/NiO@CrO x nanosheets are used as bifunctional catalysts for overall urea splitting, and a small electrolysis cell voltage of 1.44 V is needed to reach the benchmark current density of 10 mA cm -2 ., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Electrocatalytic urea oxidation (UOR) has attracted significant interest as a promising anodic half-reaction to replace sluggish oxygen evolution reaction (OER) toward water splitting. However, the activation and decomposition of urea molecule maintains a challenge during electrocatalytic process because of its 6e - oxidation procedure. Herein, Ni nanoparticles decorated NiMoO x nanorod (Ni/NiMoO x ) electrocatalyst with abundant heterojunction interfaces is fabricated and the density functional theory (DFT) calculation testifies that the interfaces are favorable for enhancing the conductivity and modulating the surface polarization of Ni/NiMoO x , thus improving its UOR's activity. The Ni/NiMoO x performs superb electrocatalytic capacities toward UOR with a potential of 1.355 V (vs RHE) at 20 mA cm -2 , and HER with an overpotential of 98 mV at 10 mA cm -2 . A hybrid two-electrode water splitting cell is further assembled via applying the Ni/NiMoO x as both anodic and cathodic electrodes with presence of 0.33 M urea, delivering 50 mA cm -2 at voltage of 1.589 V. The findings help to provide a reliable strategy for rational reconstruction of Ni based metal oxide with rich interfaces for diverse electrocatalytic reactions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

It is urgent to develop non-noble metal electrocatalysts with both excellent activity and durable stability for H 2 production via water electrolysis. Electric energy is mainly consumed by the sluggish anodic oxygen evolution reaction (OER). The electrocatalytic urea oxidation reaction (UOR) has been regarded as a promising reaction to replace OER because of its small thermodynamic oxidation potential. However, developing a facile and large-scale preparation method for bifunctional hydrogen evolution reaction (HER) and UOR electrocatalysts is still challenging. Herein, phosphate-modified (4.46 atomic%) NiMoO 4-x net-like nanostructures are formed on Ni foam (NF) via H 3 PMo 12 O 40 etching strategy at room temperature (denoted as NF/P-NiMoO 4-x ). The etched NF can directly serve as HER electrode, and delivers overpotential of 116 mV at current density of 10 mA/cm 2 with Tafel slope of 77.5 mV/dec. Furthermore, it displays excellent UOR activity with potential of 1.359 V at current density of 10 mA/cm 2 and Tafel slope of 19.3 mV/dec. The apparent activation energy of NF/P-NiMoO 4-x is 20.6 kJ/mol, lower than that of NF (37.7 kJ/mol), indicating smaller apparent barrier for CN bond cleavage in urea. The cell voltage of urea electrolysis is around 1.48 V for H 2 production to deliver current density of 10 mA/cm 2 , and better long-term stability for 50 h than that of Ir/C||Pt/C. The etching solution can be recycled for five times by addition of H 2 O 2 , turning heteropoly blue into its original state. This work develops a facile and large-scale method to prepare bifunctional HER and UOR electrocatalysts for H 2 production in a less-energy saving way via urea electrolysis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Electrocatalytic urea oxidation reaction (UOR) is a prospective method to substitute the slow oxygen evolution reaction (OER) and solve the problem of urea-rich water pollution due to the low thermodynamic voltage, but its complex six-electron oxidation process greatly impedes the overall efficiency of electrolysis. Here, density functional theory (DFT) calculations imply that the metallic Ni 3 S 2 and semiconductive MoS 2 could form Mott-Schottky catalyst because of the suitable band structure. Therefore, we synthesized MoS 2 /Ni 3 S 2 electrocatalyst by a simple hydrothermal method, and studied its UOR and hydrogen evolution reaction (HER) performance. The formed MoS 2 /Ni 3 S 2 Schottky heterojunction is only required 109  and 166 mV to obtain ±10 mA cm -2 for UOR and HER, respectively, showing great bifunctional catalytic activity. Moreover, the full urea electrolysis driven by MoS 2 /Ni 3 S 2 delivers 10 and 100 mA cm -2 at a relatively low potential of 1.44 and 1.59 V. Comprehensive experiments and DFT calculations demonstrate that the MoS 2 /Ni 3 S 2 Schottky heterojunction causes self-driven charge transfer at the interface and forms built-in electric field, which is not only benefit to reduce H* adsorption energy, but also helps to adjust the absorption and directional distribution of urea molecules, thereby promoting the activity of decomposition of water and urea. This research furnishes a tactic to devise more efficient catalysts for H 2 generation and the treatment of urea-rich water pollution., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

In this study, CoS/MnCo 2 O 4 -MnO 2 (CMM) nanocomposites were synthesized by hydrothermal and then electrochemical deposition. Their electrochemical properties were systematically investigated for supercapacitors and energy-saving H 2 production. As an electrode material for supercapacitor, CMM demonstrates a specific capacitance of 2320F g -1 at 1 A/g, and maintains a specific capacitance of 1216F g -1 at 10 A/g. It also shows 72.8 % capacitance retention after 8000 cycles. The aqueous asymmetric supercapacitor exhibited high energy storage capacity (887.86F g -1 specific capacitance at a current density of 1 A/g), good rate performance and cycling stability. Besides, CMM shows outstanding urea oxidation reaction(UOR) and glycol oxidation reaction (MOR) performances for H 2 production. Compared to oxygen evolution reaction (OER) (1.635 V) at 20 mA cm -2 , the potentials were reduced by 213 mV for UOR and 233 mV for MOR, respectively. Therefore, this study shows the promising practical applications of CMM nanocomposites for energy storage and energy-saving H 2 production., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Substituting water oxidation half of water splitting with anodic oxidation of urea can reduce the cost of H 2 production and provide an avenue for treating urea-rich wastewater. However, developing an efficient and stable electrocatalyst is necessary to overcome the indolent kinetics of the urea oxidation reaction (UOR). Accordingly, we have used the Schikorr reaction to deposit Fe 3 O 4 particles on the nickel foam (Fe 3 O 4 /NF). Results from the various analysis indicated that under the operational conditions, Fe 3 O 4 underwent surface reconstruction to produce a heterolayered structure wherein a catalytically active FeOOH layer encased a conducting Fe 3 O 4 . Fe 3 O 4 /NF outperformed RuO 2 as a UOR catalyst and delivered a current density of 10 50 and 100 mA cm -2 at low applied potentials of 1.38 1.42 and 1.46 V, respectively, with a Tafel slope of 28 mV dec -1 . At the applied potential of 1.4 V, Fe 3 O 4 /NF demonstrated a turnover frequency (TOF) of 2.8 × 10 -3 s -1 , highlighting its superior intrinsic activity. In addition, a symmetrical urea electrolyzer constructed using Fe 3 O 4 /NF produced the current density of 10 mA cm -2 at a cell voltage of 1.54 V., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Exploring highly efficient, robust, and stable catalysts for urea electrolysis is intensively desirable for hydrogen production but remains a challenging task. In this work, novel, well-aligned, self-supported NiS/Ni 3 S 4 heteronanorod arrays deposited on graphitized carbonized wood (GCW) are designed (denoted as NiS/Ni 3 S 4 /GCW) and synthesized by a facile hydrothermal sulfidation strategy. Benefitting from the optimized surface hydrophilicity/aerophobicity, enhanced electrical conductivity, and 3D hierarchical directional porous architectures, the NiS/Ni 3 S 4 /GCW show excellent activity toward the urea oxidation reaction and hydrogen evolution reaction in alkaline electrolytes. The arrays achieved a low potential of 1.33 V (vs. RHE) and 91 mV (overpotential) at 10 mA cm -2 as well as robust stability for 100 h. Significantly, when employed as anode and cathode simultaneously, the urea electrolyzer constructed by NiS/Ni 3 S 4 /GCW catalysts merely requires a low voltage of 1.44 V to drive 10 mA cm -2 with superior stability for 50 h. This work not only demonstrates the application of heterogeneous sulfide for urea-assisted hydrogen production but also provides an effective guideline for using renewable wood for designing efficient catalysts in an economical way., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Replacement of the sluggish anodic reaction in water electrocatalysis by a thermodynamically favorable urea oxidation reaction (UOR) offers the prospect of energy-saving H 2 generation, additionally mitigating urea-rich wastewater pollution, whereas the lack of highly efficient and earth-abundant UOR catalysts severely restricts widespread use of this catalytic system. Herein, Mn-doped nickel hydroxide porous nanowire arrays (denoted Mn-Ni(OH) 2 PNAs) are rationally developed and evaluated as efficient catalysts for the UOR in an alkaline solution via the in situ electrochemical conversion of NiMn-based metal-organic frameworks. Mn doping can modulate the electronic structural configuration of Ni(OH) 2 to significantly increase the electron density and optimize the energy barriers of the CO*/NH 2 * intermediates of the UOR. Meanwhile, porous nanowire arrays will afford abundant spaces/channels to facilitate active site exposure and electron/mass transfer. As a result, the Mn-Ni(OH) 2 PNAs delivered superior UOR performance with a small potential of 1.37 V vs. RHE at 50 mA cm -2 , a Tafel slope of 31 mV dec -1 , and robust stability. Notably, the overall urea electrolysis system coupled with a commercial Pt/C cathode demonstrated excellent activity (1.40 V at 20 mA cm -2 ) and durability operation (only 1.40% decay after 48 h)., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Urea electrooxidation with favorable thermodynamic potential is highly anticipated but suffering from sluggish kinetics. Deciphering the activity origin and achieving rational structure design are pivotal for developing highly efficient electrocatalyst for urea oxidation reaction (UOR). Herein, nitrogen penetrated nickel nanoparticles confined in carbon nanotubes (Ni-NCNT) is successfully achieved to drive UOR. Active origin of Ni-NCNT is decoded to be the in-situ generated Ni 2+δ O(OH) ads according to comprehensive analysis. The electrophilic Ni 2+δ and protophilic OH ads could targeted capture O and H atoms from urea, respectively, achieving molecule activation and accelerating the subsequent proton coupled electron transfer reactions. Nitrogen penetration is identified to promote prior formation of Ni 2+δ O(OH) ads and push up the d band center of Ni-NCNT, enhancing urea adsorption and subsequent molecule cleavage reactions. As a result, Ni-NCNT exhibits superior UOR performance. This work supplies valuable insights for the rational design and construction of efficient nickel-based catalyst for driving UOR., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Constructing heterostructure is an efficient method to provide more active sites and optimize electronic structure for improving the oxygen evolution reaction (OER) and urea oxidation reaction (UOR) performance. Herein, the 3D FeOOH@Co 3 O 4 heterostructure was constructed using FeOOH layer (10-20 nm) coated on the surface of Co 3 O 4 nanoneedles through the strong hydrolysis of Fe 3+ . The FeOOH@Co 3 O 4 heterostructure not only retains the nanoneedle structure with open frameworks, but also improves the specific surface area and expedites the charge transfer. The FeOOH@Co 3 O 4 -240 heterostructure affords a remarkable OER performance with low overpotential of 228 mV at 10 mA·cm -2 in 1 M KOH solution. The symmetrical urea electrolyzer using FeOOH@Co 3 O 4 -240 as both anode and cathode delivers 10 mA/cm 2 at 1.43 V. Density functional theory (DFT) calculations unveil that the FeOOH@Co 3 O 4 -240 heterostructure could adjust the electronic structure and strengthen the conductivity. This work offered a facile strategy for designing heterojunction catalysts in an economic way., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The development of highly efficient oxygen evolution reaction (OER) and urea oxidation reaction (UOR) electrocatalysts with abundant resources is necessary for green hydrogen production. Ni-based compounds have received attention as the most promising earth-abundant electrocatalysts for OER and UOR, whereas some compounds in this main group, e.g., nickel selenides and tellurides, have received little attention. Herein, we demonstrate the interfacial engineered Ni 0.85 Se/NiTe array on Ni foam as a highly efficient catalyst for the OER, which exhibits an overpotential of 200 mV to obtain a current density of 10 mA cm -2 in alkaline solutions. Meanwhile, it exhibits a low potential of 1.301 V for the UOR at a current density of 100 mA cm -2 . In particular, it even has the potential to be used in methanol oxidation reaction and ethanol oxidation reaction. The vertical NiTe array not only serves as the conductive substrate for highly improving the mass loading of Ni 0.85 Se, but also triggers the strong electron interaction between two components, leading to increased adsorption sites available for the intermediates formed in the OER and UOR on the Ni 0.85 Se surface. This study provides a broad avenue to construct hierarchical nanostructures as outstanding electrocatalysts for efficient OER and UOR., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Exploring the transition-metal-based bifunctional electrocatalysts with high performance for efficient water-splitting and urea electrolysis is significant but challenging. This work presents the in situ preparation of holey NiFe-LDH nanosheets on Ni foam (H-NiFe-LDH/NF) via a one-step hydrothermal method in the presence of PEO-PPO-PEO as the soft template. The holey NiFe-LDH nanosheets provide a high electrochemical surface area, more edge catalytic sites, and abundant oxygen vacancies. Consequently, H-NiFe-LDH/NF exhibits excellent catalytic activity to oxygen evolution, urea oxidation, and hydrogen evolution reactions (OER, UOR, and HER) with good stability in alkaline electrolytes. This electrode requires an overpotential of 261 mV for the OER, a potential of 1.480 V for the UOR to achieve a current density of 100 mA cm -2 in alkaline solutions. By employing the self-supported electrode as both the anode and cathode, this electrolysis cell (H-NiFe-LDH/NF||H-NiFe-LDH/NF) gains current densities of 10 and 100 mA cm -2 at low cell voltages of 1.575 and 1.933 V in the 1.0 M KOH solution. After adding 0.33 M urea, the voltages to deliver 10 and 100 mA cm -2 respectively decrease to 1.418 and 1.691 V. The H-NiFe-LDH/NF electrode also shows excellent stability for water-splitting and urea electrolysis. This work not only contributes to developing a low-cost, high-efficiency, bifunctional electrocatalyst but also provides a practically feasible approach for urea-rich wastewater electrolysis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The urea oxidation reaction (UOR) has been well-acknowledged as one of the promising alternatives for hydrogen production through electrochemical water splitting system because of the more favorable thermodynamic potential. But the shortage of cost-effective electrocatalysts with high catalytic activity and durability restricts its practical development. Herein, the partially amorphous fluorine-decorated nickel iron layered double hydroxides (NiFe-F) is constructed via a low-temperature fluoridation method. Our study found that HF acid etching of NiFe LDH precursor resulted in the partially amorphous feature and abundant oxygen vacancies, providing rich reaction sites. Simultaneously, the formation of ionic metal-F bond makes it easier to form high-valence metal oxygen hydroxide active sites. Specifically, the as-prepared NiFe-F-4 electrode demonstrates a superb mass activity of 1290 mA mg -1 at 1.6 V vs. RHE. Further experiments found that amorphous structure and F decorating decreased the activation energy of UOR from 30.71 kJ mol -1 (crystalline NiFe-F-4) to 20.17 kJ mol -1 (amorphous NiFe-F-4), leading to a rapid dynamic with a small Tafel slope of 31 mV dec -1 . Moreover, NiFe-F-4 casts remarkable long-term durability for 40 h without performance decay. This work holds great promise to develop advanced electrocatalysts for pollution treatment of urea-rich wastewater and energy-saving H 2 production., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Oxygen evolution reaction (OER) and urea oxidation reaction (UOR) play important roles in the field of hydrogen energy preparation and pollution treatment. In this work, by merging bimetallic Co-Mo oxides with metallic Co on the graphite felt (GF), we effectively manufacture a 3D bifunctional and highly efficient electrocatalyst (CoMoO@Co/GF) with multi-site functionality for the simultaneous reduction of water and the oxidation of urea in an alkaline medium. The presence of metallic Co causes Co-Mo oxides to evolve from amorphous to crystalline structures. The coupling interface produced between metallic Co and Co-Mo oxides is proven to facilitate electron transport in addition to extensively accessible and highly electroactive Co-Mo oxide nanoflower architecture. The experimental results reveal that the overpotentials for OER and UOR in the CoMoO@Co/GF electrode require only 269 and 115 mV to obtain a current density of 10 mA cm -2 , respectively. Furthermore, with the aid of urea, the overpotential for HER at the current density of 10 mA cm -2 is lowered to 155 mV. Most notably, the constructed CoMoO@Co/GF-based electrolytic cell only requires a 1.5 V dry battery to achieve effective H 2 evolution and noteworthy stability, outperforming the commercial catalyst-based device and many previous results. The combination of experiments and theoretical calculations further clarifies the active sites in the catalyst. What's more, the pathway of electron transfer in the catalytic process is defined., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier Inc.)

Urea electrolysis is a promising approach to produce hydrogen while simultaneously purifying urea-rich wastewater. In practice, it is highly desirable but still challenging, through the structure construction strategy, to implement a method with controllable synthesis of ultra-thin nanosheet arrays with rich interfaces, and then apply them into the catalysis operations of hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). In this work, the bifunctional electrocatalyst Ni 2 P/NiCoP nanosheets anchored nickel foam (NF) were prepared with ultra-thin rich interfaces by regulating the Co- and P-doping. The results showed that the elaborated Ni 2 P/NiCoP/NF electrode delivered the excellent electrocatalytic activities for both UOR and HER operations. Particularly for UOR, it required only a cell voltage of 1.41 V at 100 mA cm -2 , which was 400 mV lower than that in the traditional overall water splitting operation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

In recent years, low-cost, non-noble metal-based and stable catalysts have gained attention for the development of clean energy devices. Additionally, the synthesis of materials that can exhibit more than one electrocatalytic reaction is notable. In this work, stepwise electrodeposited nickel-iron hydroxide nanoarrays are investigated as anode electrocatalysts with enhanced performance towards the oxidation of water, urea, and hydrazine. The stepwise electrodeposited nickel-iron hydroxide (NiFe(OH) 2 -SD/NF) electrodes show excellent electrocatalytic activity and stability for the oxygen evolution reaction (OER) with a low potential of 1.45 V (vs RHE) at a current density of 10 mA cm -2 . These electrodes further display excellent catalytic activity towards the urea oxidation reaction (UOR) and hydrazine oxidation reaction (HzOR) with potentials lower than 1.32 V (vs RHE) and 0.06 V (vs RHE), respectively. Owing to synergistic effects, a porous structure for mass transport leads to excellent electrocatalytic performance. This non-precious-metal nickel-iron hydroxide, prepared by a simple synthesis approach, is promising for hybrid water electrolysis applications and the development of environmentally friendly clean energy reactions., (Copyright © 2019. Published by Elsevier Inc.)