Search

Seawater electrolysis offers a renewable, scalable, and economic means for green hydrogen production. However, anode corrosion by Cl- pose great challenges for its commercialization. Herein, different from conventional catalysts designed to repel Cl- adsorption, we develop an atomic Ir catalyst on cobalt iron layered double hydroxide (Ir/CoFe-LDH) to tailor Cl- adsorption and modulate the electronic structure of the Ir active center, thereby establishing a unique Ir-OH/Cl coordination for alkaline seawater electrolysis. Operando characterizations and theoretical calculations unveil the pivotal role of this coordination state to lower OER activation energy by a factor of 1.93. The Ir/CoFe-LDH exhibits a remarkable oxygen evolution reaction activity (202 mV overpotential and TOF = 7.46 O2 s−1) in 6 M NaOH+2.8 M NaCl, superior over Cl--free 6 M NaOH electrolyte (236 mV overpotential and TOF = 1.05 O2 s−1), with 100% catalytic selectivity and stability at high current densities (400-800 mA cm−2) for more than 1,000 h. The seawater oxidation reaction faces challenges from competitive chloride oxidation reaction. Herein, the authors have utilized chlorine adsorption to modulate the single-atom Ir coordination state and promote seawater oxidation and catalyst stability. [ABSTRACT FROM AUTHOR]

Understanding the correlation between the structural evolution of electrocatalysts and their catalytic activity is both essential and challenging. In this study, we investigate this correlation in the context of the oxygen evolution reaction (OER) by examining the influence of structural disorder during and after dynamic structural evolution on the OER activity of Fe−Ni (oxy)hydroxide catalysts using operando X‐ray absorption spectroscopy, alongside other experiments and theoretical calculations. The Debye–Waller factors obtained from extended X‐ray absorption fine structure analyses reflect the degree of structural disorder and exhibit a robust correlation with the intrinsic OER activities of the electrocatalysts. The enhanced OER activity of in situ‐generated metal (oxy)hydroxides derived from different pre‐catalysts is linked to increased structural disorder, offering a promising approach for designing efficient OER electrocatalysts. This strategy may inspire similar investigations in related electrocatalytic energy‐conversion systems. [ABSTRACT FROM AUTHOR]

Exploring efficient transition-metal-based electrocatalysts for oxygen evolution reaction (OER) is imperative but remain challenging for sustainable energy storage and conversion systems. Foreign species doping is a significant regulation strategy to enhance the intrinsic activity of host matrix. However, the potential relationship of structure-activity caused by guest doping elements is seldom tracked systematically. In this case, both theoretical screening and experimental verification are complementarily employed to investigate the guest doping effects of ten first-row transition metals (Sc~Zn) on bimetallic NiCo layered double hydroxide (NiCo-LDH). As a result, the optimized Fe-doped NiCo-LDH is identified as the most promising candidate toward alkaline electrocatalytic OER, which exhibits the quasi-industrial current density of 1000 mA cm-2 at overpotential of400 mV. Meanwhile, it also shows impressively long-term stability of 500 h at 500 mA cm-2 with a negligible activity loss. Moreover, in situ electrochemical Raman spectroscopy unveils the dynamic structure evolution from pre-catalytic state (Fe-NiCo-LDH) to metal oxyhydroxide (Fe-(NiCo)OOH) during the oxidation reaction, and ab-initio molecular dynamics simulations are further performed to confirm the thermodynamic stability of activated Fe-(NiCo)OOH phase. This work provides a promising platform for exploring the critical role of transition metal guest doping on host matrix in developing industrially required OER electrocatalysts. [ABSTRACT FROM AUTHOR]

The key issue in the 5‐hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co‐doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3‐fold increase in peak current density. DFT calculations and in situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+−O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+−O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+−O. [ABSTRACT FROM AUTHOR]

Developing efficient electrocatalysts for the oxygen evolution reaction (OER) is paramount to the energy conversion and storage devices. However, the structural complexity of heterogeneous electrocatalysts makes it a great challenge to elucidate the dynamic structural evolution and OER mechanisms. Here, we develop a controllable atom‐trapping strategy to extract isolated Mo atom from the amorphous MoOx‐decorated CoSe2 (a‐MoOx@CoSe2) pre‐catalyst into Co‐based oxyhydroxide (Mo‐CoOOH) through an ultra‐fast self‐reconstruction process during the OER process. This conceptual advance has been validated by operando characterizations, which reveals that the initially rapid Mo leaching can expedite the dynamic reconstruction of pre‐catalyst, and simultaneously trap Mo species in high oxidation state into the lattice of in situ generated CoOOH support. Impressively, the OER kinetics of CoOOH has been greatly accelerated after the reverse decoration of Mo species, in which the Mo‐CoOOH affords a markedly decreased overpotential of 297 mV at the current density of 100 mA cm−2. Density functional theory (DFT) calculations demonstrate that the Co species have been greatly activated via the effective electron coupling with Mo species in high oxidation state. These findings open new avenues toward directly synthesizing atomically dispersed electrocatalysts for high‐efficiency water splitting. [ABSTRACT FROM AUTHOR]

Efficient electrocatalytic reactions require a coordinated active center that may provide a properly reaction intermediates adsorption in water splitting. Herein, a Ni active center coordination reconstruction method achieved by multidimensional modulation of phase transition, iodine coordination, and vacancy defects is designed and implemented. This coordination reconstruction results in the successful synthesis of Ni5P4−xIx/Ni2P nanocorals that show outstanding bifunctional catalytic activity due to deep optimization of the adsorption energy. The overpotentials of hydrogen evolution reaction and oxygen evolution reaction at 10 mA cm−2 are 46 and 163 mV, respectively. Only 1.46 V is required to drive alkaline overall water splitting. Novel coordination environment is investigated by electron paramagnetic resonance spectroscopy and extended X‐ray absorption fine structure spectroscopy. A 4D integrated material design strategy of "thermodynamic stability‐electronic properties‐charge transfer‐adsorption energy" for water‐splitting catalysts is proposed. This coordination reconstruction concept and material design method provide new perspectives for the research of novel catalysts. [ABSTRACT FROM AUTHOR]

High-content atomically distributed W(V , VI) coordinated with O atoms as WO2 moieties anchored on FeCo layered double hydroxide (FeCo LDH) nanosheets in the structure of SAC W–FeCo LDH is obtained by a facile coprecipitation method, and it presented clearly enhanced stable OER electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Rational design of efficient non‐precious materials for oxygen redox electrocatalysis is currently a critical obstacle for rechargeable zinc‐air batteries. Herein, this work presents a strategy to modulate the activity and mass transfer performance for advanced bifunctional electrocatalysts. This is achieved via a prior vacuum heat treatment‐assisted pyrolysis approach, obtaining atomically disperse Fe/Co sites and alloy nanoparticle composites rooted in the unique well‐aligned nanotubes hierarchical architecture. The design of multiple metal active species and hierarchically porous structure facilitates the bifunctional activity and accessibility of the active sites, respectively, which affords the catalyst enhanced performance in rechargeable zinc‐air batteries, outperforming the commercial Pt/C‐Ir/C benchmarks. This work provides a new avenue to improve activity and accessibility together with single atomic catalysts as advanced bifunctional air cathodes for efficient oxygen redox electrocatalysis. [ABSTRACT FROM AUTHOR]

Uncovering the dynamics of active sites in the working conditions is crucial to realizing increased activity, enhanced stability and reduced cost of oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane electrolytes. Herein, we identify at the atomic level potential-driven dynamic-coupling oxygen on atomically dispersed hetero-nitrogen-configured Ir sites (AD-HN-Ir) in the OER working conditions to successfully provide the atomically dispersed Ir electrocatalyst with ultrahigh electrochemical acidic OER activity. Using in-situ synchrotron radiation infrared and X-ray absorption spectroscopies, we directly observe that one oxygen atom is formed at the Ir active site with an O-hetero-Ir-N4 structure as a more electrophilic active centre in the experiment, which effectively promotes the generation of key *OOH intermediates under working potentials; this process is favourable for the dissociation of H2O over Ir active sites and resistance to over-oxidation and dissolution of the active sites. The optimal AD-HN-Ir electrocatalyst delivers a large mass activity of 2860 A gmetal−1 and a large turnover frequency of 5110 h−1 at a low overpotential of 216 mV (10 mA cm−2), 480–510 times larger than those of the commercial IrO2. More importantly, the AD-HN-Ir electrocatalyst shows no evident deactivation after continuous 100 h OER operation in an acidic medium. Uncovering the dynamics of active sites in the working conditions is important yet challenging. Here the authors identify dynamic-coupling oxygen on atomically dispersed iridium sites during oxygen evolution reaction using in situ techniques. [ABSTRACT FROM AUTHOR]

Developing highly efficient and earth‐abundant electrocatalysts for the oxygen evolution reaction (OER) is significantly important for water‐splitting. Here, for the first time it is reported that the physically adsorbed metal ions (PAMI) in porous materials can be served as highly efficient OER electrocatalysts, which provides a universal PAMI method to develop electrocatalysts. This PAMI method can be applied to almost all porous supports, including graphene, carbon nanotubes, C3N4, CaCO3, and porous organic polymers and all the systems exhibit excellent OER performance. In particular, the as‐synthesized Co0.7Fe0.3CB exhibits a small overpotential of 295 mV and 350 mV at the current density of 10 mA cm−2 and 100 mA cm−2, respectively, which exceeds commercial 40 wt% IrO2/CB and most reported non‐noble metal‐based OER catalysts. Moreover, the mass activity of Co0.7Fe0.3CB reaches 643.4 A g−1 at the overpotential of 320 mV, which is nearly 4.7 times higher than that of 40 wt% IrO2/CB. In addition, the advanced ex situ and in situ synchrotron X‐ray characterizations are carried out to unravel the PAMI synthetic process. In short, this PAMI method will break the conversional understanding, i.e., the most OER catalysts are synthesized chemically, because the new PAMI method does not require any chemical synthesis, which therefore opens a new avenue for the development of OER electrocatalysts. [ABSTRACT FROM AUTHOR]

The binding strength of reactive intermediates with catalytically active sites plays a crucial role in governing catalytic performance of electrocatalysts. NiFe hydroxide offers efficient oxygen evolution reaction (OER) catalysis in alkaline electrolyte, however weak binding of oxygenated intermediates on NiFe hydroxide still badly limits its catalytic activity. Now, a facile ball‐milling method was developed to enhance binding strength of NiFe hydroxide to oxygenated intermediates via generating tensile strain, which reduced the anti‐bonding filling states in the d orbital and thus facilitated oxygenated intermediates adsorption. The NiFe hydroxide with tensile strain increasing after ball‐milling exhibits an OER onset potential as low as 1.44 V (vs. reversible hydrogen electrode) and requires only a 270 mV overpotential to reach a water oxidation current density of 10 mA cm−2. NiFe hydroxide was treated by ball‐milling to enhance its binding strength to an oxygenated intermediate. The prepared NiFe hydroxide that has induced tension shows excellent oxygen evolution performance. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate for the first time the one-step synthesis of ultrathin α-Co(OH)2 nanomeshes by an imidazole-directed route. The α-Co(OH)2 nanomeshes combine the advantages of ultrathin thickness (3 nm), small mesopores (3.7 nm), large specific surface area (181.1 m2 g−1) and high surface oxygen vacancy density, which exhibit excellent electrocatalytic performance for the oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

Ni–Co amorphous double hydroxides nanomaterials with a hollow structure and tunable Ni/Co molar ratio are synthesized using a template method. The amorphous NiCo2.7(OH)x nanocages demonstrate high surface reactivity, comparable catalytic activity, and excellent stability for efficient water oxidation. Density functional theory simulations suggest that the component‐dependent electrocatalytic activities are connected to the binding energies of oxygen radical on diverse hydroxides. [ABSTRACT FROM AUTHOR]

Developing effective catalysts based on earth abundant elements is critical for CO2 electroreduction. However, simultaneously achieving a high Faradaic efficiency (FE) and high current density of CO (jCO) remains a challenge. Herein, we prepare a Mn single-atom catalyst (SAC) with a Mn-N3 site embedded in graphitic carbon nitride. The prepared catalyst exhibits a 98.8% CO FE with a jCO of 14.0 mA cm−2 at a low overpotential of 0.44 V in aqueous electrolyte, outperforming all reported Mn SACs. Moreover, a higher jCO of 29.7 mA cm−2 is obtained in an ionic liquid electrolyte at 0.62 V overpotential. In situ X-ray absorption spectra and density functional theory calculations demonstrate that the remarkable performance of the catalyst is attributed to the Mn-N3 site, which facilitates the formation of the key intermediate COOH* through a lowered free energy barrier. Developing effective catalysts based on earth abundant elements is critical for electrochemical CO2 reduction. Here, the authors prepare a manganese single atom catalyst with high CO2 reduction performance, which can be attributed to the Mn-N3 site embedded in graphitic carbon nitride. [ABSTRACT FROM AUTHOR]

The reasonable design and construction of single-atom electrocatalysts with low-cost and excellent intrinsic activity for oxygen reduction reaction (ORR) is indispensable in metal-air batteries. Herein, a facile isolation anchoring strategy was reported for in situ formation of porous N-doped carbon catalysts (Fe 1 /NC) rich in Fe single atoms. The d -glucose, zinc gluconate and N-rich histidine were deployed as spatial isolation agents and anchoring agents to inhibit iron atom aggregation during the high-temperature pyrolysis. The as-synthesized Fe 1 /NC catalyst shows remarkable stability and superior ORR electrocatalytic activity under both alkaline and acidic conditions owing to highly dispersed Fe–N 4 sites, especially with a half-wave potential up to 0.91 V in 0.1 M KOH, exceeding 60 mV compared with Pt/C. Notably, the Fe 1 /NC-based Zn-air battery exhibits maximal power density of 164 mW cm−2, large specific capacities of 769 mA h g Zn −1, excellent cycle stability over 300 h, and great potential in renewable energy conversion electronics. A facile isolation anchoring strategy was reported to synthesize the Fe single-atom electrocatalyst that exhibits excellent ORR catalytic efficiency and long-term stability in both three electrodes system and zinc-air battery due to the abundant Fe–N 4 active sites. [Display omitted] • A facile isolation anchoring strategy was reported to prepare Fe single-atom electrocatalyst. • d -glucose, zinc gluconate and N-rich histidine were deployed as spatial isolation and anchoring agents. • The electrocatalysts exhibit superior ORR performance due to the abundant Fe–N 4 active sites. • The Zn-air battery assembled with Fe 1 /NC displays a high discharge specific capacity and excellent cyclic stability. [ABSTRACT FROM AUTHOR]

[Display omitted] Broadly, the oxygen evolution reaction (OER) has been deeply understood as a significant part of energy conversion and storage. Nevertheless, the anions in the OER catalysts have been neglected for various reasons such as inactive sites, dissolution, and oxidation, amongst others. Herein, we applied a model catalyst s-Ni(OH) 2 to track the anionic behavior in the catalyst during the electrochemical process to fill this gap. The advanced operando synchrotron radiation Fourier transform infrared (SR-FTIR) spectroscopy, synchrotron radiation photoelectron spectroscopy (SRPES) depth detection and differential X-ray absorption fine structure (Δ-XAFS) spectrum jointly point out that some oxidized sulfur species (SO 4 2−) will self-optimize new Ni–S bonds during OER process. Such amazing anionic self-optimization (ASO) behavior has never been observed in the OER process. Subsequently, the optimization-derived component shows a significantly improved electrocatalytic performance (activity, stability, etc.) compared to reference catalyst Ni(OH) 2. Theoretical calculation further suggests that the ASO process indeed derives a thermodynamically stable structure of the OER catalyst, and then gives its superb catalytic performance by optimizing the thermodynamic and kinetic processes in the OER, respectively. This work demonstrates the vital role of anions in the electrochemical process, which will open up new perspectives for understanding OER and provide some new ideas in related fields (especially catalysis and chemistry). [ABSTRACT FROM AUTHOR]

Given the efficiency, stability and sustainability, the carbon-based materials have become one of promising bifunctional electrocatalysts to the electrochemical water splitting, involving hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, there are still many challenges about the design and mechanism study of the carbon-based electrocatalysts. In this paper, we reported B, N co-doping carbon nanosheets which were synthesized via cationic intercalation stripping guar gum carbon aerogels pre-crosslinked by borate, B(OH) 4 -. This facile strategy not only realizes the structure tailoring, but also concurrently improves the doping efficiency and the stability of the hetero atoms. Specifically, the cost-efficient carbon-based bifunctional catalyst (B5/GCS) shows an outstanding HER and OER performance displaying a remarkable activity both in acidic and alkaline media, low onset potentials for both HER (39.12 mV) and OER (1.38 V) in the same electrolyte (0.5 M H 2 SO 4). Notably, when employed as the bifunctional electrocatalysts with a two-electrode electrolyzer for water splitting, the B5/GCS generated a cell voltage of 1.45 V to attain 10 mA cm−2 in 0.5 M H 2 SO 4. Furthermore, a series of experiments combining density functional theory calculations revealed that the observed superb water splitting activity could be attributed to a synergistic effect of N, B co-doping and the formation of fragmented nanosheets with topological defects, which collaboratively promotes the proton adsorption and catalytic kinetics. A advanced carbon-based bifunctional catalyst are designed and fabricated by a facile two-step strategy - borate chemical crosslinking guar gum gel and subsequent cationic intercalation stripping, as water splitting catalyst, the optimal B5/GCS exhibits extraordinary HER and OER performance – on par with the benchmark noble metal catalyst. Image 1 [ABSTRACT FROM AUTHOR]

The sluggish kinetics and high overpotential of oxygen evolution reaction (OER) at anode hinders water splitting large-scale application. Recently, an anode alternative strategy exhibits promising prospect of application to improve reaction kinetics and decrease overpotential. Here, single dispersed Ru-anchored porous Pt 3 Ni alloy (Ru 1 -Pt 3 Ni/NiF) were successfully synthesized via spontaneous galvanic reduction, over which highly selective electrooxidation of ethanol into acetate was realized. DFT calculations show that Ru modification introduced abundant active oxygen species (OH*), which not only enhanced the oxidation activity of ethanol, but also increased the selectivity for C2 oxidation pathway. Then a Ru 1 -Pt 3 Ni/NiF||Pt 3 Ni/NiF ethanol oxidation membrane-free cell was built to couple the ethanol electrooxidation with H 2 evolution, where the Faraday efficiency of H 2 production reaches 94% and the power consumption is 19.24 kWh kg H2 −1. This work provides a cost-competitive and energy-saving strategy for high-purity H 2 generation, opening new opportunities for electric energy utilization from renewable sources. [Display omitted] • Single-dispersed Ru anchored Pt 3 Ni alloys were synthesized via spontaneous galvanic reduction process. • Selective electrooxidation of ethanol to acetate was realized over Ru 1 -Pt 3 Ni/NiF. • DFT calculations revealed that Ru promoted the charge transfer and reduced the Gibbs free formation energy of OH*. • Membrane-free pure H 2 production via coupling HER and ethanol selective electrooxidation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three-dimensional ordered macroporous frameworks with NiN 4 sites were obtained. • 3DOM Ni N C was highly efficiency for ORR and OER performances in neutral condition. • The neutral zinc-air batteries exhibited outstanding long term stability of 580 cycles at 1.0 mA cm−2. • The failure mechanism of air electrode in neutral condition was revealed. Neutral zinc-air batteries prevent the carbon based catalysts from being oxidized during cycling, which show excellent potential for long-term energy storage. Three-dimensional ordered macroporous nitrogen doped carbon frameworks with NiN 4 (3DOM Ni N C) were constructed by in situ reaction of Ni nanoparticles and dicyandiamide. The 3DOM Ni N C bifunctional catalysts exhibit comparable oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) efficiency and stablity. The 3D interconnected structure of 3DOM Ni N C provides sufficient channel for mass transfer, resulting in high power density (35 mW cm−2) and long cycle life (580 cycles) of neutral zinc-air batteries. Meanwhile the failure mechanism in neutral electrolyte was discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ru clusters are immobilized on hierachical Ni 3 N arrays. • The interfacial Ru atoms enable long-range Ni atoms as active sites via electron delocalization. • The H 2 O and H* adsorption energies are strengthened and weakened, respectively. • An outperforming Pt/C benchmark activity is achieved at ≥ 125 mA cm−2. Hydrogen (H 2) production from alkaline water electrocatalysis is economically appealing yet significantly hindered by the sluggish H 2 O adsorption and H* binding kinetics on active sites during hydrogen evolution reaction (HER). Herein, we interfacially immobilize Ru clusters on the hierarchical nickel nitride (Ru-Ni 3 N) nanosheet arrays via the filling of Ru3+ species into the metal vacancies of nickel hydroxide precursors and the subsequent controllable nitridation. The optimized Ru-Ni 3 N shows the outstanding HER performance, affording a 30-fold rise in the intrinsic activity of Ni sites, a outperforming-Pt/C overpotential at ≥ 125 mA cm−2 while remaining a robust stability. We further establish by a combined study of density functional theory (DFT) calculations with experimental analyses that long-range Ni sites around Ru sites act as active sites via the electron delocalization, remarkably weakening the H 2 O adsorption and H* binding barriers for enhancing the alkaline HER kinetics. Moreover, it also demonstrates an excellent pH-universal HER and overall water splitting performance. [ABSTRACT FROM AUTHOR]

In this study, phosphate FeCo(H 3 O)(PO 4) 2 nanosheet arrays (NAs) were synthesized using an electrochemical strategy. FeCo(H 3 O)(PO 4) 2 NAs as precatalyst could undergo significant self-reconstruction, including leaching of phosphate anions and electro-oxidation of Co2+ during anodizing at the potential range of oxygen evolution reaction (OER) in 1 M KOH solution, eventually resulting in the formation of Fe 0.5 Co 0.5 OOH NAs with low crystallinity. The high content of Fe in Fe 0.5 Co 0.5 OOH NAs promoted the formation of active Fe3+–O–Fe3+ motifs that increased OER occurrence. Additionally, Fe incorporation increased the ratio of the reaction rate constants of oxygen evolution to Co3+/Co4+ (k OER /k M,ox) and enhanced the reaction order on the hydroxyl ion. These factors significantly contributed to the outstanding OER catalytic performances of Fe 0.5 Co 0.5 OOH NAs. [Display omitted] Fe 0.5 Co 0.5 OOH nanosheet arrays (NAs) were fabricated via electrochemical self-reconstruction of CoFe(H 3 O)(PO 4) 2 NAs. Benefiting from the formation of active Fe3+–O–Fe3+ motifs, Fe incorporation increased the ratio of the reaction rate constants of oxygen evolution to Co3+/Co4+ (k OER /k M,ox) and enhanced the reaction order on the hydroxyl ion, Fe 0.5 Co 0.5 OOH NAs exhibited outstanding catalytic performances of oxygen evolution reaction. • Fe 0.5 Co 0.5 OOH was synthesized via self-reconstruction of CoFe(H 3 O)(PO 4) 2. • High content of Fe promoted the formation of [di-μ-O(OH)] Fe3+–O–Fe3+ in Fe 0.5 Co 0.5 OOH. • [di-μ-O(OH)] Fe3+–O–Fe3+ motifs in oxyhdroxide acted as OER active sites. • Fe incorporation varied the electrokinetic parameters of oxyhydroxide. • [di-μ-O(OH)] Fe3+–O–Fe3+ motifs further increased the reaction order on the OH-. [ABSTRACT FROM AUTHOR]

Tandem Catalysis on dual active sites A highly-efficient electrocatalyst containing dual active sites of Fe-NiOOH and NiC 4 single atoms was synthesized, and a tandem catalysis mechanism of OER on dual active sites was proposed to reveal the high-activity origin of the catalysts. This work provides a new concept of tandem catalysis to develop the electrocatalysts with many elementary steps, like OER and ORR. [Display omitted] • A highly-efficient electrocatalyst containing dual active sites of Fe-NiOOH and NiC 4 single atoms was synthesized. • The dual active site electrocatalyst shows obviously better OER performance than the corresponding single active site one. • A tandem catalysis mechanism was proposed to reveal the synergistic catalysis of two active centers. • This work provides a new concept of tandem catalysis to develop the electrocatalysts with many elementary steps, like OER and ORR The high voltage in oxygen evolution reaction (OER) often causes structural change in electrocatalysts and forms multiple active sites. Therefore, exploring the synergy of various active sites is extremely significant to develop catalysts for OER with multiple elementary steps. Herein, we adopt the physically adsorbed metal ions method to successfully synthesize a highly-efficient electrocatalyst containing the dual active sites of Fe-NiOOH and NiC 4 single atoms (marked as Ni SAs/Fe-NiOOH). The Ni SAs/Fe-NiOOH displays outstanding OER performance with an overpotential of 269 mV to deliver current density of 10 mA/cm2 that shows 55 mV superior to commercial IrO 2 /CB at the same condition. Experiments and density functional theory calculations indicate that the excellent OER activity of Ni SAs/Fe-NiOOH catalyst is attributed to the synergy of dual active sites of NiC 4 SAs and Fe-NiOOH. A tandem catalysis mechanism is also proposed to reveal the synergism of two active centers, which makes the potential-determining step more facile and accordingly decreases the OER overpotential. This work offers a new concept of tandem catalysis to develop the electrocatalysts with many elemental steps, like OER and oxygen reduction reaction catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Self-supported electrocatalysts are prepared via solid-state diffusion. • Effective mass-transfer between carbon-layers and Ni endowing electrocatalyst with ultrahigh activity. • The district confinement of CNTs and heteroatomic doping collaboratively promotes kinetics. To satisfy the practical requirements of electrochemical water splitting, developing a flexible, effective and sustainable approach for scalable production of bifunctional electrocatalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a tremendous issue to be rationally addressed. Herein, a solid-state diffusion strategy with Ni foam and N-doped carbon layers is applied to prepare multi-interfacial, self-supported and N-doped carbon nanotube (NCNT) encapsulated Ni nanoparticles (NPs) array bifunctional electrocatalyst (NCNT-NP@NF). Prominently, this NCNT-NP@NF is scalable to meet the application requirements and can be used as a binder-free electrode for direct the water splitting. The optimal sample demonstrate outstanding HER/OER performance in 1.0 M KOH, with low overpotential (η 10) at 10 mA cm−2 during HER (96.1 mV) and OER (240 mV) process, which is extremely superior to the most reported metal-based electrocatalysts and even better than commercial IrO 2 (400 mV at 10 mA cm−2 for OER). Strikingly, when these bifunctional electrocatalysts are employed in a dual-electrode electrolyzer for water splitting, the NCNT-NP@NF only needs cell voltage of 1.54 V to drive overall water splitting in 1.0 M KOH, and displays excellent long-term stability (150 h for water splitting). Moreover, experiments combined with density functional theory (DFT) calculations clarify that the remarkable electrochemical activity and stability are mainly attribute to the synergistic effect of the uniform distribution of Ni NPs, heteroatomic doping, as well as district confinement effect of NCNT leading to enhanced electronic multi-interfacial transmission, all these factors co-accelerate electrocatalytic kinetics. Accordingly, this solid-state diffusion method possesses a favorable potential to construct a multi-interfacial and self-supported electrocatalysts in the fields of sustainable supply of clean energies. [ABSTRACT FROM AUTHOR]

A novel structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) composed of defect-rich NiO phase and Ni clusters anchored on outside of nanotubes is presented. The d-band downshifted by Fe-doping, coupled of Ni clusters and defect-rich nature greatly improve electrocatalytic performances of Fe-NiO-Ni CHNAs toward oxygen evolution reaction. • A multi-level structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) was synthesized as a catalyst for OER. • Fe-NiO-Ni CHNAs exhibits overpotential of 245 mV at 10 mA cm−2 and outstanding durability that surpasses most of transition metal oxides. • The improved OER activity is mainly because Fe doping downshifts the d-band of metal sites. • Fe-NiO-Ni CHNAs obeyed the adsorbate evolution mechanism with a nonconcerted proton-electron transfer pathway. Herein we present a novel multi-level structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) grown on carbon fiber cloth as an efficient catalyst for oxygen evolution reaction. In this multi-level structure, rocksalt-type Fe-doped NiO phase hybrids with Ni clusters coupled into the nanospheres anchored to the outside of nanotube, forming a unique 3D corn-like structure. This novel multi-level structure represents a large specific area for catalytic reaction. X-ray absorption fine structure indicates that the defect-rich Fe-doped NiO phase has abundant coordinative unsaturated sites as active sites, and Fe doping downshifts the d-band of metal sites, which is the main contribution to the improved oxygen evolution reaction catalytic activity. The OER of Fe-NiO-Ni CHNAs obeys the adsorbate evolution mechanism with the nonconcerted proton-electron transfer pathway as a rate-determining step. Thus Fe-doped NiO CHNAs exhibits excellent OER performance and outstanding durability that surpasses most of transition metal oxides. [ABSTRACT FROM AUTHOR]

• Inherent chemical cross-linking gives M-SA@NCA an ultra-high single-atom loading. • More active sites and excellent stability in overwater splitting process. • Pivotal synergy optimize electric structure via different configuration. Rationally designing single-atom catalysts (SACs) is a potential strategy to reach efficient energy conversion as they combine the merits of both maximizing atomic utilization and minimizing the cost of the heterogeneous catalysts. However, when increasing the loading capacity of single-atoms, how to effectively prevent the aggregation of metal single atoms to achieve higher atom utilization efficiency is an urgent issue. Herein, we develop an in-situ pre-crosslinking method to prepare a series of metal single-atoms anchored on nitrogen-doped carbon aerogel (M-SA@NCA, M = Co, Ni, Mo) as high-efficiency bifunctional catalysts for hydrogen/oxygen evolution reactions (HER/OER). Thanks to the intrinsic chemical crosslinking ability between the metal ions and the substrate functional groups, these metal single-atoms can be effectively and stably anchored in the three-dimensional network as crosslinked point of the substrate, thus endowing M-SA@NCA with ultrahigh single-atom loading (Co, ~27.30 wt%; Ni, ~18.35 wt%; Mo, ~18.16 wt%), and therefore display more active sites, and excellent stability (up to 100 h for water-splitting in 1.0 M KOH). Furthermore, the systematic X-ray absorption fine structure (XAFS), in-situ attenuated total internal reflection (in-situ ATR spectra) and density functional theory (DFT) calculation are used to acquire deep insight on the bonding modes between metal single-atoms and substrates, and the influence of different configuration on the catalytic performance. The combined results reveal that Co atoms facilitate the formation of pyrr-N, and the optimal configuration is CoN 4 in HER process with smallest onset potential of 12.5 mV, closing to the Pt/C (20 wt%); while the best OER catalyst is Ni-SA@NCA with NiC 2 N 2 -o-5 moieties, outperforming the benchmarked IrO 2. This work provides a solution for investigating the interaction between single-atom-substrate configuration and catalytic performance, and represents a critical step towards the rational design and synthesis of SACs with extremely high single-atom loading, maximum atomic utilization efficiency and thus superior catalytic activity. [ABSTRACT FROM AUTHOR]

Seeking the cost-effective and stable electrocatalysts is urgent for oxygen evolution reaction (OER). The surface reconstruction is the key to improve the OER activity of catalysts. Herein, a simple and scalable pyrolysis approach is applied to prepare a novel self-supported electrode. This electrode is consisted of cobalt molybdate (CoMo 1 O 4) nanoparticles in-situ grow on carbon fiber paper (CP), termed as CoMo 1 O 4 @CP. And Mo-doped cobalt oxyhydroxide (Mo 1 –CoOOH) is generated from structural evolution occurring on the surface of CoMo 1 O 4 @CP. The Mo 1 –CoOOH@CP exhibits highly OER activity, which is verified by a low current overpotential of 274 mV at 10 mA cm−2, small Tafel slope (66 mV dec−1) and long-term stability (100 h) in 1 M KOH solution. In-situ Raman spectroscopy and density functional theory (DFT) calculations jointly reveal that etching of MoO 4 2- enable the surface structure of CoMo 1 O 4 @CP electrode transformation to Mo 1 –CoOOH@CP, and thereby bring dramatically enhanced OER activity. This study presents an effective approach on surface self-reconstruction of catalysts, with the characteristic of favorable OER activity, simple process and low cost. Accordingly, this sort of electrocatalyst demonstrates feasible applications in the fields of energy storage and conversion. • CoMo 1 O 4 @CP was synthesized via a facile pyrolysis approach. • The etching of MoO 4 2- cause the in-situ formed oxohydroxide. • The Mo 1 –CoOOH@CP shows low overpotential and long-term stability for OER. • This study presents an effective approach on surface reconstruction of catalysts. [ABSTRACT FROM AUTHOR]