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Ni-doped CoTe nanorods have been prepared for 5-hydroxymethylfurfural oxidation reaction. The doping of Ni facilitates the oxidation of Co2+ to high-valent CoO 2 to achieve efficient electrosynthesis of the valuable 2,5-furandicarboxylic acid. [Display omitted] • A crude nanorod structure CoNiTe was prepared by two-step hydrothermal reactions for HMFOR. • Ni doping modulates the electronic structure of Co and improves the electrocatalytic performance of CoNiTe. • The generation of high-valent cobalt is the key for excellent HMFOR. Replacing the anodic oxygen evolution reaction (OER) in water splitting with 5-hydroxymethylfurfural oxidation reaction (HMFOR) can not only reduce the energy required for hydrogen production but also yield the valuable chemical 2,5-furandicarboxylic acid (FDCA). Co-based catalysts are known to be efficient for HMFOR, with high-valent Co being recognized as the main active component. However, efficiently promoting the oxidation of Co2+ to produce high-valent reactive species remains a challenge. In this study, Ni-doped CoTe (CoNiTe) nanorods were prepared as efficient catalysts for HMFOR, achieving a high HMFOR current density of 65.3 mA cm−2 at 1.50 V. Even after undergoing five successive electrolysis processes, the Faradaic efficiency (FE) remained at approximately 90.7 %, showing robust electrochemical durability. Mechanistic studies indicated that Ni doping changes the electronic configuration of Co, enhancing its charge transfer rate and facilitating the oxidation of Co2+ to high-valent CoO 2 species. This work reveals the effect of Ni doping on the reconfiguration of the active phase during HMFOR. [ABSTRACT FROM AUTHOR]

Herein, we report an easily oxidized Co–Fe perovskite fluoride as an efficient catalyst for the oxygen evolution reaction (OER). In situ Raman spectroscopy showed that the presence of F promotes reconstruction to form highly active (Co3+Fe3+)OOH, and the current density of 10 mA cm−2 can be achieved at the overpotential of only 118 mV in 1 M KOH aqueous solution. This work helps to understand the role of fluoride during the OER. [ABSTRACT FROM AUTHOR]

We reported that Cu octahedra modified with low-coordinated Cu nanocluster (Cu oct @Cu_NCs) as an efficient electrocatalyst for CO 2 RR to C 2 H 5 OH. Cu oct @Cu_NCs has been synthesized by a simple solution precipitation and electroreduction. In situ Raman spectra confirmed that the defect-sites-rich Cu nanoclusters can promote the adsorption of *CO and increase the *CO coverage on Cu octahedra enclosed by Cu(1 1 1), hence facilitating the formation of C 2 H 5 OH. Thus, compared to the bare Cu octahedra, the Cu oct @Cu_NCs exhibit superior C 2 H 5 OH selectivity. [Display omitted] • Cu oct @Cu_NCs, Cu octahedra modified with low-coordinated Cu nanoclusters, were prepared by solution precipitation and electroreduction methods. • The defect-sites-rich Cu nanoclusters can promote the adsorption of *CO and increase the *CO coverage on Cu octahedra enclosed by Cu(1 1 1). • Cu oct @Cu_NCs have excellent selectivity for CO 2 RR to C 2 H 5 OH, which deliverd the FEs toward C 2 H 5 OH and C2 + products as high as 48.16 % and 83.31 % at −1.17 V vs. RHE. Copper (Cu) electrocatalysts for carbon dioxide reduction reaction (CO 2 RR) have attracted much attention due to their ability to produce high value-added C 2+ products (e.g., C 2 H 4 , C 2 H 5 OH, and n-propanol). However, achieving high selectivity of Cu electrocatalysts for C 2 H 5 OH in aqueous-based electrolytes remains a significant challenge. In this paper, we report Cu octahedra modified with low-coordinated Cu nanoclusters (Cu oct @Cu_NCs) as an efficient electrocatalyst for CO 2 RR to C 2 H 5 OH. Notably, the defect-site-rich Cu nanoclusters can promote the adsorption of *CO and increase the *CO coverage on Cu octahedra enclosed by Cu(1 1 1), thus promoting CO 2 RR to C 2 H 5 OH. We achieved a high Faradaic efficiency (FE) of 48.16 % for C 2 H 5 OH, and that of the C 2+ products is 83.31 % at −1.17 V vs. RHE. This study provides a surface nanostructured route for rationalizing efficient and selective copper electrocatalysts for CO 2 RR. [ABSTRACT FROM AUTHOR]

Using density functional theory (DFT) calculations, the interactions of H and H 2 with different types of CuO(1 1 1) surfaces, including the perfect, oxygen-vacancy and pre-covered oxygen surfaces, have been systematically investigated to probe into the effect of surface structures on H 2 adsorption and activation. Our results show that the outermost surface oxygen site (O SUF ) is the active center for H adsorption both on the perfect and oxygen-vacancy surfaces, while H favorably adsorbs at the pre-covered oxygen site (O pre ) on the pre-covered oxygen CuO(1 1 1) surface. In the case of H 2 adsorption and activation, H 2 is the dissociative adsorption on the perfect surface, two dissociative H atoms adsorbed at the same O SUF site pull out the O SUF atom from the surface to form a H 2 O molecule adsorbed at the subsurface copper site (Cu SUB ), which ultimately contributes to the formation of oxygen-vacancy site on CuO(1 1 1) surface. For the oxygen-vacancy surface, H 2 adsorbed at the singly (Cu 1 ) and doubly (Cu 2 ) coordinated Cu SUB sites via the side-on mode are two favorable configurations, moreover, the dissociation barriers for these two favorable configurations is higher than their corresponding adsorption energies, namely, H 2 dissociation is difficult to occur on the oxygen-vacancy surface. For the pre-covered oxygen surface, H 2 initially adsorbed at O SUF site with the side-on or end-on modes is the dissociative adsorption, in which one H is still adsorbed at O SUF site, the other H is adsorbed at the adjacent pre-covered oxygen site; meanwhile, H 2 initially adsorbed at O pre site with the side-on mode is also the dissociative adsorption. Thus, H 2 dominantly exists in the form of the dissociative adsorption with the adsorbed H atoms on the perfect and pre-covered oxygen surfaces, whereas, H 2 mainly exists in the form of molecular adsorption H 2 on the oxygen-vacancy surface, suggesting that the adsorption and activation behaviors of H 2 over CuO(1 1 1) surface are particularly sensitive to the surface structure. [ABSTRACT FROM AUTHOR]

A Cu-C i oxygen-evolution catalyst (C i is inorganic carbonate) is prepared from of the abundant elements copper. They are generated in situ in carbonate solution (pH 10.25) with copper(I) complex under mild conditions (room temperature, atmospheric pressure, and near-neutral solution). The result indicates that the prepared Cu-C i catalyst is amorphous. The average oxygen-evolution rate is 33.88 μmol h −1 cm −2 . An oxygen evolution overpotential of 263.8 mV is required at a current density of 1 mA cm −2 . Factors affected catalytic activity during water splitting, including temperature and type of electrolyte, are investigated. The phase, structure, morphology, composition, and catalytic activity of Cu-C i catalyst are analyzed using a variety of characterization methods, namely, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and electrochemical measurement. [ABSTRACT FROM AUTHOR]

The development of efficient and stable electrocatalysts is of great significance for improving water splitting. Among them, transition metal oxyhydroxides show excellent performance in oxygen evolution reactions (OER), but there are certain difficulties in direct preparation. Recently, Metal–organic frameworks (MOFs) as precatalysts or precursors have shown promising catalytic performance in OER and can be decomposed under alkaline conditions. Therefore, using a mild and controllable way to convert MOFs into oxyhydroxides and retaining the original structural advantages is crucial for improving the catalytic activity. Herein, a rapid electrochemical strategy is used to activate well-mixed MOFs to prepare Co/Ni oxyhydroxide nanosheets for efficient OER catalysts, and the structural transformation in this process was investigated in detail by using scanning electron microscope, X-ray diffraction, Raman, X-ray photoelectron spectroscopy and electrochemical methods. It is discovered that electrochemical activation can promote ligand substitution of well-mixed MOFs to form porous oxyhydroxide nanosheets and tune the electronic structure of the metal (Co and Ni), which can lead to more active site exposure and accelerate charge transfer. In addition, the change of structure also improves hydrophilicity, as well as benefiting from the strong synergistic effect between multiple species, the optimal a-MCoNi–MOF/NF has excellent OER performance and long-term stability. More obviously, the porous CoNiOOH nanosheets are formed in situ during electrochemical activation process through structural transformation and acts as the active centers. This work provides new insights for mild synthesis of MOFs derivatives and also provides ideas for the preparation of highly efficient catalysts. [Display omitted] • CoNiOOH nanosheets derived from the well-mixed MOFs by electrochemical activation. • Porous CoNiOOH species can directly act as real active center for water oxidation. • Porous structures and hydrophilic oxyhydroxide nanosheets play a key role in OER. • The optimal a-MCoNi–MOF/NF exhibits 227 mV overpotential and long-term stability. [ABSTRACT FROM AUTHOR]

Novel nickel nanotube arrays (NTAs) on foamed nickel (NF) are developed by a facile electrochemical dealloying method to achieve a high hydrogen evolution reaction. Meanwhile, three dimensional heterostructure NiFe layered-double-hydroxide (LDH)@Ni NTAs electrode materials with strong interfacial interaction are prepared on NF by coupling ultrathin NiFe LDHs with Ni NTAs by electrochemical deposition, which demonstrate an excellent catalytic performance for oxygen evolution compared with NiFe LDH. Ni NTAs/NF require an overpotential of 101 mV to force the current density of 10 mA cm−2 for hydrogen evolution reaction because of the unique NTAs structure and the active sites for water dissociation provided by Ni2+ on the Ni NTAs surface. NiFe LDH@Ni NTAs/NF exhibit a low overpotential of 191 mV at a current density of 10 mA cm−2 for oxygen evolution reaction due to the reliable electron transfer from the intermediate metallic Ni NTAs to the external the NiFe LDH layer and more active sites that are exposed by highly dispersed ultrathin NiFe LDH nanosheets. The development of self-supporting NiFe LDH@Ni NTAs and Ni NTAs electrodes for efficient overall water splitting in an integrated alkaline electrolyzer is achieved a current density of 10 mA cm−2 at 1.51 V, accompanying excellent long-term durability. Image 1 • NiFe LDH@Ni NTAs is prepared by electrochemical dealloying and coupling methods. • NiFe LDH@Ni NTAs increases the electron transfer rate and number of active sites. • NiFe LDH@Ni NTAs exhibits an excellent catalytic performance for OER. • The combination of Ni(OH) 2 and Ni on the surface of Ni NTAs promotes HER. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Co 3 O 4 @Fe-B-O/NF was synthesized by a facile immersion method. • Heterostructure tunes the electronic structure and provides more active sites. • Co 3 O 4 @Fe-B-O/NF shows excellent OER performance in both alkaline and neutral media. • Co 3 O 4 @Fe-B-O/NF anode exhibits great potential for overall water splitting and CO 2 RR. Developing highly efficient OER catalysts is essential for producing hydrogen from water electrolysis to compensate for conventional fossil fuel shortages. Here, the oxygen-vacancy-rich heterostructure grown on the Ni foam (NF) (Co 3 O 4 @Fe-B-O/NF) is fabricated. The synergistic effect between Co 3 O 4 and Fe-B-O has been proven effectively modulate the electronic structure and produce highly active interface sites, ultimately leading to enhanced electrocatalytic activity. Co 3 O 4 @Fe-B-O/NF requires an overpotential of 237 mV to drive 20 mA cm−2 in 1 M KOH, and 384 mV to drive 10 mA cm−2 in 0.1 M PBS, superior to most catalysts currently used. Moreover, Co 3 O 4 @Fe-B-O/NF as an oxygen evolution reaction (OER) electrode shows great potential in overall water splitting and CO 2 reduction reaction (CO 2 RR). This work may provide effective ideas for designing efficient oxide catalysts. [ABSTRACT FROM AUTHOR]

The Co 8 FeS 8 @CoFe–MOF/NF heterojunction array with abundant phase interface was formed on the surface of nickel foam (NF) via a simple solvothermal method for water and urea splitting. The designed Co 8 FeS 8 @CoFe–MOF/NF heterojunction electrocatalyst exhibits superior activity towards oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and urea oxidation reaction (UOR), which only requires low overpotentials of 213 mV, 191 mV and 81 mV to reach a current density of 10 mA cm−2, respectively. Moreover, it shows low cell voltages of 1.62 V and 1.55 V at 10 mA cm−2 for overall water and urea splitting, respectively. [Display omitted] 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. [ABSTRACT FROM AUTHOR]

A green strategy was developed to synthesize CoFe–MOF@Pa with vacancies and hydrophilicity by a simple and controllable phytic acid (Pa) etching technique. The resulting vacancies and enhanced hydrophilicity can expose a large number of electrocatalytically active sites, promote electron and ion transport and facilitate sufficient contact between the electrolyte and active sites. As a result, the CoFe–MOF@Pa exhibits excellent water splitting performance and long-term stability compared to pristine CoFe–MOF. [Display omitted] • CoFe-MOF@Pa with vacancies and hydrophilicity was prepared by Pa etching. • The vacancies can tune the electronic structure and act as adsorption sites. • The hydrophilic structure facilitates adequate contact of active sites and electrolyte. • CoFe–MOF@Pa exhibits excellent water splitting performance and long-term stability. Deliberate engineering of the structures and components of Metal–organic frameworks (MOFs) can provide unlimited potential for developing efficient electrocatalysts for water splitting. Herein, we develop a green strategy to synthesize CoFe–MOF@Pa via a simple and controllable phytic acid (Pa) etching technique. The Pa etching strategy can break the M−O in CoFe–MOF to create vacancies and introduce hydrophilic groups on the surface of CoFe–MOF to enhance the hydrophilicity. The obtained porous CoFe–MOF@Pa with vacancies not only creates more active sites and facilitates charge redistribution, but also the improved hydrophilicity promotes the adequate contact of electrolytes with active sites, thereby enhancing the fast electrochemical reactions. As a result, the CoFe–MOF@Pa shows excellent OER performance (203 mV at 10 mA cm−2) and low Tafel slope (57.1 mV dec-1). Furthermore, CoFe–MOF@Pa&CoFe–MOF@Pa for water splitting, it only requires a cell voltage of 1.66 V without iR compensation at 10 mA cm−2. More importantly, CoFe–MOF@Pa also shows long-term activity and stability compared to pristine CoFe–MOF. This feasible strategy in this study is expected to provide insights into the preparation of efficient and robust electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]

[Display omitted] • The easily oxidized amorphous-abundant NiO x H y /NF for the efficient HMFOR was obtained by the pre-oxidisation. • Ni(III)OOH was the active intermediate in the electrochemical HMFOR investigated by in-situ Raman. • NiO x H y /NF exhibits a low onset potential of 1.35 V, a high FDCA yield of 98.5%, and a high FE of 98.3% for the HMFOR. • This universal electro-oxidation strategy is also suitable for improving the HMFOR properties of Co and V. The electrocatalytic production of 2,5-furandicarboxylic acid (FDCA) via the 5-hydroxymethylfurfural oxidation reaction (HMFOR) is an effective and more suitable alternative to the oxygen evolution reaction (OER) in electrocatalytic water splitting. High-valence Ni(III) is critical for the HMFOR, but the formation is greatly limited by the difficult in situ self-oxidation. In this study, the pre-oxidization-derived amorphous NiO x H y nanosheet presents more accessible Ni(III) for efficient HMFOR. In addition, NiO x H y /NF exhibits a low onset potential of 1.35 V, a high FDCA yield of 98.5 %, and a high Faradaic efficiency of 98.3 % for the HMFOR in 0.1 M KOH with 10 mM HMF. In situ Raman spectroscopy results indicate that Ni(III)OOH is an active intermediate in the electrochemical HMFOR. This work provides a strategy for promoting the formation of high-valence Ni(III) and boosting biomass oxidation. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of CO2 to produce valuable multi‐carbon products is a promising avenue for promoting CO2 conversion and achieving renewable energy storage, and it has also attracted considerable attention recently. However, the synthesis of Cu electrode with a controllable electrochemical active surface area (ECSA) to understand its role in CO2 reduction to C2H4 remains challenging. Herein, a series of Cu electrodes with different ECSA is synthesized through a simple oxidation‐reduction approach. We reveal that the improved selectivity of C2H4 is proportional to the ECSA of Cu in the low ECSA range, and a further increase in ECSA has a negligible effect on its selectivity. The enlarged surface area could strengthen the local pH effect near the surface of Cu electrode and suppress the generation of C1 products as well as H2. The study provides a feasible strategy to rationally design electrocatalysts with high electrochemical CO2 reduction performances. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is crucial for hydrogen production. However, OER with four‐electron transfer requires electrocatalysts to speed up its sluggish kinetics in alkaline solutions. Herein, amorphous CoV phosphate (denoted as CoV−Pi) nanosheets synthesized by a straightforward one‐step hydrothermal approach is reported, which provide a low overpotential of 320 mV at 10 mA cm−2, a small Tafel slope down to 48.8 mV dec−1 and long‐term durability over 80 h. The efficient activity is ascribed to the amorphous nanosheets structure, high electrochemically active surface area, enhanced surface wettability and the synergistic effect of the active metal atoms. This study significantly indicates that CoV−Pi is a promising alternative to replace expensive noble metal‐based catalysts for electrochemical water splitting. [ABSTRACT FROM AUTHOR]

In this paper we synthesized a crystalline Ag-C i oxygen-evolution catalyst with an entirely new composition and structure in situ in a carbonate solution (pH = 8.3) with Ag+ at 70 °C. We studied the factors that influenced the synthesis of the oxygen-evolution catalyst (electrolyte environment temperature, silver ion concentration, concentration of carbonates) under mild conditions. The structure, morphology, composition, and catalytic activity of Ag-C i catalyst were analyzed using techniques such as X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electrochemical measurements. Our results showed that the diffraction peaks of the Ag-C i catalysts synthesized at 70 °C were consistent with the AgO phase and that the catalytic composition of the Ag-C i catalyst was the AgⅠO/AgⅡO redox couple. The oxygen-evolution rate of the catalyst synthesized in a carbonate solution (pH = 8.3) at 70 °C was 50 times higher than that synthesized at 5 °C (18.3 μmol h−1); additionally, its oxygen evolution overpotential decreased to 246.7 mV. The electrolyte solution and Ag+ ion concentration greatly impacted the catalytic activity of the Ag-C i catalyst for water splitting. [ABSTRACT FROM AUTHOR]

Abstract: A weakly acidic H3BO3 solution (pH = 5.1) was used to synthesize new oxygen-evolution catalysts for water splitting under mild conditions. Two novel oxygen-evolution catalysts, Co–BA i and Mn–BA i (BA i = inorganic boric acid), were obtained in the H3BO3 solution with added Co2+ and Mn2+, respectively. The average oxygen evolution rate in the H3BO3 solution with Co2+ was 0.3133 μmol/h, about 70 times greater than the rate without a metal ion; the rate with Mn2+ was 1.13 μmol/h, about 250 times greater. The phases, morphologies, and compositions of the Co–BA i and Mn–BA i catalysts were analysed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. [Copyright &y& Elsevier]

[Display omitted] The development of available dual-function electrocatalysts is of great significance to the effective storage of excess electricity. Here, we obtained a three-dimensional Co(OH) 2 nanosheet with high surface area on nickel foam (Co(OH) 2 /NF) via conventional hydrothermal. NiFe-coated Co(OH) 2 nanosheet array (NiFe@Co(OH) 2 NSAs/NF) was further constructed by electrodeposition for water splitting. By optimizing and regulating the deposition time, NiFe@Co(OH) 2 NSAs/NF with a deposition time of 500 s (NiFe-500@Co(OH) 2 NSAs/NF) only needs 98 mV of overpotential and can be stabilized for 100 h for hydrogen evolution at 10 mA cm−2 due to the rich density active components for NiFe alloy/oxyhydroxide layer and interaction with Co(OH) 2 nanosheets. Thanks to the excellent 3D nanosheet array structure and the close integration between Co(OH) 2 and the upper layer NiFe, NiFe@Co(OH) 2 NSAs/NF with a deposition time of 200 s (NiFe-200@Co(OH) 2 NSAs/NF) can provide 10 mA cm−2 with only 204 mV and maintain constant catalysis within 100 h. Therefore, the constructed NiFe@Co(OH) 2 NSAs/NF (500||200) double-electrode cell for water splitting requires only 1.58 V drive potential and can maintain 24 h durability at 10 mA cm−2. The design of the catalyst opens up new ideas for the large-scale application of transition metals in water splitting. [ABSTRACT FROM AUTHOR]

A NiFe alloy was designed on nickel foam (NF) as a precursor using cathodic electrodeposition. NiFe 2 O 4 –Ni 3 S 2 nanorods (NRs) composite catalysts were prepared by Fe3+ impregnation and further hydrothermal sulfuration methods. NiFe 2 O 4 –Ni 3 S 2 nanosheets (NSs) were also prepared by direct hydrothermal sulfuration of the NiFe alloy for comparison. Compared to the dense NS structure of the NiFe 2 O 4 –Ni 3 S 2 NSs/NF, the NiFe 2 O 4 –Ni 3 S 2 NRs/NF showed better oxygen evolution performance due to its unique weed-like NR array structure composed of additional oxygen evolution reaction (OER) active sites, with a strong electron interaction for Ni and Fe and the active sulfide synergistic effect with oxides. Therefore, Driving a current density of 10 mA cm−2 only requires an overpotential of 189 mV and the catalyst could provide 100 mA cm−2 continuously and be constant for more than 80 h in 1.0 M KOH. This experiment indicated that Fe3+ immersion had an indirect regulating effect on the morphological growth of the catalyst, which provided a novel concept for designing better OER catalysts. [Display omitted] • The NiFe 2 O 4 –Ni 3 S 2 nanorod array was constructed on Ni foam by a three-step method. • The impregnation of Fe3+ promoted the formation of 3D nanorod array structure. • The transformation of the active substances NiOOH and NiFe oxides accelerates OER. • NiFe 2 O 4 –Ni 3 S 2 NRs/NF required lower overpotential 189 mV to drive 10 mA cm−2. • The maintenance of nanorod and active sites make catalyst obtain good stability. [ABSTRACT FROM AUTHOR]

A series of bimetallic metal‐organic frameworks (MOFs) were prepared on three‐dimensional nickel foam (NF) using a one‐pot synthesis, marked as NiFe‐MOF/NF. The structure of the as‐prepared NiFe‐MOF/NF was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), X‐ray photoelectron spectroscopy (XPS), FT‐IR and Raman. Compared with the monometallic Ni‐MOF material, the incorporation of Fe greatly changes the inherent properties of Ni‐MOF. Electrochemical measurement results show the optimized NiFe‐MOF/NF [Ni : Fe=3 : 7 (molar ratio)] has better electrocatalytic performance and the current densities of 50 mA cm−2 and 100 mA cm−2 have low overpotentials of 225 mV and 251 mV, respectively, for the oxygen evolution reaction in alkaline solution. In particular, the inverse curve of linear sweep voltammetry shows an ultralow overpotential of only 160 mV at current density of 10 mA cm−2. NiFe‐MOF/NF also has excellent stability and can run continuously for at least 50 h. NiFe‐MOF/NF has remarkable OER performance, which is mainly due to the high conductivity, the large specific surface area and the synergistic effects of Fe and Ni in MOFs. The work presents a general strategy for the synthesis of electrocatalytic materials for effective and scalable electrocatalytic water oxidation. [ABSTRACT FROM AUTHOR]

• IrO 2 @SL-NiFe LDHs was synthesized by anchoring IrO 2 nanoparticles to SL-NiFe LDHs. • –NH 2 acted as a coordination site to control the growth of IrO 2 nanoparticles. • Formation of oxygen defects on SL-NiFe LDHs increased OER performance. • DFT results indicated that IrO 2 and SL-NiFe LDHs synergistically catalyze OER. A hybrid oxygen evolution catalyst, IrO 2 @single-layer NiFe layered double hydroxides (SL-NiFe LDHs), is successfully synthesized by anchoring highly dispersed IrO 2 nanoparticles to SL-NiFe LDHs nanosheets with oxygen vacancies. Typically, during the synthesis process, the functional group –NH 2 from the external anchor formamide acts as a coordination site to control the nucleation and growth of nanoparticles, which can ensure high dispersion without aggregation of IrO 2 on SL-NiFe LDHs. In addition, this reducing synthetic environment causes a large number of holes and grooves in the NiFe-LDHs nanosheets, which result in the formation of oxygen vacancies in the SL-NiFe LDHs. The loading of IrO 2 nanoparticles and the formation of oxygen vacancies endow IrO 2 @SL-NiFe LDHs with excellent performance for the oxygen evolution reaction (OER). IrO 2 @SL-NiFe LDHs nanosheets display outstanding OER performance with an overpotential of 270 mV at a current density of 10 mA cm−2 and good stability. Density functional theory (DFT) calculations indicate that the hybridization of IrO 2 and SL-NiFe LDHs accelerates the reaction step. Notably, the Ir sites at the edges are more conducive to the formation of oxygen, and the oxygen sites on SL-NiFe LDHs are more conducive to the cleavage of the O–H bond, thereby improving the OER activity. This work highlights a potential synthetic strategy that can combine nanoprecious metals with transition metals to prepare highly active electrocatalysts for efficient water oxidation reactions. [ABSTRACT FROM AUTHOR]

Although metal‐organic frameworks have proven to be excellent electrocatalytic materials, their application as electrode materials remains limited. The preparation of heterostructures is considered an effective method to improve catalytic activity. Herein, we describe the design and assembly of a dual‐MOF heterostructure (CoNi−ZIF‐67@Fe−MIL‐100, denoted ZIF@MIL). Specifically, we grew a layer of MIL‐100 in situ on a bimetallic ZIF‐67 surface using a solvothermal method. We demonstrate that the ZIF@MIL has remarkable OER electrocatalytic performance, requiring a low overpotential and showing a small Tafel slope, compared to pure ZIF‐67 and MIL‐100 in 1.0 m KOH. More importantly, it has excellent operational durability for 50 h at 100 mA cm−2. The high catalytic activity of ZIF@MIL can be attributed to the heterostructure that can expose more active sites, the synergistic effect between ZIF‐67 and MIL‐100, and improvement of electron transfer ability. Our work provides a new way to design and prepare dual‐MOF crystals with different structures as electrocatalysts. [ABSTRACT FROM AUTHOR]

Hydrogen production from electrolyzed water is a mature technology and has great development prospects in terms of energy conversion and utilization. However, the kinetically sluggish oxygen-evolution reaction becomes the limiting step in the electrolysis of water. Copper-based materials have been reported as a good choice to catalyze the oxygen evolution reaction, but their performance is poor. We describe a Cu 2-x Se@CuO/copper foam core–shell structure from the in situ electrochemical oxidation of Cu 2 Se/copper foam to promote the oxygen-evolution reaction performance. The presence of a semi-metallic Cu 2-x Se core and nanostructured CuO shell at a current density of 10 mA cm−2 requires a low overpotential of 253 mV. The Tafel slope was only 73 mV dec−1. The preparation of Cu 2-x Se@CuO on three-dimensional copper foam facilitates the reaction. Image 1 • Cu 2-x Se@CuO core-shell structure forms by the in situ electrochemicall oxidation of Cu 2 Se. • A formation model for the core-shell structure catalyst is proposed. • The phase change of copper selenide is clearly explained in OER process. • The presence of semi-metallic Cu 2-x Se promotes the OER performance of CuO. [ABSTRACT FROM AUTHOR]

Silver-based catalysts with an adjustable structure are promising as efficient oxygen evolution catalysts. Four types of silver-oxide (AgO) morphologies were obtained by potentiostatic deposition in situ in organic carboxylate by altering the amount of ammonia as the complexing agent. AgO films can be used in the oxygen-evolution reaction; AgO that is formed by using potassium acetate that contains 1.32 mM ammonia as an electrolyte exhibits preferable performance. Catalyzed water oxidation occurs in 0.1 mol/L potassium phosphate solution (pH 12.3) with an average activity of 3.5 mA/cm 2 , and persists for at least 10 h at 2.03 V (vs. Reversible Hydrogen Electrode, RHE). Overpotential is 438 mV at a current density of 1 mA/cm 2 . The Faradaic efficiency is 94.4%. Samples were well characterized by X-ray powder diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

An efficient Ag-P i oxygen-evolving catalyst was fabricated in situ in a phosphate electrolyte solution (pH 12.4). The catalyst approaches an amorphous structure, unlike the reported Ag-based oxygen-evolving catalysts. The catalytic activity for water oxidation of the Ag-P i catalyst is 11.1 μmol h −1 cm −2 and it has a modest oxygen-evolution overpotential of 457.0 mV at 1 mA cm −2 in 0.1 M K 3 PO 4 electrolyte. The effects of different electrolytes on the formation of the Ag-P i catalyst were investigated. The active component of the Ag-P i oxygen-evolving catalyst as a water-splitting catalyst is the AgO phase as determined by X-ray diffractometry and X-ray photoelectron spectroscopy analysis. A Ag-P i mechanism that includes the Ag(I) and Ag(III) cycles is proposed to explain the electrocatalytic oxygen evolution. [ABSTRACT FROM AUTHOR]

NiFe-layered double hydroxide (NiFe–OH) is one of the most promising candidate materials for the oxygen evolution reaction (OER) in an alkaline electrolyte. However, it is difficult to be oxidized into Ni3+FeOOH active species with high valence Ni under mild conditions; thus, the activity under mild conditions is inferior. We report here that NiFe–OH is converted to amorphous NiFeO x H y (a3-NiFe-OH) with easily oxidized electron-deficient Ni2+ after pre-oxidation in an alkaline solution boosts the OER performance under mild conditions. The amorphous structure of a3-NiFe-OH also enlarges the electrochemically active area to expose more active sites. It merely needs an overpotential of 350 mV at 10 mA cm−2 in 0.1 M KHCO 3 electrolyte. The corresponding Tafel slope is as low as 89 mV dec−1. This work affords a strategy for developing (near) neutral OER catalysts. [Display omitted] • NiFeO x H y with electron-deficient Ni2+ and amorphous structure was prepared. • The electron-deficient Ni2+ can easily be oxidized during oxygen evolution reaction. • The amorphous structure helps to expose more active sites. • NiFeO x H y exhibits enhanced oxygen evolution reaction activity in mild condition. [ABSTRACT FROM AUTHOR]

We describe the preparation of three partially ordered iron-based catalyst films (Fe-OAc, Fe-Pro, Fe-But) with nanoporous structure by electrodeposition from organate electrolytes containing Fe 2+ . The anions of the organic acids assisted the partial ordering of the nanostructured Fe(III) catalysts for water oxidation. A model involving an electrical double layer is invoked to explain the role of the organate electrolyte system in their formation. Analytical results have revealed the main component of the iron-based films to be a β-FeOOH structure. The Fe-But catalyst catalyzed water oxidation in 0.1 m potassium carbonate solution with an average activity of 1.48 mA cm −2 and an overpotential of 433 mV. [ABSTRACT FROM AUTHOR]

We describe a novel nanostructured iron oxide catalyst film electrodeposited from iron(II) triflate under mild conditions (room temperature, atmospheric pressure, and near-neutral solution) that can catalyze water oxidation in potassium carbonate solution. The structure, morphology, composition, and catalytic activity of the catalyst were characterized by X-ray diffractometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical measurements. The results indicate that nanostructured iron oxide is an active electrocatalyst for water oxidation at higher catalytic current and low overpotential. [ABSTRACT FROM AUTHOR]