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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]

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]

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]

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 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]