In Situ Formation of Efficient Cobalt‐Based Water Oxidation Catalysts from Co²⁺‐Containing Tungstate and Molybdate Solutions

Abstract

Replacing rare and expensive noble-metal catalysts with inexpensive and earth-abundant ones is of great importance to split water either electrochemically or photoelectrochemically. In this study, two amorphous cobalt oxide catalysts (Co-W film and Co-Mo film) with high activity for electrocatalytic water oxidation were prepared by fast, simple electrodeposition from aqueous solutions of Na2WO4 and Na2MoO4 containing Co(2+). In solutions of Na2WO4 and Na2MoO4, sustained anodic current densities up to 1.45 and 0.95 mA cm(-2) were obtained for Co-W film at 1.87 V versus a reversible hydrogen electrode (RHE) and Co-Mo film on fluorine-doped tin oxide (FTO) substrates at 1.85 V versus RHE. For the Co-W film, a much higher current density of 4.5 mA cm(-2) was acquired by using a stainless-steel mesh as the electrode substrate. Significantly, in long-term electrolysis for 13 h, the Co-W film exhibited improved stability in cobalt-free buffer solution in comparison with the previously reported Co-Pi film.

Remarkable Improvement in Water Oxidation Catalysis by Moderate Heat Treatment of a Crystalline Silver‐Based Thin Film Developed In‐Situ From Silver‐ions in Acetate Solution

“…An overpotential of ca. 320 mV for the onset of water oxidation is significantly lower,,, (MnO x , Fe−Ci, Cu(OH) 2 , Cu 2 O η range 350−470) and comparable,,, (Co−Pi, η =330 mV; Co(PO 3 ) 2 , η =310 mV; Co−Mo, η =280 mV; Ni−Bi, η =320 mV) to the recently reported catalysts for OER in the literatures. However, these onset overpotential are still higher than some other previously reported cobalt oxide electrocatalysts (Co−Ci, Co−Hi, Co−W), which corresponds to the onset potentials are 130, 230, 200 mV, respectively ,,…”

“…At the same time, the roughness of the surface also increases as observed in atomic force microscopy (AFM) images of the modified FTO surfaces (Figure S1 in the Supporting Information). The rough structure of the annealed Ag x O film provides a larger specific area, which is expected to facilitate oxygen evolution . These results clearly indicate that heat treatment causes significant microstructural change.…”

“…This was a clear difference relative to the other transition metal oxide‐based catalysts (Co−Pi, Co−Ci, Co−Hi, Co−W, Ni−Bi, Fe−Ci etc. ), which showed no diffraction peaks ,,,,,. Furthermore, the composition and the chemical states of the annealed catalyst film (Ag x O) at 100 °C were analyzed by energy dispersive X‐ray (EDX) and X‐ray photoelectron spectroscopy (XPS), respectively, which all confirmed the deposition of Ag‐based materials on the FTO electrode.…”

Interconnected Network of Core–Shell CoP@CoBiPi for Efficient Water Oxidation Electrocatalysis under Near Neutral Conditions

“…Assuming ao ne-electron process for oxidation of Co centeri n CoBiPi, [24,25,48] the upper limit of active sites was calculated to be 0.569 mmol cm À2 .T OF was determined to be 819 h À1 for CoP@CoBiPi/Tia ta no verpotential of 610 mV (j = 50 mA cm À2 ). [49] The high TOF of CoP@CoBiPi/Tit oward OER could be attributed to the combination of several factors including the enrichment of activeC o 4 + ions on the surface, high conductivity of the CoP core, larger surface area, and facile diffusion of the reactants and products. [49] The high TOF of CoP@CoBiPi/Tit oward OER could be attributed to the combination of several factors including the enrichment of activeC o 4 + ions on the surface, high conductivity of the CoP core, larger surface area, and facile diffusion of the reactants and products.…”

“…This value compares favorably to the behavioro fm any other reported OER catalysts in near neutralm edium, such as NiBi/ITO (36 h À1 , h = 610 mV,I TO:i ndium-doped tin oxide), [39] FeBi/ITO (612 h À1 , h = 600 mV), [41] NiO x /FTO (39.6-54 h À1 , h = 610 mV,F TO:f luorine-doped tin oxide), [44] and CoW/FTO (36 h À1 , h = 640 mV). [49] The high TOF of CoP@CoBiPi/Tit oward OER could be attributed to the combination of several factors including the enrichment of activeC o 4 + ions on the surface, high conductivity of the CoP core, larger surface area, and facile diffusion of the reactants and products. [32,[50][51][52] Stability is another critical factor that defines the performance of catalyst.…”