Magnetic-field-assisted electrodeposition regulates the Ni:Fe ratio for water oxidation

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Nickel iron (oxygen) hydroxide (NiFeOx(OH)y) has been extensively studied as a promising electrocatalyst for oxygen evolution reaction (OER). Reasonable control of the ratio of Ni to Fe can improve its catalytic performance but has not yet been effectively achieved. In this work, we designed a magnetic-field-assisted electrodeposition method, which combined the magnetohydrodynamic effect and the corrosion effect of nickel foam substrate in the electrolyte to adjust the mass transfer and surface microenvironment (pH), thereby adjusting the Ni and Fe ratio in a large range. As a result, we use the foamed nickel substrate as the nickel source. As the deposition magnetic field increases, the composition of the catalyst evolves from Ni-doped FeOOH (Ni-FeOOH) to Ni-FeOOH/Ni(OH)2 p-n junction. The introduction of Ni and the p-n junction are beneficial to the electron transfer during the OER process. The sample Ni-FeOOH/Ni(OH)2-500 has an overpotential of only 264 mV at a current density of 20 mA cm−2, which is 34 mV lower than Ni-FeOOH-0.