Fe-based “electron pump” involving NiCo-LDH enables robust and highly-selective electrocatalytic methanol oxidation to formic acid

Abstract

Nucleophile oxidation reactions, represented by the incomplete methanol oxidation reaction (i-MOR) to formic acid, can effectively lower the potential of electrolytic hydrogen production while generating high-value products. In order to achieve an industrial grade i-MOR coupled with hydrogen production, designing efficient catalysts toward the i-MOR becomes crucial. In this work, a nickel–cobalt-layered double hydroxide (NiCo-LDH) catalyst incorporating an Fe-based “electron pump” is developed in accordance with the classic two-step NOR mechanism of Ni-based active sites. The coordinating effect of Co effectively reduces the oxidation potential of Ni(II/III) in NiCo-LDH, thus reducing the potential differential between it and the oxidation potential of Fe(II/III), consequently establishing an efficient electron transport pathway from Ni to Fe. Owing to the spontaneous dehydrogenation of methanol, elemental Fe can achieve a valence change during the i-MOR catalytic process. The “electron pump” composed of valence-change Fe effectively enhances the electron transfer, thus ensuring the efficient utilization of electron-deficient active Ni sites throughout the catalytic process. Therefore, Fe^EP-NiCo-LDH demonstrates outstanding i-MOR catalytic activity, with a potential requirement of 1.349 V (vs. RHE) and 1.430 V to deliver current densities of 10 mA cm⁻² and 100 mA cm⁻², respectively, while maintaining a Faraday efficiency of ca. 95%.