Direct Electrocatalytic Methanol Oxidation on MoO3/Ni(OH)2: Exploiting Synergetic Effect of Adjacent Mo and Ni.

Abstract

Ni-based materials have been widely investigated as methanol oxidation reaction (MOR) catalysts. The formation of NiOOH and its reduction to Ni(OH)2 are generally regarded as essential steps for methanol oxidation. However, in such an indirect route, the efficiency of proton coupled electron transfer is fundamentally limited by the rate of transition from Ni(OH)2 to NiOOH back and forth. Herein we demonstrate a direct MOR pathway on MoO3/Ni(OH)2 without the formation of a NiOOH mediator. The MoO3/Ni(OH)2 exhibits a benchmark electrocatalytic MOR current density of 1000 mA cm-2 at 1.52 V vs. RHE with a nearly 100% faradic efficiency, outperforming all the state of art MOR electrocatalysts. In-situ Raman spectroscopy confirms that NiOOH is not formed during the electrocatalytic MOR process on the MoO3/Ni(OH)2. Density functional theory calculations suggest that Ni2+ in MoO3/Ni(OH)2 serves as the methanol adsorption site while the doped Mo6+ plays a key role in capturing the deprotonated H·. Benefiting from the Mo-Ni synergistic effect, the energy barrier of the CH2O* → CHO* + H* process is significantly reduced, avoiding the NiOOH formation and leading to the direct MOR. Our research unravels a direct electrochemical MOR pathway that does not rely on NiOOH formation and provides a facile strategy of regulating the intermediate process barrier for MOR.