Paired formate and H2 productions via efficient bifunctional Ni-Mo nitride nanowire electrocatalysts

Abstract

Electrocatalytic water splitting provides a potentially sustainable approach for hydrogen production, but is typically restrained by kinetically slow anodic oxygen evolution reaction (OER) which is of lesser value. Here, free-standing, hetero-structured Ni3N-Ni0.2Mo0.8N nanowire arrays are prepared on carbon cloth (CC) electrodes for hydrogen evolution reaction (HER) and glycerol oxidation reaction (GOR) to formate with a remarkably high Faradaic efficiency of 96%. A two-electrode electrolyzer for GOR-assisted hydrogen production operates with a current density of 10 mA cm−2 at an applied cell voltage of 1.40 V, 220 mV lower than for alkaline water splitting. In-situ Raman measurements identify Ni (III) as the active form of the catalyst for GOR rather than Ni (IV) and in-situ Fourier transform infrared (FTIR) spectroscopy measurements reveal pathways for GOR to formate. From density functional theory (DFT) calculations, the Ni3N-Ni0.2Mo0.8N heterostructure is beneficial for optimizing adsorption energies of reagents and intermediates and for promoting HER and GOR activities by charge redistribution across the heterointerface. The same electrode also catalyzes conversion of ethylene glycol from polyethylene terephthalate (PET) plastic hydrolysate into formate. The combined results show that electrolytic H2 and formate production from alkaline glycerol and ethylene glycol solutions provide a promising strategy as a cost-effective energy supply.