NiS/MoS2 Mott-Schottky heterojunction-induced local charge redistribution for high-efficiency urea-assisted energy-saving hydrogen production

Abstract

Urea-assisted water electrolysis possesses the prospective prospect for high-efficiency hydrogen production by replacing oxygen evolution reaction (OER) with thermodynamically more favorable urea oxidation reaction (UOR). Modulating the electronic structure of electrocatalysts through constructing metal–semiconductor heterointerface represents an effective strategy to promote the electrochemical performances. Herein, we construct a Mott-Schottky bifunctional electrocatalyst by in-situ growth of NiS/MoS2 hetero-nanoflowers on the conductive carbon cloth (CC) substrate (abbreviated as NiS/MoS2@CC hereafter) for both hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). Thanks to the Mott-Schottky effect, the self-driven charge transfer occurs across the NiS/MoS2 heterointerfaces, which results in the built-in electric field, the accelerated charge transfer rate, and the modified chemisorption free energies for reaction intermediates, ultimately expediting the dissociation of water and urea molecules. Consequently, the as-fabricated NiS/MoS2@CC electrode only requires an overpotential of 87 mV for hydrogen evolution reaction (HER) in 1.0 M KOH and a potential of 1.36 V for UOR in 1.0 M KOH solution with 0.5 M urea to attain a current density of 10 mA cm−2, respectively. Moreover, when served as the free-standing anode and cathode simultaneously, the NiS/MoS2@CC-assembled urea electrolyzer requires a cell voltage of 1.46 V at 10 mA cm−2, which is 200 mV smaller than that of the pure water splitting counterpart. This study may deepen the understanding of electronic modulation via Mott-Schottky establishment.