Coupling biomass-derived substrate oxidation with the HER: hexagonal NiS for low-voltage, high-efficiency hydrogen production

Abstract

Developing a sustainable process for ultrapure hydrogen production is essential for achieving a carbon-free society. This study presents a coupling of cheap biomass-derived substrates' oxidation reaction and the hydrogen evolution reaction to produce hydrogen via water electrolysis utilizing hexagonal NiS, synthesized via a rapid solution combustion method, as an efficient and cost-effective electrocatalyst. The water electrolyzer, employing biomass-derived substrates such as glucose, glycerol, and ethylene glycol, showed superior performance, particularly with glucose. The glucose-based electrolyzer exhibited a low onset potential of 1.27 V vs. RHE and an overpotential of 1.34 V vs. RHE at 400 mA cm⁻² in a three-electrode configuration with a high turnover frequency (TOF) value of 0.076 s⁻¹ and mass activity of 1.5 A g⁻¹. The glucose-assisted electrolyzer (H-cell), composed of hexagonal NiS, required 1.57 V at 10 mA cm⁻² while the glucose-assisted single stack cell, composed of NiS, required a small potential of 1.33 V at 10 mA cm⁻². Further, the glucose-assisted stack cell exhibited 10.3% energy saving competence compared to the conventional electrolyzer composed of hexagonal NiS with more than 90% faradaic efficiency towards H₂ and formate formation. In agreement with the experimental findings, DFT calculations conducted on the NiS (110) surface to determine the adsorption mechanism showed that glucose has a high adsorption energy value of −9.286 eV, higher than those of glycerol (−8.794 eV) and ethylene glycol (0.557 eV). These findings highlight the potential of the glucose-assisted electrolyzer composed of hexagonal NiS for sustainable hydrogen production.