Sulfide-oxidation-assisted electrochemical water splitting for H2 production on a bifunctional Cu2S/nickel foam catalyst

Abstract

Replacing the sluggish oxygen evolution reaction (OER) by the sulfide electro-oxidation reaction (SOR) could be a promising way to decrease the energy consumption for the hydrogen evolution reaction (HER) and to treat the waste H₂S simultaneously. However, promoting the catalyst activity and stability in sulfide solution remains a great challenge. In this work, a sulfur-tolerable bifunctional Cu₂S micro-flake catalyst supported on nickel foam (Cu₂S/NF) was fabricated for catalyzing the SOR-assisted electrochemical water splitting. The Cu₂S/NF electrode exhibited good activity and stability for both the SOR (0.26 V vs. RHE) and HER (−0.18 V vs. RHE) at 10 mA cm⁻². The anodic product obeyed the chain-growing mechanism of HS⁻ → S_n²⁻ (polysulfides) in alkaline solutions. Moreover, for a two-electrode SOR-assisted water splitting system, a current density of 100 mA cm⁻² was successfully obtained at a cell voltage of only 0.64 V. Compared to the normal water splitting (OER + HER), our system (SOR + HER) can save 74% energy consumption when producing the same amount of H₂, close to the theoretic energy-saving value of 86%. This work proposed a new way for not only generating highly efficient hydrogen but also reusing the toxic sulfide waste, which shed light on the low-cost and scaling-up hydrogen production using waste resources.