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

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− → Sn2− (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.