SnO2/CoS1.097 heterojunction as a green electrocatalyst for hydrogen evolution linking to assistant glycerol oxidation

Abstract

Hydrogen is a green and sustainable energy source, and water splitting is recognized as the most promising way to obtain hydrogen energy. At present, traditional electrocatalysts suffer from high cost and the high overpotential of the oxygen evolution reaction (OER). Herein, a Sn-based heterojunction combined with CoS_1.097 is prepared, and different ratios of Sn and Co are designed. On the other hand, glycerol is an oversupply byproduct in the world and can be oxidized to some useful intermediates via the glycerol oxidation reaction (GOR) in water splitting, meanwhile it reduces the overpotential of the OER. The as-obtained 0.5SnO₂/0.5CoS_1.097 heterojunction shows good electrocatalytic performances with an OER overpotential of 358 mV at 10 mA cm⁻² and hydrogen evolution reaction (HER) overpotential of 93 mV at 10 mA cm⁻² in 1 M KOH, which are superior to the commercial RuO₂ and Pt/C electrocatalysts. But the 0.5SnO₂/0.5CoS_1.097 has a lower GOR overpotential of 154 mV at 10 mA cm⁻² in 1 M KOH + 0.1 M glycerol. The glycerol is oxidized into useful intermediate organics including glyceraldehyde, glyceric acid, and formic acid through the GOR process, and the Faraday efficiency is 90%. Furthermore, the splitting voltage of 0.5SnO₂/0.5CoS_1.097 is 1.18 V at 10 mA cm⁻² in 1 M KOH + 0.1 M glycerol. Density functional theory (DFT) calculations successfully reveal the mechanism of the SnO₂/0.5CoS_1.097 heterojunction, which is derived from the modulation of the density of state (DOS) and HER pathway.