Accelerate oxygen evolution reaction by adding chemical mediator and utilizing solar energy

The electrochemical water splitting to produce clean hydrogen is severely restricted by oxygen evolution reaction (OER) due to the sluggish kinetics of its complicated oxidation process. In this work, the cobalt sulfide nanosheets directly grown on nickel foam (Co–S/Ni3S2@NF) demonstrated an outstanding OER performance with a potential of 1.57 V (vs. RHE) to achieve a current density of 20 mA cm−2, favorably comparing the performance of the noble metal-based catalyst IrO2@NF. The same current density (20 mA cm−2) could be reached at an extremely low potential of 1.35 V (vs. RHE) by adding 0.1 M glycerol, indicating adding chemical mediator is a possible approach to replace the sluggish OER by the corresponding oxidation of chemical mediator. The activation energy comparison of glycerol oxidation reaction (GOR) and OER (21.9 kJ/mol and 28.2 kJ/mol) further proved this conclusion. The solar energy can be captured and utilized to improve OER in the electrochemical water splitting. The anodic current density at ∼1.6 V (vs. RHE) can be increased 10 times by adding glycerol and raising temperature. This work provides solutions to accelerate OER for H2 production.