Unrevealing the Correlation between Temperature and Electrocatalytic Activities of Cobalt Sulfide for Oxygen Evolution and Glycerol Oxidation Reactions

Abstract

The drastic depletion of carbon-based conventional fossil fuels with significant release of greenhouse gases have stimulated research interest towards the development of renewable energy resources. The electrochemical water splitting is considered a promising approach for the sustainable production of clean hydrogen. However, it is severely restricted by oxygen evolution reaction (OER) due to the sluggish kinetics of its complicated oxidation process. Hence, the electrocatalytic performance of OER has a significant impact on the overall water splitting rate and energy efficiency. In this work, we reported two efficient strategies to accelerate OER by adding glycerol as chemical mediator and increasing temperature. The cobalt sulfide nanosheets directly grown on nickel foam (Co-S/Ni3S2@NF) were prepared by hydrothermal method and demonstrated an outstanding OER performance with an overpotential of ~ 340 mV (1.57 V) to achieve a current density of 20 mA cm-2 in alkaline solution, favorably comparing the performance of the noble metal-based catalyst IrO2@NF. This electrocatalyst only requires a potential of ~ 1.35 V to reach the same current density by adding glycerol to the alkaline electrolyte, indicating that glycerol oxidation reaction (GOR) has great potential to replace the sluggish OER. In addition, we found that the OER/GOR electrocatalytic activity increased with increasing temperature. Double current densities for both OER and GOR can be obtained at a potential of 1.60 V when the temperature increased to ~55 oC. This study provides two efficient approaches to overcome the sluggish kinetics of OER and offers new perspectives to improve the energy efficiency for clean hydrogen production.