Anionic regulated cobalt phosphosulfide with enhanced activity for hydrogen evolution reaction

Hydrogen is by far one of the most promising and clean alternative source of sustainable energy for our future energy usage. However, noble metal electrodes are still needed for efficient water-splitting process to produce hydrogen, making it too costly for production of hydrogen energy to be put into commercial use. As such, it is necessary to discover and develop cheaper materials with comparable or better electro-catalytic performance than noble metals to achieve cost effective hydrogen production. \nTherefore, this report reviews a phase conversion strategy to synthesize pyrite-type ternary cobalt phosphosulfide (CoPS) nanosheets. Defects engineering and atomic structure tailoring were also employed to enhance the material’s performance as an electrocatalyst for water splitting. CoPS3 bulk crystals were first exfoliated by liquid phase exfoliation (LPE) process to produce its nanosheets. These CoPS3 nanosheets were then reduced to non-layered CoPS nanosheet by treating them with 1-octadecene and oleylamine. We theorize that this process may create S and P vacancies, open cobalt sites and form possible strain field in the nanosheets. Adjustment of reaction time for this reduction process can tune the phase and interface of layered CoPS3 and pyrite-type CoPS to further enhance the electrocatalytic activity for HER. \nThe non-layered pyrite structure CoPS nanosheet has shown promising performance in HER with a low overpotential of 119mV to achieve current density of -10mA/cm-2 and low Tafel slope of 77mV dec-1. This performance is comparable to the current promising HER electrocatalysts that has been reported. It also shows a high operation stability over long period of time.