Layered Transition Metal Dichalcogenides As Electrocatalysts for Hydrogen Evolution and Their Trends Emerging from Electrochemical Treatment

Abstract

Layered transition metal dichalcogenides (TMDs) are thrust into the limelight within the scientific community thanks to their properties that can be exploited for a myriad of applications in electrochemistry and electrocatalysis of hydrogen evolution reaction (HER). Of interest, we investigate the correlation between electrochemical treatment of exfoliated MoS2, WS2, MoSe2 and WSe2 nanosheets in the hopes of electrochemically activating their electrochemical and electrocatalytic properties. In the electrochemical aspect, we show that electrochemical activation is achieved, for all TMDs except WS2, via electro-reduction at selected reductive potentials based on their innate electrochemistry while all TMDs become electrochemically deactivated upon electro-oxidation. Across all TMDs, MoSe2 exhibits most prominent charge transfer activation. Scrutinizing further, we conclude that molybdenum metal and selenium chalcogen type are more prone to electrochemical activation than tungsten metal and sulfur chalcogen type. Contemporary research into TMDs as prospective electrocatalysts for hydrogen evolution has been overwhelming; driven by the ardent pursuit of cheaper alternatives to the rare precious metal platinum, which is the best electrocatalyst to date. TMDs are abundant in nature and also exhibit promising electrocatalytic performance for HER. It provides an interesting perspective to explore the influence of electrochemical potential on the efficiency of the TMDs as a HER electrocatalyst. We found that MoS2 demonstrated better HER performance upon electro-reduction whereas the electro-oxidation of WS2 deteriorated the HER performance significantly. Conversely, the HER efficiency of MoSe2 and WSe2 remained largely unperturbed by electrochemical pretreatment. Therefore, in terms of HER electrocatalysis, we conclude that sulfur-containing TMDs are more receptive to electrochemical redox treatment compared to selenium-containing TMDs. These findings are advantageous towards the electrochemistry of TMDs and provide insights into the effectiveness and feasibility of electrochemical activation for charge transfer and HER electrocatalysis applications. The administration of such knowledge to electrochemical and energy applications in future will be indefinitely beneficial.