Effect of 'water-in-salt' electrolytes in the electrochemical hydrogen evolution reaction of carbon nanotubes

Abstract

Super-concentrated electrolytes based electrochemistry is an emerging trend in electrochemical processes (Borodin et al 2020 Joule 4 69-100), where unprecedented properties were reported recently. Such an 'electrolyte engineered approach' can find applicabilities in modern batteries and catalysis. Here we report the use of such high concentration lithium ions (Li+) containing electrolytes for enhancing the electrocatalytic hydrogen evolution (HER) performance of carbon nanotubes (CNTs), contrary to that observed with platinum. Different types of CNTs, namely metallic multi-wall (MWCNTs) and semiconducting single wall (SWCNTs), are tested towards the Li+ effect in the HER performance and similar trends are obtained. Further, different lithium salts having counter ions such as TFSI−, OTf−, ClO4−, Cl−, and OH− are also tested to verify the mechanism, and the role of Li+ in the HER augmentation of CNTs is established. The studies are conducted in different electrolytes having a range of pH values too (0-13), and the cation induced CNT's HER enhancement is generalized. This study shows that even the sluggish HER kinetics of CNTs in alkaline medium can be augmented by such an electrolyte engineering approach where catalyst's surface do not undergo any permanent modification. Further, such electrodes are found to be highly stable towards the long term HER performance.