Enhanced activity and chlorine protection in prolonged seawater electrolysis using MoS2/sulfonated reduced graphene oxide

Abstract

Electrolyzer technology necessitates the use of seawater instead of freshwater to achieve a comprehensive supply of clean and economical energy. However, the tendency of chloride ions (Cl−) to significantly erode the metal surface is a major challenge during seawater electrolysis. Therefore, designing an electrode that is resistant to chloride ions is of great importance to develop an efficient seawater electrolyser. In this work, we present a double layer anode consisting of a molybdenum sulfide electrocatalyst uniformly deposited over sulfonated graphene sheets coated over an Ni foam. The developed electrode (GNiMoOS) helps selectively convert H<inf>2</inf>O into H<inf>2</inf> and O<inf>2</inf> rather than chloride (Cl−) ions into ClO− in a seawater environment by resisting corrosion due to the Cl− ions in seawater. The chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) provides solid evidence that the GNiMoOS electrocatalyst blocks the chloride oxidation reaction owing to its distinct resistance to Cl−. In addition, density functional theory (DFT) calculations clearly validated the preference of sulfonic moieties towards OH− compared with Cl− ions, confirming the chlorine repelling properties of the GNiMoOS electrode. The successful in situ functionalisation of sulfonic moieties into the reduced graphene oxide (RGO) skeleton with simultaneous development of flower-like MoS<inf>2</inf> was well confirmed using XPS, Raman, SEM, TEM, and FT-IR techniques. GNiMoOS delivered an impressive current density of 100 mA cm−2 for OER and HER at room temperature, requiring remarkably low overpotentials of just 180 mV and 201 mV, respectively. Industrial faradaic current densities (400-600 mA cm−2) were reported with the active electrode at combined overpotentials of ≤600 mV at room temperature. The unique morphology of MoS<inf>2</inf> provides more active sites for the HER/OER, while sulfonated functional groups over graphene impart much-needed anticorrosion properties to the system. Moreover, the electrical coupling between MoS<inf>2</inf> and RGO can make the electron transfer to RGO easier. Therefore, the synergistic interactions among MoS<inf>2</inf>, SO<inf>3</inf>H and RGO lead to improved catalytic activity and prolonged stability. © 2025 The Royal Society of Chemistry.