Composition-Graded MoWS_x Hybrids with Tailored Catalytic Activity by Bipolar Electrochemistry

Among transition metal dichalcogenide (TMD)-based composites, TMD/graphene-related material and bichalcogen TMD composites have been widely studied for application toward energy production via the hydrogen evolution reaction (HER). However, scarcely any literature explored the possibility of bimetallic TMD hybrids as HER electrocatalysts. The use of harmful chemicals and harsh preparation conditions in conventional syntheses also detracts from the objective of sustainable energy production. Herein, we present the conservational alternative synthesis of MoWS_x via one-step bipolar electrochemical deposition. Through bipolar electrochemistry, the simultaneous fabrication of composition-graded MoWS_x hybrids, i.e., sulfur-deficient Mo_xW_(1-x)S₂ and Mo_xW_(1-x)S₃ (MoWS_x/BPE_cathodic and MoWS_x/BPE_anodic, respectively) under cathodic and anodic overpotentials, was achieved. The best-performing MoWS_x/BPE_cathodic and MoWS_x/BPE_anodic materials exhibited Tafel slopes of 45.7 and 50.5 mV dec^-1, together with corresponding HER overpotentials of 315 and 278 mV at -10 mA cm^-2. The remarkable HER activities of the composite materials were attributed to their small particle sizes, as well as the near-unity value of their surface Mo/W ratios, which resulted in increased exposed HER-active sites and differing active sites for the concurrent adsorption of protons and desorption of hydrogen gas. The excellent electrocatalytic performances achieved via the novel methodology adopted here encourage the empowerment of electrochemical deposition as the foremost fabrication approach toward functional electrocatalysts for sustainable energy generation.