Performance evaluation of electrodes developed from self-assembled graphene molybdenum chalcogenides for vital hydrogen/oxygen evolution and oxygen reduction reactions

Abstract

The development of efficient and durable multifunctional electrocatalysts is critical for green energy technologies. Herein, we report a facile one-step hydrothermal synthesis of three-dimensional (3D) self-assembled, freestanding graphene-supported molybdenum chalcogenides: MoOS-G (sulfides), MoOSe-G (selenides), and MoO-G (oxides). Among them, MoOS-G exhibits the best electrocatalytic performance for overall water splitting in acidic media, requiring an overpotential of only 280 mV to deliver a current density of 10 mA cm⁻², compared to 390 mV for MoO-G and 540 mV for MoOSe-G. In addition to HER and OER, MoOS-G and MoOSe-G show high activity and stability toward H₂S splitting in Na₂S + NaCl (simulated seawater), generating H₂ at the cathode and elemental S at the anode, with MoOS-G achieving 35 mA cm⁻² at 350 mV. Furthermore, MoOS-G catalyzes the four-electron oxygen reduction reaction (ORR) with an onset potential of 0.97 V vs. RHE in alkaline media. Comprehensive structural and surface analyses (XRD, Raman, SEM, TEM, XPS) confirm the material's integrity and highlight the synergistic effect between Mo–S moieties and in situ developed sulfonated graphene. These features endow MoOS-G with high conductivity, abundant active sites, and excellent durability.