Co-decorated Co9S8/MoS2 heterostructures anchored to ultrathin graphene nanosheets as trifunctional electrocatalysts for self-powered universal-pH overall water splitting

• The preparation of Co-Co 9 S 8 /MoS 2 @NG catalyst via a simple and efficient interface engineering strategy based on self-assembly. • The Co-Co 9 S 8 /MoS 2 @NG catalyst shows an excellent universal-pH OER activity of 210, 238, and 230 mV at 10 mA/cm 2 in alkaline, neutral, and acidic media • An overall water splitting cell based on Co-Co 9 S 8 /MoS 2 @NG as both electrodes required low cell voltages of 1.58, 1.55, and 1.52 V in alkaline, neutral, and acidic media. • A self-actuating electrolytic water device was assembled using Co-Co 9 S 8 /MoS 2 @NG also presented an excellent performance in the universal-pH overall water splitting reaction. The design of multifunctional catalysts demonstrating exceptional efficiency in complete water electrolysis reactions across various pH environments represents a critical advancement for large-scale generation of renewable hydrogen. This study presents an exceptionally effective catalytic system consisting of cobalt-decorated Co 9 S 8 /MoS 2 heterostructures supported on ultrathin nitrogen-doped graphene nanosheets (denoted as Co-Co 9 S 8 /MoS 2 @NG). The hybrid architecture integrates transition metal sulfides with conductive graphene substrates through strategic cobalt decoration and nitrogen doping, achieving optimized electronic configurations for enhanced catalytic performance. The Co 9 S 8 /MoS 2 @NG composite demonstrates outstanding catalytic performance and durability across various pH conditions for oxygen generation processes, achieving overpotentials of 210, 238, and 230 mV at 10 mA/cm 2 in alkaline, neutral, and acidic environments respectively. Notably, this bifunctional catalyst also shows remarkable efficiency in hydrogen production applications. When implemented in a customized water-splitting electrolyzer utilizing Co-Co 9 S 8 /MoS 2 @NG for both anode and cathode functions, the system achieved operational voltages of 1.58, 1.55, and 1.56 V under alkaline, neutral, and acidic conditions correspondingly. The synthesized Co-Co 9 S 8 /MoS 2 @NG composite demonstrates remarkable catalytic performance, requiring only 1.52 V to maintain 10 mA/cm 2 current density across alkaline, neutral, and acidic electrolytes. This material surpasses commercial Pt/C||Ir/C systems (showing 1.64 V, 1.68 V, and 1.66 V in corresponding media) while maintaining competitiveness with state-of-the-art catalysts documented in recent studies. These findings demonstrate the multifunctional capabilities of Co-Co 9 S 8 /MoS 2 @NG as an efficient tri-electrode material for enhanced water electrolysis systems, offering new possibilities for sustainable energy conversion technologies.