Sulfur vacancy-rich Co9S8@MoS2 core-shell heterostructures anchored on carbon nanofibers for electrochemical overall water splitting

•Co9S8@MoS2 core-shell nanoparticles on porous carbon nanofibers are prepared.•Co-S-Mo heterojunction promotes the charge transfer between two phases.•S vacancies increase the localized state of Mo atoms for improved catalytic activity.•Overall water electrolytic cell requires a low potential of 1.41 V at 10 mA/cm2. The introduction of heterojunction and defects into electrocatalysts is an effective way to modulate the electronic structure and accelerate the electrocatalytic kinetics. In this work, we prepare well-distributed Co9S8@MoS2 core-shell nanoparticles on porous carbon nanofibers (CNFs). The N-doped CNFs improve the conductivity and dispersibility of the carried catalyst, and the porous structure introduces abundant ion diffusion pathways. The Co9S8 cores can effectively stabilize the MoS2 shells with exposed (002) crystal planes, and the Co-S-Mo heterojunction promote charge transfer between the two phases to optimize the electronic structure. Particularly, sulfur vacancies are created in the annealing process to improve the intrinsic conductivity and extensively increase the quantity of active sites in MoS2. Consequently, Co9S8@MoS2/CNFs demonstrate a highly efficient hydrogen/oxygen evolution catalytic performance. The constructed Co9S8@MoS2/CNFs-based electrolytic cell displays a low potential of 1.41 V@10 mA/cm2 for overall water splitting along with a super long-term stability. This work emphasizes the comprehensive design of heterogeneous structure, elemental doping and anion vacancies in transition metal-based catalysts for the practical application in electrocatalytic water splitting. [Display omitted]