Nitrogen-Doped Carbon and MoS₂ Nanosheets Grown on Co_1–xS Nanorods for Hydrogen and Oxygen Evolution

Developing cost-efficient bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is of paramount importance to realize the viability of H2 energy generated via water electrolysis. In this work, a hierarchical-array structure is elaborately established, with the characteristics of each Co1–xS nanorod (NR) enwrapped by nitrogen-doped carbon (NC) and a vertically aligned MoS2 nanosheet (NS) array, and the Co1–xS NRs themselves as arrays in situ grown on carbon fibers of the substrate. Such an open array framework sufficiently guarantees rapid mass/charge diffusion/transport and a high utilization of active centers, wherein hexagonal Co1–xS NR and MoS2-NS edges separately personate as active sites for OER and HER. Furthermore, their electrocatalytic activities are intrinsically improved after being integrated as a composite. The synthesized Co1–xS(NR)@MoS2(NS)-NC composite exhibits an HER overpotential of merely 66 mV at 10 mA cm–2, with a Tafel slope of 44 mV dec–1 and an extremely high TOF of 1.54 s–1 at 200 mV overpotential, and, meanwhile, sponsors an OER overpotential of 234 mV at 10 mA cm–2 and an exceptionally low Tafel slope of 51 mV dec–1 in 1 M KOH solution. Only a cell voltage of 1.56 V is required for the overall water splitting.