Bridging NiCo layered double hydroxides and Ni3S2 for bifunctional electrocatalysts: The role of vertical graphene

Abstract

Abstract In this work, we report a bifunctional electrocatalyst with nickel sulphide (Ni3S2) as the template, vertical graphene (VG) as the bridging material, and nickel-cobalt layered double hydroxides (NiCo LDHs) nanosheets as the active catalyst. The hybrid Ni3S2/VG@NiCo LDHs catalyst exhibits excellent activity in alkaline solution for both OER (overpotential ∼320 mV at a current density of 100 mA cm-2) and HER (overpotential ∼120 mV at a current density of 10 mA cm-2). In addition, the hybrid catalyst possesses superior stability with 99% retention of voltage upon a continued current density of 20 mV cm-2 for over 24 hours. It is found that the transitions of Ni2+/Ni3+ and Co2+/Co3+ ions enable excellent HER and OER performances, and VG bridging between NiCo LDHs and Ni3S2, enable fast charge-transfer and a high density of active sites, resulting in the improved electrical conductivity, intrinsic activity, and electrochemical stability. This work provides a guideline to design the architecture of bifunctional catalysts for highly efficient water splitting applications.