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

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 h. 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.