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

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.