Hierarchically Porous Nitrogen-Doped Graphene–NiCo₂O₄ Hybrid Paper as an Advanced Electrocatalytic Water-Splitting Material

In this work, we report a three-dimensional (3D) oxygen evolution reaction (OER) catalyst with hierarchical pores for water splitting. The remarkable features of well-developed in- and out-of-plane pores, 3D conductive networks, and N-doping have greatly promoted the transport in electrodes and assured high catalytic efficiency. The 3D hybrid paper of N-doped graphene-NiCo2O4 has shown a remarkable OER catalytic activity that was comparable to that of previously reported noble metal catalysts (IrO2). The catalytic process occurred with favorable kinetics and strong durability. The dual-active-site mechanism is responsible for the excellent performance of the hybrid catalyst; that is, the edges of NiCo2O4 and the N (O)-metal (Ni or Co) bonds are both active sites. This study affords a new strategy to achieve optimal performance in 3D catalysts, which may be extended to the preparation of other 3D hybrid materials for a broad range of technological applications.