In situ confined vertical growth of a 1D-CuCo2S4 nanoarray on Ni foam covered by a 3D-PANI mesh layer to form a self-supporting hierarchical structure for high-efficiency oxygen evolution catalysis

Abstract

Inspired by the patchwork of artificial turf, where planting in a smaller area can result in a more uniform lawn that grows in one direction, here, we defined the growth position and orientation of a CuCo₂S₄ nanoarray for the first time by electroplating a PANI mesh layer onto a Ni foam to obtain a self-supporting hierarchical electrode material. The nitrogen species derived from the PANI building blocks act as bridging sites to bind with metal ions, which provides a strong coupling effect for the in situ growth of CuCo₂S₄. At the same time, the mesh structure of PANI divides the growable location into smaller blocks. Compared with a mesh plane with uniformly distributed nitrogen sites, only a small portion of the nitrogen sites are located on the narrow-width fence structure, which may make it difficult for CuCo₂S₄ to grow onto the fence structure, thereby limiting the self-growth space and confining CuCo₂S₄. The uniformly distributed growth sites direct CuCo₂S₄ to grow perpendicular to the plane while limiting their growth size. The excellent structural features further enhance the electrochemical oxygen evolution activity, and the oxygen evolution overpotential at a current density of 100 mA cm⁻² is only 291 mV, which is superior to that of the currently known cobalt–copper-based catalyst materials. In addition, the stable structure provides excellent electrode cyclic stability. The preparation of hierarchical self-supporting cobalt–copper bimetallic sulfide nanoarrays provided a reference direction for other transition metal catalytic materials and provided a basis for industrial applications.