Self-Supported Composite of (Ni,Co)₃C Mesoporous Nanosheets/N-Doped Carbon as a Flexible Electrocatalyst for pH-Universal Hydrogen Evolution

Scalable synthesis of highly efficient and nonprecious metal based catalysts for pH-universal hydrogen evolution reaction (HER) is a daunting challenge. In this work, we fabricated self-supported composites of (Ni,Co)₃C mesoporous nanosheets/N-doped carbon with adjustable sizes from 1 cm × 1 cm to 25 cm × 25 cm using a facile and rapid electrodeposition, which was then followed by carbonization. The as-prepared catalyst shows small overpotentials of 58, 118, and 71 mV at 10 mA cm^-2 in acid, neutral, and basic electrolytes, respectively with high exchange current densities. The above HER activities exceeded most non-noble metal caride-based catalysts in a pH-universal electrolyte. Theoretical calculations suggest that bimetallic carbide is favorable for HER because of its metallic conductivity, close-to-zero Gibbs free energy change (ΔG_H*), and downshifted d-band center (ϵ_d) revealed by density of states (DOS). The outstanding performance can be attributed to the tunable ultrathin nanosheet-like structure, large specific surface area, and electronic structure modulations. Our work developed an efficient, controllable, and large-scale synthesis of a cost-effective, highly efficient, high performance, and stable catalyst for hydrogen evolution reaction, which can operate in a wide pH range.