In situ nitridation of carbon-based Ni3N electrocatalysts for the hydrogen evolution reaction: Synthesis and mechanistic insights

Abstract

Nickel nitride (Ni₃N) exhibits promising electrochemical activity for the hydrogen evolution reaction (HER) in alkaline media. However, the synthesis of Ni₃N without employing an ammonia atmosphere or mixed amine-based precursors remains unexplored, and the mechanism by which carbon-based Ni₃N enhances HER catalytic performance is still not fully understood. Herein, we report for the first time a simple and environmentally friendly in situ nitridation method to synthesize a Ni₃N/rGO electrocatalyst via direct heating, and demonstrate its application as an efficient HER electrode material. Characterization results show that C₄K₂N₄Ni·xH₂O serves as both the nitrogen and nickel source. Following a hydrothermal reaction, the catalytically active sites are uniformly dispersed on the rGO surface via ion exchange, and homogeneous Ni₃N/rGO is successfully synthesized through heating under a nitrogen atmosphere. The rGO matrix enhances contact between the catalytic active sites and the electrolyte, enabling excellent HER performance even with extremely low metal loading (Ni₃N/rGO (0.98) are 195 mV at −10 mA/cm², and 305 mV at −80 mA/cm²). First-principles density functional theory (DFT) calculations reveal that the Ni₃N/rGO electrocatalyst possesses lower free energy and a reduced reaction energy barrier. Under optimized conditions, Ni₃N/rGO (0.98) exhibits a comparable overpotential (ECSA-normalized) to that of commercial 20 % Pt/C, along with outstanding stability during cyclic testing at high current densities. Moreover, substituting anion exchange resin as the carbon source also yields similar catalytic performance. The proposed synthesis strategy for carbon-based Ni₃N electrocatalysts offers a scalable approach for the fabrication of high-performance HER electrode materials.