Ligand-engineered synthesis of carbon encapsulated Ni nanoparticles for efficient alkaline hydrogen oxidation reaction

The development of high performance non-precious metal-based hydrogen oxidation reaction (HOR) catalysts under alkaline conditions is important for achieving low cost hydroxide exchange membrane fuel cells (HEMFCs). Herein, we report a high performance Ni-based HOR catalyst through engineering of the ligand of its precursor. Carbon encapsulated Ni nanoparticles are synthesized through pyrolysis of the Ni complex. It is found that the nitrogen content in the ligands determines the nitrogen doping level in the final catalysts, which controls the hydrogen binding energy of the catalysts. The position of functional groups in the ligands regulates the electronic state of Ni, which controls the metallic Ni content in the final catalysts. Ni-Py-3-AO synthesized using pyridine-3-amidoxime as the ligand achieves a high HOR exchange current density of 138 µA cm_Ni ^-2 and a mass activity of 94.1 A g_Ni ^-1 at 50 mV of overpotential. A high peak power density of 554 mW cm^-2 is achieved for the HEMFC using Ni-Py-3-AO as the anode. Mechanistic studies reveal that its superior HOR activity originates from modulated hydrogen binding energy as well as well-structured interfacial water.