Volcano Relationship of Electron Polarization Degree in Core–Shelled Ni@C Catalysts and Catalytic Activity for Hydrogen Oxidation Reaction

Abstract

Developing efficient nonprecious electrocatalysts for the hydrogen oxidation reaction (HOR) is crucial for advancing alkaline exchange membrane fuel cells (AEMFCs). A promising approach to enhance the performance of a HOR catalyst involves tuning metal–support interaction by encapsulating metal nanoparticles in carbon shells. However, the precise impact of the carbon shell on catalytic activity remains to be fully understood, yet it is crucial to guide the rational design of core–shell structured catalysts. In this study, with a sequence of well-designed Ni catalysts coated by heteroatom-doped-carbon layers (including Ni@BNC, Ni@SNC, and Ni@NC), we discover a volcano-type relationship between the electron polarization degree and the HOR activity. Experimental and theoretical analyses show heteroatom doping adjusts the carbon layer’s electron-withdrawing ability, modulating the Ni core’s d-band center and hydrogen binding energy (HBE). Additionally, heteroatom doping shifts the potential of zero charge (PZC) negatively and enhances hydrogen bond connectivity, facilitating hydroxyl ion transfer. As a result, Ni@BNC achieves optimal HBE and enhanced water adsorption, placing it at the volcano summit for the HOR activity. This study establishes a delicate volcano relationship between the electron polarization degree and the HOR activity of core–shelled catalysts by shedding light on the underlying determining factors, both the d-band center of metals and the surface PZC, related tightly with the HBE and hydrogen bond connectivity/water adsorption.