Synthesis and electrocatalytic performance of ZrO₂@g-C₃N₄ heterostructures for the hydrogen evolution reaction

Abstract

The development of efficient and economical electrocatalysts for the hydrogen evolution reaction (HER) remains crucial for sustainable hydrogen production. In this study, the effect of incorporating graphitic carbon nitride (g-C₃N₄) into cubic ZrO₂ (c-ZrO₂) was systematically investigated to elucidate the material's electrocatalytic activity. The ZrO₂@g-C₃N₄ composites were prepared in various compositions (30-90 wt.%) of g-C₃N₄ and characterized by XRD, TGA, FE-SEM, CV, LSV, and EIS. The low-temperature cubic ZrO₂ phase was stabilized at room temperature using XRD, and the crystallite size was 4.0-6.7 nm, which was attributed to the effects of interfacial strain and confinement caused by the g-C₃N₄ matrix. The FE-SEM images showed intimate contact between the ZrO₂ nanoparticles and g-C₃N₄ nanosheets, forming a hierarchical porous structure. Importantly, the HER activity of the composite showed a non-monotonic trend with composite loading, being highest for the composite containing 30 wt. % g-C₃N₄. It was found that the 30 wt.% composite had an overpotential of 1300 mV at 10 mA/cm 2 and exhibited much better charge-transfer kinetics than pure ZrO 2 . The charge-transfer resistance was found to drop significantly with the incorporation of g-C₃N₄, as indicated by EIS data, due to heterojunction formation and an optimized electron transport pathway. The 90 wt.% composite showed good stability and poor catalytic activity, indicating a fundamental balance between access to the active site and its protection. The results indicate that ZrO₂@g-C₃N₄ heterostructures are promising, earth-abundant electrocatalysts and provide important guidelines for optimizing their electrocatalytic performance through loading.