Metal-Free h-BN/Carbon Nano-Onion Heterostructure Electrocatalyst with Enhanced Hydrogen Evolution Activity Under Acidic Media

Developing effective metal-free electrocatalysts for acidic hydrogen evolution is challenging because both catalytic activity and electronic conductivity must be optimized simultaneously. Here, h-BN/carbon nano-onion (CNO) hybrid electrocatalysts were synthesized by integrating layered hexagonal boron nitride with conductive carbon nano-onions to generate accessible heterointerfaces for the hydrogen evolution reaction (HER). Structural characterization by XRD, SEM/TEM, and STEM-EDS confirmed intimate contact between h-BN sheets and quasi-spherical CNO domains. Similarly, XPS revealed B–N-rich frameworks with interfacial B–C/C–N surface environments and oxygen-associated defect sites. Among the prepared compositions, the h-BN/CNO20 eletrocatalyst exhibited the best apparent HER performance in 0.5 M H2SO4, delivering an overpotential of ~270 mV at 5 mA cm−2 and a Tafel slope of 76 mV dec−1, along with stable chronoamperometric behavior for 15 h. The improved electrocatalytic activity is due to the enhanced charge transport through the CNO network, suppression of h-BN restacking, increased exposure of interfacial sites, and charge redistribution across B–N/C heterojunctions. These findings identify h-BN/CNO20 as the optimum composition within this series and demonstrate that heterointerface engineering between boron nitride and curved graphitic nanocarbons is a promising strategy for developing metal-free HER electrocatalysts. However, further validation using a non-Pt counter electrode is necessary to confirm intrinsic catalytic activity.