Mechanistic Investigation of Nitrogen Defects in Boron Nitride for Enhanced Hydrogen Evolution through Water Radiolysis

Defects play a pivotal role in enhancing hydrogen production from water radiolysis. To elucidate the influence of defects in boron nitride on radiolytic hydrogen evolution, boron nitride samples with various nitrogen defects (denoted as Nv-BN1, Nv-BN2, and Nv-BN3) were prepared through ball milling, gamma irradiation, and thermal calcination, respectively. Through these operations, samples with different relative densities of three-boron center nitrogen defects (TBC defects) were successfully obtained. Among the synthesized materials, the Nv-BN1 sample with an ultralow solid loading (0.075 wt %) achieved a saturated radiolytic hydrogen yield of 0.65 × 10^-7 mol J^-1, while Nv-BN2 (0.025 wt %) with higher defect density exhibited an even greater saturated yield of 0.70 × 10^-7 mol J^-1. In contrast, the calcined Nv-BN3 showed reduced activity due to the passivation of defect sites. Fluorescence experiments revealed elevated levels of both •OH and e_aq^- in suspensions containing TBC defect samples compared to pure water, suggesting that water molecules at the defect-rich solid-liquid interface undergo enhanced radiolytic dissociation. Notably, the •OH yield was lower than that of e_aq^-, implying that partial consumption of •OH occurred at electron-deficient boron sites. This hypothesis is supported by X-ray time-resolved in situ infrared spectroscopy, which showed the gradual emergence of a characteristic B-O band near 1190 cm^-1 during irradiation, a spectral feature absent in pristine h-BN sample. Complementary density functional theory (DFT) simulations further corroborate this mechanism, suggesting that water molecules preferentially adsorb at TBC defect sites, where the intramolecular O-H bond is weakened, thereby facilitating bond cleavage. Collectively, these results highlight the unique role of TBC defects as catalytic centers that enhance water radiolysis, offering fundamental mechanistic insights into defect-mediated interfacial chemistry and presenting a promising strategy for advancing radiation-driven energy conversion technologies.