Boron-Modulated Nitrogen-Doped Hollow Carbon Nanofibers as a Metal-Free Electrocatalyst for Nitrate to Ammonia Conversion

Abstract

Metal-free carbon-based materials have emerged as promising electrocatalysts for the nitrate reduction reaction (NO3–RR) because of their low cost, earth abundance, and environmental compatibility. Among them, carbon nanofibers (CNFs) are attractive because of their unique structural features, yet their catalytic performance remains limited by low intrinsic activity. Herein, boron and nitrogen co-doped hollow carbon nanofibers (BN-HCNFs) are developed as a metal-free electrocatalyst for nitrate-to-ammonia conversion. Owing to boron-induced electronic-structure modulation, BN-HCNFs exhibit improved NO3–RR performance relative to pristine N-HCNFs. In situ electrochemical studies reveal a hydroxylamine-related pathway on BN-HCNFs prior to NH3 formation. Theoretical calculations further show that boron doping shifts the carbon p-band center closer to the Fermi level, thereby optimizing NOx intermediate adsorption, promoting stepwise deoxygenation/hydrogenation, and lowering the rate-determining energy barrier. This work provides an effective strategy for designing metal-free carbon electrocatalysts for nitrate-to-ammonia conversion and offers mechanistic insights into the promotional role of boron doping in NO3–RR.