Boron and Oxygen Dual-Doped Carbon Nitride Nanotubes with Frustrated Lewis Pairs for Efficient Electrocatalytic Ammonia Synthesis.

This work reports boron and oxygen dual-doped carbon nitride nanotubes (B/O-CNNTs) prepared via a copolymerization process for electrocatalytic ammonia synthesis from nitrogen gas (NRR) and nitrate (NORR) sources, respectively. By adjusting the dosage of boron oxide precursor, the texture and content of B/O dual dopants and the coordination environment in the resulting 1D CNNTs can be tuned. The best B/O-CNNTs can achieve maximum Faradaic efficiencies of 35% and 96% at -1.1 V versus RHE with corresponding ammonia yields of 16.7 and 211.4 µg h mg, respectively. A comparatively higher selectivity is achieved in the NRR process compared to NORR. The B/O-induced coordinations boost electron transfer rates along the longitudinal axis. The presence of carbon vacancies and the unique 1D nanotubular structure enhance interactions among reactants. Concurrently, the formed frustrated Lewis pairs are pivotal in activating chemisorbed nitrogen gas or nitrate, resulting in notable accelerations of ammonia generation kinetics. In situ UV-vis spectroscopy reveals that the ideal potential of -1.1 V versus RHE facilitates the involvement of free electrons in the reaction, as it aligns with the conduction potential of B/O-CNNTs. This study paves the way for the design of non-metal-based electrocatalysts with dual dopants for sustainable electrocatalysis toward ammonia synthesis.