Boosting electrochemical ammonia production via accelerating dinitrogen activation on electrospun mesoporous tungsten oxynitride nanofibers

Abstract

Electrochemical nitrogen (N<inf>2</inf>) reduction reaction (ENRR) is a promising alternative to the traditional Haber–Bosch process for ammonia (NH<inf>3</inf>) production, offering milder conditions with lower environmental impact. However, there are significant limitations to achieving efficient ENRR, including low Faradaic efficiency (FE) and limited NH<inf>3</inf> production rates, due to the slow inert N<inf>2</inf> activation and competing hydrogen evolution reaction (HER). This study introduces mesoporous tungsten oxynitride nanofiber (mWON<inf>x</inf> NF) as highly efficient electrocatalysts for ENRR. Synthesized via electrospinning, calcination, and nitridation processes, the mWON<inf>x</inf> NF features multivalence states and oxygen vacancies, enhancing N<inf>2</inf> activation by providing abundant active sites and facilitating electron transfer to the N<inf>2</inf> molecule. Moreover, the three-phase boundary (TPB), a key factor in enhancing ENRR, is facilitated by the one-dimensional mesoporous structure of the material, thereby increasing local N<inf>2</inf> concentration near the catalyst surface while suppressing the HER. Consequently, the mWON<inf>x</inf> NF achieves a remarkable FE of 32 % at −0.2 V<inf>RHE</inf> and an NH<inf>3</inf> production rate of 27 μg h−1 cm−2 at −0.5 V<inf>RHE</inf> in 0.1 M HCl. This work not only demonstrates the viability of tungsten-based electrocatalysts for sustainable NH<inf>3</inf> production but also emphasizes the importance of TPB formation strategies in electrochemical applications involving poorly soluble gases.