Evoking dynamic Fe–N x active sites through the immobilization of molecular Fe catalysts on N-doped graphene quantum dots for the efficient electroreduction of nitrate to ammonia

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 12; no. 33; pp. 22070 - 22081
• Main Authors: Rinawati, Mia, Chiu, Yen-Shuo, Chang, Ling-Yu, Chang, Chia-Yu, Su, Wei-Nien, Septiani, Ni Luh Wulan, Yuliarto, Brian, Huang, Wei-Hsiang, Chen, Jeng-Lung, Yeh, Min-Hsin
• Format: Journal Article
• Language: English
• Published: 20.08.2024
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/D4TA03246B

The excessive energy demand of the conventional Haber–Bosch process for ammonia (NH 3 ) generation, coupled with the disruptive effects of nitrate (NO 3 − ) pollution on the global nitrogen cycle, has made the electrocatalytic nitrate reduction reaction (NO 3 − RR) an essential exit strategy for sustainable NH 3 synthesis. However, the intricate multi-step proton and electron transfer process posed a great challenge in achieving high-efficiency electrocatalysts. In this study, we report a selective and highly active NO 3 − RR electrocatalyst featuring molecular M–N x sites derived from the immobilization of Fe ions within N-doped graphene quantum dots (NGQDs). We demonstrated that the formation of molecular Fe–N x coordination activated the NO 3 − RR of NGQDs-Fe, despite the initial inactivity of NGQDs. In situ Raman analysis revealed that those Fe–N x sites served as favourable adsorption sites for *NO 3 . Such catalyst achieved an FE of 93% and a yield rate of 15.41 mmol h −1 cm −2 for NH 3 at −0.8 V ( vs. RHE) in an alkaline medium. These findings revealed the preferential sequential 2e − and 6e − transfer pathways over the direct 8e − pathway in the NO 3 − RR, which provides new mechanistic insights into the nitrate reduction reaction.