Carbon spheres with oxygen functional groups for electrocatalytic nitrate reduction reaction to ammonia

Electrosynthesis of NH 3 via the nitrate reduction reaction (NO 3 − RR) represents a promising strategy for producing NH 3 and addressing nitrate pollution. Heteroatom doped carbon materials as NO 3 − RR electrocatalysts have many advantages but their catalytic performance remains controversial. In this study, the carbon spheres (CS) with rich oxygen functional groups derived from glucose were investigated as a NO 3 − RR electrocatalyst. The results demonstrate that the intrinsic activity of CS is quite low. Interestingly, CS/Ni(OH) 2 composite exhibits significantly higher NO 3 − RR catalytic activity and selectivity for NH 3 compared to single Ni(OH) 2 . A serial of experimental data highlight the crucial role of CS which adjusts the electronic state of Ni 2+ in Ni(OH) 2 due to their strong interaction and facilitates the mass transfer. Furthermore, Ag/CS/Ni(OH) 2 composite was fabricated based on the tandem effect between Ag and CS/Ni(OH) 2 , which displays superior NO 3 − RR catalytic performance, achieving a Faradaic efficiency for NH 3 production of 93.27% and an NH 3 yield rate of 1.19 mmol h −1 cm −2 at −0.5 V vs. RHE. This study not only highlights the essential role of oxygen doped carbon materials in NO 3 − RR electrocatalysis, but also presents an effective strategy that harnessed both synergistic and tandem effects for the design of efficient NO 3 − RR electrocatalysts. • CS significantly improve the NO 3 − RR catalytic activity and NH 3 selectivity of Ni(OH) 2 . • The Ag/CS/Ni(OH) 2 composite exhibits excellent NO 3 − RR catalytic performance. • The tandem effect contributes to the higher performance of Ag/CS/Ni(OH) 2 .