Enhanced nitrate-to-ammonia electroreduction on manganese-doped ceria with oxygen vacancies

• We successfully synthesized Mn-CeO 2− x nanoparticles , where Mn 2+ is stabilized within the CeO 2− x host lattice. • Mn-CeO 2− x attains the highest NH 3 FE of 91.8 % at −0.60 V RHE and the maximum NH 3 yield rate of 1.01 mmol h −1 cm −2 . • Mn doping optimizes the electronic structure of CeO 2− x catalysts, leading to the generation of ample active hydrogen. Electrochemical NO 3 – reduction reaction (NO 3 − RR) represents a promising avenue for efficient and sustainable synthesis of ammonia (NH 3 ), with active hydrogen playing a pivotal role in multiple hydrogenation steps. Manganese (Mn)-based electrocatalysts have demonstrated potential in modulating active hydrogen, however, achieving atomically dispersed Mn active sites poses a fundamental challenge. To address the issue, we synthesize Mn-doped ceria with oxygen vacancies (Mn-CeO 2− x ) nanoparticles , where Mn 2+ is stabilized within the CeO 2− x host lattice, to facilitate efficient NO 3 − reduction to NH 3 . The highest NH 3 FE of 91.8 % is observed over Mn-CeO 2− x catalyst at −0.60 V RHE and the maximum NH 3 yield rate reaches 1.01 mmol h −1 cm −2 , outperforming other metal (M = Fe, Co, Ni, and Cu) doped and undoped CeO 2− x nanoparticles . Experimental analysis and density functional theory (DFT) calculations cooperatively elucidate that the Mn doping optimizes the electronic structure of CeO 2− x catalysts, leading to the generation of ample active hydrogen, improve the reaction kinetics and promote the *NH 2 O → *NH 2 OH step in NO 3 − RR. Our study introduces a rare-earth metal oxide platform for dispersing transition metal active sites, enabling the regulation of active hydrogen and the enhancement of electrocatalytic performance in NO 3 − RR.