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

Abstract

Electrochemical NO₃^– reduction reaction (NO₃⁻RR) represents a promising avenue for efficient and sustainable synthesis of ammonia (NH₃), 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 Mn²⁺ is stabilized within the CeO_2−x host lattice, to facilitate efficient NO₃⁻ reduction to NH₃. The highest NH₃ FE of 91.8 % is observed over Mn-CeO_2−x catalyst at −0.60 V_RHE and the maximum NH₃ 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 *NH₂O → *NH₂OH step in NO₃⁻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 NO₃⁻RR.