Controlled proton accessibility through carboxylic-based organic ligands for highly efficient and selective ammonia electrosynthesis

Abstract

Competing hydrogen evolution reaction (HER) and sluggish multi-electron/proton-involved steps are the major obstacles to improving the efficiency and selectivity of electrochemical nitrate reduction to ammonia (eNO<inf>3</inf>RR). Herein, we modified Co<inf>3</inf>O<inf>4</inf> nanoparticles with doped rare-earth La atoms and carboxylic (COO⁻)-based organic ligands. The COO⁻ groups efficiently reduce the water activity around the active sites by forming hydrogen bonds, thus controlling proton accessibility and regulating the adsorption selectivity between nitrate ions and protons. Simultaneously, introducing oxygen vacancies through La doping establishes active sites with a strong affinity for nitrate ions and an electron-rich local environment conducive to eNO<inf>3</inf>RR. The electrocatalyst exhibits superior activity and selectivity with an ammonia Faradaic efficiency of up to 99.41% and a yield rate of 5.62 mg h⁻¹ mg<inf>cat</inf>⁻¹ at −0.3 V vs. reversible hydrogen electrode (RHE). Notably, the catalyst maintains over 90% Faradaic efficiency for NH<inf>3</inf> production across a broad potential range of 400 mV, surpassing most recently reported eNO<inf>3</inf>RR electrocatalysts.