Hydroxyl adsorption identified as key factor in electrocatalytic ammonia production

Compared with the energy-intensive Haber-Bosch process, renewable energy-driven electrocatalytic nitrate reduction reaction (NO₃⁻RR) provides a low-carbon route for ammonia synthesis under mild conditions. Using nitrate from wastewater as the nitrogen source and water as the hydrogen source, this route has the potential to produce ammonia sustainably while mitigating water pollution.

Copper (Cu)-based catalysts show a good performance for NO₃⁻RR to ammonia. However, they suffer from issues including high overpotential, competing nitrite (NO₂^–) formation, and low overall energy efficiency.

In a study published in ACS Catalysis, a team led by Prof. Bao Xinhe and Prof. Gao Dunfeng from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences, along with Prof. Wang Guoxiong from Fudan University, proposed hydroxyl (*OH) adsorption as a selectivity descriptor for ammonia synthesis via NO₃⁻RR over Cu catalysts.

Using a size- and shape-selected Cu nanocube model catalyst, researchers investigated how electrode potential and NO₃⁻ concentration affect NO₃⁻RR product distribution. They found that more negative potentials and lower NO₃^– concentrations can improve ammonia selectivity over NO₂^– formation, which is an effect strongly correlated with weakened *OH adsorption.

Moreover, researchers proposed *OH adsorption as a descriptor for product selectivity, as it controls the availability of surface adsorbed hydrogen (*H) generated during water dissociation. They demonstrated that using *OH adsorption as a descriptor can guide the design of both catalysts and electrolytes to lower NO₃⁻RR overpotentials.

“Our work underscores the importance of *OH adsorption as a selectivity descriptor for designing more efficient systems towards ammonia electrosynthesis from nitrate,” said Prof. Gao.