Ammonia (NH₃) is essential for agriculture and plays an important role in next-generation carbon-free energy systems. Renewable NH₃ synthesis is a supplementary or alternative to the traditional Haber-Bosch process. The electrochemical nitrate reduction reaction (NO₃⁻RR) to NH₃ offers a promising route for sustainable NH₃ production and effective nitrogen recovery. However, slow reaction kinetics and the competing hydrogen evolution reaction (HER) hinder the efficiency.

In a study published in Nature Synthesis, a team led by Prof. BAO Xinhe from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences developed a copper-palladium (CuPd) bimetallic catalyst, which dynamically formed abundant Cu-PdH_x interfacial sites with high intrinsic catalytic activity in situ under NO₃⁻RR conditions.

Under NO₃⁻RR operating conditions, the CuPd bimetallic catalyst exhibited high intrinsic catalytic activity, achieving an NH₃ production rate of 19.9 mmol h⁻¹ cm⁻² with a current density of 5 A cm^–2 at a full-cell voltage of 2.56 V in a membrane electrode assembly (MEA) electrolyzer. It demonstrated good durability, maintaining a Faradaic efficiency of about 86.8% at 2 A cm⁻² for over 1,000 hours.

Researchers revealed that the enhanced performance was attributed to the superior intrinsic activity of the Cu-PdH_x interfaces. The hydrogen redistribution induced by the overflow at the Cu-PdH_x interface modified the local electronic structure of the active sites, which optimized the NO₃⁻ adsorption, promoted the NH₃ desorption, and provided a more energetically favorable reaction pathway for NH₃ synthesis.

A scale-up demonstration using an electrolyzer stack with five 100 cm² MEAs achieved an NH₃ production rate of 8.7 mol h^–1 at 500 A, and continuously produced 1.6 mol h^–1 of NH₃ at 100 A for 100 hours, underscoring the industrial applicability.

This study provides new insight into the structure-activity relationship of CuPd bimetallic sites. And it provides an effective strategy for enhancing intrinsic catalytic activity through the in situ construction of beneficial interfaces, enabling efficient conversion of nitrate pollutants into value-added NH₃.