Synergistic Brønsted/Lewis acid sites in amorphous ZrPO for Tandem electrocatalytic nitrate reduction to ammonia

Electrocatalytic nitrate reduction to ammonia (NO₃^-RR) is a highly promising pathway for wastewater treatment and sustainable nitrogen cycling. However, the electrocatalytic efficiency in conventional crystalline electrocatalysts is limited by sluggish proton-coupled electron transfer (PCET) kinetics, resulting from the lack of atomic sites for active *H generation and rapid proton transfer. To address this issue, we fabricate amorphous zirconium pyrophosphate (ZrPO) benchmark catalysts that featuring a high density of Brønsted and Lewis acid sites. In situ electrochemical attenuated total reflection infrared spectroscopy and differential electrochemical mass spectrometry elucidated that Lewis acid sites readily promote the adsorption and activation of NO₃^-. Kinetic isotope effect (KIE), tert-butanol quenching experiments and theoretical calculations demonstrate that Brønsted acid sites can facilitate H₂O dissociation to generate active *H species and accelerate their migration. The synergistic interplay between Brønsted and Lewis acid sites ensures the efficient conversion of NO₃^-, the effective supply of active *H species and rapid surface proton transfer, which collectively lower the kinetic barrier of the PCET process. Thus, amorphous ZrPO with both lewis and Brønsted acid sites achieves the NH₃ yield rate of 2.57 mol g_cat⁻¹ h⁻¹ and a Faradaic efficiency of 95.0%, which is about 2-fold higher than crystalline ZrPO without Brønsted acid sites. This work not only provides new insights into the electrochemical mechanism of NO₃^-RR but also offers guidance for the rational design of high-performance electrocatalysts.