Regenerable surface-reconstructed silver mesh enables high-throughput electrocatalytic nitrate-to-nitrite conversion for near-perfect N<sub>2</sub> selectivity in a tandem system.

Abstract

Nitrate contamination in water is a persistent global challenge. While electrocatalytic nitrate reduction is a promising remediation strategy, achieving high selectivity towards benign N₂ in chloride-free systems, coupled with high processing rates, remains difficult. This study introduces a high-performance surface-reconstructed silver mesh (SRSM) electrode prepared from commercial silver mesh via a facile oxidation-reduction treatment. The SRSM electrode serves as a robust electrocatalyst for the highly selective reduction of nitrate to nitrite, which represents the critical first step in a tandem (stepwise) nitrate to nitrogen conversion strategy. Subsequent chemical reduction of the produced nitrite with sulfamic acid (HSA) completes this tandem process. The SRSM demonstrated exceptional nitrite selectivity (up to 99.5 %) over a broad potential range, operating via a proton-coupled electron transfer mechanism. Significantly, in a flow-through system, the SRSM achieved a remarkable treatment capacity of up to 500 L·m^-2·h^-1 (26.2 g_nitrate·m^-2·h^-1), representing a substantial improvement in throughput compared to the previously developed silver nanowires membrane electrode designed for such tandem approaches. The electrode maintained high selectivity over 108 h of continuous operation, during which two regeneration cycles were employed to restore full activity upon deactivation, demonstrating excellent operational stability and effective catalyst regeneration. The integrated tandem system achieved an exceptional overall N₂ selectivity of up to 99.5 %, setting a new benchmark for chloride-free nitrate electroreduction systems. This work not only presents a superior electrocatalyst for the tandem nitrate-to-N₂ conversion but also significantly advances the practical viability of tandem catalytic strategies for nitrate remediation.