Enhancing Electrocatalytic Ammonia Oxidation Using Super-Concentrated Electrolytes

The electrocatalytic ammonia oxidation reaction (EAOR) holds significant promise for energy conversion and wastewater treatment applications. However, even the most active Pt-based catalysts are constrained by high overpotentials and poor stability, which hinder their practical implementation. Despite extensive efforts to improve catalyst performance, progress has remained limited. In this study, we propose a simple yet effective strategy utilizing super-concentrated electrolytes to enhance EAOR performance. By increasing the KOH concentration from 1 M to near saturation, we achieve a nearly 150 mV reduction in onset potential for pristine Pt catalyst (0.43 V vs RHE), which is among the lowest ones reported for EAOR to date. Moreover, this is accompanied by a 6.5-fold increase in peak current density and a nearly 100-fold extension in stable operating time. These substantial enhancements are attributed to the unique solution structure of super-concentrated electrolytes, which markedly differs from that of dilute solutions. In these concentrated media, the hydrogen-bonding network is altered, leading to the formation of highly nucleophilic H₃O₂⁻ species. These species effectively lower the activation energy for NH₃ deprotonation, thereby reducing the onset potential of EAOR and significantly boosting current density. Additionally, H₃O₂⁻ species promote the conversion of EAOR intermediates, preventing their accumulation, and thus improving EAOR stability. This super-concentration strategy is also applicable to non-noble metal catalysts, demonstrating its broad applicability for enhancing EAOR.