Polarity-inverted perovskite LaFeO₃ promotes nitrate electroreduction by intensifying the adsorption effect

The electrochemical nitrate reduction reaction (NO₃RR) offers a promising solution to nitrate pollution, with effective nitrate adsorption on the cathode surface being a critical prerequisite for achieving high efficiency. Recently, defect engineering (e.g., introduction of oxygen vacancies) has emerged as a vital method for enhancing nitrate adsorption. In this study, we present a novel and effective polarity-inversion strategy that facilitates in-situ etching of perovskite LaFeO₃ to construct defects. Characterizations including ICP-MS, TMS, and EPR confirm that lanthanum (La) was selectively etched away, leading to the formation of La and O vacancies (LaVs and OVs) in the polarity-inverted LaFeO₃ (LFO-PI). As a result, LFO-PI achieved a remarkable 5.2-fold increase in NO₃⁻-N removal efficiency compared to pristine LaFeO₃ (LFO-Pri). This enhanced NO₃RR performance was attributed to the increased surface potential and an upward shift of the d-band, which promoted the adsorption and accumulation of nitrate ions on the cathode surface. A 90 h, 30-cycle NO₃RR experiment demonstrates the outstanding stability of LFO-PI. Additionally, the polarity-inversion strategy shows strong potential for application in other perovskite oxide catalytic reactions, such as the oxygen reduction reaction (ORR). This study thus provides a simple and environmentally friendly approach for developing high-activity perovskite oxide electrocatalysts, advancing their application in NO₃RR and other electrocatalytic processes.