Operando XPS and NEXAFS to link the OER mechanism with the fast electro-oxidation of organic pollutants on a porous NiMnO3–rGO anode

Abstract

Electro-oxidation is one of the most promising and eco-friendly technologies for water decontamination. However, its industrial application is still limited by the high cost, poor faradaic efficiency, low durability, and potential toxicity of common high-power oxidation anodes. These challenges have been addressed by developing a novel composite comprising a mixed metal oxide (NiMnO₃) and reduced graphene oxide (rGO). The NiMnO₃–rGO anode allowed the fast and complete removal of phenol. Among different highly porous substrates, graphite felt (GF) led to the highest energy efficiency, since the GF/NiMnO₃–rGO anode yielded 100% phenol removal within only 30 min at a current density as low as 10 mA cm⁻², which was accompanied by 85% COD removal at 120 min. This anode demonstrated excellent stability, maintaining 100% phenol removal efficiency across five consecutive cycles while also showing low energy consumption (60–65 Wh (kg COD)⁻¹). Operando X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) analysis provided mechanistic insights. It is demonstrated that rGO shifts the ˙OH production pathway towards the lattice oxygen mechanism (LOM), in contrast to the adsorbate evolution mechanism (AEM) observed for NiMnO₃ alone. This mechanistic shift supports the enhanced stability and sustained electrocatalytic activity, contributing to the high performance of the GF/NiMnO₃–rGO composite anode in the context of a more sustainable technology for treating organic contaminants.