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.