Spinel high-entropy oxides as powerful electrocatalysts for degradation of recalcitrant organic pollutant

In this work a high entropy spinel oxide xerogel (X_HEO), (MnCoFeNi)₃O₄, was synthesized and proposed as a feasible heterogeneous catalyst for electrochemical degradation process. The physicochemical analysis allowed the identification of a structure belonging to the Fd-3m group and crystalline phases of Fe, Co, Ni, and Mn were detected. A high catalytic activity based on its electrochemical properties was also observed, with an η 10 of 307 mV, a Tafel slope of 35.12 mV/dec, and enhanced charge transfer kinetics. The performance of X_HEO as a heterogeneous catalyst was evaluated in the electrooxidation of Rhodamine B and the treatment conditions optimized. The reaction kinetics in the presence of X_HEO increased 2.9 times compared to a process in its absence, attaining 96.67% removal in 30 min at a current density of 1.6 mA/cm². The reaction mechanism was found to follow a non-radical pathway, dominated by the electrochemical activation of high-valence oxo-metal specie, as supported by XPS analysis and scavenger experiments. Likewise, TOC analysis revealed a mineralization of 91.51% in 240 min, and the eco toxicity of the final sample was reduced by a factor of 26 times compared to the initial value. X_HEO also showed high electrocatalytic degradation capabilities for pesticides. In particular, total degradation of pymetrozine was reached in just 15 min, with a 45.73% reduction in TOC by the end of the treatment and the detection of short-chain carboxylic acids confirmed the mineralization process. X_HEO proved to have great potential as a heterogeneous catalyst in electrooxidation treatment and also as sustainable and energy-efficient alternative for the removal of recalcitrant pollutants.