Fe-Based Deep Eutectic Solvents for Amorphous Carbon-Encapsulated Fe₃O₄ Nanoparticles as Electrocatalysts for H₂O₂ Synthesis

The production of hydrogen peroxide (H2O2) by electrochemical reduction of oxygen to the 2e– pathway, rather than the 4e– pathway to water, is gaining increasing importance as an environmentally friendly method. The identification of cost-effective catalysts with high activity and selectivity is crucial for the widespread employment of this technique. Deep eutectic solvents (DESs) provide a versatile platform for constructing high-performance electrocatalysts. Here, a novel DES was designed using FeCl3·6H2O and xylitol and was used for the first time as an all-in-one platform (serving as a solvent, template, and reactant precursor) to synthesize amorphous carbon-encapsulated Fe3O4 nanoparticles (Fe3O4@C) through a simple two-step annealing process. Fe3O4@C was found to be an efficient electrocatalyst for H2O2 electrosynthesis in alkaline media, with high H2O2 selectivity (about 90–95% over a wide potential range from 0.15 to 0.65 V vs reversible hydrogen electrode (RHE)) and long-term stability (>92% H2O2 selectivity after 12 h at 0.6 V vs RHE). The catalyst is also capable of producing up to 68.1 mg L–1 h–1 of H2O2 with an excellent Faraday efficiency (95.0%) in an H-cell at 0.3 V vs RHE. The analysis of the catalytic mechanism indicates that the Fe3O4 nanoparticles play a crucial role in regulating the oxygen reduction reaction (ORR) toward the 2e– pathway.