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

The production of hydrogen peroxide (H 2 O 2 ) 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 FeCl 3 ·6H 2 O 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 Fe 3 O 4 nanoparticles (Fe 3 O 4 @C) through a simple two-step annealing process. Fe 3 O 4 @C was found to be an efficient electrocatalyst for H 2 O 2 electrosynthesis in alkaline media, with high H 2 O 2 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% H 2 O 2 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 H 2 O 2 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 Fe 3 O 4 nanoparticles play a crucial role in regulating the oxygen reduction reaction (ORR) toward the 2e – pathway.