Janus Electrode of Asymmetric Wettability for H₂O₂ Production with Highly Efficient O₂ Utilization

Aeration-based electrochemical systems to produce H2O2 face two major challenges: O2 mass transfer limitation and low utilization efficiency of sparged oxygen. To mitigate these problems, a Janus electrode (JE) of asymmetric wettability with hydrophobic gas storage layer (GSL) and hydrophilic catalyst layer (CL) was successfully fabricated by substrate hydrophobization and a subsequent catalyst-coating treatment. When O2 was sparged at 6 mL min–1, the JE obtained a H2O2 generation rate of 2.8 ± 0.02 mg h–1 cm–2 with oxygen utilization efficiency (OUE) of 5.0 ± 0.7% at −0.4 V vs Ag/AgCl, much higher than those of hydrophobic electrodes (1.1 ± 0.3 mg h–1 cm–2, OUE of 2.0 ± 0.5%) and hydrophilic electrodes (0.1 ± 0.004 mg h–1 cm–2, OUE of 0.2 ± 0.01%). The improved performance with JE was attributed to an adequate oxygen supply from hydrophobic GSL and abundant active sites in hydrophilic CL. With the critical aeration rate of 0.5 mL min–1, the JE obtained an extremely high OUE of 37.4 ± 3.7%. With the applied potential increase to −1.0 V vs Ag/AgCl, the H2O2 generation rate of JE consequently improved to 19.5 ± 0.4 mg h–1 cm–2. This asymmetric structure of the Janus electrode successfully mitigated the O2 mass transport limitation and reduced the O2 bubble waste for H2O2 production, enabling more energy-efficient and cost-effective electrochemical remediation processes.