Insight into the deterioration mechanism of gas diffusion electrode during long-term electrosynthesis of hydrogen peroxide under industrially relevant current densities

Abstract

The long-term stability of gas diffusion electrodes (GDEs) is critical for industrial H2O2 electrosynthesis from two-electron oxygen reduction reaction (2e-ORR), but has rarely been investigated. Herein, we evaluated the stability of carbon black-polytetrafluoroethylene (CB-PTFE) based GDEs during H2O2 electrosynthesis in sodium sulfate (Na2SO4) electrolytes under industrially relevant conditions. Results show that the GDEs maintained stable H2O2 production with Faradaic efficiencies (FEs) of ∼75 % for ∼300 h under 150 mA/cm2. However, FEs then declined gradually to eventually ∼15 % at 840 h, after which the GDE failed due to water flooding. Increasing applied current density to 200 mA/cm2 accelerated the deterioration process and caused electrode failure after 350 h operation. Characterizations of the GDEs used for varying durations indicate that the deterioration of GDEs is mainly caused by oxidation of CB catalysts, defluorination of PTFE, and intercalation of Na in CB particles during H2O2 electrosynthesis. These three interrelating mechanisms gradually decreased the hydrophobicity, the 2e-ORR activity and selectivity of GDEs, and increased the porosity of GDEs. These changes in turn promoted H2O2 decomposition and progressive water intrusion into the internal pores of GDEs during H2O2 electrosynthesis, thus causing the gradual decreases of FEs and electrode flooding. Due to the gradual changes of GDE properties, it is challenging to maintain long-term stable H2O2 production under industrially relevant current densities. More studies are needed to improve the design and operation of GDEs to resolve the deterioration process of GDEs and thus extend their lifetime during H2O2 electrosynthesis.