Atomically-dispersed transition metal electrocatalysts supported on lignin-derived carbons for cathodic hydrogen peroxide synthesis using a gas-diffusion electrode

Abstract

Hydrogen peroxide (H2O2) is nowadays a commodity chemical, with a particularly relevant application in wastewater treatment. However, its industrial production is energy demanding, highly polluting and potentially dangerous. Lately, oxygen reduction reaction (ORR) conducted on a gas-diffusion electrode (GDE) has been explored to deploy a more sustainable synthesis route. In this work, a set of lignin-derived carbons, either metal-free or loaded with atomically dispersed transition metals (Fe, Co and Ni), was successfully synthesized for the electrogeneration of H2O2. For some electrocatalysts, the rotating ring-disk electrode (RRDE) analysis showed a peroxide selectivity () over 90% and a number of transferred electrons of ∼2. Accordingly, the type of metal and the carbon porosity had a major influence on the performance of GDEs during bulk electrolysis. In galvanostatic assays conducted in 0.05 M Na2SO4 medium at pH 5.9 and 10 mA cm−2, the carbon obtained from direct lignin pyrolysis at 400 °C outperformed a commercial GDE, showing the highest H2O2 yield (13.8 mM after 360 min), with a maximum current efficiency of 85% and relatively low energy consumption (∼ 8 ). Such optimum performance is related to its optimal porosity and hydrophobicity. Moreover, upon functionalization with Fe, an effective electro-Fenton (EF) catalyst was obtained, allowing a 97% removal of the drug lisinopril using only 0.1 g L−1 of suspended catalyst. This work demonstrates the possibility of producing cost-effective electrocatalysts from waste for H2O2 production and wastewater treatment.