Evaluating key properties of carbon materials as cathodes for the electrogeneration of hydrogen peroxide

Twenty two carbon materials of different origins (e.g., graphite, graphene, carbon black, hydrochars, activated carbons, carbon nanotubes and nanofibers) and with varied physicochemical characteristics (e.g., electrical conductivity, structural order, surface functionalization, porosity) were investigated as cathodes in the electrochemical production of hydrogen peroxide. A screening of the electrocatalytic performance was carried out in 0.2 cm2 (inks casted on a glassy carbon) and 4 cm2 electrodes (Toray paper). The highest H2O2 production yields were obtained for carbon nanotubes and carbon nanofibers, outperforming common carbon benchmarks for this application -i.e., carbon black, carbon felt-. Furthermore, a good catalytic activity was obtained with low-cost and disordered carbon cathodes with moderate electrical conductivity and density of structural defects (e.g., nanoporous carbons), both in terms of overall production rate, selectivity and energy consumption. Data also revealed that the H2O2 production yield and the faradaic efficiency are closely related to the structural parameters of the carbon materials (i.e., density of structural defects), rather than to the electrical conductivity, composition or porous features. An AD/AG threshold value of 1.5 can be used to discriminate the electrocatalytic activity of carbon cathodes for the production of H2O2 through a 2e-ORR, in terms of high production rates and good faradaic efficiencies.