The catalytic effect of graphene oxide with varying degrees of oxidation with respect to the water dissociation reaction on bipolar membranes

Abstract

The article presents the results of a study on the catalytic activity in the water dissociation reaction and the chemical structure of oxidized graphene samples with various degrees of oxidation. The catalytic activity was investigated using asymmetric bipolar membranes with a homogeneous anion-exchange layer based on a copolymer of N,N-diallyl-N,N-dimethylammonium chloride and ethylmethacrylate. It was shown that graphene oxidized by the Hummers’ method significantly accelerates the water dissociation process due to the presence of carboxyl and phenolic groups in its chemical structure. Graphene reduced by sodium borohydride and graphene oxidized by sodium dichromate exhibited significantly lower catalytic activity (U_b = 2.9 V and 2.8 V, respectively, at 3.75 mA/cm²) than graphene oxidized by Hummers’ method (U_b = 0.39 V at 3.5 mA/cm²). Compared to the initial asymmetric bipolar membrane (U_b = 7.0 V at 3.75 mA/cm²), a more than two-fold decrease in the overvoltage of the bipolar region was observed. In the first case, this is attributed to the high electronic conductivity of the catalyst, and in the second case, to the residual content of carboxylic and phenolic groups. The chemical structure of the oxidized and reduced graphene samples was studied by IR spectroscopy and quantum chemical methods at the r2scan-3c level. The presence of hydroxyl, carboxyl, carbonyl, and epoxy groups in the structure of oxidized graphene was confirmed both experimentally and theoretically. It was also established that the Lerf-Klinowski model of oxidized graphene agrees best with the experimental data.