Electrocatalytic reduction of hydrogen peroxide in solution in the presence of polyacrylic acid and copper ions: Application for gaseous hydrogen peroxide detection

A comprehensive voltammetric investigation into the electrocatalytic electrode mechanism for the reduction of hydrogen peroxide in an aqueous polyacrylic acid solution, in the presence of Cu2+ ions, is presented. The primary objective is to lay the groundwork for the development of a straightforward electrochemical sensor for the detection of gaseous H2O2. Various electrode reaction pathways have been observed depending on the potential applied to the glassy carbon electrode. At potentials approximately −0.400 V vs. Ag/AgCl (3 mol L−1 KCl), an electrochemical reduction of H2O2 occurs. In this context, the Cu2+/Cu+ redox couple, stabilized by polyacrylic acid, acts as a redox mediator, following the EC' reaction scheme. Additionally, a complex Fenton-like spontaneous redox chemistry takes place between Cu2+/Cu+ and H2O2 within the bulk of the polyacrylic aqueous solution. This results in the generation of a variety of reactive oxygen species (ROS), with the superoxide anion and hydroxyl radical being the most probable intermediates. The electrochemical reduction of ROS species effectively recycles H2O2 near the electrode surface, constituting an electrocatalytic mechanism of the second order. This particular electrocatalytic process is evident as a prominent reduction current tail at potentials more negative than −0.400 V. This, in conjunction with the adsorption and stabilizing influence of polyacrylic acid, facilitates exceptional analytical sensitivity for the detection of gaseous H2O2. The sensor exhibits the capability to detect concentrations of gaseous H2O2 as low as 10−11 mol L−1, accomplished through the utilization of square-wave voltammetry and other advanced voltammetric techniques.