Solar thermal decoupled water electrolysis process III: The anodic electrochemical reaction in a rotating disc electrode cell

Abstract The electrochemical oxidation of C o 2 + is studied at 45 °C using a rotating disc electrode to elucidate the impacts of fluid motion and solid C o 3 + product formation on the anode reaction rate. The electrolyte is 40% KOH saturated with C o 2 + and the anode is nickel. Inducing laminar flow with rotation at speeds up to 2500 RPM is shown to increase the current density from 1 mA c m - 2 to 2--5 mA c m - 2 at potentials greater than -0.21 Volts vs. Ag/AgCl. At higher current densities anticipated for commercial application, electrode passivation is a relevant concern. However, bulk electrolysis and cyclic voltammetry---with the latter interpreted using a reaction model to account for the fluid motion---demonstrate that the solid C o 3 + deposit is not passivating, but electrochemically active. Deposits up to ≈ 1 mm thick increase the current, with a sixfold increase demonstrated at 2000 RPM.