The oxidation of formaldehyde on high overvoltage DSA type electrodes

The electrochemical oxidation of formaldehyde is studied on dimensionally stable anodes prepared by thermal decomposition of precursors (the corresponding chlorides). The working electrodes used were: Ti/Ir0.3Ti0.7O2, Ti/Ru0.3Ti0.7O2 and Ti/Ir0.2Ru0.2Ti0.6O2. The electrolyses were performed galvanostatically in a filter press cell with 0.5 mol L-1 H2SO4 solutions with initial formaldehyde concentration equal to 100 mmol L-1. The concentration of formaldehyde decreases fast with the electrolysis time, with the ternary anode (Ir + Ru + Ti) presenting the best performance for this step. The anode containing only Ir, despite presenting the higher superficial charge, is the one with the lowest electrocatalytic activity. For the formic acid oxidation step, the presence of iridium in the anode composition does not promote the process, the anode containing only ruthenium being the most effective for this step.