Formaldehyde Electro-oxidation on Copper Metal and Copper-based Amorphous Alloys in Alkaline Media

Copper metal and copper-based amorphous alloys, a-Cu35Ti65 and a-Cu33Zr67, exhibit a very high and stable activity for the anodic HCHO oxidation in aqueous NaOH and Na2CO3. The oxidation current was already observable at electrode potentials as low as 0.1 V (RHE) and, in particular, the HF-treated amorphous alloys gave high current densities around 40 mA cm−2 (apparent) at 0.2 V. Kinetic data, roughly first order both in HCHO and OH− concentration, are in favour of the mechanism in which the oxidation proceeds via hydroxymethanolate ion (HOCH2O−) formed from HCHO and OH−, producing HCOO− and H2: This ion is readily oxidized on the copper metal or copper-based amorphous alloy electrodes. The Tafel slope was in general agreement with the reaction mechanism assuming a rate-determining one-electron transfer step.