Application of hydrogen diffusion anodes in electrolytic processes using methanol-water mixtures

The current density response of H-2-fed (1 atm) Pd foil anodes in MeOH-water mixtures has been studied by current vs. voltage measurements and scanning electron microscopy. The current density response of different hydrogen-diffusion anodes, based on 25 mu m thick Pd foils coated on both sides with electrodeposited Pd black, has been tested for aqueous and MeOH (70% volume per volume)-water mixtures containing NH4Cl at concentrations near saturation. The anode current density response increased with temperature, but decreased in the presence of MeOH in the electrolyte. The best anode current density response was obtained with Pd black electrodeposited at 50 degrees C and current densities about -15 mA cm(-2) in acid (i.e., with 40 g dm(-3) NH4Cl and set to pH 0 with HCl) with 2% PdCl2. In this case, quasi-stationary current densities ca. 50 mA cm(-2), with hydrogen oxidation efficiency of 100%, in MeOH-water mixtures containing 1 mol dm(-3) NH4Cl at 20 degrees C were obtained. A possible mechanism of the process is discussed.