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 a nd scanning electron microscopy. The current density response of diffe rent hydrogen-diffusion anodes, based on 25 mu m thick Pd foils coated on both sides with electrodeposited Pd black, has been tested for aqu eous 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 t he electrolyte. The best anode current density response was obtained w ith Pd black electrodeposited at 50 degrees C and current densities ab out -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 dens ities 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 wer e obtained. A possible mechanism of the process is discussed.