Anodic Oxidation of Molecular Hydrogen at Low Temperatures

Noble metals and some of their alloys are materials that offer sufficient resistance to corrosion in acid media and are good electrocatalysts at the same time. The mechanism of the anodic H2 oxidation is discussed for noble metals and their alloys in section 1 of this chapter. The conclusions derived for acid solutions can be easily transferred to alkaline electrolytes since mass transport processes are rate-determining under regular conditions. Less expensive nickel electrodes perform satisfactorily in alkaline solutions. Section 2 deals with studies of the H2 oxidation on different types of nickel electrodes. Results of studies of the H2 oxidation at platinum in contact with an ion exchange membrane are described in section 3. 

Mechanism of the H2 Oxidation on Noble Metals and Noble Metal Alloys 

It was concluded first by Knorr and coworkers [1] that diffusion of molecular hydrogen is the rate-determining step of hydrogen evolution on smooth platinum and palladium electrodes pretreated anodically. The same conclusion holds for the anodic processes given by Eq. 1 and 2. The interpretation based on steady-state measurements [1] is valid at cathodic current densities — i 1 mA/cm in strong acid electrolytes (0d.H+ 1)- The correctness of this interpretation has been substantiated by a number of independent techniques which allow the concentration Ch2 of H2 molecules adjacent to the surface to be determined  

The increase of Ch with overvoltage rj was found to agree well with that computed according to Nernst s equation from the measured 

The good agreement between experimental curves and i — U curves computed according to Eq. IV, 38 with the experimental values of I d h2 is demonstrated in Fig. 23. The theoretical curves are represented 

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