Kinetics and Mechanism of Hydrogen Electrode Reaction on Platinum at Elevated Temperatures

The present work explored the kinetics and mechanism of the hydrogen electrode reaction on a platinized nickel electrode in alkaline solution over a wide temperature range from 18oC to 220oC using a controlled hydrodynamic cell. Quasi-steady state polarization data were obtained, and the Butler-Volmer equation was used to fit the data. The extracted transfer coefficients for the hydrogen oxidation and evolution branches display opposite temperature dependencies, resulting in the Tafel slope of the hydrogen evolution reaction (HER) being temperature independent (approximately 120mV/dec). The reaction mechanism at ambient temperature is most probably the Volmer-Tafel sequence. The exchange current density at ambient temperature is 0.55mA/cm2 rising to 9.43mA/cm2 at 200oC, and yields an activation energy of 17.3kJ/mole from an Arrhenius analysis. This value is lower than that found for other forms of platinum electrodes (e.g., single crystal) in alkaline s olution.