OH* Electro-Adsorption Kinetics on Pt (111) in Alkaline: Comparison to the H* Electro-Adsorption

OH* electro-adsorption of platinum plays a critical role in the electrocatalysis of small molecules, including carbon monoxide and methanol. Recently, the OH* electro-adsorption has also been linked to the electrocatalysis of hydrogen evolution reaction and hydrogen oxidation reaction (HER and HOR), widely believed to be the result of the Pt-OH on the Pt-H formation. In addition, OH* is part of the oxygen reduction reaction (ORR) in alkaline fuel cells. In this contribution, we report our investigation on the OH* electro-adsorption of platinum using cyclic voltammetry (CV) as a function of scan rate. Our approach builds on the recently reported rate-dependent CV methodology, which we have developed to measure the kinetics of the Pt-H formation. The adsorption mechanisms are determined by comparing OH* electro-adsorption kinetics as a function of electrolyte chemistry, from pH to the chemistry of cation. Our results show that OH* electro-adsorption rate depends strongly on the ionic strength but weakly on pH. What’s more, the OH* electro-adsorption rate is at least an order of magnitude faster than H* electro-adsorption rate in alkaline. Therefore, we think that the water forming in HOR is limited by H* formation or H2O recombination and the OH* electro-adsorption in ORR is likely not the rate-limiting step.