Deciphering the linear relationship in the activity of the oxygen reduction reaction on Pt electrodes: A decisive role of adsorbates

Despite substantial efforts in developing high-performance catalysts for the oxygen reduction reaction (ORR), the persistent challenge lies in the high onset overpotential of the ORR, and the effect of the electrolyte solution cannot be ignored. Consequently, we have systematically investigated the impact of adsorbate species and concentration, as well as solution pH, on the ORR activity on Pt(111) and Pt(poly) electrodes. The results all tend to establish a linear quantitative relationship between the onset potential for ORR and the adsorption equilibrium potential of the adsorbate. This finding indicates the decisive role of adsorbates in the onset potential for ORR, suggesting that the adsorption potential of adsorbates can serve as an intuitive criterion for ORR activity. Additional support for this conclusion is derived from experimental results obtained from the oxygen evolution reaction on Pt(poly) with different adsorbate species and from the hydrogen evolution reaction on Pt(111) with iodine adsorption. We further propose both an empirical equation for the onset potential for ORR and the concept of a potential-regulated adsorbate shielding effect to elucidate the influence of adsorbates on ORR activity. This study provides new insights into the high onset overpotential of the ORR and offers potential strategies for predicting and enhancing ORR activity in the future.