Modeling Anion Poisoning during Oxygen Reduction on Pt Near-Surface Alloys

Electrolyte effects play an important role in the activity of the oxygen reduction reaction (ORR) of Pt-based electrodes. Herein, we combine a computational model and rotating disk electrode measurements to investigate the effects from phosphate anion poisoning for the ORR on well-defined extended Pt surfaces. We construct a model including the poisoning effect from phosphate species on Pt(111) and Cu/ Pt(111) based on density functional theory simulations. By varying the subsurface Cu content of the Cu/Pt(111) alloy, we tune the *OH binding energies on the surface by means of ligand effects, and as a result, we tune the ORR activity. We have investigated the effect of adsorbed phosphate species at low overpotentials when tuning *OH binding energies. Our results display a direct scaling relationship between adsorbed *OH and phosphate species. From the model, we observe how the three-fold binding sites of phosphate anions limit the packing of poisoning phosphate on the surface, thus allowing for *OH adsorption even when poisoned. Our work shows that, regardless of surface site blockage from phosphate, the trend in the catalytic oxygen reduction activity is predominantly governed by the *OH binding.

Automated summary

In this study, the effects of phosphate anion poisoning on the oxygen reduction reaction (ORR) activity of Pt-based electrodes were investigated using a computational model and rotating disk electrode measurements. By varying the subsurface Cu content of a Cu/Pt(111) alloy, the *OH binding energies on the surface were tuned through ligand effects, resulting in tuning of the ORR activity. The adsorbed phosphate species on the surface were found to directly affect the adsorption of *OH, and the three-fold binding sites of phosphate anions limited the packing of poisoning phosphate, allowing for *OH adsorption even when the surface was poisoned.