Acid Anion Electrolyte Effects on Platinum for Oxygen and Hydrogen Electrocatalysis

Abstract

Platinum (Pt) plays a key role as an electrocatalyst in renewable electrochemical energy technologies such as fuel cells and electrolyzers. Better understanding the interfacial phenomena at the Pt-electrolyte interface can help guide microenvironment engineering to tune performance via electrolyte effects. Herein, we investigate the effect of electrolyte, and more specifically anion, identity on the activity of Pt for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and hydrogen oxidation reaction (HOR) at pH 1. In short, while we see the HER/HOR performance is similar across all three electrolytes, ORR activity trends as HClO4 > HNO3 > H2SO4, and OER activity trends as HClO4 > HNO3 ~ H2SO4. Notably, we observe ORR performance in HNO3 can be improved 4-fold compared to in H2SO4. With combined experimental-theoretical methods, namely cyclic voltammetry and density functional theory anion free energy of adsorption calculations, we hypothesize that the role of the ClO4 –, NO3 –, and HSO4 –/SO4 2– anions can vary as a function of applied potential. Moreover, we note that our rather innovative measurements of Pt hydrogen and oxygen electrocatalysis in nitric acid suggest that a nitrate-like microenvironment in Pt membrane electrode assemblies (MEAs) could present opportunities to enhance the catalyst-ionomer-membrane interface in electrochemical devices such as fuel cells and electrolyzers. This works provides guidance for rational design/engineering of electrocatalyst microenvironment and highlights the microenvironment importance in modulating catalytic performance.