Understanding the hydroxyl adsorption behavior at Pt electrode surface in high-temperature alkaline solutions

Abstract

Since the application in fuel cell, the electrochemical adsorption of hydroxyl has received considerable attention in recent years. While most research mainly focus on the room temperature, in this paper, the electrochemical adsorption of hydroxyl in alkaline solution at high temperature was investigated. An unusual oxidation peak was observed at −0.27 V, suggesting new behavior of hydroxyl adsorption occurred. As is known two kinds of cation hydrated clusters exist in alkaline solution, (H 2 O) x− 1 M + --H 2 O--O ad H and (H 2 O) x M + --O ad H. For K + and Cs + , the cluster shows unstable structure due to the weak interaction between hydrated cation and OH − especially at high temperature. However, For Li + , Na + the cluster structure would be stable, as the interaction force between the hydrated cation and OH − is so strong. It was revealed that the unusual oxidation peak has some relationship with the (H 2 O) x −1 M + --H 2 O--O ad H cluster (K + and Cs + ) absorbed at Pt electrode surface. When the temperature was raised, (H 2 O) x −1 M + --H 2 O- and -O ad H was disconnected, then the O ad H absorbed at Pt surface got oxidated. Based on the SEM observation, it was showed the unusual electrochemical oxidation reaction would generate platinum oxides, blocking the reactive sites at Pt electrode surface, thus reducing the electrochemical reactivity of Pt electrode. Accordingly, parameters of alkaline concentration and temperature were systematically studied, it was found that increase temperature or alkaline concentration was in favor of the unusual oxidation reaction. This study provides more understanding of hydroxyl adsorption behavior at Pt electrode surface for the high temperature water solution environment.