Alumina contamination through polishing and its effect on hydrogen evolution on gold electrodes

Abstract

In this work we show how the contamination of gold electrodes with alumina particles by electrode polishing leads to an enhancement in activity for hydrogen evolution (HER). Polishing is one of the most used electrode treatments, however, we show that particles from the polishing media cannot be easily removed from the electrode surface by standard cleaning procedures. Comparing the HER activity of gold disc electrodes polished with either diamond suspension or alumina paste, we show that the latter leads to higher current densities, specifically for the water reduction to hydrogen. A similar enhancement in HER activity was observed by the addition of Al3+ cations to the electrolyte, demonstrating that the particles are not catalytically active, but that the Al3+ species released in solution due to corrosion promote the water reduction reaction. Due to an increase in the local OH− concentration during HER, the contaminating Al3+ cations precipitate and may deposit at the electrode surface as Al(OH)3. In the presence of a high enough Al3+ concentration, layered Al(OH)3 plates cover the whole electrode surface. The plates are composed of Al(OH)3 sheets intercalated by sulphate anions. Surprisingly, the Al(OH)3 sheets do not affect the gold blank voltammetry, and therefore remain undetected by simple electrochemical characterization methods.