The influence of O2 on the electrochemistry of thin film, hydrogen storage, electrodes

The influence of oxygen on the electrochemical response of magnesium-scandium (Mg-Sc) thin film electrodes has been investigated. It was found that the impact of oxygen dissolved in the electrolyte is two-fold. Firstly, it gives rise to a mixed-potential under open-circuit conditions that is much more positive than the true equilibrium potential of the hydride material, thus yielding incorrect thermodynamic data. Secondly, it causes self-oxidation of the hydrogenated thin films, making calculations regarding hydrogen storage capacities (mAh/g) not straightforward. A novel oxygen-scrubbing device was developed to de-oxygenate the argon used as purging gas during the electrochemical measurements. This self-regenerative system is based on the high reactivity of the methylviologen single radical towards oxygen. A comparison between various electrochemical responses of identical Mg-Sc thin film electrodes, measured with and without the presence of oxygen, showed distinct deviations in equilibrium potential and hydrogen storage capacity. (c) 2004 Elsevier Ltd. All rights reserved.