Multicomponent electrodes for water oxidation: From combinatorial to individual electrode study

Combinatorial screening of platinum group metal (PGM) microelectrodes supported on graphite paper was carried out in a search for useful electrodes for water oxidation. This screening utilized a fluorescent acid-base indicator to identify the most active electrodes in 10 x 10 arrays. Individual Pt, Pd, Ir, Ru, Os, and Rh samples and mixtures of these metals were used to investigate their activities as electrodes for water oxidation. Supported Ru was the most active (i.e., had the lowest overpotential for water oxidation), but it was unstable when the applied potential was more than 1 V. A mixture of Ru and Ir showed significantly improved stability and activity for water oxidation. The most effective electrodes were composed of the four metals Ru, Pd, Ir, and Pt in a 47:15:23:15 atomic percent ratio. Bulk electrodes were also prepared for Pt/Pd mixtures by a sol-gel method. The optimal ratio of Pt to Pd found in the supported electrodes gave the highest activity for the bulk electrodes as well.