In 2018, Galan-Mascaros and co-work

In 2018, Galan-Mascaros and co-workers reported a water oxidation catalyst on insoluble salts of cobalt-based POMs with cesium or barium counter-cations that performed well and could compete with noble metals in strongly acidic conditions. Particularly, the barium salt of a cobalt-phosphotungstate polyanion (Ba[Co-POM]) showed an overpotential of 189 mV vs. RHE at 1 mA cm−2, outperformed the IrO2 catalyst even in an acidic electrolyte (pH < 1). The significant influence of barium dications in the activity of the [Co-POM] indicates that by changing the coordinated cations the catalytic performance of POMs can be tuned. The POMs offered an intrinsic advantage in this regard, because their polyanionic nature made them easy to selectively incorporate the desired ancillary counter-cations close to their active sites, without structurally or chemically affecting their appropriate environment. In addition, it was demonstrated that the carbon-paste conducting support with a hydrocarbon binder could improve the stability of metal-oxide catalysts in acidic media by providing a hydrophobic environment (Fig. 12).