In situ/operando X-ray absorption and photoelectron spectroscopies applied to water-splitting electrocatalysis

The production of hydrogen by water electrolysis allows storing electrical energy into chemical bonds, therefore providing a convenient and carbon-free option to regulate the intermittency of renewable energy sources. The large-scale use of this process requires efficient catalysts, which are currently based on noble metals such as iridium (for the oxygen evolution reaction) and platinum (for the hydrogen evolution reaction). Efforts are being undertaken to decrease the amount of catalysts required in electrolyzers, while maintaining their efficiency. These efforts are backed up by fundamental studies describing the structure of the catalysts, the critical reaction intermediates involved and their failure modes. Such information can be collected during the reaction with synchrotron-based techniques, such as X-ray photoelectron and X-ray absorption spectroscopies. We give here an overview of the potential of these techniques and of their application to the water electrolysis reaction.