On the Operando Structure of Ruthenium Oxides during the Oxygen Evolution Reaction in Acidic Media

In the search for rational design strategies for oxygenevolutionreaction (OER) catalysts, linking the catalyst structure to activityand stability is key. However, highly active catalysts such as IrO x and RuO x undergostructural changes under OER conditions, and hence, structure-activity-stabilityrelationships need to take into account the operando structure ofthe catalyst. Under the highly anodic conditions of the oxygen evolutionreaction (OER), electrocatalysts are often converted into an activeform. Here, we studied this activation for amorphous and crystallineruthenium oxide using X-ray absorption spectroscopy (XAS) and electrochemicalscanning electron microscopy (EC-SEM). We tracked the evolution ofsurface oxygen species in ruthenium oxides while in parallel mappingthe oxidation state of the Ru atoms to draw a complete picture ofthe oxidation events that lead to the OER active structure. Our datashow that a large fraction of the OH groups in the oxide are deprotonatedunder OER conditions, leading to a highly oxidized active material.The oxidation is centered not only on the Ru atoms but also on theoxygen lattice. This oxygen lattice activation is particularly strongfor amorphous RuO x . We propose that thisproperty is key for the high activity and low stability observed foramorphous ruthenium oxide.

Automated summary

In the search for rational design strategies for OER catalysts, understanding the link between catalyst structure and activity and stability is crucial. Highly active catalysts like IrO x and RuO x undergo structural changes under OER conditions, requiring consideration of the operando structure of the catalyst. X-ray absorption spectroscopy (XAS) and electrochemical scanning electron microscopy (EC-SEM) were used to study the activation of amorphous and crystalline ruthenium oxide under OER conditions. The data showed that the activation of the oxygen lattice, especially in amorphous RuO x , is key for its high activity and low stability.