In the search for rational design strategies for oxygen
evolution
reaction (OER) catalysts, linking the catalyst structure to activity
and stability is key. However, highly active catalysts such as IrOxand RuOxundergo
structural changes under OER conditions, and hence, structure–activity–stability
relationships need to take into account the operando structure of
the catalyst. Under the highly anodic conditions of the oxygen evolution
reaction (OER), electrocatalysts are often converted into an active
form. Here, we studied this activation for amorphous and crystalline
ruthenium oxide using X-ray absorption spectroscopy (XAS) and electrochemical
scanning electron microscopy (EC-SEM). We tracked the evolution of
surface oxygen species in ruthenium oxides while in parallel mapping
the oxidation state of the Ru atoms to draw a complete picture of
the oxidation events that lead to the OER active structure. Our data
show that a large fraction of the OH groups in the oxide are deprotonated
under OER conditions, leading to a highly oxidized active material.
The oxidation is centered not only on the Ru atoms but also on the
oxygen lattice. This oxygen lattice activation is particularly strong
for amorphous RuOx. We propose that this
property is key for the high activity and low stability observed for
amorphous ruthenium oxide.