Résumé
The development of efficient water splitting heterogeneous catalysts in acidic media is largely hampered by both the slow kinetics of the oxygen evolution reaction (OER) and the limited stability of the electrocatalyst under these harsh working conditions. At the origin of both the activity and the instability of iridium oxides used as OER catalysts in acid conditions is the formation of high-valence IrOx intermediates such as IrO3. Nevertheless, owing to its reactivity with water, this intermediate was never stabilized, and its electrochemical/chemical behavior was never studied in depth. Here, we report a strategy to stabilize this elusive IrO3 intermediate. Furthermore, we demonstrate that upon reactivity with water, gaseous oxygen is generated, while the intermediate is protonated following the reaction IrO3 + xH2O → H2xIrO3 + x/2O2. The resulting hydrated iridium oxide H2IrO3, which possesses three-dimensional proton intercalation/deintercalation channels, can be considered as an enlightening OER model electrocatalyst in acidic media. Owing to its unique proton insertion ability, we could study a yet ill-described charge compensation mechanism upon OER relying on the bulk reversible exchange of protons, which shows remarkable performances and stability. Indeed, enhanced OER is measured, with a dissolution rate lower than the one measured for the “stellar” IrOx/SrIrO3 catalyst. Such a finding opens the route toward the design of new catalysts enlisting proton insertion that could be competitive for water splitting in acidic media.