Department Interface Design
Electrocatalysis for water splitting
Stability-enhanced, mixed Ir-TiOx oxygen evolution reaction catalysts
One option for storing energy from intermittent renewable energies, like sun or wind, is the production of "green" hydrogen through water electrolysis. Hydrogen stores energy in chemical form and releases it during combustion, producing only water as a byproduct. Currently, iridium is used as the "state-of-the-art" anode catalyst. However, iridium gradually dissolves in the acidic environment of the electrolytic cell, leading to a decline in catalytic activity. The close relationship between titanium and iridium can increase the electrocatalyst's stability without harming its intrinsic activity, as we have shown for a thin-layer Ir-TiOx electrocatalyst co-deposited by sputtering (Ir-TiOx compositional library with iridium content varying from 20% to 70%.).
We used X-ray spectroscopic methods like hard X-ray photoelectron spectroscopy (HAXPES) at the SISSY I endstation at BESSY-II and Ti L2,3- and O K-edge XANES to analyze how the chemical structure changed depending on the iridium content in the mixed iridium-titanium oxide samples. Several effects were noted: some titanium oxides dissolved faster in the aqueous electrolyte than iridium, creating micropores on the surface, allowing more iridium atoms from the lower layers to come into contact with the electrolyte, accelerating the oxygen evolution reaction. But most importantly, the presence of titanium sub-oxides (such as TiO and TiOx) reduced the dissolution of iridium, especially in compositions with high iridium abundance (70% Ir, 30% Ti). With higher electronic conductivity, these sub-oxides seem crucial for stabilizing metallic iridium without impairing its performance.
More information:
ACS Catalysis (2023): The Chemical and Electronic Properties of Stability-Enhanced, Mixed Ir-TiOx OER Catalysts Marianne van der Merwe, Raul Garcia-Diez, Leopold Lahn, R. Enggar Wibowo, Johannes Frisch, Mihaela Gorgoi, Wanli Yang, Shigenori Ueda, Regan G. Wilks, Olga Kasian, and Marcus Bär; https://doi.org/10.1021/acscatal.3c02948
