Nanostructured Titanium Oxynitride-Supported Iridium Oxide Oxygen Evolution Electrocatalysts for Water Splitting
Proton exchange membrane water electrolyzers (PEM-WE) have garnered much interest lately because of their ability to produce storable hydrogen from the simple inputs of water and electricity. Two half reactions drive the production of hydrogen and oxygen gas at the cathode and anode respectively. Electrocatalysts are needed to improve the efficiency of such devices, especially at the kinetically hindered anode. Iridium, a precious metal, has been the ideal catalyst for many years due to its excellent activity for the oxygen evolution reaction (OER) and reasonable stability in the harsh PEM-WE environment. The scarcity of this metal makes it prohibitively expensive for upscaled devices. Support materials have been studied to help reduce the cost of utilizing iridiumbased catalysts. Traditionally, carbon has been used as support material in many other catalytic applications, but its stability is poor in a PEM-WE due to the low pH and high anodic potentials required to promote the OER. This study evaluates the use of a nanostructured titanium oxynitride (TiOxNy) as a support material for an iridium OER electrocatalyst. A three-step process was used to synthesize the material: (i) solvothermal synthesis of high surface area titanium oxide (TiO2) nanosheets, (ii) heat and atmosphere treatments to transform TiO2 into conductive TiOxNy, and (iii) deposition of iridium onto the TiOxNy support material. The initial OER mass activity of the titanium oxynitride-supported iridium catalyst (TiO2-N800-Ir-EO) was measured to be six times larger than a standard iridium oxide material. The stability of TiO2-N800-Ir-EO showed significant degradation after an accelerated endurance test. Support materials that provide enhanced activity and improved stability with reduced precious metal loading will allow for the wider use of upscaled PEM-WE devices in electrical grid integration and automotive hydrogen fuel stations.
Water splitting, Oxygen evolution reaction, Iridium oxide electrocatalyst
Archer, R. (2018). <i>Nanostructured titanium oxynitride-supported iridium oxide oxygen evolution electrocatalysts for water splitting</i> (Unpublished thesis). Texas State University, San Marcos, Texas.