Amorphous Anodized Porous Titania as IrO2 Substrate for the Electrochemical Oxygen Evolution Reaction

This study investigates amorphous anodized porous TiO2 (a-TiO2) as a substrate for iridium-based oxygen evolution catalysts. The substrates were prepared via anodization of Ti foil in a glycerol-based solution for 15 min @ 60 V. Nickel was subsequently electrodeposited to act both as a conductive and sacrificial layer for the galvanic deposition of iridium from an Ir(IV) chloro-complex solution. Electrochemical anodization resulted in a uniform IrOx layer on the a-TiO2 substrate, featuring Ir aggregates ~250 nm in size and an Ir:Ni atomic ratio of ca. 7, as determined by EDS analysis. The quantity of Ni determined by ICP-MS bulk analysis indicated that Ni resided also within the porous matrix. Varying the Ni deposition charge density (qNi) revealed that an intermediate loading (1463 mC cm−2) provided the best balance between Ir accessibility during the galvanic replacement step and electronic continuity. The optimized IrOx/Ir-Ni/a-TiO2 electrode achieved excellent OER performance (η = 344 mV @ 10 mA cm−2; 1.68 mA μgIr−1 @ η = 300 mV) at an ultra-low Ir loading of 2.15 μgIr cm−2 and demonstrated good short-term stability, with only a 20 mV potential increase over 4 h of continuous operation at 5.5 mA cm−2. Overall, this strategy offers a scalable pathway for producing efficient OER electrodes with minimal noble metal loading.