Morphology engineering of iridium electrodes via modifying titanium substrates with controllable pillar structures for highly efficient oxygen evolution reaction

•Morphology engineering of iridium electrodes with pillar-structured ti substrates is developed.•Surface treatments of Ti substrates with different acids and etching times are optimized.•The electrode morphology, interfacial resistance and catalytic activity are investigated.•The pillar-structured electrodes exhibit enhanced oxygen evolution reaction performances. Nowadays, Ti is the well-chosen anode substrate material for proton exchange membrane electrolyzer cells (PEMECs) and modifications of the substrate surfaces are essential for the fabrication of highly efficient electrodes. Herein, we introduce the morphology engineering of Ir/Ti electrodes with different acid treatments of hydrochloric acid (HCl) and oxalic acid (OA), and the comparative benefits of these two acid treatment methods are studied from the aspects of their impacts on the morphology, interfacial contact resistance (ICR), and oxygen evolution reaction (OER) performances of resultant electrodes. Notably, compared to the flat surface from OA treatment, Ti substrates with the pillar structure could be successfully achieved via HCl etching. The HCl and the oxalic acid (OA) treatments would reduce the interfacial contact resistance (ICR) to 15.2% and 5.5% of the pristine Ti substrate at 1.38 MPa, respectively. By iridium electrodeposition on Ti substrates, Ir/Ti electrodes with different catalyst loadings are fabricated. With similar low-loadings of about 0.05 mgIr cm−2, an Ir/Ti electrode with HCl treated substrate exhibits a lower overpotential of ∼283 mV at 10 mA cm−2 current density than 305 mV from OA treatment, due to the boosted reaction areas from HCl treatment. [Display omitted]