Hybrid Metal/Spinel Oxide Coating with Microcone Arrays to Stimulate a Photothermal‐Augmented Oxygen Evolution Reaction

To boost the kinetic process of the oxygen evolution reaction (OER), hybrid CoNiFe/Fe(Fe,Mo,Al)2 O4 coatings are deposited on pure Ti substrates (namely, CoNiFe/Fe(Fe,Mo,Al)2 O4 /Ti electrodes). This new coating features a dense inner layer together with an outer layer of microcone arrays (MCAs). The electrochemical surface area of the electrodes is modulated by controlling the geometrical factors of the MCAs. For the OER in 1.0 m KOH, the electrodes require minimum overpotentials of 245 and 333 mV to realize current densities of, respectively, 10 and 100 mA cm-2 . Furthermore, the high aspect ratio of the MCAs enables the electrodes to exhibit strong sunlight capture. Under 10 min of simulated 1.0 sun illumination, the electrode's temperature can rise by up to 108.2 °C. The number of active sites and the OER reaction rate of the electrodes are further increased by photoassistance, with only 234 and 296 mV overpotentials, respectively, needed to generate current densities of 10 and 100 mA cm-2 with a Tafel slope as low as 40.9 mV dec-1 . Therefore, the application of this composite coating, which exhibits photothermal effects with respect to conventional Ti electrodes, provides an inspiration for further improvement of OER catalytic efficiency.