For the immersion method, both Solutions A and B (50 mL for each) are mixed in a 250-mL beaker. Afterwards, the substrate (ITO glass) that was taped (using a doublesided tape) under a floating object (expanded polystyrene block), and with the coating side face-down for a direct contact with the precursor solution for a film-growth time of 15 minutes. The immersion-coated ITO was then rinsed with water and dried under N2 stream prior to use. We named this series of immersion-method oxide coatings with "-IOC" suffix to be distinguished from the spray coating samples. To create the two-metal oxide coating (CoMn-IOC), only Co 2+ and MnO4 -precursors were used into the growth solution. The growth solutions for the cases of three-metal (CoMnCu-IOC) and the four-metal (CoMnCuZn-IOC) coatings were prepared by additionally spiking the corresponding cation precursors (0.80 mM each) into the growth solutions of CoMn-IOC. The coating containing all the five metals is named as CoMnCuZnAg-IOC.