The sample preparation using an automated pipetting robot is described in detail elsewhere. In short, 12 mM inks of Co, Mn, Sb, and Sn were prepared in a 2 mL solution containing 70% v/v 1% HNO3 and 30% v/v glycerol. A 12 mM Ti ink was prepared similarly, except using 2 M instead of 1% HNO3 to retain the Ti in the solution. A 12 mM ink corresponds to 7 mg of Co(NO3)2*6H2O, 6 mg of Mn(NO3)2*4H2O, 0.292 mL of a 10 mg mL -1 Sb stock solution in tartaric acid/HNO3, 8 mg of SnCl4*5H2O, and 8 μL of Ti-butoxide. An IrOx benchmark was prepared as well, for which 10 mg of H2Cl6Ir*xH2O was used to achieve a 12 mM ink. The FTO substrate was first cleaned by ultrasonicating 5 min each in a 2% Hellmanex III solution, water, and IPA. The FTO was then air-dried and subjected to a silanization step by immersing the substrate in a 6% v/v dichlorodimethylsilane solution in hexane for 5 min. This step was used to render the FTO surface hydrophobic, which helped locally contain the deposited droplet on the substrate. The FTO was subsequently rinsed with hexane to remove the residual silane solution and dried in air before final use. The drop-casting volume for the mixed inks was 0.3 μL. Subsequent annealing in air first at 300 °C for 10 min using a heating rate of 1 °C min -1 and then at 500 °C for 4 h using a heating rate of 2.5 °C min -1 using a box furnace (KLC 10/14, Thermconcept) converts the mixed transition metals into their oxide form.