CLRS250523_#10_Co3O4_spin coated_05

ElabID: CL250528_001_Co3O4_QCM#10, Preparation Procedure: The Co₃O₄ nanoparticle electrodes with a small catalyst loading were fabricated by spin-casting (Laurell WS-400BX-6NPP/LITE) 20 µL of Co₃O₄ ink at 4000 rpm for 5 min onto a gold-coated quartz crystal microbalance (QCM, BeamTech) resonator, which served as the current collector. The ink was prepared by dispersing Co₃O₄ nanoparticles (cpy_131_repro_calc) in Milli-Q water to achieve a concentration of 0.1 mg mL⁻¹. The exact catalyst loading cannot be directly derived from the dispersion’s concentration and cast volume. It is, however, approximated to be 1.7 µg cm⁻² at the maximum, as excess solution is expelled from the substrate during spinning.

The nanoparticles were provided from the Schulz-Group. Synthesis description: For the synthesis of spherical Co₃O₄ nanoparticles, 1.164 g Co(NO₃)₂·6 H₂O (4.0 mmol) was dissolved in 200 mL water in an open reactor vessel. Subsequently, 3.24 mL of ammonium hydroxide solution and 240 µL of H₂O₂ were added. The black reaction mixture was then heated to 60 °C for 15 minutes. A solution containing 0.58 g Co(NO₃)₂·6 H₂O (2 mmol) dissolved in 80 mL water was added and the reaction temperature was maintained at 60 °C for 3 hours. After cooling to room temperature, the nanoparticles were collected by centrifugation at 3000 rpm, washed with water and acetone and dried in air. The particles were then heated at a rate of 4.5 °C min^-1 to 300 °C, where the temperature was maintained for 15 minutes before cooling to room temperature.