IO-TiO2 electrodes were fabricated by adapting a previously reported procedure . Titanium foil was pre-cut into pieces of dimensions 1 × 2 cm 2 and were thoroughly cleaned by sonication in ethanol for 30 minutes prior to use. TiO2 nanoparticles (30 mg) were first homogeneously dispersed by sonication in a water/methanol mixture (300 µL, 4:1 volume ratio) for 2 h. A suspension of polystyrene beads (1 mL) was then centrifuged at 10000 r.p.m., followed by supernatant removal to obtain a compact polystyrene bead pellet. The pellet was further re-dispersed in 1 mL of MeOH and subjected to centrifugation at 10000 r.p.m. for removal of the supernatant. The TiO2 nanoparticle suspension (300 µL) was subsequently added to the polystyrene bead pellet and sonicated for 5 minutes in ice cold water (< 5 °C) to obtain a homogeneous mixture. The resulting dispersion was drop-cast onto the Ti foil over a well-defined geometrical surface area of 0.19 cm 2 , as demarcated by a Parafilm ring. The electrodes were then left to dry prior to removal of the Parafilm ring template. All electrodes were subsequently annealed in an oven at 1 °C min -1 ramp rate from room temperature and sintered at 500 °C for 20 minutes, removing the polystyrene beads to yield an inverse opal structure. The IO-TiO2 electrodes were then wired to metal rods using copper tape, and all electrical connections were protected from water infiltration via layers of Parafilm and Teflon tape. Kapton tape with pre-cut circular holes were also attached onto the Titanium foil, defining an active area of 0.19 cm 2 for each electrode.