The Influence of Electrode Thickness on the Structure and Water Splitting Performance of Iridium Oxide Nanostructured Films.

For a safe environment, humanity should be oriented towards renewable energy technology. Water splitting (WS), utilizing a photoelectrode with suitable thickness, morphology, and conductivity, is essential for efficient hydrogen production. In this report, iridium oxide (IrO x ) films of high conductivity were spin-cast on glass substrates. FE-SEM showed that the films are of nanorod morphology and different thicknesses. UV-Vis spectra indicated that the absorption and reflectance of the films depend on their thickness. The optical band gap ( E g ) was increased from 2.925 eV to 3.07 eV by varying the spin speed (SS) of the substrates in a range of 1.5 × 10 3 -4.5 × 10 3 rpm. It was clear from the micro-Raman spectra that the films were amorphous. The E g vibrational mode of Ir-O stretching was red-shifted from 563 cm -1 (for the rutile IrO 2 single crystal) to 553 cm -1 . The IrO x films were used to develop photoelectrochemical (PEC) hydrogen production catalysts in 0.5M of sodium sulfite heptahydrate Na 2 SO 3 · 7H 2 O (2-electrode system), which exhibits higher hydrogen evaluation (HE) reaction activity, which is proportional to the thickness and absorbance of the used IrO x photocathode, as it showed an incident photon-to-current efficiency ( IPCE %) of 7.069% at 390 nm and -1 V. Photocurrent density ( Jph = 2.38 mA/cm 2 at -1 V vs. platinum) and PEC hydrogen generation rate (83.68 mmol/ h cm 2 at 1 V) are the best characteristics of the best electrode (the thickest and most absorbent IrO x photocathode). At -1 V and 500 nm, the absorbed photon-to-current conversion efficiency ( APCE %) was 7.84%. Electrode stability, thermodynamic factors, solar-to-hydrogen conversion efficiency ( STH ), and electrochemical impedance spectroscopies (EISs) were also studied.