Influence of chromium and lanthanum incorporation on the optical properties, catalytic activity, and stability of IrOx nanostructured films for hydrogen generation

Abstract

Hydrogen production (HP) by photocatalytic water splitting (PWS) is becoming more and more popular on a global scale. The world's largest and most accessible renewable energy source—the Sun—as well as widely accessible metal oxide-based photoelectrodes are both utilized in this process. The preparation of pure and doped iridium oxide (IrOx) films is attempted in this work in an effort to better understand how Cr and La affect optical and HP efficiency as well as electrode stability. By using FE-SEM, the films' varying thicknesses and nanorod-like morphologies were detected. UV–Vis spectra reveal that the composition has an impact on the films' absorption and reflectance. IrOx has an optical band gap (Eg) of 2.9 eV, and this value decreased/increased after Cr doping/La codoping. The micro-Raman spectra, which showed that the Eg mode of Ir–O stretching was red-shifted from 563 to 553 cm−1, validate the films' amorphous nature. The resultant (IrOx) films were utilized in the HP via the solar photoelectrochemical (PEC) process. The codoped film, which has a solar-to-hydrogen conversion efficiency of 2.32% and a hydrogen evolution rate of 23.5 mmol h−1cm−2, is the most efficient and stable photoelectrode among the electrodes under examination. The highest absorbed photon-to-current conversion efficiency (APCE%) values for pure and codoped IrOx photoelectrodes were 3.62%@460 nm and 5.54%@490 nm, respectively. With enhancement factors of 2.77, 1.89, and 2.90 for pure IrOx, IrOx:5% Cr, and IrOx:Cr,2.5% La, respectively, the Jph increased to 1.58, 1.70, and 1.83 mA cm−2 at 90 °C. After ten runs, the codoped photoelectrode still has 99.2% of its initial photocurrent, compared to 80.8% and 82.8% for pure and Cr-doped IrOx. Calculated Tafel slopes, corrosion rates, and PEC thermodynamic parameters show how codoping and doping affect photoelectrode performance and stability.