Photoelectrolysis of water to hydrogen in p-SiC/Pt and p-SiC/n-TiO2 cells

The rates of photoelectrolysis of water to hydrogen and oxygen in p-SiC/Pt cells were found to depend on the surface treatment of p-SiC by aqua-regia-HF solution and also on electrocatalytic Pt metal islet deposition. The limiting currents were not dependent on the surface treatments by aqua-regia-HF solution or Pt metal islet deposition. The optimum etching time and Pt electrodeposition time were found to be 3 min and 5 s, respectively. The electrode potential under illumination of intensity was 50 mW cm(-2) and at open circuit condition was found to be 1.25 V Saturated calomel electrode (SCE) and was not dependent on the surface treatments. The photocurrent onset potential was found to be dependent on surface treatments. The surface treatments by etching and Pt metal islet electrodeposition shifted the onset potential, DeltaE maximum by 0.27 V. The maximum photocurrent density of 0.135 mA cm(-2) at 00 V SCE-1 was obtained on aqua-regia-HF etched and Pt metal islet deposited p-SiC surface. The photoconversion efficiency was found to be 0.17% at an applied potential of 0.45 V and the corresponding total conversion efficiency was 0.27%. The bandgap energy was found to be 2.92 eV for the p-SiC sample. The flat band potential of 1.42 V SCE-1 and the donor density of 3.8 x 10(18) cm(-3) was found from the Mott-Schottky plots at AC frequency range between 600 and 1000 Hz. The p-SiC/n-TiO2 cells were found to photosplit water without the use of any external applied potential with maximum photocurrent density of 0.05 mA cm(-2) and the corresponding efficiency of 0.06%. The low cell photocurrent density and the photoconversion efficiency for the p-SiC/n-TiO2 self-driven system for the water-splitting reaction were due to high bandgap energies of both semiconductors and high recombination of photo-generated carriers mainly in the covalent bonded p-SiC. (C) 2002 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.