A solar water splitting cell composed of WO3, Polymer Electrolyte Membrane (PEM) and Pt was constructed for producing hydrogen from deionized water in sunlight. Spectral responsivity measurements under various temperatures and bias voltages were conducted for the cell using the Incident Photon to Current Efficiency (IPCE) method. For comparison, a known WO3 Photo Electro Chemical (PEC) cell containing H3PO4 electrolyte, WO3/ H3PO4/ Pt, was tested using the same test method. The WO3/ PEM H2O/Pt cell showed better Quantum Efficiency (QE) performance compared to that obtained from the cell with the chemical electrolyte. For the first time, spectral responsivity of photo water splitting process without bias power was unveiled in the new WO3 cell, demonstrating the self-sustained photo electrolysis capability. Bias voltage effect on Solar to Hydrogen (STH) conversion efficiency was dramatic in the range from 0.2 V to 1.2 V and suppressions of STH were observed when high bias voltages were applied. In addition, a strong temperature effect on the energy conversion efficiency at high bias voltage was observed in the cell containing PEM-H2O, revealing that the STH at 54 degrees C is nearly five times that at 14 degrees C. (C) 2009 Elsevier Ltd. All rights reserved.