ENERGY-CONVERSION BY PHOTOELECTROLYSIS OF WATER - DETERMINATION OF EFFICIENCY BY INSITU PHOTOCALORIMETRY

By means of a power balance analysis for a water-splitting photoelectrolysis cell, relations have been derived for determining the energy conversion efficiency, with respect to absorbed monochromatic light, from photocalorimetric in situ measurements at the semiconductor photoanode. It is shown that a quantity readily obtainable from the potential dependence of the heat-monitoring signal represents the upper limit of the energy efficiency attainable with a given photoanode. For a cell with additional power losses associated with overvoltage from hydrogen evolution at the counterelectrode and with ohmic resistance of the electrolyte, the energy efficiency can be determined using the internal photocurrent quantum efficiency obtained by photocalorimetry and the voltage applied to the cell. Results are given for 360-nm photoelectrolysis of water at pH 0.5-13.5 in a cell employing a TiO2 (rutile) thin-film anode and a platinum cathode. Quantum and energy efficiencies are discussed in the light of previously reported findings.