Solar driven water electrolysis based on silicon solar cells and earth-abundant catalysts

In the present work “proof of concept” upscaling steps were taken for a PV-EC device of 100 cm² substrate size. The active thin film silicon solar cell area was increased to 64 cm², while earth-abundant nickel based catalysts were scaled up by a factor of 100 to electrode areas of 50.3 cm². Implementing the thin film silicon solar cell into the PV-EC device in combination with the earth-abundant catalysts yielded a solar-to-hydrogen efficiency of 5.1 %, which is significantly improved compared to a PV-EC device based on nickel electrodes. It is shown that noble metal catalysts can be replaced by earth-abundant materials without performance losses. The long-term stable operation of the scaled up PV-EC devices is ensured by the use of metal sheet electrodes serving as substrate for the catalyst deposition. Regarding the catalyst stability, an excellent performance over 4 days under day-night-cycling was found for the earth-abundant nickel based system. Furthermore, the characterization of integrated PV-EC devices was expanded to illumination conditions similar to those obtained outdoors. All components used in water splitting devices are usually optimized under standard test conditions in the laboratory, which only represent one set of a wide range of possible outdoor operating conditions. For a combined PV-EC system the generation of hydrogen will only occur for output voltages above a certain value (thermodynamic potential + overpotential losses). This means, any illumination conditions shifting the illuminated current-voltage curve of the coupled system such that the voltage at the operating point is too low, will switch the system off. The influence of the operating temperature has been investigated prior to the present work, but studies concerning other possible illumination conditions were missing and therefore investigated in the present work. Additionally, a first estimation of the annual hydrogen output is given to compare devices based on different multi-junction cells and employing different catalyst systems for spectral data reported in literature