MSc Candidate, Mrs. Rawan Halabi
Department of Materials Science and Engineering, Technion – Israel Institute of Technology
Solar energy is the most abundant source of renewable energy, but it requires large scale energy storage for grid balancing and conversion to fuel. This challenge may be addressed by solar water splitting using photoelectrochemical (PEC) cells that convert water and sunlight to hydrogen and oxygen. In this research we explore an innovative PEC cell configuration with separate oxygen and hydrogen cells in order to facilitate centralized hydrogen production at the end-user place, whereas oxygen is produced in distributed PEC solar cells as in PV solar fields. The cell separation is achieved by using auxiliary electrodes made of NiOOH/Ni(OH)2 redox couple which mediate the ion exchange between the anode and the cathode.
To demonstrate this new device architecture, we developed a two cell system using hematite photoanode in tandem with a Si PV module in the oxygen cell and Pt-coated titanium mesh cathode in the hydrogen cell. We fabricated 10×10 cm2 hematite photoanodes deposited by ultrasonic spray pyrolysis (USP) on transparent conductive (FTO-coated glass) substrates. The influence of the different process parameters on the photoanode microstructure and PEC performance was examined. Next, the electrochemical properties of NiOOH/Ni(OH)2 electrodes extracted from commercial Ni-Fe batteries were characterized. Finally, following initial tests and optimization, we tested the complete system both indoor using the solar simulator as well as outdoor. In the final demonstration we obtained stable operation while producing hydrogen and oxygen separately during ten cycles of 8 hours.