טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHalabi Rawan
SubjectPhoto-Electrochemical Water Splitting in Separate
Oxygen and Hydrogen Cells
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Avner Rothschild


Abstract

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 (2H2O 4hn à 2H2 O2). Despite the obvious attractiveness of this elegant approach, it requires extensive R&D in materials, devices and systems to assess its technological feasibility. 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 archived 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 with separate hydrogen and oxygen cells and demonstrated standalone solar water splitting without external power supply. Toward this end 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 photoelectrochemical  performance was examined. The next step involved characterizing the electrochemical properties of NiOOH/Ni(OH)2 electrodes that we extracted from commercial Ni-Fe batteries. The appropriate charging conditions for operation within our system was determined. Next, the two cells system was designed and constructed, using the USP hematite photoanode in tandem with a Si PV module in the oxygen cell and Pt-coated titanium mesh cathode in the hydrogen cell. 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. By doing this, we achieved the goal of the research and proved that the new architecture we proposed enables photoelectrochemical water splitting in a system with separate cells to generate hydrogen and oxygen.