Solar water splitting

Splitting into the relevant reduction and oxidation half reactions gives Eqs. (14) and (15)  

FIGURE 7. Solar spectrum. (Adopted with permission from www.lbl.gov/Sdence-Articles/Archive/MSD-fuU-spectrum-solar-cell.html.) 

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Murphy AB, Barnes PRF, Randeniya LK, Plumb 1C, Grey IE, Home MD, Glasscock JA (2006) Efficiency of solar water splitting using semiconductor electrodes. Int J Hydrogen Energy 31 1999-2017... 

S. Licht, B. Wang, S. Mukerji, T. Soga, M. Umeno, H. Tributsch, Efficient solar water splitting, exemplified by Ru02-catalyzed AlGaAs/Si photoelectrolysis,... 

S. Takabayashi, R. Nakamura, Y. Nakato, A nano-modified Si/TiC>2 composite electrode for efficient solar water splitting, J. Photochem. Photobiol. A Chem. 166 (2004) 107-113. 

While for a solar water splitting cell, light is directly absorbed by the semiconductor electrode (anode or cathode). The separation of electron-hole pairs is achieved in the built-in electric field near the semiconductor surface. The electric field is formed due to the charge transfer between the semiconductor electrode and the electrolyte as schematically shown in Fig. 17.5(b) [28]. Take an n-type semiconductor electrode for example... 

Agrafiotis C, Roeb M, Konstandopoulos AG, Nalbandian L, Zaspalis VT, Sattler C, Stobbe P, Steele AM (2005) Solar water splitting for hydrogen production with monolithic reactors. Sol Energy 79 409-421... 

Fig. 8.9 Schematic diagram of PV-electrolysis systems proposed for solar water splitting (a) Electricity generated from photovoltaic cell driving water electrolysis (b) PV assisted cell with immersed semiconductor p/n junction as one electrode.

The principal solar water-splitting models predict dual-band gap photoelectrolysis efficiencies of 16% [40], and 10-18% [41]. 

Litcht S (2005) solar water splitting to generate hydrogen fuel- a photothermal electrochemical analysis. Int J Hydrogen Energy 30 459-470... 

Over 18% solar energy conversion to generation of hydrogen fuel theory and experiment for efficient solar water splitting, Int J Hydrogen Energy 26 653-659... 

Licht S, Halperin L, Kalina M, Zidman M, Halperin N (2003) Electrochemical potential tuned solar water splitting. Chem Commun 3006-3007... 

As explained earlier, photoelectrochemical splitting of water was done for the first time in 1972 (Fujishima and Honda). However, the efficiency of this cell was very low (about 1%) and hence not practical. A number of advances have brought an economical standalone, one-step solar water-splitting technology much nearer. There have been four steps in these advances. 

Solar Water Splitting with Quantum Boost... 

The process for hydrogen production by solar water splitting with quantum boost has been developed by Science Applications International Corporation (SAIC), San Diego, California, and the Florida Solar Energy Center at the University of Central Florida (FSEC-UCF), Cocoa Beach, Florida with the collaboration of the author s group (see Figure 9.22) [153],... 

Lubitz W, Reijerse EJ, Messinger J. Solar water-splitting into H2 and O2 design principles of photosystem II and hydrogenases. Energy Environ Sci. 2008 1(1) 15—31. 

Walter MG, Warren EL, McKone JR, Boettcher SW, Mi Q, Santori EA, Lewis NS. Solar Water splitting cells. Chemical Reviews. 2010 110(11) 6446—6473. 

Reece SY, Hamel JA, Sung K, et al. Wireless solar water splitting using silicon-based semiconductors and earth-abundant catalysts. Science. 2011 334 645-8. 

Sivula K, Le Formal F, Gratzel M. Solar water splitting progress using hematite (a-Fe2C>3) photoelectrodes. ChemSusChem. 2011 4 432 49. 

Thermochemical and Thermal/Photo Hybrid Solar Water Splitting... 

Fig. 1. Alternate configurations varying the number of photo harvesting units and electrolysis units for solar water splitting.3 The photoconverter in the first system generates the requisite water electrolysis voltage and in the second system generates twice that voltage, while the photoconverter in the third and fourth units generate respectively only half or a third this...

Thermochemical and Thermal/Photo Hybrid Solar Water Splitting Table 1. The pressure equilibrium constants of the water dissociation reaction.24... 

It is also noted that Eg > 3.0 eV is in adequate for efficient use of the solar spectrum. Representative results from Fig. 12 for solar water splitting to H2 systems from AMI.5 insolation include a 50% solar energy conversion for a photoelectrolysis system at 638 °C with 0 = 500 p 2 = 1 bar and r phot = 0.32. 

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