Photoelectrochemical Energy Conversion

Photoelectrochemical Energy Conversion Energy Conversion Bruce Parkinson Department of Chemistry School of Energy Resources University of Wyoming US-China Workshop on Nanostructured Materials for Global Energy and Environmental Challenges

Issues for Advanced Solar Cells Energy storage Sun does not always shine Need energy at night or for transportation 75% of current energy use is fuels

Scalability - even scaling current technologies will not meet projected power demands. Higher efficiencies - 3rd generation cells > Shockley-Queisser limit

Dramatically lower costs/watt Nanostructuring can contribute to both 2

Our Energy Related Research Combinatorial search for oxide

semiconductors for efficient solar water splitting. (DOE, NSF and Dreyfus) Fundamental studies of sensitizer/oxide semiconductor single crystal interface (DOE) Understand Grätzel cell photoprocesses Quantum dot sensitization

New materials for scalable thin film solar cells Cu2ZnSnS4 (CZST) “forgiving material” containing only earth abundant elements (CRSP)

 Characterization of electrocatalysts for water

oxidation and water reduction (NSF)

3

A Potentially Efficient Configuration

Nanoparticle films Separate hydrogen and oxygen compartments Photons used more effectively

Materials for Photoelectrolysis of Water Must:  Have

a band gap between 1.2 and 2.0 eV  Be stable for many years under illumination in aqueous electrolytes (oxide semiconductor)  Have conduction band and valence band positions that straddle water oxidation and reduction potentials  Have some catalytic activity for hydrogen or oxygen evolution from water  Be cheaper than a solid state solar cell connected to an electrolyzer

Millions of Possibilities Make a Combinatorial Search Necessary Must be simple, inexpensive and high throughput 

Our approach: 

Ink jet print overlapping patterns of metal oxide precursors • Metal nitrate salts • Sol gel chemistry, oxometallates, nanoparticles

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Use conductive glass as substrate - pyrolysis at ~500 °C

Screen by laser scanning in solution and look for photocurrent generation: • In acid, base and neutral electrolytes • At positive and negative biases • Stability with higher power and extended illumination

Wavelength and Bias Scans Co, Fe Cs, Al

+ 0.5 V Bias

- 0.5 V Bias

532 nm

532 nm

633 nm

633 nm

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“Distributed Screening” Engage 1000s of Researchers

 Develop

inexpensive screening kits to distribute to undergrad and high school students   

Students have their future at stake Learn about the energy problem and chemistry Recruit labs to help with characterization of promising compositions

 Progress     

so far:

Lego Mindstorms® based scanning station Created on-line data base and bulletin board Diode laser and USB powered electronics 11 “beta” test kits distributed Dreyfus and soon NSF funding