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Docket #: S13-238

Efficient High-temperature Photoelectrochemical Cell

Stanford engineers have developed an efficient photoelectrochemical cell (PEC) that uses a mixed ion electron conductor (MIEC) heterojunction to enable high temperature (hundreds of oC) conversion of concentrated sunlight to chemical fuel (such as hydrogen). At the heart of the solid state PEC is a semiconductor light absorber coated with a thin MIEC layer for improved catalytic activity, electrochemical stability and ionic conduction. This provides a facile path for the ionic carriers to reach the solid electrolyte. This integrated photo-thermochemical device captures both thermal and photon energy to recover solar energy that would otherwise be lost. The single-device, isothermal design is potentially more scalable than more complex conventional thermochemical and hybrid photo-thermochemical water-splitting routes. This technology significantly enhances conversion of solar energy into chemical fuels to help overcome the inherently intermittent nature of solar radiation.

Schematic of elevated-temperature photocathode-based, oxygen-ion conducting PEC (a) with energy band diagram (b). (CB=conduction band and VB=valence band)

Stage of Research


    Simulation - predicted solar to hydrogen efficiency of 17% and 11% at 723 and 873oK respectively (for an oxygen-ion-conducting photocathode in 1-D with a non-degenerate light absorber with 2.0 eV band-gap and uphill band offset of 0.3 eV)
    Experimental - experimental demonstration of this new type of PEC is ongoing

Applications

  • Photoelectrochemical cell (PEC):
    • efficient conversion of solar energy to chemical fuel to enhance total solar energy utilization
    • low cost energy storage in solar power plants

Advantages

  • Extended operating temperature - the MIEC layer allows this new class of PEC to operate at elevated temperature with concentrated solar flux
  • Increased efficiency:
    • simulations show 17% and 11% at 723 and 873oK respectively
    • free energy to dissociate water decreases by 16% from 1.23V at room temperature to 1.04V at 600oC
    • good utilization of the solar spectrum
    • thermally enhanced carrier transport, electrocatalysis and fast removal of products in the gas phase decreases probability of carrier recombination
    • suppresses dark current
  • Single device:
    • integrated photo-thermochemical device captures both thermal and photon energy from concentrated sunlight at temperatures between 673 and 973oK
    • potentially more scalable than alternative water-splitting technology
  • Isothermal
  • No additional energy supply - energy for heating reactants is supplied by waste heat

Publications

Patents

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