Photoelectrochemical cell (PEC)

Materials needed

Application

Working principle

Environment protection

  1. Photoactive semiconductor - working electrode
  2. Platinum - counter electrode
  3. Electrolyte

consists a single photoelectrode (photoanode) and cathode, both of which are immersed in an aqueous electrolyte

Exposure of the photoanode to sunlight results in charge transport within the PEC and
evolution of gases at the photoanode and cathode.

Supply of energy from the Sun to the Earth is gigantic: 321024 joules a year. By covering 0.1% of the Earth’s surface with solar cells with an efficiency of 10% would satisfy our present needs

Commonly been used: TiO2

Advantages

  1. stable
  1. non-corrosive
  1. environmentally friendly
  1. abundant
  1. cost-effective
  1. energy levels are appropriate to initiate the water-splitting reaction. (CB of TiO2 is more negative than 0V; VB is more positive than oxidation (+1.23V))

Challenges:

  1. Electrons in CB may recombine with VB holes quickly to release energy in form of photon
  2. Decomposition of water into H and O will release large Gibbs free energy and backward process will easily proceeds.
  3. Large bandgap of TiO2 hence only UV can be utilized
  1. Electrochemiluminescence - process where species generated at electrodes undergoes
    electron transfer reactions to form excited states that emit light
  1. photoelectrochemical water electrolysis (Photoelectrolysis): separation of H and O from water
  1. Anode and cathode in a PEC cell can be used for oxidizing and reducing materials
  1. Silicon photoelectrodes for PEC CO2 reduction - PEC reduction of CO2 at the cathode by using electrons and protons released from the oxidation of water at the anode is regarded as an artificial way to recycle CO2.
  1. Solar‐recharging Redox‐Flow Batteries(RFB) - RFBs can be charged under solar illumination by PEC oxidation and reduction of the discharged species
  1. Dye sensitized solar cells (DSSC)

Improvement on PEC

  1. doping for enhancing visible light absorption in the wide bandgap semiconductor
  1. morphology control for enhancing the light absorption and shortening transfer distance of minority carriers
  1. surface treatment for removing segregation phase or surface state
  1. sensitization, passivating layer, and band structure engineering using heterojunction structures

Green Technology

  1. Electrochemical water splitting is a promising approach for the H2 production, which is sustainable and pollution-free
  1. Hydrogen production can be done by chemical process rather than combustion which is more not environmental friendly
  1. Hybrid Fuel Cell Systems
  1. By products of these chemical reactions are only water and heat
  1. Renewable resources