Photoelectrochemical production of hydrogen from H2S
Global power demands of a rapidly growing population are expected to double by 2050, when fossils fuels will no longer be a viable option if climate-change is to be avoided. Renewable sources of energy, such as solar radiation, which provides ca. 1.2x1017 W on earth, are among the best candidates for solving electrical energy demands.
However, the intermittency of these energy sources requires energy storage, for instance in chemical bonds (fuel) to be later converted into electrical energy in fuel cells. Hydrogen is considered the fuel of the future due to its environmentally benign nature and its high energy density.
In the proposed research, a photoelectrochemical cell (PEC) will be developed in order to produce hydrogen by splitting hydrogen sulfide using solar energy as the driving force. This process requires less energy and is faster compared to water splitting, and can also be used for treating effluents containing hydrogen sulfide, such as sour water. Therefore the aims and objectives are to:
- Find a suitable semiconductor to absorb solar photons, generating electrons and holes with energies that will enable the reduction of protons to hydrogen and oxidation of hydrogen sulfide ions to polysulfide ions (Sn-2).
- Fabricate the semiconductor from earth-abundant, inexpensive, efficient and stable materials and determine its physical and chemical properties.
- Determine the kinetics and efficiencies of the splitting process, and the effect of sulfide concentration, pH, mass transport rate coefficient, arrangement and geometrical optimization of the electrodes.
- Compare experimental data to finite element model predictions of spatial distributions of potential and (photo-) current densities / H2 evolution kinetics. To enable improved reactor design, predictions will also be presented for the so-called wireless ‘photo-diode’ geometry, in which the ionic current path in the electrolyte solution extends below (vertical) photo-anode / counter electrode surfaces. For membrane-separated reactors, the effects of membrane properties on H2 losses due to H2-O2 cross-over will also be reported.