Photoelectrochemical Water Splitting

Abstract

To halt the buildup of carbon dioxide (CO2), the main greenhouse gas, the development of an alternative energy source to fossil fuels becomes more and more important. Hydrogen (H2) has the potential to meet the requirements as a clean non-fossil fuel in the future, if it can be produced using our primary source of energy, the sun, and stored and transported safely. The present article will give a short review on different approaches on semiconductor-based photoelectrochemical water splitting into hydrogen and oxygen (O2) using sunlight as the energy input, also generally described as photoelectrolysis.

Electronic structure and phase stability of oxide semiconductors: Performance of dielectric-dependent hybrid functional DFT, benchmarked againstGWband structure calculations and experiments

“…Accurately knowing the electronic band structure of the material is certainly paramount in the field of photocatalysis. For example, in semiconductor-based photocatalytic water splitting [34], the band gap of the material has to exceed the redox potential of water ( E H 2 O redox = 1.23 eV) and in real devices should be no lower than 1.9 eV. Furthermore, the valence band maximum and conduction band minimum of the semiconductor have to lie higher than the water reduction potential and lower than the water oxidation potential, respectively, in order to be able to reduce or oxidize water and produce molecular hydrogen or oxygen.…”

Perovskite solar cell for photocatalytic water splitting with a TiO2/Co-doped hematite electron transport bilayer

“…1,2 In spite of these encouraging properties, progress towards the manufacture of useful water splitting devices has been limited. The free energy change required to split one molecule of H 2 O to H 2 and 1/2O 2 under standard conditions is 237.2 kJ mol À1 while the cell voltages are in the order of 1.8-2.0 V. 3,4 This potential requirement could be attained from a semiconductor photoanode with appropriate valence and conduction bands illuminated by visible light. Such a reaction involves the use of a single semiconductor that absorbs two photons to generate a molecule of H 2 .…”

Towards Solar Fuels from Water and CO2

“…[19] There are three possible approaches. Arrangements using either photovoltaic cells (PV approach) or semiconductor-liquid junctions (SCLJ approach), or a combination of the two (PV/SCLJ approach) can be realized.…”

“…We thus forecast that in the medium term, solar fuels will be competitive, particularly for decentralized production and if enough R&D is made. [19,20] Paths to Solar Fuels Bioroutes Plants and some bacteria convert incident solar radiation into stored chemical energy. Two protein assemblies participate in the process.…”