Water splitting reaction

Domen, K., Kondo, J.N., Hara, M., and Takata, T., Photo- and mechano-catalytic overall water splitting reactions to form hydrogen and oxygen on heterogeneous catalysts, Bull. Chem. Soc. ]pn., 73,1307,2000. 

The main reaction product is water vapor. The water splitting reaction is endothermic and the energy required for a significant hydrogen production rate is high. 

Figure 7.14 Photosensitised water-splitting reaction based on a photoredox reaction...

Apply simple ideas regarding energy levels to a predictive understanding of the feasibility of semiconductor-photosensitised redox reactions, including water-splitting reactions. 

Figure 11.9 Principle of the sensitised water-splitting reaction using SrTiOj irradiated at 388 nm...

The composites described in this chapter present superior quality which is demonstrated by their surface properties and performance in comparison with the parent components, GO and MOF or other inorganic phases. The important aspect of these composite formations is taking advantage of the promising properties of both phases and the creation of the hybrid, which exhibits the surface features of both phases and, as a bonus, new unique properties created on the interface. Moreover, the specific behavior of the individual components when placed together can open the door for new applications, not foreseen in this concise chapter. One should see that the detailed characterization of these materials as adsorbents is only one example of their application, which we could explore in detail. Nevertheless, the zinc (hydr)oxide story, where the enhanced photoactivity and water splitting reactions were noticed while investigating the adsorption phenomena, is one more example of the open book of the usefulness of such new materials. 

This is the maximum amount of useful work that can be derived from the system on driving the reaction in the opposite direction. Thus, Vrev corresponds to the reversible work and is consequently called the thermodynamic reversible potential. At 25°C and 1 bar, the AG for the water-splitting reaction is 237.178 kj/mol [10]. Therefore,... 

For hydrogen production from water, pure water (pH=7.0) is seldom used as an electrolyte. Water is a poor ionic conductor and hence it presents a high Ohmic overpotential. For the water splitting reaction to proceed at a realistically acceptable cell voltage the conductivity of the water is necessarily increased by the addition of acids or alkalis. Aqueous acidic and alkaline media offer high ionic (hydrogen and hydroxyl) concentrations and mobilities and therefore possess low electrical resistance. Basic electrolytes are generally preferred since corrosion problems are severe with acidic electrolytes. Based on the type of electrolytes used electrolyzers are... 

V°rev = 1.229V is the standard state reversible potential for the water splitting reaction and Vaoc is the anode potential at open circuit conditions. Term Vmeas-Vaoc arises from the fact that Voc represents the contribution of light towards the minimum voltage needed for water splitting potential (1.229V) and that the potential of the anode measured with respect to the reference electrode Vmeas has contributions from the open circuit potential and the bias potential applied by the potentiostat (i.e. Vmeas= Vapp+Vaoc). The term Vmeas-Vaoc makes relation (3.6.16) independent of the electrolyte pH and the type of reference electrode used. Thus the use of V°rev in relation (3.6.16) instead of VV or V°hz as in the case of relation (3.6.15) is justified. 

Khan SUM, Akikusa J (1998) Stability and photoresponse of nanociystalline n-Ti02 and n-Ti02/Mn203 thin film electrodes during water splitting reactions. J Electrochem Soc 145 89-93... 

Photo-electrochemical (PEC) processes can produce hydrogen in one step - splitting water by illuminating a water-immersed semiconductor with sunlight. There are two types of photo-electrochemical processes. The first uses soluble metal complexes as catalysts. When these complexes dissolve, they absorb solar energy and produce an electrical charge that drives the water splitting reaction. This process mimics photo-synthesis, however, currently there is minimal experience in this process. 

The reaction requires a sensitizer because water itself does not absorb above 200 nm. Transition-metal complexes exhibiting photoredox properties are useful as sensitizers for this reaction. The main problem, however, is that most transition-metal complexes involve one electron transfer per photon absorbed, whereas the water-splitting reaction... 

In plants, both the water-splitting reaction and electron flow through the cytochrome baf complex are accompanied by proton pumping across the thylakoid membrane. The proton-motive force thus created drives ATP synthesis by a CF0CF complex similar to the mitochondrial F0Fi complex. 

Equilibrium Constant for Water-Splitting Reactions The coenzyme NADP+ is the terminal electron acceptor in chloroplasts, according to the reaction... 

The water splitting reaction is efficient and clean. The energy consumed is only 20% greater than that readily calculated from Gibbs Free Energy relationship shown below. For the disso iation of water at 70°C one can calculate 0.874 volts. 

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