From water splitting

Development of hydrogen production technology from water splitting. 

The urea route does not involve any specific carbon source for hydrogen and C02, as does that of methanol synthesis. Ideally, hydrogen should be produced chiefly from water splitting, and C02 from flue gas. 

Apart from water splitting, T102 used in the form of particles or as a photoelectrode has been shown to catalyse also numerous other photoreactions. They include so different processes as, for example, photodegradation of chlorinated hydrocarbons " " hydroxylation of aromatic hydrocarbons photoreduction of dinitrogen water-gas shift reaction ... 

A combined procedure for the co-production of hydrogen and electricity from water splitting and coal has been proposed with the following reaction system... 

The experimental effects reported above are readily understood in terms of the known photochemical properties of PS II and PS I particles. The l t reaction of PS II particles results in the oxygen evolution from water splitting and the reduction of an elecrron acceptor such as ferricyanide. The l t reaction of PS I particles leads to NADP teduction in the presence of a donor such as DCPIH2. 

The particular configuration of the PEC cell is determined by the type of light source (discussed below) as well as the rates of gas production from water splitting (lower rates may require smaller volume cells). Figure 9.3 shows some examples of PEC reactors, including a (a) batch, (b) flow and (c) recirculating batch reactor. 

Franca, R. V., Thursfield, A., Metcalfe, 1. S. (2012). Lao.6Sro.4Coo.2Feo.803 8 microtubular membranes for hydrogen production from water splitting. Journal of Membrane Science, 389, 173-181. 

Tang, J.W., et al.. Mechanism of 0-2 Production from Water Splitting Nature of Charge Carriers in Nitrogen Doped Nanocrystalline Ti02 Films and Factors Limiting 0-2 Production. Journal of Physical Chemistry C, 2011. 115(7) p. 3143-3150. 

As indicated by the overall steam methane reformation reaction, reaction (9.9), two moles of hydrogen produced from steam reforming are from methane and the other two moles are from water splitting. 

Zhao, W., Ai, Z., Zhu, X., Zhang, M., Shi, Q., and Dai, J. (2014) Visible-light-driven photocatalytic H2 evolution from water splitting with band structure tunable solid solution (AgNb03)i, (SrTi03),e. 

The produced CO can either be used as a fuel (2.6) or used in combination with H2 obtained from water splitting for the production of liquid fuels (2.7). 

As discussed in section 5.3 (eqn (5.4) and (5.5), Table 5.1), the evolution of molecular hydrogen from water splitting and the reduction of CO2 to hydrocarbons involve the transfer of multiple electrons. In particular, light driven reduction of CO2 to methane or methanol with concomitant water oxidation, is kinetically very demanding due to the involvement of four or six proto/ electron transfers, respectively. Additionally, the one electron reduction of CO2 to C02 is thermodynamically unfavourable E°= —1.9 vs. NHE at pH 7). The development of bio-inspired reduction catalysts that lower the activation barrier and facilitate such reactions is currently being pursued by several research groups and a number of important achievements have been reported in recent years. ... 

There is a possibility that the key processes in photosynthesis involving C, N and S metabolism could be mimicked using the electrons and protons from water splitting. Artificial systems using photochemical and/or photobiological processes might be possible in the future. 

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