Water hydrogen from

Hydrogen can be obtained by direct electrolysis, by direct thermal conversion, ther-mochemically, photochemically, photoelectrochemically, and biochemically from water. 

Water electrolysis involves passing an electric current through water to separate it into hydrogen (H ) and oxygen (O ). Hydrogen gas rises from the cathode elec- 

0 + 4e 2H, + 40H-Oxidation anode electrode 40H- 2H,0 + 0,+ 4e Complete cell reaction  

The values of the cathode and anode half-cell potentials are known to be 0.401 V and -0.828 V, respectively, at 298 K at a pH of 14. If the activities of water and the gaseous species are considered to be equal to unity, the cathode (E ) and anode (E ) potentials required according to Nemst equation will be  

The potential required to split water into and O, i.e., (E - E is equal to 1.229 V. Though the theoretical potential is 1.23 V for water electrolysis, in practice the actual water decomposition will occur only above 1.7 V. The extra potential, which is essential for the water decomposition, is called overpotential. Overvoltages are composed of activation or charge transfer overvoltage, concentration or diffusion or mass transfer overvoltage and resistance overvoltage. Overvoltage is evaluated mainly as a function of current and temperature (Viswanathan, 2006). 

---

Half-reaction (i) means that Co(II) in aqueous solution cannot be oxidised to Co(III) by adding ammonia to obtain the complexes in (ii), oxidation is readily achieved by, for example, air. Similarly, by adding cyanide, the hexacyanocobaltate(II) complex becomes a sufficiently strong reducing agent to produce hydrogen from water ... 

In multistep thermochemical water spHtting, two or more reactions are used to produce hydrogen from water. A hypothetical example is... 

The reason for the poor conversion efficiency to synthetic fuels is the high energy cost in liberating hydrogen from water (thermal dissociation, electroly-... 

A form of corrosion whereby cracking of steel occurs, caused by the pressure generated from the reaction of hydrogen (from water) and carbon (from steel) producing hydrocarbons. 

Suppose wc are generating hydrogen from water to use as a fuel and need to know how much hydrogen a given mass of water can provide. What is the mass percentage of hydrogen in water ... 

A photoelectrochemical cell is an electrochemical cell that uses light to carry out a chemical reaction. This type of cell is being considered for the production of hydrogen from water. The silicon electrodes in a photoelectrochemical cell react with water ... 

Calculate the standard cell potential for the reaction between silicon and water in a cell that also produces hydrogen from water and write the balanced equation for the cell reaction. See Box 12.1. 

Type 66 nylon is a polyamide first commercialized by DuPont just prior to World War II. At that time, the needed hexamethylenediamine was made from adipic acid by reaction with ammonia to adiponitrile followed by reaction with hydrogen. The adipic acid then, like now, was made from cyclohexane. The cyclohexane, however, was derived from benzene obtained from coal. The ammonia was made from nitrogen in the air by reaction with hydrogen from water obtained in the water-gas shift reaction with carbon monoxide from the coal. So, in the 1950s, nylon was honestly advertised by DuPont as being based on coal, air, and water. 

Harada H (2001) Isolation of hydrogen from water and/or artificial seawater by sonophoto-catalysis using alternating irradiation method. Int J Hydrogen Energy 26(4) 303-307... 

Equation 3.2 offers a large-scale method for the production of hydrogen from water and coal, which are readily and inexpensively obtained to meet hydrogen energy needs worldwide. 

Funk, J.E. and Reinstrom, R.M., Energy requirements in the production of hydrogen from water, I EC Process Design Dev., 5,336,1966. 

Kasahara, S. et al., Effects of process parameters of the IS process on total thermal efficiency to produce hydrogen from water, /. Chem. Eng. Jpn., 36, 887, 2003. 

Leygraf, C., Hendewerk, M., and Somorjai, G.A., Magnesium- and silicon-doped iron oxides for the photocatalyzed production of hydrogen from water by visible light (2.2 eV < hv < 2.7 eV),. Catal., 78,341,1982. 

H. Harada (2001)Isolation of hydrogen from water and for artificial seawater by sono-photocatalysis using alternating irradiation method Int J. Hydrogen Energy, 26 3003-2007... 

At present, several stable photocatalytic systems for production of hydrogen from water and organic compounds are made of semiconducting oxides and suitable proton reducing catalyzer. An efficient electron transfer between inorganic semiconductor and bacterial hydrogenase was shown to result in hydrogen photoproduction. 

H. H. Weetal, L. O. Krampitz (1980) Production of hydrogen from water using biophotolytic methods. J. Solid-Phase Biochem., 5 115-124... 

---