Hydrogen generation rate

Figure 15. Relationship between electron transfer rate constant ke and hydrogen generation rate constant. (Reprinted from Ref [194], 2000, with permission from lUPAC.)...

Recently five monometallic (Au, Pd, Pt, Ru, Rh) nanoparticles were investigated as electron mediators together with four core/shell bimetallic (Au/Pd, Au/Pt, Au/Rh, Pt/ Ru) nanoparticles [53,194-196]. The linear relationship was observed between the electron transfer rate coefficients and the hydrogen generation rate coefficient as shown in Figure 15. 

Xu, S. and Sun, D.D. (2009) Significant improvement of photocatalytic hydrogen generation rate over Ti02... 

Under UV (320-400 nm, 100 mW/cm ) illumination a maximum photoconversion efficiency of 7.9% was obtained for short nanotube arrays anodized in boric acid contained electrolyte [103], with a hydrogen generation rate of 42 mL/h W. Under full spectrum illumination (AM 1.5, 100 mW/cm ), a photoconversion efficiency of 0.45% was obtained. The enhanced photoresponse of the boric acid anodized sample is not due solely to a modified nanotube array structure since the maximum nanotube array length achieved is about 600 nm. It is possible boron, which is difficult to identify by XPS, remains inside the titania matrix and affects its charge transfer properties. 

The Zone 2A canyon eievator pit and Room 109 are the only two areas in the HCF where waste will be accumulated. By the time that the waste is moved into Room 109, the hydrogen generation rate is sufficiently low as to preclude accumulation to flammable levels (Mitchell and Naegeli 1999). The normal Zone 2A ventilation flow of 1800 cfm (which Includes flow into the SCB s) will preclude any appreciable hydrogen concentrations in Room 109 or the Zone 2A canyon. 

If the above hydrolysis reaction occurs without the presence of catalysts, the hydrogen generation rate is quite slow (-0.6 mL min when 1.2 mmol sodium borohydride is dissolved in 10 ml distilled water [5]). To speed up the hydrogen generation reactions various catalysts can be used such as noble metals (Ru, Pt, Rh, Pd, Pt-Ru, Pt-Pd alloys) and non noble transition metals or related compounds (Cu, Co, Ni, Co-B, Co-P-B, Co-W-B, Ni-SiO, Fe-Ni alloys) [3]. 

There are also efforts combining iron and cobalt to synergistically increase hydrogen generation rates. Similarly in the FeB case, once Fe-Co-B is formed, the reactions stabilized to slower rates. The typical reaction is given as below [23] ... 

On the other hand, the hydrogen generation rate is reported as volume generated per unit area such as mL min" cm when a substrate in foam form is used [21,41,45,46,60]. 

Alternatively hydrogen generation rate is expressed as moles of generated hydrogen per unit time such as mol min" [37,61] or mmol mim [35]... 

Figure 5.3 (a) Influence of amount of catalysis (Fe) on hydrogen generation rates,... 

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