Hydrogen production efficiency

Koca and Sahin (2002) carried out different series of experiments in order to compare the amounts of hydrogen evolved by different compositions of CdS/ZnS. Table 5.7 shows the rates of hydrogen evolution, which was dependent upon the percentage of CdS and ZnS in each photocatalyst. These results show that 33% ZnS is the most active (Koca and Sahin, 2002). CdS was sensitized with a coprecipitation by using a hot mixture of Cd(CH3COOH)j, Zn(CH3COOH)2 and Na S Zn ions loaded on CdS, and this enhanced hydrogen production efficiency of the photocatalyst system. 

The gasifier fuel gas quality is an important issue for the RP development. The effect of the fuel gas composition has been modeled. The modeling showed that the potential hydrogen production efficiency is strongly dependent on the combustion products/syngas (CP/SG) ratio [(C02+Hj0)/(C0+H2) = CP/SG] of the fuel gas. 

Further examples of recent attempts to reduce the consumption of electrical energy are the electrolysis of aqueous solutions of methanol (but CO2 is still produced at the anode) [78, 79] and water electrolysis using ionic liquids as electrolytes [80]. In the latter case, the authors claimed the possibility of obtaining high hydrogen production efficiencies using an inexpensive material such as low-carbon steel. 

Fe20s, doped with various metal ions have been applied to photocatalytic hydrogen production in the presence of methyl viologen (MV ) that serves as an electron donor [147]. The photocatalytic hydrogen production efficiency of y-Bi203 has shown... 

The target cost of nuclear hydrogen production must be cheaper than that of the conventional electrolysis subtracting the distribution cost. Hydrogen production efficiency of EED-aided SI thermochemical cycle is expected around 43% with current knowledge (Cho, 2009). 

Hydrogen production efficiency, t/h (m3/h), minimum - steam methane reforming - high-temperature water electrolysis 4 x 12.5 (138.75-103) 4x6.76 (75-103)... 

Figure 1 Overall HTE hydrogen production efficiencies for the VHTR/recuperated direct Brayton cycle, as a function of per-cell operating voltage...

Figure 2 (a) Overall hydrogen production efficiency as a function of hydrogen production rate, with air sweep (b) effect of steam utilisation on overall hydrogen production efficiency... 

The figure shows results for both HTE and low-temperature electrolysis (LTE). In addition, an efficiency curve for the SI thermochemical process is shown (Brown, 2003). The results presented in Figure 3 indicate that, even when detailed process models are considered, with realistic component efficiencies, heat exchanger performance, and operating conditions, overall hydrogen production efficiencies in excess of 50% can be achieved for HTE with reactor outlet temperatures above 850°C. For reactor outlet temperatures in the range of 600-800°C, the supercritical C02/recompression power... 

The thermodynamics of these reactions have been found favorable. However, the hydrogen production efficiency of the process is limited to about 40 percent, owing to the melting point of Ca-Br2 at 760°C (Schultz et al., 2002). 

The hydrogen production efficiency, Hp, which is the ratio of the actual to the ideal hydrogen production rate, is given by... 

FIGURE 5.13. Intensity dependence of the quantum efficiency Q for n-Si (111) and the corresponding hydrogen production efficiency Tin measured in the ring-disk arrangement. Electrolyte 1.0moldm NH4F, pH 4.7. A, 632.8 nm. Rotation rate 20 Hz. (Reprinted from Blackwood et al. 1992, with permission from Elsevier Science.)... 

The capital cost of POX can be high because of the need for post treatment of the raw syngas to remove carbon and acid gases. There are also issues of coke and soot formation if the oxidation temperature becomes too low or the mixing of the feed components is incomplete. The addition of steam to the process allows for greater flame temperature control and suppression of carbon however, the hydrogen production efficiency is reduced due to more fuel being consumed in the combustion... 

TGC has demonstrated the operation of membrane reformer at a hydrogen fueling station for FCV in downtown Tokyo in 2004-2005. The system performance, efficiency and long-term durability/reliability were confirmed by producing >99.99% hydrogen at 40 Nm /h for more than 3 000 hours with hydrogen production efficiency of about 80% (HHV). 

---