hydrogen production from water using solar cells powered nafion ...

More documents

Recommendations

Info

total efficiencies of the fermentation systems are very low at about 5-10%. Levin and coworkers calculated that 758m 3 of photo-fermentation bacteria tank were required to supply a necessary amount of H 2 to a 5kW PEM fuel cell. The volume could be decreased to 1.25m 3 for CO-oxidation bacteria bioreactor, and 1 m 3 for dark fermentation mesophilic bacteria (Levin et al. 2004). It is projected for photo-fermentation bacteria that their low investment costs could overcome this low efficiency problem. The major challenges for dark fermentation and CO-oxidation bacteria are the mass transfer problems of their bioreactors. The researchers were not able to scale up the experiments because they cannot achieve high reactant gas concentrations for the bacteria in the solution. High volume hydrogen bioreactors require new reactor designs and may require radically new technologies. Another way to produce hydrogen is to use water electrolysis which is electricity depended hydrogen production method. In general, electrolysis is a process that the ionic compound is dissolved in a solvent so that its ions are available in the liquid. Current is applied between a pair of inert electrodes immersed in the liquid. Each electrode attracts ions which are of the opposite charge. In the water electrolysis case, cations are hydrogen ions and anions are the oxygen atoms. The energy required to separate these ions, and cause them to migrate to the respective electrodes, is provided by an electrical power supply. Therefore electrolysis is an electricity depended process and it could be viable if the electricity is cheap. Hydrogen production using electrolysis cannot be classified as a renewable method because it depends on the source of the electricity. For example, wind, solar PV, wave and geothermal energies can all be a source to produce renewable hydrogen using electrolysis while fossil or nuclear fuel based electricity depended electrolysis cannot be classified as renewable hydrogen production. The Figure 2.1 below categorizes the hydrogen production methods according to their energy source. 10
2.2. Electrolyzers Figure 2.1. Various Sources for electrolysis There are two mature electrolyzer types: Alkaline electrolyzers and Proton Exchange Membrane (PEM) electrolyzers. Alkaline electrolyzers are the most commonly used electrolyzers in industry. Their hydrogen output is above 99% purity, although usually requires a further purification unit due to corrosive electrolyte vapor especially in fuel cell applications. Generally, 25 – 30 weight percent potassium hydroxide solution is used as a liquid electrolyte. Hydrogen production with this method has an efficiency of up to 80% (based on the high heating value of hydrogen). They are most effective when running on low current densities at about 0.3Amp/cm 2 or lower. However, disadvantages of this type of electrolyzers are their liquid electrolyte which is highly corrosive in high temperatures, thus resulting in relatively low electrolyzer lifetime (Barbir 2004). The proton exchange membrane (PEM) fuel cell operated “in reverse” is actually a PEM electrolyzer. But the optimum operating conditions for the power and hydrogen production are significantly different than that one could expect to obtain from a PEM fuel cells operating in reverse. Although a lot of research and development was done on PEM 11
Page 1 and 2: HYDROGEN PRODUCTION FROM WATER USIN
Page 3 and 4: ACKNOWLEDGEMENTS This study was car
Page 5 and 6: ÖZET GÜNEŞ PĐLLERĐ ĐLE ÇALI
Page 7 and 8: 4.2. Results on a Single Cell PEM E
Page 9 and 10: Figure 4.16. Hydrogen Production an
Page 11 and 12: CHAPTER 1 INTRODUCTION World energy
Page 13 and 14: Table 1.1. Turkey`s energy usage as
Page 15 and 16: atmosphere according to their hydro
Page 17 and 18: The reaction goes through two half
Page 19: 2.1. Hydrogen Production Methods CH
Page 23 and 24: electrode design are being sought t
Page 25 and 26: 1 285,830J/mol + H 2O(l) → H 2(g)
Page 27 and 28: another optimization should be done
Page 29 and 30: Figure 2.3. Molecular Formula of Na
Page 31 and 32: hydrophobic substances in electrode
Page 33 and 34: Different than Grigoriev’s work,
Page 35 and 36: voltages. This concept is also vali
Page 37 and 38: Interdigitated flow field is a diff
Page 39 and 40: generator is always working at its
Page 41 and 42: ecord the voltage and the current s
Page 43 and 44: Figure 3.2. Anode side of the elect
Page 45 and 46: 6. Cover the cathode GDL with 1mm t
Page 47 and 48: to deliver water. The front side of
Page 49 and 50: 5. Place the cathode side GDL into
Page 51 and 52: electrolyzer to monitor the potenti
Page 53 and 54: Figure 4.1. “X” type flow field
Page 55 and 56: MEA, there were no electrolysis on
Page 57 and 58: In fact, it was observed on the dis
Page 59 and 60: In each run, current density was in
Page 61 and 62: Voltage 2,25 2,20 2,15 2,10 2,05 2,
Page 63 and 64: Therefore, for the current cell des
Page 65 and 66: 8Amp, respectively. The calculated
Page 67 and 68: At 500mAmp/cm 2 , the potential dif
Page 69 and 70: The installed system had 6 of this
Page 71 and 72:
At 11.00 AM, as the current density
Page 73 and 74:
Figure 4.19 shows solar radiance da
Page 75 and 76:
On Iztech campus, the system constr
Page 77 and 78:
voltage temperature trend observed
Page 79 and 80:
REFERENCES Grigoriev S.A.,Porembsky
Page 81 and 82:
British Petrol World Statistical Re
Page 83 and 84:
Hydrogen Production (ml/min) Hydrog
Page 85 and 86:
Hydrogen Production (ml/min) Hydrog
Page 87 and 88:
APPENDIX B MASS BALANCE OF A FIVE C
Page 89 and 90:
Table B.3. Mass Balance of Species
Page 91 and 92:
Stream3; Species stream 3 at 314.6K
Page 93 and 94:
Figure B.3. Input and output stream
show all

hydrogen production from water using solar cells powered nafion ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?