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FUEL CELLS: CONTAMINATION AND RECENT ADVANCEMENTS FOR ITS STABILIZATION

A Fuel cell will soon be a very robust weapon to replace current highly carbonized fossil fuel generation of electricity by a more cleaner and efficient source of generation. The kind of electricity generation that is being used nowadays impacts environment badly and contributes to Global Warming. In this context, Fuel Cell can prove to be significant in generation of cleaner energy. In addition to this, fuel cell is more efficient as it doesn't operate as any heat engine; so not bound up to Carnot efficiency. Certain impurities either from the fuel that is being supplied or from the environment might result into undesirable reactions that cause fuel cell contamination. This becomes the reason for the dramatic drop in the performance of a fuel cell that has been observed from our working "Solar Hydrogen Plant" A model. For testing and extending the life of a fuel cell by detecting and mitigating the cause of degradation, the researchers has passed the sample of distilled water and Ultra-pure water (Type I) after electrolysis through Ion Chromatographer, Total Dissolved MATTER: International Journal of Science and Technology ISSN 2454-5880 Available Online at: http://grdspublishing.org/ 29 Solid test, Electrical Conductivity Test, and pH test. The cell has been allowed to run in the lush green campus of Banaras Hindu University whose environmental conditions are considered to be less polluted in the Varanasi. Henceforth, the researchers also tested atmospheric situations and its effect on fuel cell. The results of this paper will be useful in designing a device which can mitigate contamination and will ensure successful domestication of Fuel cell. In this paper, various methods of obtaining pure hydrogen gas like Pressure Swing Adsorption (PSA), High & Low Temperature Diffusion, Solvent absorption of CO and CO2 are also discussed. . A new model of fuel cell installation is also discussed with an additional stage of hydrogen fuel filtration using PSA, TSA to supply hydrogen fuel with purity up to 99.8%.


Introduction
With incipiently developed technology which uses electrical input, we cannot deny the over exploitation of fossil fuel to meet the growing electricity demand. A Proton-Exchange Membrane or Polymer electrolyte membrane fuel cells, has its properties of being able to produce a cleaner electrical energy with a very good efficiency. Platinum is a relatively inactive metal but the unusual property of being able to adsorb hydrogen gas at moderate temperature creates its great significance in fuel cells. Hydrogen Fuel cell has withal its great paramountcy in space shuttle operation as it engenders di-hydrogen monoxide i.e. water as a byproduct which makes astronaut be able to survive in space. Fuel cells do not operate utilizing a thermal cycle, precisely not be working as a heat engine so it's not bound to Carnot efficiency and hence can show very high conversion efficiency in the range of 40%-60%.

Production of Hydrogen Gas
It is well known that there is abundance of hydrogen element in Earth's crust therefore; hydrogen gas can be produced from various sources such as natural gas, coal, hydrocarbons and by many other chemical reactions. Hydrogen gas can also be produced by splitting water by electricity which is called as electrolysis. Here, in our experiment researchers are using electrolyser for electrolysis of distilled water. The commercial production of hydrogen by electrolysis of water achieves an efficiency of 70-75%. However, the cost of hydrogen produced by this route is several times higher than that produced from fossil fuels (] P.P. Edwards, V.L. Kuznetsov, W.I.F. David). At current stage of technology, reformation of hydrocarbons including methane from natural gas is the most significant sources for the production of hydrogen gas. This method bounds us to install a purifying stage consisting of PSA, High & Low temperature diffusion since, reformation produces impurities like CO, CO2 and H2S along with the production of hydrogen gas.
Steam reforming and partial oxidation or auto thermal reforming are usually used to produce hydrogen-rich gas called "reformate," which typically contains 40 to 70% H2, 15 to 25% CO2, 1 to 2% CO, small quantities of inert gases (water vapor and nitrogen), and sulfur impurities (Xuan Cheng, Zheng Shi, et al).

Methods to Obtain Pure H2 Fuel
Because of wide range of use of hydrogen scientists have developed many techniques which can be used to obtain pure hydrogen gas. Here, we'll discuss methods to draw pure hydrogen gas which can be used to supply pure hydrogen gas to the fuel cell. Henceforth pure H2 supply will cause minimal poisoning of fuel cell.

Pressure Swing Adsorption
Pressure swing adsorption (PSA) processes are used for the production of high purity hydrogen from steam methane reforming off-gas (SMROG) and refinery off gases (ROG)( S. SIRCAR & T. C. GOLDEN (2000) ). Pressure swing adsorption systems for oxygen production were first used  Prosser,M.M. Shah,10). This technology for the separation of gasses utilizes the fact that under high pressure, gases tend to be attracted to solid surfaces, or "adsorbed". The higher the pressure, the more gas is adsorbed. When the pressure is reduced, the gas is released, or desorbed.
PSA method uses different adsorbents which have the ability to differentiate mixture of gasses.
Examples of few adsorbents used in PSA are activated carbon, silica gel, alumina, resin and zeolite.

High & Low Temperature Diffusion
In this technique, the raw gas is diffused through a metal membrane such as palladium. In the 1980's Johnson-Matthey sold hydrogen generators based on steam-reforming methanol which used a palladium diffuser to provide very high purity hydrogen for various specialized uses (J. E. Philpott(1985)). High cost and limited supply of palladium are the major disadvantages of this system.
Nowadays, nickel membranes have been tested as a possible substitute for palladium (Y. Sakamoto, H. Tanaka, et al).
In case of low temperature diffusion the gas has to diffuse through polymer membrane. The

Solvent Absorption of CO2 and CO
This method is mainly used in chemical industries to remove impurities from mixture of gasses. The basic step is to dissolve unwanted impurities to solvent and hence high purity hydrogen gas can be extracted as a product. Chemical absorption systems have been in use since the 1930s for the 29 capture of CO2 from ammonia plants for use in food applications and hence, are a commercially realized technology, though not at the scale required for power plants (Anusha Kothandaraman(2006)).

Electrode Contamination & its Mitigation
The contamination can be because of fuel impurities such as CO, CO2 or NH3; air pollutants (NOx, SOx, CO, and CO2); and few cationic ions like Fe 3+ and Cu 2+ (Xuan Cheng, Zheng Shi, et al).

CO Contamination
CO binds with the Platinum surface intensely which causes decrement in surface area available for hydrogen adsorption and oxidation. So, it's obvious to reach out to conclusion that CO poisoning on Pt catalyst will increase, with increase in exposure time. Nowadays, various techniques such as current-voltage polarization and EIS (Electrochemical Impedance Spectroscopy) (Prudenziati, M., & Hormadaly, J. (2016)) can be used to quantify the effects of CO poisoning on H2 oxidation. Benesch and Jacksier (R. Benesch and T. Jacksier) reported that the time it took for cell voltages to decay to a threshold value of 0.3 V were 1 and 9 h, respectively, when the cells were exposed to 50 and 10 ppm of CO. However, utmost care should be taken while using EIS techniques as stated in recently Moreover, temperature has also its effects on performance of a fuel cell. When the anode was fed with H2 containing 250 ppm of CO, the performance at temperatures below 80°C was much lower than that at 100°C (Divisek, J., Oetjen, et al (1998)).

Mitigating CO Poisoning
There exist three methods to mitigate the effect of CO poisoning: (i) the use of a platinum alloy catalyst, (ii) higher cell operating temperature and (iii) introduction of oxygen into the fuel gas flow (A. Rodrigues, J. C. Amphlett, et al). Analysis of cited publication shows that a pure Pt catalyst experiences more CO poisoning than a Pt-alloy catalyst. Ralph and Hogarth confirmed that a PtRu alloy catalyst is more tolerant to CO poisoning than a pure Pt Electrocatalysts by experiments using a fuel cell operated at 80°C with hydrogen containing 10, 40, and 100 ppm CO (T.R. Ralph, M.P.

Hogarth).
Air-bleed on the anode side of the stack is a well-known technique for mitigating CO poisoning (Gottesfeld 1988) (Johannes Tjønnås, Federico Zenith, et al). Unconverted carbon monoxide from the reformer can significantly reduce the activity of the fuel cell's anodic catalyst. For this, corrective action is to increase the air bleed to oxidise CO to CO2 (Johannes Tjønnås, Federico Zenith, et al).

Air Contaminants
Fuel cell is also highly sensitive towards poisoning caused by air impurities. Few effects caused by air impurities (SO2, CO2, NO2 etc) are reversible, and some are non-reversible. Though, reversible poisoning can be eliminated but certainly it has been observed that long time exposure to

MATTER: International Journal of Science and Technology ISSN 2454-5880
it degrades the fuel cell permanently. In the presence of SO2 in the air stream, the fuel cell current density dropped by over 50% (R. Mohtadi, W. Lee, J.W. Van Zee).
The performance degradation with NOx present in the air stream was also observed by a recent electrochemical impedance measurement (D. Yang, J. Ma, et al). However, the performance loss induced by the presence of NO2 could be recovered by reintroducing neat air into the contaminated cathode (ZhengShi, D.S., HuiLi, KhalidF., et al).

Experiments
For testing and extending the life of a fuel cell, the researchers carried out electrolysis by both Distilled water and Ultrapure water (Type I).

Ion Chromatography using Ultrapure Water
Ion chromatography is a process that separates ions and polar molecules based on their affinity to the ion exchanger. Solar Hydrogen Plant a is allowed to operate in the open-environment of Banaras Hindu University. Volume of fuel supplied and time is noted, and then sample is tested for ions by chromatography. The samples are taken after electrolysis of 24mins.

Instrument Specification
Instrument name: Ion chromatography Metrohm (930 compact IC, Switzerland) Column used: Metrosep C4 (for cation) Metrosep A Supp.5 (for anion) In this experiment, the samples are taken after an electrolysis of ultrapure water for 24mins.
After electrolysis, the sample of both H2 and O2 chamber are taken separately and stored in a closed tube of 45ml and then sent to CIF BHU for Ion chromatography. The sample obtained after the solar-hydrogen plan model is exposed in an open environment for electrolysis and generation of hydrogen gas for the operation of the fuel cell is then passed through Ion chromatography test whose result detected some ions indicating contamination of fuel cell. ISSN 2454-5880

Observation & Result
The major hurdle in the domestication of a fuel cell is its delegate nature and high sensitivity towards impurities when exposed to work. Though utmost care has been taken by researchers while taking samples from both the chambers still some traces of ions like Sodium, Lithium, Chloride, Fluoride, Magnesium is detected by our chromatographer. The source of these foreign ions might be impurities in tube, chamber and sweat by skin contact (reason for the detection of Na + , Cl -). Retention time and peak in the curve has been seen in case of few ions for which the chromatographer is not calibrated. The name of these unknown ions can be drawn by using reverse engineering.
During electrolysis environmental impurities like Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2) initiates the following reactions: Above reactions are the reasons for the detection of Nitrate and sulfate ions in the samples.
Fortunately, these reactions serve in a good way by increasing the rate of electrolysis as it add ups to the ions of water which increases its conductivity. From the experimental results, it has been found that graphite is a good choice for the production of maximum hydrogen compared to various other electrodes (Yuvaraj, A.L. AU -Daniel, et al). But ensure that we must use platinum as electrodes in electrolyser to avoid further reactions of produced acids with C which would result into the production of NO2 and CO2.

pH Test
Researchers have used distilled water for electrolysis and then the sample is tested for it pH.
The samples are taken after electrolysis of 30mins. From above test the shift in pH has been noted which clearly indicates the change in nature of distilled water after electrolysis. It can be observed that the distilled water in H2 chamber turned more basic in nature whereas the distilled water in O2 chamber tends to decrease in pH which indicates formation of some acidic component inside the chamber.

Electrical Conductivity Test
Researchers have used distilled water for electrolysis and then the sample is tested for it pH.
The samples are taken after electrolysis of 30mins. There is significant increase in the value of electrical conductivity from the value of distilled water. This increase in EC signifies formation of some ionic components during the process of electrolysis. The reason for this increment in the value of EC is the reaction that occurred inside the chamber due to gasses like SO2 and NO2.

Total Dissolved Solid Test
Researchers have used distilled water for electrolysis and then the sample is tested for it pH.
The samples are taken after electrolysis of 30mins. Above carried out tests resulted into the conclusion that change (either increase or decrease) in pH or electrical conductivity of sample indicates addition of impurities in to the fuel supplies to the fuel cell. Also, the increase in TDS of sample implies the addition of dissolved foreign particles that are causing the contamination in fuel cell.

Proposed Model
The new model has been proposed with an aim of achieving long term utilization of fuel cells as a domestic source of electricity generation. The political-economic analysis and payback period of this model is a very interesting future research topic. Researchers are trying to analyze every aspect of this model before giving it a physical significance.

Conclusion
This paper is an introduction to the working of a fuel cell in electricity generation sector.
According to the U.S. Department of Energy, the number of fuel cell systems shipped worldwide per year increased from 10 000 to more than 60 000 units, from 2008  The proposed model would be able to supply high purity hydrogen which will cause negligible contamination in the fuel cell.