Fuel Cells for use in Automotive Applications

Introduction

Before going into details of Fuel Cell Technology, first of all we have to understand the terminology Fuel Cell; what it does? Fuel Cell can be composed of an individual cell or maybe it is a stack (Number of individual cells make up of a stack) depends upon the condition in which electrochemical process is taken place; chemical energy is converted into useable electrical energy which can then be used. Besides the major component electricity, byproducts are also produced like water and heat and then it be further renewed to produce hydrogen fuel gain for fuel cells by applying specified conditions and practices. This is actually what a fuel cell does or due to which it has been used.

 If we talk about applications, due to minimal pollution and greater efficiency as in comparison with petroleum fuel’s combustion, there are numerous applications from small to large scale in which fuel cells can be used. Let’s talk briefly about transportation in which it can be used just like vehicles, buses, trucks, marine vessels, lift trucks, ground support equipment and auxiliary power units. Besides all this, fuel cells can also be used as power for remote locations, backup power, distributed power generation and in cogeneration too in which excess heat is released as a byproduct during the production of electricity in electrochemical reaction which can then be used in other applications.1

 Main Types of Fuel Cell & Applications

From composition point of view regarding Fuel Cells, it totally depends upon what type of electrodes (anode and cathode) in correspondent with electrolyte is used and a catalyst (an element or a substance which is usually used to fast the electrochemical reaction) is also used. Moreover, fuel in the fuel cell as its name suggests, also requires fuel. Let’s take five main fuel cell types for going into further details. Name of those five fuel cells are Polymer Electrolyte Membrane or abbreviated as PEM, Alkaline Fuel Cell (AFC), Phosphoric Acid Fuel Cell (PAFC), Molten Carbonate Fuel cell (MCFC) and Solid Oxide Fuel Cell (SOFC). These fuel cells are characterized by electrolyte, electrode’s material, temperature at which they operate, differences in reaction chemistry, efficiency, catalyst used, their applications, advantages and challenges that are faced. Now the first one, Polymer Electrolyte Membrane (PEM) which is also called Proton Exchange Membrane is usually known for its light weight and deliver high power density thus constitutes favorable power to weight ratio (P/W). These types of cells just need Hydrogen, water and oxygen from air in order to operate. These operate at low temperatures, normally 80?C(176?F) due to which these cells start quicky and this simply means they require less warm-up time, resulting in better durability. A catalyst (typically Platinum) actually increases its cost which is used for the separation of Hydrogen’s Electrons and Protons and in some cases an additional reactor is also needed which further adds its cost making it more expensive. Due to its good P/W and quick start-up time, these cells are usually considered for passenger’s vehicles like car and buses.2
Figure 2.1 (PEM Fuel Cell)

The second one is named as Alkaline Fuel Cell. The electrolyte used in it is Potassium Hydro-oxide in Water. So, liquid electrolyte is used in it in comparison with PEM in which solid electrolyte is used which reduces corrosion and electrolyte management problems. Due to all this, it is susceptible to poison by CO₂  (Carbon-dioxide) resulting in decrement of cell’s performance and its durability. This is actually the challenge which has been faced in this type of cell. Besides these challenges, effective electrolyte management as in PEM and electrolyte conductivity are also the major ones. However, AMFC instead of AFC where AMFC stands for Alkaline Membrane Fuel Cell cope-up the problems addressed in AKF. These are especially used for W to KW scales. In addition to transportation, these are also used in Military.2
Figure 2.2 (AFC)

Phosphoric Acid Fuel Cell (PAFC) uses liquid phosphoric acid as an electrolyte. The rate of the electrochemical reaction is very important in every type of cell. AFC performs at high level due to the rate of the electrochemical reaction takes place in it. PAFC is considered to be the first generation of the modern fuel cell and it was the first one that was used commercially. The efficiency of these cells are at very high pace when these are used for co-generation (releasing then byproducts too) but are less efficient when used alone for electricity generation. Furthermore, platinum catalyst makes it too expensive. The operating temperature ranges from 150 - 200?C and such a high operating temperature usually require long start-up time which is actually its major disadvantage.2
Figure 2.3 (PAFC)

For Coal based and natural gas power plants, regarding recent developments, Molten Carbonate Fuel Cell (MCFC) is being developed for applications like military, industrial and electricity; the major one. The interesting thing in this cell is its fabulous advantage over cells like PEM, AKF, PAFC in which there is an external reformer to reform gases into Hydrogen gas but in MCFC, due to its extra ordinary high operating temperature roughly 650?C (1200?F), there is no need for an external reformer as due to high temperature, methane and light hydrocarbons are easily converted into hydrogen by reformation process internally so this reduces the cost of external reformer. Besides all this, there is something bad related to its high operating temperature and that is its long start-up time.2
Figure 2.4 (MCFC)

The last and the fifth type of cell that includes in one of the major fuel cell too is Solid Oxide Fuel Cell (SOFC) and the electrolyte used in it is hard, non-porous ceramic compound. Operating temperature is sufficient high in comparison with other fuel cells in this type of cell due to which its stat-up time is very slow but due to higher temperature, no any external reformer is used as gases are reformed internally by high temperatures. Temperature is roughly 1000?C (1830?F). Still developments are being made regarding SOFC in order to reduce its operating temperature without compromising its durability and performance.2
Figure 2.5 (SOFC)
 
All above discussed Fuel Cell types have some advantages and disadvantages over one another and that actually make a differences too between different cell types. Pros and Cons are with respect to temperature, corrosion, effective management of electrodes and cost that plays an important role. Scientists are bringing improvements and developments in fuel cells in order to mitigate the cons related to above stated factors just like to minimize the temperature in SOFC without compromising its performance and durability.

Fuel Cell’s System by Cussons P9040 Unit

Now come to the working of the Fuel Cell’s System by Cussons P9040 Unit by which we are also able to investigate the performance of a fuel cell. This is the major part which must be understood in order to understand the whole fuel cell. The above stated unit will basically help us or facilitate us for understanding fuel cell’s working. Before starting this Cussons Unit, everybody must make sure for safety precautions which are very necessary for handling this equipment. As Hydrogen gas is used for fueling purpose in this system, must make sure that system to which gas is being applied or given is properly sealed or there is no leakage. Moreover, no external electrical supply will be given as the whole system is self-contained. Everybody knows that Hydrogen gas is highly flammable and very dangerous so be careful when doing this cussons’s experiment.3. Kindly find herewith a practical diagram regarding cussons’ unit;

3.1.Constituents of Cussons Unit & Experiment (Working of Unit)

Cussons Unit basically constitutes the control Unit on which the stack of fuel cells is mounted. As discussed above, there is no need of external electrical supply, only Hydrogen gas is needed or used as a fuel. In this unit, Fuel cell is an air breathing device which uses oxygen from air and just uses Hydrogen gas in order for its operation. It basically consists of ten (10) connected cell to form a stack to give an output of 10 to 12watts at 6volts DC (Direct Current). While Control Unit is a self-contained instrumentation unit which usually takes the whole control of the system’s operation. A self-contained unit means a unit that does not require any external electrical supply while Hydrogen is used for its whole operation as a fuel. Control unit basically constitutes voltmeter and ammeter to display the cell’s output voltage and current respectively, to show inlet and outlet air temperatures, a pyrometer is used and rheostat; for load test on fuel cell. A quantity of 2 (two) psi and a flow rate of 160 cc/min is used for supplying of Hydrogen gas as a fuel. Where as psi stands for ponds per square inch that indicates pressure of a gas and cc/min that is the flow rate basically stands for cubic centimeter per minute.

Now we will talk about p9040’s operation/working; to start the stack of fuel cell, spray the distilled water from the air holes of the stack. Pass 2 psi 100 cc/min Hydrogen gas for few seconds (roughly 1 to 2 seconds) by removing the pipe on the outlet of the stack. Set the flow rate of Hydrogen of about 75 cc/min and also set the rheostat for the production of 0.5 to 0.8 amperes which will be shown on ammeter. Run this whole condition for about 10 to 11 minutes Replace the pipe on the cell’s outlet. The system is now in running mode. For stopping the stack, Select the selector switch (it is used for on and off state) then increase the load to its maximum. Do not give the supply of hydrogen fuel at this stage or step and when voltage reaches to zero, turn off the selector switch. Finally isolate the hydrogen supply. The last one step to isolate the hydrogen supply from the system is very important as of now, the system has been shutdown so it is not in running mode so in this condition or whenever the system is not in used, disconnect the supply of hydrogen. This is also in safety measures. Moreover, make sure to experiment this whole operation in ventilated environment or room for safety purposes as hydrogen is very dangerous and is highly flammable gas.

We are right now at the stage that we may understand the working knowledge regarding above said equipment and the Fuel Cell, which is very important as this whole unit is presented here in order to understand the scenario of Fuel Cell. If we talk about experiments, basically experiments give us the concise values and make the situation more clear for understanding purpose. So, right now, we will deal with some physical quantities and equations that have interfered with this whole experiment.

Lets first talk about the quantities; current, voltage and power. Actually, we will have to plot the parameter current against voltage and power for better understanding with and without fan assistance. Repeat the above discussed whole operation/experiment in order to plot the values of current against voltage and power with and without fan assistance. Now what does with and without fan assistance means? Actually, by doing this whole experiment with fan assistance means to blow air force with fan across the cell causing more air to flow resulting more oxygen and this gives us finally more power output. In contrary, if we repeat this experiment without fan assistance, we will observe less power output in comparison with fan assistance. Now come to the point to do the experiment for calculation of current voltage and power values. To calculate the values, set the selector switch for recording the voltage, current and hydrogen flow. Do this again and again for a number of different values of load in order to come across the concrete results. Now we are able to plot the graph of the above said quantities and this will actually show the characteristics of a fuel cell. Also make a graph to plot hydrogen consumption against power (with and without fan assistance).

Experimental Results with Graphs (by different variables)

Now to further discuss regarding physical quantities for more and better understanding the fuel cell with cussosns unit, we will discuss one more factor regarding the effect of load on rate of response. First of all, we will plot these quantities and will discuss in detail each and every graph after plotting.

The above shown graphs from figure1 to figure5 are just for viewing the relationships among physical quantities for getting a better idea regarding fuel cell’s characteristics and performance. By view at any graph, one can easily depict characteristics or performance. However, we discuss some brief details regarding each graph. Now one more thing, everything is designed or every experiment is done to finally calculate the efficiency. This simply means what we get from doing something. So, in short, we are now going to show the formula of current efficiency and overall efficiency of the fuel cell.
Current Efficiency (%) = (Current Observed/Theoretical Current) *100. While overall efficiency of the fuel cell can be easily calculated by the formula; Overall Efficiency (%) = (Observed Efficiency / Theoretical Efficiency) *100. Both the stated formulae are very useful for calculations. Now calculations can be easily done by these formulae by simply putting the values.

 Now coming forward to conclude all this P9040 Unit’s detail, we have come across with the results; the above plotted graphs between different physical quantities and with two important formulae regarding efficiencies. Already above plotted graphs are enough to extract data and results in mind but we are going to touch each graph a little bit in order to conclude or finalize results. So, by going through first figure regarding current, voltage and power, you may easily see that by current’s incremental, voltage and power, both are being reduced. No doubt the values of voltage and current are high in start while values of current are minimum but slowly and gradually, values of voltage and power reduce. As per our graph in figure1, we can take this whole situation without fan assistance but if we take assistance of a fan, as you know that fan will produce air flow resulting more oxygen and finally this will give us more output. So, in figure2, power is increasing just because of fan assistance in comparison with figure1 in which value of the power is going down and down. Now with respect to figure3 in which hydrogen consumption is shown with power and time and in this case, this graph is also discussed with and without fan assistance too. So, Hydrogen consumption’s rate is increasing in both (without and with fan) cases. However, power seems to be stable but clear growth is seen in power (somehow) with fan’s assistance. So, these all cases are very helpful to understand fuel cell with P9040 unit. Finally, the last one is effect of load on rate of response means power. This last one graph is also very helpful in understanding the fuel cell’s performance Everyone knows the relationship between power and load ; direct relationship means increase in one quantity will produce increment in another quantity too. Moreover, for this last one plotted graph, to collect the results (to draw this graph), please make sure to first set the load to its maximum then note down the flow of hydrogen. After this, as soon as possible, change the load to its minimum value and then note down the time taken for hydrogen flow to reduce to stable or steady reading. So, keep in mind this last statement when you are doing to plot the graph between load and power (rate of response.

Conclusion

As discussed briefly in our early section that Fuel Cells are very fabulous thing in terms of producing excellent efficiency and with contributing no any pollution in an environment as comparison with traditional petrol which is used normally and of which efficiency is very minimum (30 to 35 %) and which contributes too much pollution in an environment. A typical fuel cell can yield an efficiency of about 70 % + (plus seventy percentage) with clean greenhouse effect. Different variety of fuel cell have already been discussed earlier in detail but if we talk about transportation, then yes, some of the fuel cells discussed above are very important in this regard. Scientist and engineers are thinking deeply over these fuel cells as these are good in comparison with other tradition petrol fuels. Some developed governments have decided to move forward with vehicles in coming years that are supplied electrically without using traditional petrol fueling system and have also decided to make a ban on vehicles that use combustion fueling system or petroleum fueling.

No doubt, with these fuel cells, there are lot of cons and challenges for which scientists and engineers are struggling hard to cope-up with or to mitigate those cons. Now come to the point regarding transportation, as transportation or vehicle requires immediate start and stops and also requires quick start-up time. So, by keeping all these scenarios in mind, the best one recommended fuel cell by engineers is PEM or Proton Exchange Membrane. Engineers have actually chosen this fuel cell due to its good P/W ratio (power to weight ratio) as discussed above. That means these are light weight cells and deliver high power density. Their quick start-up time means these operate at low temperature in comparison with other fuel cells. The best thing of these cell is; they just need hydrogen gas as a fuel while oxygen (from air) and water is also needed. So, these are basically hydrogen fuel cells. As discussed, there are cons too with these cells, so the con with this cell is; its precious catalyst named as platinum is used to segregate the hydrogen ions into protons and electrons. This is the major disadvantage of this cell due to which it is very costly and developments regarding this fuel cell is being done in order to cope-up this problem and come with a non-precious catalyst. However, its efficiency is good that reaches at around 60% and platinum catalyst used in it in its solid form due to which there are minimal chances regarding corrosion and the one last good thing in it is, it is good at electrolyte management problems. All these pros are best but the one major drawback is its cost by using precious catalyst. Moreover, engineers’ technical goal is to achieve direct hydrogen fuel in buses/transport/vehicle with 65% efficiency and with durability of 5000-hours. Furthermore, they are in search of that hydrogen fuel which is stored on board and supplied by hydrogen fueling and infrastructure to the fuel cell. Refer above discussed cussons P9040 unit for better understanding. 

The other fuel cell named AFC (Alkaline Fuel Cell) as discussed above is also being suggested for transportation like in buses and in vehicles like in cars. These are same as PEM but uses liquid electrolyte instead of solid as in PEM. Due to the liquid electrolyte, there are serious problems that are faced in these cells regarding electrolyte management. Moreover, due to liquid electrolyte, these are sensitive to CO₂ present in fuel and in air and this can cause corrosion problems too in these type of fuel cells. However, as stated earlier, these are like PEM, so, there is an advantage of quick start-up time and low operating temperature as in PEM. Due to the stated problems in these fuel cells, AMFC or Alkaline Membrane Fuel Cell was introduced to mitigate these issues. However, still there are challenges regarding its sensitivity from CO₂   and its durability and developments are being still done in order to bring improvement in these cells as these are very good for transportation pruposes.

Besides all this, developments are being done regarding other fuels cells too named as MCFC or Molten Carbonate Fuel Cell and SOFC or Solid Oxide Fuel Cells for other application purposes. But to commercialize all these cells, with other problems, the major one is their durability and cost for which engineers are struggling hard to obtain desired results. The cost may be increased in fuel cells because of precious usage of electrolyte and other materials too like electrode’s material etc due to which problems are arisen for commercialization. For this reason, special bodies are assigned the task to find-out the non- precious catalyst; not the catalyst used in PEM but trying to reduce quantity of platinum as a catalyst or no use of such type of catalyst which actually plays an important role in increasing the cost. Moreover, with fuels cells like AMFC, there are issues like corrosion due to liquid electrolyte, so, in short, the problems are generated regarding corrosion in these types of cells and currently activities are being done and in order to mitigate corrosion element or to produce solid electrolytes in comparison with liquid ones. Temperature is also the element which produces challenges like high temperature causes corrosion problems with breakdown of fuel cell’s components. Still too much development is needed regarding fuel cell’s commercialization. However, scientists and engineers are doing their part to do the best to improve the overall performance and durability in order to commercialize the said product. Besides catalyst, work on membranes is also going on regarding to improve the conductivity matter and for this purpose PEM fuel cell is under consideration. In addition to this, regarding PEM, engineers are trying to increase mechanical, chemical and thermal stability with improving its conductivity. For all this, different types of models (like one discussed above; P9040), tools and diagnostic’s equipments are being made to test for the best fuel cell. All these works and tasks are going on in order to provide good transportation to the public especially in terms of public buses.

Durability and cost’s factors are the major barriers (as discussed earlier) in the process of commercialization of fuel cells. As discussed, target for bus transport or for vehicles is 5000-hours durability by keeping all parameters in mind. Whereas, 3900 hours durability was achieved during testing in laboratory. Regarding cost, not just platinum like electrolytes plays role in increasing the cost but membrane of fuel cell, hardware used, reformers used (in case of gas is reformed into hydrogen gas), reactors, bi-polar plates, all these factors play role in cost increment. As compared to conventional gasoline vehicles/buses, these fuel cells are very costly but are very favorable in creating pollution free environment but engineers need to think over all such stated factors due to which we have to pay too much for these fuel cells and no doubt, as discussed before, developments are being going on for advancements and for improvements. Durability factor actually come over due to frequent start and stop of buses/vehicles, impurities in the fuel, chemical and mechanical in-stability, materials and components, all these play their role to introduce durability issues. These are actually the technical barriers which are being faced.

Performance is another key factor which must be improved further to give better output power and efficiency with cost and durability factors. Performance in degradation may result form several factors like from cell issues, stack water management, system thermal, water and air management and start-up/shutdown times. We will discuss here cell isuues and start-up/shutdown times for ease and convenience which are also the key issues with respect to degradation in performances in fuel cells. Regarding cell issues, lets take an example to understand this key issue, like bad or poor cathode’s operation resulting over-potential issues of 0.4v or greater and this actually decreases the over all performance with efficiency too. Means, loss of around one-third energy due to this poor cathode’s operation. Moreover, for cathodes, at high current densities with reducing quality factor of Platinum catalyst also introduce losses which are also under observation and need to be improved. Membrane issues in fuel cells regarding their conductivity also degrade performance resulting decrease in efficiency. So, a lot of factors must need to be improved to provide good results with ease in commercialization. Now moving towards the next key issue with respect to performance that is start-up/shutdown times. Briefly, as discussed before in detail that automotive applications just like buses must start as soon as possible or in rapid action so there is a need of quick start-up time and as all knows that vehicles/buses use frequent start and stops. So, there are cells which can do that but still, there is a need of improvements in a lot of sectors regarding this start-up/shutdown times in order to finally improve the performance. In short, in future, in coming years, people will soon see this technology in transportation.

References

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