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Motor Vehicles
As usual, I would like to begin with a little bit of background. It is not every country in the world that manufactures their cars. As a consequence of this fact, some countries have to buy from other countries where cars are produced. Depending on the economy of the importing country, the citizens may be able to afford new, high-end and luxury vehicles or used, cheap and basic ones. However bad the economy of a country is, the citizens manage to buy some cars and other vehicles that drive the transportation sector and therefore the economy.
According to WardsAuto, as at 2010, the average number of motor vehicles per capita (meaning, per head) was 148 per 1000 individuals. In Nigeria, the figure stood at 61 motor vehicles per 1000 individuals. Overall, Wards estimates that there were about 1.015 billion vehicles in use in the world by the year 2010. Were you just thinking about the world's population? I am too. If we are still about 7 billion of us, then it means that on average, there is one car for every seven people. Of course, this average is skewed to the right for countries like the US where there is one car for every 1.3 people. [1] With leadership in technology and Global Warming initiatives, it is to be expected that the US would have a large number of alternative fuel powered motor vehicles too.
Apart from few vehicles running on electric motor and a few others that combine combustion engines and electric motor such as hybrid or hybrid plug-in, majority of the vehicles on the roads today run of some fossil fuel.
These motor vehicles are propelled by a combustion engine when some form of fossil fuel is burnt in the combustion chamber pushing the piston up and down, resulting in motion. Imagine, if you will, one billion motor vehicles, scattered all over the world! Every day, for these vehicles to work, they must have gas in their tanks. This practically makes our planet one mighty filling station or as some call it gas station. The gas, in this case, is petrol and we may, one day soon, run out of them as time goes on. To solve this problem, we must find alternative means of powering our vehicles. One of such means is Fuel Cell.
Fuel Cell
Most cars are propelled using a combustion engine. Now imagine you have an engine but instead of a petroleum-based fuel tank, it has a pressurised hydrogen tank. However, the hydrogen in the tank does not burn like the fuel in a combustion engine. Instead, in a fuel cell powered car, hydrogen reacts with oxygen from the air in a similar process to how a battery produces electric current. The result is an electric power which drives the electric motor of the car, propelling it. Unlike batteries, their power does not run down so. Theoretically, they can work perpetually as long as there is hydrogen in the tank.
What is a Fuel Cell and How Does it Work?
A fuel cell is a cell in which oxygen or another oxidizing agents react with hydrogen fuel and in the process converts chemical energy to electrical energy and generating water as a by product.
Batteries and fuel cells are known as electrochemical cells, but unlike batteries, fuel cells require a continuous supply of hydrogen and oxygen to sustain the electrochemical process and must continue to produce electricity once there are hydrogen and oxygen. Batteries, on the other hand, deplete the chemical with which they function and must be replaced when they run down.
When we discussed Electrolysis as a Basis for Electroplating, we mentioned that the setup is such that there are a positively charged cathode and a negatively charged anode, both of which are immersed in a conductive liquid called an electrolyte. Batteries have a setup similar to that of electrolysis and so do fuel cells. In the case of a fuel cell, however, there is a negatively charged anode and a positively charged cathode both of which are separated by an electrolyte much like two pieces of bread is separated by ham and vegetables in a hamburger as shown in Figure 3.
The term Proton-Exchange Membrane is used interchangeably with Polymer Exchange Membrane to mean a solid polymer electrolyte (SPE) developed for the fuel cell in transport applications. We shall use this type of fuel cell to describe the operation of a fuel cell.
As shown in Figure 4, pressurised hydrogen comes into the fuel cell around the negatively charged another. The following describes in details, how electricity is generated by the cell:
In between the negatively charged anode and the positively charged cathode, there is the Proton-Exchange Membrane.
Pressurised hydrogen is channelled through the field flow plates as hydrogen gas to the part of the cell containing the negatively charged anode while oxygen enters the positively charged cathode on the other side of the cell.
With the help of platinum catalyst at the anode, hydrogen loses an electron and becomes positively charged temporarily becoming just a proton since hydrogen had only one proton and one electron ab initio.
That is: H = H+ + e-
Now, because the anode is demarcated from the cathode using the PEM, which work is to block off all negatively charged particles while allowing positively charged ones to pass, the electrons are stuck at the another while hydrogen ions (also called protons) easily migrate to the cathode.
The electrons are forced to migrate to the cathode through the external circuit shown in Figure 4. This migration causes current to flow in the circuit.
Meanwhile, oxygen from air or other oxidising agents is channelled to the cathode on the other side of the PEM.
When the proton and electron finally make it to the other side, they will react with oxygen to produce very pure water, good enough to drink and the process is relatively silent.
That is: 4H+ + 4e- + O2 = 2H2O
Conclusion
Hydrogen, like batteries, is an energy carrier which can be exploited in the generation of power through an electrochemical process similar but also different from that of batteries. Polymer Exchange Membrane is a kind of electrolyte used in some fuel cells instead of other alkaline options.
It would be nice to keep going on about how hydrogen can help us solve impending energy crisis with the challenges of dwindling fossil fuel reserves and global warming issues, but the truth is that even though hydrogen is one of the most abundant elements in the Universe, it hardly occurs isolated in nature. The process of separating hydrogen from water using electrolysers is inefficient especially when combined with the inefficiency of solar panels. If we want to use more efficient hydrogen extraction process, we may have to burn fossil fuel which is the devil from which we were running.
There is hope that technology would turn up better ways to extract hydrogen and make fuel-cell-powered vehicles good alternatives to combustion-engine-powered but for now, we are stuck between the Devil and the Red Sea.
References
- Ward AutoWorld | World Vehicle Population Tops 1 Billion Units
- Wikipedia | Fuel Cell
- Europa.eu | Electrolyser
- Explain that Stuff | Fuel Cells
- Wikipedia | Proton Exchange Membrane
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