Electrochemical systems in relation to environmental issues
Posted by Syeilendra Pramuditya on December 12, 2010
There are many environmental problems today, among them all, probably problems that can be considered related to the discussion of electrochemical systems are about global warming/green house gases, fossil fuels, pollutions, and energy security for sustainable development. Generally speaking, electrochemical system is any device used for generating electricity from chemical reactions. The basic working principle of any electrochemical system is the same, in which the electric current is generated by the chemical reactions releasing and accepting electrons at the different ends of a conductor. There are various types of electrochemical systems, such as fuel cells, super capacitors, various type of primary and secondary batteries, etc. Among them all, I think two most popular today, and also strongly related to the mitigation of some environmental problems, are the secondary batteries and the fuel cells.
The first one is the secondary battery. A secondary battery can be restored to full charge (recharged) by the application of electrical energy. In other words, they are electrochemical systems in which the electrochemical reaction that releases energy is reversible. Rechargeable electrochemical cells are therefore a type of accumulator. So what is the relation between these secondary batteries with the mitigation of environmental problems? As we know that CO2 emission today is released in a very large amount to the atmosphere, by the combustion of fossil fuel from conventional vehicles, one solution is to replace these conventional vehicles with the electric vehicles. These electric vehicles always need secondary batteries as their energy storage system, in this way the secondary batteries plays some role to reduce some environmental problems. Another technology that could mitigate the environmental problems is photovoltaic system, this system also always need secondary batteries to store the power generated from photovoltaic arrays during the day to be used at night or cloudy weather.
And the second one is the fuel cell. A fuel cell is an energy conversion device. Basically, an energy conversion device takes a fuel, and converts the energy in the fuel into something that we can use. There are several different types of fuel cells. The main differences between these fuel cells are the materials that they are made from and the temperature that they operate at. Both of these factors determine what type of fuel can be used. A typical fuel cell consumes H2 and O2 as input, and produce electricity and H2O as output. The big difference between a fuel cell and an internal combustion engine is that a fuel cell has no moving parts, no explosions, just electrochemical reactions. Fuel cells require the fuel to be a gas though. So, that is the basics of what a fuel cell is: fuel in, electricity out. Every fuel cell has 3 main components, which are: Cathode, Anode, and Electrolyte. The cathode and the anode are known as electrodes. In all fuel cells, the cathode breaks down oxygen (electrochemical reduction), the anode breaks down the fuel, such as H2 (electrochemical oxidation). Electrons that are produced at the anode, travel around an external circuit to the cathode, this movement of electrons is of course the electricity. There is one more thing in this system, the ion, which travels through the electrolyte. The type of ion and what electrode it is generated in, depends on the type of fuel cell. These ions can be H+, OH-, or O2-.
According to the explanation above, we can see that the working principle of a fuel cell is very environmentally friendly, it produce nothing but electricity, water, and some waste heat, no pollution at all. But there is one important thing to consider, unlike fossil fuels, hydrogen is not naturally available, that means that we must somehow produce it artificially. One potential problem is how to do this without raising another environmental problem. Hydrogen is usually produced from other energy sources via fossil fuel combustion or other renewable energy sources. Commonly used methods to produce hydrogen are steam reforming, electrolysis, or coal gasification. When hydrogen is produced through electrolysis, the energy usually comes from conventional power sources, such as fossil fuel, geothermal, or nuclear. Though the fuel cell itself will only emit heat and water as waste, pollution is often caused when generating the electricity required to producing the hydrogen that the fuel cell uses as its power source. This will be the case unless the hydrogen is produced using electricity generated by clean (CO2 free) power sources; hydrogen is only as clean as the energy sources used to produce it. An integrated approach has to take into consideration the environmental impacts of this hydrogen production process.
I believe that only if we able to produce hydrogen economically, efficiently, and environmentally friendly, we can utilize the fuel cell in a mass production scale. I agree that fuel cells are effectively useful as power sources for electric vehicles, gadgets, or in remote locations. But to power the entire big city or area, I think this is not a good practice. Hence, in my opinion, although electrochemical systems look quite promising, I think we still need that kind of centralized large power generation systems, such as geothermal plant, or nuclear power station.