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| Fig. 1: The working reactions of a typical Hydrogren Fuel Cell. (Source: Wikimedia Commons) |
Climate change continues to demand a more sustainable means to drive transportation methods ensuring the new effort to be powerfully efficient and renewable. Thus, working to try and implement such a drastic transition from today's polluting heavy combustion engines requires a comprehensive survey of all the potential alternatives that exist in terms of energy harvesting. One of the latter technologies that stands as both a viable and strong contender is the hydrogen fuel cell. Running entirely on compressed hydrogen fed into a fuel stack to produce electrical energy, hydrogen fuel cell vehicles boast zero emissions and energy outputs comarable to those of a typical electric car.
What makes fuel cells such an attractive option is the fact that no external byproducts are produced as the expense of the chemical reaction taking place in order to produce the energy. Essentially, the process involves nothing more than Hydrogen molecules reacting with Oxygen, resulting in electricity to be harnessed and water vapor. A Proton Exchange Membrane (PEM) readily takes in the O2 from the atmosphere and reacts it with H2, which can be derived from an electrolysis process.
Within this stack of cells, there exist two electrodes for the chemicals to diffuse through as the reaction takes place. The anode, the negative post of the cell, conducts electrons that are stripped from the hydrogen molecules to be utilized for electricity supplied to an external circuit. The cathode on the other hand, the positive post of the fuel cell, conducts the electrons from the external circuit to the catalyst, where H2 and O2 meet, creating water vapor, as illustrated in Fig. 1. [1] The electrolyte thus allows for the proper dispersion of ions from anode to cathode. By the converting these negative ions into electrons, which are then utilized as useful work, hydrogen fuel cells pose a very viable solution as a cost-efficient and clean energy source.
Fuel cells are more attractive than combustion engines becuse the latter produce pollutants and contribute to greenhouse gas (GHG) buildup. However, fuel cells and combustion engines hve similar working mechanisms: both engines consume fuel that is stored externally in an onboard tank on the vehicle. However, the uncontrolled chemical reactions of the combustion engine result in huge inefficiencies. A fuel cell, by contrast, operates like a rechargeable battery, in that both transform chemical energy from a compound into electricity through electrochemistry. With both resulting in zero pollutants, the difference between the two technologies lies in the storage of fuel. A battery converts a finite amount of a chemical compound stored internally into electricity. Thus, the question really becomes what are the capabilities that a fuel cell could operate at? The NECAR 5 is the latest prototype fuel cell automobile - with virtually no pollutant emissions, the efficiency of this particular device is a factor of 2 higher than the internal combustion engine (operating at about 20-25% efficiency). Essentially existing within the same physical capabilities of a typical commercial car, the NECAR 5 drives at a top speed of over 150 km/hr with a power output of 75 kW. It has the potential to make significant positive change. [2]
With electrical energy demands continuing to increase throughout the world, options such as fuel cell stacks continue to gain traction. With the energy consumption for America growing at nearly 2.4% since 1997, more sustainable and efficient technologies need to find their way into the economy. [2] While hydrogen is difficult to obtain, with few processes available, such as steam methane reforming, today's society has a major decision to make on what is necessary for tomorrow's vehicles. We need to question the methods of obtaining the energy and weigh the consequences of the transition.
© William Mangram. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Fuel Cell Technology," College of the Desert, December 2001.
[2] B. Cook, "An Introduction to Fuel Cells and Hydrogen Technology," Heliocentris, December 2001.
