The Environmental Engineering Hub

Porous and electrically conductive material is the kind of material that is used for gas diffusion backings. Usually, the gas diffusion layer is single or composite, and the last means that there is a junction with a micro-porous layer. Water management and electrical properties can be improved with a treatment composed of fluoropolymer and carbon black . Diffusion of the reactant gases to the membrane/electrode assembly are improved with these material types. The structure is made it so that it spreads out the gas to maximize the contact surface area of the catalyst layer membrane. Carbon cloth and carbon paper are the most usually used GDL materials. The purpose of the GDL is to limit the amount of water that reaches the membrane/electrode assembly. Additionally, it helps with the removal of liquid water from the cathode side to prevent excess flooding. One required characteristic for this layer is that it has to be water-proofed so that the layer does not get clogged with wat...

Most fuel cells use hydrogen as fuel because of its high reactivity for the electrochemical reaction in the anode and the water release from oxidation, which is harmless to the environment. Thus, vehicles that employ PEMFCs (Proton-exchange Membrane Fuel Cells) may be classified as zero-emission. However, hydrogen is not readily available in most places and it has be generated before fuel cells can be used. One common way of producing hydrogen is through the electrolysis of water, which is the reverse process of a fuel cell. Even though the method may seem perverse, it is in fact a very convenient way of providing hydrogen for mobile fuel cells. Another method of providing fuel is through biological processes that can break down fossil or bio-fuel. Some of these methods are based on enzymes, bacteria or light. In other cases, hydrogen is produced in large central plants, or by electrolysers and is stored for use in fuel cells. There is already something of an infrastruct...

Most of the time, the designer doesn't have the choice between air and oxygen when assembling a PEM fuel cell. Oxygen is employed in systems that don't depend on air to operate, such as submarine and spacecraft (when that is not the case, air is used). However, the performance of a PEM fuel cell is greatly improved when oxygen is used. That happens because of three factors: The increase in partial pressure of oxygen makes the 'no loss' open circuit voltage rise, as appointed by the Equation of Nernst (https://en.wikipedia.org/wiki/Nernst_equation). Use of better catalyst sites reduces the activation over-voltage. The mass transport or concentration over-voltage losses are reduced by the increase in the limiting current, which is an event caused by the absence of nitrogen(a gas that contributes for this kind of loss at high current densities. Some results have showed that the change from air to oxygen in a PEMFC can increase performance by as much as 30%.  R...

In large PEMFC systems, the hydrogen fuel usually comes from a fuel reforming system. These systems always involve a reaction that produces carbon monoxide, like the reaction between steam and methane: CH 4 + H 2 O → 3H 2 + CO Fuel cells that work in high temperatures can use this carbon monoxide as fuel, which is different from FCs that employ platinum as part of the catalyst, since small amounts of the compound can negatively affect the anode. One of the strategies to overcome this limitation is the transformation of carbon monoxide to carbon dioxide through the increased insertion of steam:   CO + H 2 O → H 2 + CO 2 Which is a reaction commonly known as the water gas shift reaction . However, this process never fully transforms all the CO to CO2. The best systems usually leave 0.25 to 0.5% of the original concentrations of CO in the PEMFC. What the carbon monoxide does it to occupy platinum catalyst sites because of its relative affinity, which prevents ...

The thing that puts most sponsors off financing FC applications if the cost. However, there are several advantages that balances that and makes researching FCs a way to pave for a promising future. These are: Efficiency: FCs are, in general, more efficient than combustion engines. Adding to that, small FC systems can be just as efficient as large ones.  Simplicity: since FCs have no or few moving parts, they are considered to have a simple and reliable design.  Low emissions: the only by-product of a FC is pure water, thus making them almost emission-less. That characteristic is specially well received in car engine applications, since there is an international trend to reduce emissions from cars. Silence: since they have no or few moving parts, FCs tend to be very quiet during operation.   These advantages are particularly interesting in combined heat and power systems and on mobile power systems, like vehicles, portable computers, mobile tele...

There's a lot of promise behind the biological fuel cells, which normally use an organic fuel, like methanol or ethanol. In these cases, it is the enzymes, instead of conventional chemical catalysts like platinum, that help speed up the electrode reactions. These Fuel Cells attempt to copy nature in a way that energy is obtained from organic fuels. However, these fuel cells are not anywhere near to becoming commercial applications. Reference: LARMINIE, James; DICKS, Andrew. Fuel Cell Systems Explained. 2. ed. West Sussex, England: Wiley & Sons Ltd., 2003. 418 p.

Hydrogen reacts at the anode and releases energy. However, that doesn't mean that the reaction proceeds at an unlimited rate just because energy is liberated. Activation energy must be involved so that the process can get over the "energy hill". If the probability of a molecule having sufficient energy is low, then the reaction won't proceed at normal speeds. This is the case for fuel cell reactions, with the exception of situations which involve high temperatures. The 3 best known ways of dealing with slow reaction rates are: the use of catalysts, increasing the electrode area and raising the temperature. The first two solutions can be employed to any chemical reaction. The third, however, is present in fuel cells only. When considering the following reaction 2H 2 + 4OH - → 4H 2 O + 4e - It can be noticed that fuel gas and OH- ions coming from the electrolyte need to be present alongside the activation energy. Additionally, the "meeting" betw...

The basic functioning of a hydrogen fuel cell (FC) is simple. One way of looking at it is to say that the hydrogen is burned or combusted as according to the following reaction:                                                                        2H 2 + O 2 → 2H 2 O However, instead of heat energy being produced, it is electrical energy that is released. At the anode of an acid electrolyte FC, the hydrogen gas suffers ionization, liberating electrons and creating H+ ions (protons):                        ...

The environmental problems that come from the utilization of fossil fuels are a great reason for the future implementation, in large scale, of different energetic matrices. Hydrogen is one of the most promising options, being the theme of intense scientific investigation geared towards a "Hydrogen Economy", a world scenario which consists of having hydrogen and electricity as its protagonists. The hydrogen gas can be obtained through different processes, among some one can point out the electrolysis and the natural gas reformation, with the last one being responsible for over 48% of such worldwide production. The reformation of natural gas has, as an advantage, its low cost, but the hydrogen produced by that process has high levels of carbon monoxide contamination, which is a limiting factor for some applications. The most efficient and cleanest form of extracting electrical energy from hydrogen is through fuel cells (FCs). Differently from internal combustion mach...