The Environmental Engineering Hub

Usually, society's power come from fossil fuels, which have many disadvantages: production of pollutants in large quantities, limited availability and being the cause of conflicts around the world. Fuel cells have the ability to power cellphones, cars and even houses. Their advantages are specially important for applications that are energy limited. A good example is the power for portable devices, which is limited and needs constant recharging. Studies have shown that fuel cell systems are capable of providing the same amount of energy as batteries with a smaller system weight and volume, which is a great advantage for portable power systems. Future markets for the fuel cells could be the transportation, portable and stationary sectors. Each market could make use of fuel cells for different reasons. The portable sector needs fuel cells to power devices for longer periods of time. Convergence of devices is the current trend in electronics, and the amount of power require...

Petroleum is made of gaseous, liquid, and solid hydrocarbon-based chemical compounds from sedimentary rock deposits around the planet. Crude petroleum, when refined, provides high-value liquid feeds, solvents, lubricants, and other products. Petroleum-based fuels make up almost one half of the energy supply in the world. Simple distillation is enough to make gasoline, diesel, aviation fuel and kerosene out of petroleum. How much is obtained, in terms of fractions, from the crude oil depends on the origin of the supply. When fuel cells are considered, it is important to understand the physical and combustion characteristics of the fuel, as well as its chemical composition (it is this factor that determines the fuel processing type).  Different technologies have to be employed to convert the many fraction types of the petroleum into hydrogen for FCs.  A special case is when the fuel is catalytically converted and generates various trace compounds that may be poisonous...

There are four major causes of voltage drops in fuel cells: Activation losses: they are caused because of the low speed of the reactions that take place on the surface of the electrodes: Because the electrons have to move to and from the electrode, a portion of the generated voltage is lost to drive the chemical reaction.  Fuel crossover and internal currents: this energy loss results from the portion of the fuel that passes through the electrolyte and the electron movement through it. In an ideal case, the fuel should not have that behavior, but real cases always have that phenomenon. Ohmic losses: this voltage drop comes from the resistance of the materials of the fuel cell to the transport of electrons. Mass transport or concentration losses: these happen due to the change in concentration of the reactants at the surface of the electrodes. Reference: LARMINIE, James; DICKS, Andrew. Fuel Cell Systems Explained. 2. ed. West Sussex, England: Wiley & Sons Ltd., 2...

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...