An ink of catalyst, carbon, and electrode are sprayed or painted onto the solid electrolyte and carbon paper is hot pressed on either side to protect the inside of the cell and also fuel cell fundamentals ryan o hayre pdf download as electrodes. A stream of hydrogen is delivered to the anode side of the MEA.
At the anode side it is catalytically split into protons and electrons. The newly formed protons permeate through the polymer electrolyte membrane to the cathode side. The electrons travel along an external load circuit to the cathode side of the MEA, thus creating the current output of the fuel cell. The reversible reaction is expressed in the equation and shows the reincorporation of the hydrogen protons and electrons together with the oxygen molecule and the formation of one water molecule. The potentials in each case are given with respect to the standard hydrogen electrode. The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover.
Splitting of the hydrogen molecule is relatively easy by using a platinum catalyst. Unfortunately however, splitting the oxygen molecule is more difficult, and this causes significant electric losses. An appropriate catalyst material for this process has not been discovered, and platinum is the best option. Vladimír Matolín in the development of PEMFC. The PEMFC is a prime candidate for vehicle and other mobile applications of all sizes down to mobile phones, because of its compactness. A platinum-ruthenium catalyst is necessary as some carbon monoxide will unavoidably reach the membrane. The most commonly used membrane is Nafion by Chemours, which relies on liquid water humidification of the membrane to transport protons.
C, since the membrane would dry. Teflon binder increases the hydrophobicity of the electrode to minimize potential flooding. The GDL electrically connects the catalyst and current collector. It must be porous, electrically conductive, and thin. The reactants must be able to reach the catalyst, but conductivity and porosity can act as opposing forces. The carbon particles used in the GDL can be larger than those employed in the catalyst because surface area is not the most important variable in this layer.
Due to the simplicity of manipulating or substituting the metal centers and ligands, there are a virtually limitless number of possible combinations, which is attractive from a design standpoint. As electrolyte materials, the inclusion of MOFs seems at first counter-intuitive. Fuel cell membranes generally have low porosity to prevent fuel crossover and loss of voltage between the anode and cathode. Additionally, membranes tend to have low crystallinity because the transport of ions is more favorable in disordered materials. A low temperature example is work by Kitagawa, et al. A high temperature anhydrous example is PCMOF2, which consists of sodium ions coordinated to a trisulfonated benzene derivative. To improve performance and allow for higher operating temperatures, water can be replaced as the proton carrier by less volatile imidazole or triazole molecules within the pores.
To date, the highest proton conductivity achieved for a MOF electrolyte is 4. Some recent experiments have even successfully produced thin-film MOF membranes instead of the traditional bulk samples or single crystals, which is crucial for their industrial applicability. Pt cathode is significantly slower than the fuel oxidation reaction at the anode, and thus non-PGM and metal-free catalysts are being investigated as alternatives. Examples of these approaches are given in the following sections. As mentioned above, platinum is by far the most effective element used for PEM fuel cell catalysts, and nearly all current PEM fuel cells use platinum particles on porous carbon supports to catalyze both hydrogen oxidation and oxygen reduction. C catalysts are not feasible for commercialization. One method of increasing the performance of platinum catalysts is to optimize the size and shape of the platinum particles.
Decreasing the particles’ size alone increases the total surface area of catalyst available to participate in reactions per volume of platinum used, but recent studies have demonstrated additional ways to make further improvements to catalytic performance. Since the most common and effective catalyst, platinum, is extremely expensive, alternative processing is necessary to maximize surface area and minimize loading. Pt surface area while the carbon allows for electrical connection between the catalyst and the rest of the cell. The most effective ways of achieving the nanoscale Pt on carbon powder, which is currently the best option, are through vacuum deposition, sputtering, and electrodeposition.
The platinum particles are deposited onto carbon paper that is permeated with PTFE. However, there is an optimal thinness to this catalyst layer, which limits the lower cost limit. Below 4 nm, Pt will form islands on the paper, limiting its activity. A second method of increasing the catalytic activity of platinum is to alloy it with other metals. Further efficiencies can be realized using an Ultrasonic nozzle to apply the platinum catalyst to the electrolyte layer or to carbon paper under atmospheric conditions resulting in high efficiency spray. Another practical approach is through multi-layer configuration catalyst layer,. This idea was promoted by the highly spatial variation of reaction rate through the catalyst layer, which is measured by a new dimensionless parameter, h.
Presently, pure hydrogen gas is becoming economical to mass-produce by electrolysis. In addition, researchers have been investigating ways of reducing the CO content of hydrogen fuel before it enters a fuel cell as a possible way to avoid poisoning the catalysts. CO to form CO2, a much less harmful fuel contaminant. The challenge for the viability of PEM fuel cells today still remains in their cost and stability.