The Environmental Engineering Hub

The California Energy Commission has voted to approve an $8 million grant for the development of a high-capacity hydrogen fueling station. In a statement Wednesday the Commission said the fueling station, at the Port of Long Beach, would be used to service and promote the expansion of zero-emission fuel cell electric Class 8 drayage trucks. Drayage trucks are used to take freight from ports to warehouses and other locations, the Commission said. The Commission added that the promotion of zero-emission vehicles would help to "reduce greenhouse gas emissions and air pollution at the nation's second busiest container port." The station, according to the Commission, will source its hydrogen "from 100 percent renewable biogas." Hydrogen is becoming an attractive fuel source for many types of transport. A fleet of hydrogen fuel cell buses is currently in operation in the Scottish city of Aberdeen. In September, European railway manufacturer Alst...

Conduction is the process which dictates the transport of charges through the fuel cell layers, except for the membrane. That means that the lack of adequate contact between the diffusion layer, bipolar plates and cooling plates is the cause of most of the ohmic losses outside of the membrane. There is where most of the overall ohmic loss occur. To help solving that problem, either the membrane needs to be made thinner, or its material needs to be more conductive. History and tests given that, have told us that making the membrane thinner is easier than the alternative. The challenge with making the membrane material more conductive balancing that property with its thermal and chemical stability.  The image below describes the relationship between membrane thickness and local conductivity: Source: SPIEGEL, Colleen.  PEM Fuel Cell Modeling and Simulation Using MATLAB ® .  Burlington, MA, USA: Academic Press, 2008. 440 p.

California dominates the scene when it comes to having hydrogen fuel cell refueling stations in the United States. In 2013, the New York Times reported 10 stations in the country, with one located in Columbia, SC, eight in Southern California and one in Emeryville. In 2016, that number increased to 31 stations in the US, with California having the most of them (28). Iceland used to have a refueling station for three buses for the public transport of Reykjavik, which operated from 2003 to 2007.  The station had the capacity of generating its own hydrogen through a electrolyzing unit. Japan is one of the countries with the greatest number of hydrogen fuel cell refueling stations. Up May 2017, they had 91 stations. Sources:  Berman, Bradley. "Fuel Cells at Center Stage" , New York Times, 24 November 2013, p. AU1.   Alternative Fueling Station Counts by State , Alternative Fuels Data Center, accessed December 2, 2016.   ECTOS 2003-7" , Icelandic New Energy, a...

For a fuel cell to run efficiently, there needs to be proper control of its temperature and heat generation. Some fuel cells work well in room temperature, but others require temperatures as high as 1000 ºC, and any value outside of the accepted range results in lowered efficiency of the device. Higher temperatures lead to faster kinetics and voltage, and lower temperatures cause shorter warm-up times, lower thermodynamical stresses and retardation of corrosion and other temperature-dependent processes. For fuel cells, higher temperatures also mean greater vaporization of the liquid water and, as a result, more of the waste heat becomes the latent vaporization heat.  The temperature profile in a fuel cell is ever-changing, even when the flow rate of the gases is constant. That happens because of the transfer of heat and phase change of some reactants. The accurate prediction of the temperature and heat distribution is essential to determine temperature-dependent parameters a...

The main objective when design flow fields is balancing the pressure drop and the amount of gas that is distributed to the GDL and catalyst layers. Parallel, serpentine and interdigitated designs are the most popular for fuel cell channels. In relatively small fuel cells, the serpentine design is usually used because the hydrogen reaction is not rate limiting and water blockage in the humidified anode can happen. In the image below, you can see a serpentine flow field design. The flow path is continuous and relatively efficient in distributing gas across the fuel cell. However, since the path is longer than in other designs, pressure loss might be a problem. One advantage of the design if that a block in the path does not compromise activity downstream. A disadvantage is that more gas needs to be input into the fuel cell because the design favors the depletion of the components. Another disadvantage is the build up of water in the cathode during extended periods of operation of ...

The Gibbs free energy changes vary with temperature, pressure and gas concentration in fuel cells. Take into account the following generation reaction: j J + k K → m M Where k moles of K react with j moles of J to generate m moles of M. Both the reactants and products have an associated 'activity'. We can call this 'activity' a, aj and ak for the reactants and am for the product activity. When gases behave close to ideal conditions (as is the case with fuel cells), we know that: a=P/P0 Where P is the pressure/partial pressure of the gas and the standard pressure is P0 (around 0.1 MPa). This simple equation is useful because fuel cells are, in a general way, gas reactors. When dissolved chemicals are involved, the activity can be linked to the molarity or strength of the solution. The case of water in fuel cells is complex to deal with, but in steam form, it can be stated that the activity of water is equal to the partial pressure of water divided by...