Phosphoric acid fuel cells stack

Miki H, Shimizu A (1998) Dynamic characteristics of phosphoric-acid fuel-cell stack cooling system. Appl Energy 61 41-56... 

In the phosphoric acid fuel cell as currently practiced, a premium (hydrogen rich) hydrocarbon (e.g. methane) fuel is steam reformed to produce a hydrogen feedstock to the cell stack for direct (electrochemical) conversion to electrical energy. At the fuel electrode, hydrogen ionization is accomplished by use of a catalytic material (e.g. Pt, Pd, or Ru) to form solvated protons. 

Bipolar graphite plates having special channels for reactant supply and distribution over the entire electrode surface, which are now widely used in polymer electrolyte membrane fuel cell stacks, were for the first time used in phosphoric acid fuel cells. 

Oka Y (2009) Fuel Cells—Phosphoric acid fuel cells cells and stacks, encyclopedia of electrochemical power sources 568-578. doi 10.1016/ B978-044452745-5.00277-X... 

The cell stack assembly is the heart of the power plant which produces both electrical and thermal energy by electrochemically combining H2 in fuel and O2 in air. The basic description of a phosphoric acid fuel cell is shown in Fig. 12.2. 

Non-repeat components. The components described in the previous section are usually referred to as repeat components since every cell has those components with multiple cells present in a cell stack. Non-repeat components are those that are used only once in a cell stack. The main non-repeat components in a cell stack assembly are pressure plates, coolant inlet and outlet manifolds, reactant inlet and outlet manifolds, and manifold seals. Multiple cells placed between coolers are stacked between two stainless steel pressure plates and loaded axially to arotmd 60 psi with the help of tie rods that run the entire length of the cell stack. Reactant manifolds are then assembled onto the cell stack with manifold seals placed between the cell stack and the manifold. These reactant manifolds are made of stainless steel and coated with PTFE coating to prevent phosphoric acid attack of the manifolds. It is very essential to ensure that there are no pin holes in the PTFE coating for the same reason mentioned above. In phosphoric acid fuel cells, manifold seals made... 

Phosphoric acid fuel cells have been generally used in the initial commercialization of stationary fuel ceU systems. These enviromnentally friendly systems are simple, reliable, and quiet. They require minimal servicing and attention. Natural gas is the primary fuel however, other fuels can be used, including gas from local landfills, propane, or fuels with high methane content. All such fuels are reformed to hydrogen-rich gas mixtures before feeding to the fuel cell stack. Over 200 (phosphoric acid fuel cells) units, 200 kW each are currently in operation around the world [11]. 

Fig. 19.9 Phosphoric acid uptake in different bipolar plates after >3000 h HT-PEM fuel cell stack operation. The samples based on PPS and PVDF contained the same type of synthetic graphite, whereas the sample called...

An important aspect of the development of fuel cell stacks is to make them more compact, and a key to that is to develop thinner bipolar plates preferably from metal. Especially low temperature automotive PEMFC stacks have reached impressive power densities with metallic bipolar plates. However, because of the free phosphoric acid and the elevated temperature, research and demonstration of HT-PEMFCs has so far been done almost exclusively with plates of graphite and its composite materials. 

These cells operate only with hydrogen as the anode fuel and, moreover, the hydrogen must be pure since sulphur compounds and carbon monoxide adversely affect the performance of the Pt catalyst. Each cell consists of two teflon-bonded gas diffusion electrodes on a porous conducting support (see Fig. 10.21). At both anode and cathode the catalyst is platinum particles dispersed on carbon and a recent success has been a reduction in Pt loading from 10 mg cm to 0.75 mg cm ". The electrolyte is concentrated phosphoric acid absorbed onto a solid matrix and the cell operates at 200°C to improve the electrode kinetics. The cells are then mounted in stacks to increase the power output. 

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