Fuel cell modeling and optimization

Detailed analysis of the membrane physics, chemistry and electrochemistry. This is fundamental to understanding the operation of the cell and ultimately the fuel cell stack and system.

What are the rate-limiting phenomena? Which parameters (for example, kinetic rate constants) have a critical impact on operation and therefore need to be determined as accurately as possible through further R&D?

Accurate determination of the flow channel architecture. Is the current design effective? Are there areas that are starved of fuel or air? Are there significant temperature differences across the wafer?

What sort of temperature differentials are seen when changing load rapidly? How will modifications to the flow channel patterns affect these?

Materials analysis, ranking and selection. Given the temperature differentials determined above, which materials are likely to be able to withstand thousands of hours of operation?

Which materials can be screened out immediately, thus saving lengthy and costly testing?

Heat transfer. How well does the stack dissipate heat under normal operating conditions? Are local hot spots generated during load changes, leading to early loss of effectiveness of areas of the cell?

Water and heat recovery. Is the water recovery unit correctly sized? How does it interact with the rest of the tightly-integrated fuel cell flowsheet? What degree of heat integration can be achieved, bearing in mind the dynamic performance requirements?

Fuel preparation system. What is the optimal reformer design? What is the optimal level of heat integration? How does the integrated system work under load changes? What level of additional heat source needs to be required for start-up?

Determine optimal operating conditions. What are the optimal feed concentrations for the maximum cell voltages for the required current densities? What is the optimum operating temperature and fuel to air mix?

Catalyst. Is it possible to reduce the amount of platinum in the catalyst? What formulation minimises production of carbon monoxide? How do you reduce temperatures in critical areas to avoid catalyst burnout?

Water management (PEMFCs). Is hydration too fast or too slow during load changes? What other key issues need to be resolved?

Control scheme design and verification. What is the optimal control configuration required to maintain a steady ratio between reactant and oxygen, while balancing all the other system requirements?

What are the optimal control parameter settings to ensure the required behaviour for a variety of typical operating scenarios? How do you manage temperature in the cell to avoid damage through thermal loading?

Investigate system interactions. Fuel stack designs are often made on an assumption of the performances of the system, and vice versa. Modelling allows investigation of the interactions across the tightly-integrated fuel cell flowsheet.

Build-up of poisons. What is the likely build-up of destructive chemicals over the lifetime of the cell? Which operations are most likely to result in poisoning? What are the optimal operating conditions and strategies to avoid these?

Start-up and load change. What is the optimal start-up policy to get to required production in the minimum time while remaining within critical material and other operating constraints? What level of auxiliary heating is required during start-up? How does the system perform during load changes? What sort of temperature differentials are observed in critical materials? How can you optimise performance?

Durability. As with catalyst degradation in chemical reactors, advanced simulation can be used to simulate the ageing behaviour in cell materials and determine operating conditions – furnace temperature, current density and cell potential – that limit it. Time requirements can be reduced through modelling from thousands of hours of physical testing.