Alkaline Polymer Electrolyte Fuel Cells

Lead Research Organisation: Cranfield University
Department Name: Cranfield Defence and Security


The first viable large scale fuel cell systems were the liquid electrolyte alkaline fuel cells developed by Francis Bacon. Until recently the entire space shuttle fleet was powered by such fuel cells. The main difficulties with these fuel cells surrounded the liquid electrolyte, which was difficult to immobilise and suffers from problems due to the formation of low solubility carbonate species. Subsequent material developments led to the introduction of proton-exchange membranes (PEMs e.g. Nafion(r)) and the development of the well-known PEMFC. Cost is a major inhibitor to commercial uptake of PEMFCs and is localised on 3 critical components: (1) Pt catalysts (loadings still high despite considerable R&D); (2) the PEMs; and (3) bipolar plate materials (there are few inexpensive materials which survive contact with Nafion, a superacid). Water balance within PEMFCs is difficult to optimise due to electro-osmotic drag. Finally, PEM-based direct methanol fuel cells (DMFCs) exhibit reduced performances due to migration of methanol to the cathode (voltage losses and wasted fuel).Recent advances in materials science and chemistry has allowed the production of membrane materials and ionomers which would allow the development of the alkaline-equivalent to PEMs. The application of these alkaline anion-exchange membranes (AAEMs) promises a quantum leap in fuel cell viability. The applicant team contains the world-leaders in the development of this innovative technology. Such fuel cells (conduction of OH- anions rather than protons) offer a number of significant advantages:(1) Catalysis of fuel cell reactions is faster under alkaline conditions than acidic conditions - indeed non-platinum catalysts perform very favourably in this environment e.g. Ag for oxygen reduction.(2) Many more materials show corrosion resistance in alkaline than in acid environments. This increases the number and chemistry of materials which can be used (including cheap, easy stamped and thin metal bipolar plate materials).(3) Non-fluorinated ionomers are feasible and promise significant membrane cost reductions.(4) Water and ionic transport within the OH-anion conducting electrolytes is favourable electroosmotic drag transports water away from the cathode (preventing flooding on the cathode, a major issue with PEMFCs and DMFCs). This process also mitigates the 'crossover' problem in DMFCs.This research programme involves the development of a suite of materials and technology necessary to implement the alkaline polymer electrolyte membrane fuel cells (APEMFC). This research will be performed by a consortium of world leading materials scientists, chemists and engineers, based at Imperial College London, Cranfield University, University of Newcastle and the University of Surrey. This team, which represents one of the best that can be assembled to undertake such research, embodies a multiscale understanding on experimental and theoretical levels of all aspects of fuel cell systems, from fundamental electrocatalysis to the stack level, including diagnostic approaches to assess those systems. The research groups have already explored some aspects of APEMFCs and this project will undertake the development of each aspect of the new technology in an integrated, multi-pronged approach whilst communicating their ongoing results to the members of a club of relevant industrial partners. The extensive opportunities for discipline hopping and international-level collaborations will be fully embraced. The overall aim is to develop membrane materials, catalysts and ionomers for APEMFCs and to construct and operate such fuel cells utilising platinum-free electrocatalysts. The proposed programme of work is adventurous: however, risks have been carefully assessed alongside suitable mitigation strategies (the high risk components promise high returns but have few dependencies). Success will lead to the U.K. pioneering a new class of clean energy conversion technology.


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Mamlouk M (2011) Characterization and application of anion exchange polymer membranes with non-platinum group metals for fuel cells in Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy

Description Despite being around for over 150 years, fuel cells have never been commercialised as an everyday power source due to a number of reasons, including cost and component stability. The Alkaline Polymer Electrolyte Fuel Cell (APEFC) is a new class of fuel cell where much pioneering work has been carried out in UK universities. The main motivations for developing this fuel cell are: there is no liquid electrolyte; non-precious catalysts can be utilised at the electrodes eg. nickel and manganese oxide, which are much cheaper and more abundant than the catalysts required for other types of fuel cell (eg. platinum, ruthenium);there are more materials that are corrosion resistant in alkali than in acid environments and nonfluorinated membranes are feasible.

This research programme involves the development of a suite of materials and technology necessary to implement the
APEFC. A consortium of four Universities, Cranfield University, Imperial College, University of Newcastle and University of Surrey will undertake research to develop the components required.

The research carried out by Cranfield University as part of this project was based on the synthesis and characterisation of alkaline anion exchange membranes (AAEM) using radiation grafting. Radiation grafting is a process whereby a polymer sheet can be modified using suitable monomers to produce polymers with the additional properties of the monomer (eg. ion conductivity, water uptake) while retaining the integrity of the original polymer film. This technique has been used commercially for a number of years for making battery separator membranes.

The key outcomes of this work are summarised below:

1. Methodology

AAEMs have been successfully synthesised from various hydrocarbon and fluoropolymer films of different thicknesses using various radiation grafting techniques. A number of chemistries have been investigated and tested. The membranes were characterised by simple tests, such as areal resistivity and ion exchange capacity to asses their suitability for fuel cell use. Membranes with the most promising properties were passed onto the other universities for further characterisation and fuel cell tests.

2. Membrane cost reduction

The cost of the producing these membranes was cut significantly by reducing the amount of monomer required by a factor of 10 for the mutual grafting reaction. An alternative technique was also developed, emulsion grafting (using water instead of solvents) which decreased the amount of monomer used even further, reducing the environmental impact of the membrane production process significantly. The most successful membranes synthesised were based on low density polyethylene (LDPE), a relatively cheap and abundant starting material.

3. Scale Up

It has been demonstrated that the membrane production process can be scaled up. Mutually grafted membranes can be made in sizes of 0.3m x 20m and the emulsion technique had been scaled up from pieces 10cm x 5cm to 0.3m x 1m, with scope to increase this; showing that this is a viable process for commercialisation.

4. Stability

These membranes have been shown to be stable in an alkali environment for at least 6 weeks at elevated temperature. Membranes based on LDPE and ethylene tetrafluoroethylene were shown to be stable in an oxidative environment.

5. Performance

Newcastle University have shown that selected Cranfield membranes have high conductivity in the temperature range 20- 90degC from 0.03 to 0.068 S/cm (Cl- form), easily meeting one of the project's objectives. These were also tested in an APEFC (University of Newcastle) and have achieved the highest peak power densities reported in the literature to date. At a high potential of 500 mV, peak power densities of 823 mW cm-2 at 60degC, 718 mW cm-2 at 50degC and an outstanding peak power density of 648 mW cm-2 at 20degC under oxygen (atm).
Exploitation Route Using the radiation grafting route, low cost, repeatable anionic anion exchange membranes were produced with good conductivity, chemical & physical stability. Methods were developed to reduce the amount of solvent required for the manufacture of these membranes. These membranes could be used and further developed for Alkaline Polymer Electrolyte Membrane Fuel Cells to find out whether this would be a true alternative to the more conventional Solid Polymer Electrolyte Membrane Fuel Cell that uses an acidic membrane.
Sectors Energy,Transport,Other

Description Findings proved that this type of fuel cell may be a viable alternative to the polymer electrolyte membrane fuel cell.
First Year Of Impact 2012
Sector Other