NEWS

8Membrane Technology September 2008

FEATURE

In the USA, engineers working at the Massachusetts Institute of Technology (MIT) claim they have improved the power output of one type of fuel cell by more than 50% through tech-nology that could help these environment-friendly, energy storage devices find a much broader mar-ket, particularly in portable electronics.

According to the research team, the new material – key to the work – is also consider-ably less expensive than its conventional indus-trial counterpart, among other advantages.

Replacement‘Our goal is to replace traditional fuel-cell mem-branes with these cost-effective, highly tunable and better-performing materials,’ said Paula Hammond, Bayer Professor of Chemical Engineering and leader of the research team. She notes that the new mate-rial also has potential for use in other electrochemi-cal systems such as batteries.

Like a battery, a fuel cell has three principal parts: two electrodes (a cathode and anode) sepa-rated by an electrolyte. Chemical reactions at the electrodes produce an electronic current that can be made to flow through an appliance connected to the battery or fuel cell. The principal differ-ence between the two sources of power is that fuel cells get their energy from an external source of hydrogen fuel, while conventional batteries draw from a finite source in a contained system.

Direct methanol fuel cellsThe MIT team focused on direct methanol fuel cells (DMFCs), in which the methanol is directly used as the fuel and the reforming of alcohol into hydrogen is not required.

Such a fuel cell is attractive because the only waste products are water and carbon dioxide (and the latter is produced in small quantities).

Also, because methanol is a liquid, it is easier to store and transport than hydrogen gas, and is safer (in that it will not explode). Methanol also has a high energy density – a little goes a long way – making it especially interesting for port-able electronic devices.

LimitationsThe DMFCs currently available on the market have limitations. For example, the material currently used for the electrolyte ‘sandwiched’ between the electrodes is expen-sive. Even more important, materials such as Nafion are permeable to methanol, which allows some of the fuel to seep across the centre of the fuel cell.

Among other disadvantages, this wastes fuel and lowers the efficiency of the cell because the fuel is not available for the reactions that gener-ate electricity.

Alternative materialUsing a relatively new technique known as layer-by-layer assembly, the MIT researchers created an alternative material to Nafion.

‘We were able to tune the structure of [our] film a few nanometres at a time,’ commented Professor Hammond – essentially getting around some of the problems associated with other approaches. The result is a thin film that is two orders of magnitude less permeable to methanol but compares favourably to Nafion in proton conductivity.

To test their creation, the engineers coated a Nafion membrane with the new film and incor-porated the whole unit into a direct methanol fuel cell. The result was an increase in power output of more than 50%.

The team is now exploring whether the new film could be used by itself, completely replacing Nafion. To that end, they have

been generating thin films that stand alone, with a consistency much like plastic wrap.

SupportThis work was supported by the DuPont–MIT Alliance throughout 2007. It is currently sup-ported by the National Science Foundation.

This research has been reported in a paper by Hammond, Avni A. Argun and J. Nathan Ashcraft, entitled ‘Highly conductive, metha-nol resistant polyelectrolyte multilayers’, which appears in a recent issue of Advanced Materials (Volume 20, Issue 8, pages 1539–1543; DOI: 10.1002/adma.200703205). Argun is a post-doctoral associate in chemical engineering and Ashcraft is a graduate student in the same depart-ment at MIT.

PhotovoltaicsIn addition, Hammond and colleagues have begun exploring the new material’s potential use in photovoltaics.

That work is funded by the MIT Energy Initiative. This Institute-wide initiative includes research, education, campus energy management and outreach activities – an interdisciplinary approach that covers all areas of energy supply and demand, security and environmental impact.

(PolyFuel Incorporated, a US company that specialises in engineered membranes for fuel cells, has developed the first functional ver-sion of its prototype power supply for note-book-class computers. For further details, see ‘PolyFuel develops prototype fuel-cell power supply for notebook computer’, on page 1 of this issue.)

Contact:

Paula Hammond, Bayer Chair Professor of Chemical

Engineering, Executive Officer, Department of Chemical

Engineering, Massachusetts Institute of Technology,

Room 66-546, 77 Massachusetts Avenue, Cambridge,

MA 02139, USA. Tel: +1 617 258 7577, Email:

hammond@mit.edu, http://web.mit.edu/hammond/lab

New material for fuel cells increases power output by more than 50%In the USA, engineers at the Massachusetts Institute of Technology have significantly improved the power output of a direct methanol fuel cell by using a new material that is also considerably less expensive than conventional membranes. Here, we briefly look at the technology.

FEATURE

September 2008 Membrane Technology9

In the USA, Koch Membrane Systems (KMS) of Wilmington, Massachusetts, has been select-ed to provide Puron membrane modules for a membrane bioreactor (MBR) wastewater treat-ment plant at the Vacation Village Resorts in Hancock, Massachusetts.The installation, which is built ‘below grade’, is the first use of Puron modules in a private development project in the USA, says the firm.

Retrofitted

Vacation Village has selected Puron PSH 500 membrane modules to be retrofitted into an existing biological wastewater treatment system.The entire plant will be installed with most of the equipment located underground to preserve the aesthetic characteristics of

the environment at the Berkshires-based resort, while still providing premium waste-water treatment. Vacation Village Resorts is the brand name of The Berkley Group Incorporated, an employee-owned company founded during 1981. The resort offers 364 fully furnished suites decorated in a traditional New England style and includes furnished balconies with mountain views, pools, jacuzzi, fitness room, arcade, Internet room and many other amenities. Through its affiliates, The Berkley Group owns and operates dozens of timeshare resorts throughout the USA.

High-quality effluent‘The project not only allows the resort to expand, but the plant upgrade will also produce high-qual-

Amorphous metal alloy catalyst improves efficiency of DMFCs and reduces their costA chemist at the University of the Basque Country in Spain has developed an amorphous metal alloy catalyst that is expected to make it possible to make cheaper and more efficient direct methanol fuel cells (DMFCs).

Graduate research student José E. Barranco, a Ph.D candidate at the University of the Basque Country, focused his thesis on the development of new metallic materials of an amorphous nature for use in DMFCs.

Lower quantities of expensive platinumThe catalyst normally used in DMFCs is expensive platinum, so Barranco’s aim was to devise a catalyst composed of a metal alloy containing significantly lower quantities of the metal. His research focused on a fundamental problem – the electro-oxidation

of methanol produces CO, which adheres to the metal and inhibits its catalytic activity. After inves-tigating several metals, Barranco made alloys that enabled the reduction of the proportion of plati-num to 1%. These alloys, composed of elements such as nickel, niobium, antimony or ruthenium, among others, can convert CO into CO2, which does not adhere to the catalyst.

Increasing efficiencyOnce a suitable catalyst was found, Barranco set out to increase its efficiency. He found that if the platinum alloy is structured amor-phously, its electrical conduction properties are enhanced and it undergoes less corrosion – an advantage for the medium in which it will operate. Moreover, its activity is on the order of 80–100 times greater than crystalline platinum.

Also, for the catalyst, made on this basis of amorphous metal alloys, to be incorporated into the fuel-cell membrane, Barranco decided to change its form. The result is a very fine powder that is placed in a container and used to ‘spray paint’ the membrane.

An additional benefit of this approach is that it further enhances catalyst activity by a factor of 9–13. It is claimed that this catalyst is able to improve overall DMFC efficiency by more than 50%.

Alcohols oxidation fuel cell researchBarranco’s work falls within the remit of the alcohols oxidation fuel cell research being undertaken in the Industrial Chemistry & Electrochemical Engineering Laboratory at the Polytechnic University School in Donostia-San Sebastián. A research group led by Dr Ángel Rodríguez Pierna aims to develop a DMFC solely and totally devised at this lab.

Contact:

Professor Ángel Rodríguez Pierna, Industrial

Chemistry & Electrochemical Engineering Laboratory,

Polytechnic University School, Donostia-San

Sebastián, Spain. Tel: +34 43 455022 ext. 2420,

Email: iapropia@sp.ehu.es,

www.sc.ehu.es/iaweb/ESP/presesp.htm

News from Koch Membrane Systems published earlier this year covered the first municipal order that the company had received from Spain for its Puron modules. These are being used in a membrane bioreactor plant sited at Ontígola in the province of Toledo. The case studies that appear here provide details of a further two projects which, according to the manufac-turer of membranes and membrane-based separation and filtration systems, involve an area and application where the technology is again being used for the first time.

Holiday resort and fruit juice producer benefit from using membrane modules