Oxford University Crest

The Armstrong Research Group
Inorganic Chemistry Laboratory

Third floor ICL, rooms: T7–T12, T17
Phone: T12 (Fraser’s office): +44 (0)1865 272647
e-mail: fraser.armstrong@chem.ox.ac.uk

Enzymatic Fuel Cells

Fuel cells are devices which interconvert chemical and electrical energy. Conventional fuel cells use precious metals such as Pt as both the anode and cathode catalysts, and use fuels such as H2 as energy sources. Our research is focussed on using enzymes to catalyse the oxidation of H2 to protons, and in coupling this reaction to an enzyme-catalysed reduction, such as that of O2 to O2-, producing water and electricity as the only products.

The enzymes which catalyse the oxidation of H2 are known as hydrogenases. As shown, (right) the active site is buried deep within the protein matrix and is electrically linked to the surface via a chain of three [Fe-S] clusters. O2 reduction is catalysed by multi-copper enzymes known as laccases and bilirubin oxidases. Alternatively, other oxidants can be used; for example, fumarate can be reduced to succinate by fumarate reductase.

One of the major advantages of using enzymes over precious metals as fuel cell catalysts is that they are specific (i.e. they catalyse only one reaction). For example, whilst Pt catalyses both the oxidation of H2 and the reduction of O2, thus requiring a proton exchange membrane (PEM) to separate the anode and cathode compartments of the fuel cell, a hydrogenase-coated anode and a laccase-coated cathode can be placed in the same compartment, meaning that, in theory at least, biofuel cells can be incredibly tiny. In addition, there is no need to separate the fuel and oxidant, and indeed a mixture of dilute H2 in air (below the combustion limit of 4% H2 in air) can be used as an energy source.

Enzymes can also be tolerant of chemical species that are usually considered as poisons to conventional catalysts. For example, the membrane-bound hydrogenases from Ralstonia eutropha H16 and Ralstonia metallidurans CH34 can oxidise H2 even in an excess of CO. By contrast, even ppm (parts per million) levels of CO irreversibly poison conventional Pt catalysts, although some alloys, such as Pt-Bi, do show enhanced resistance to damage by CO. The tolerance of Ralstonia hydrogenases to CO has great implications for technology development, as it means that the hydrogen used does not need to be highly purified - a considerable financial advantage to fuel cell development.

A ribbon representation of the crystal structure of the [NiFe]-hydrogenase from D. gigas.
[NiFe]-hydrogenase from D. fructosovorans
A ribbon representation of the crystal structure of Laccase from Trametes versicolor, showing the copper atoms.
Laccase from T. versicolor

The work done in the Armstrong group on developing the biofuel cell has recieved considerable recognition in the last few years. Although work is still at a "proof-of-concept" stage, and many fascinating challenges are still waiting to be solved, we recently received the Carbon Trust's "Low Carbon Innovator of the Year Award 2003" (Academic Institutions and R&D Facilities Category). Our work has been published in various journals, including recent publications in PNAS (Proceedings of the National Academy of Sciences), Chemical Communications, and Dalton Transactions.

Carbon Trust Innovation Award Winners 2003
Carbon Trust Innovation Award Winners 2003
Carbon Trust Innovation Award Presentation 2003
Carbon Trust Innovation Award Presentation 2003

Left to right: Dr Aj Sharman (Environmental Technology Manager, Begbroke Science Park University of Oxford), Jasmine Pandher (ISIS Innovation), Dr Kylie Vincent, Kirsty Young (presenter of Five Live News) Tom Delay, Chief Executive of the Carbon Trust, and Professor Fraser Armstrong.

Relevant publications:

Our work on biofuel cells is protected by patent. For further information, visit the Isis Innovation Website.