Three-dimensional laccase electrodes for miniaturised fuel cell power sources

Laccase is a protein excreted by white-rot fungi that works as well or better than precious metals at catalysing the reduction of oxygen to water. This chemical reaction is central to almost all low-temperature fuel cells that work in air.Fuel cells are devices that convert chemical energy from a fuel like methanol or hydrogen directly and efficiently into electrical energy. In contrast, when fuel is burned in a generator, the fuel's chemical energy is converted into thermal energy (hot gases) and mechanical energy (moving pistons) before it becomes electrical energy. Each energy conversion step has losses from heat loss and friction and from inescapable inefficiencies governed by the laws of thermodynamics; fuel cells, on the other hand, can have greater efficiencies by bypassing these intermediate stages.In most fuel cells the oxygen reduction reaction takes place on the surface of particles of expensive precious metals (usually platinum). Laccase catalyses the same reaction using only four copper atoms per enzyme molecule. Laccase catalysis is more energetically efficient, nearly as rapid, and more selective against catalyst-killing gaseous impurities.There are two key problems with using laccase in fuel cells. The first is stability: enzymes are complex and often fragile biological polymers that need to be properly oriented to work in a fuel cell. However, I have developed a technique that extends the working lifetime of laccase in a fuel cell from hours to several months. The second is the amount of electric current that is generated from a given area or volume. The platinum surface can host thousands of reactions at once while the each laccase molecule can only react one oxygen molecule at a time. To compensate for this, I am proposing introducing laccase into porous, three-dimensional electrode materials, essentially taking laccase from working on a open plain and moving it to a multi-storey office complex. For laccase to function as efficiently as possible, it needs to have its reaction needs met: a good supply of oxygen (fast gas diffusion), a constant concentration of hydrogen ions (buffered pH), and a well-connected electrical supply. Designing and building this infrastructure requires a thorough understanding of the interactions between the enzyme's surface and the surface to which it is attached and careful control of how material flows through the pores. Extending the surfaces into the third dimension lets us make more compact power sources that are suitable, for example, for small electronics like portable music players and mobile phones.Most of the surface area of porous materials is on the inside of the structure and probing an interior surface is always a challenge. I will use small gaseous molecules explore the interior, high-energy beams of metal ions to cut open the structure, high-resolution electron microscopy to examine it, and electronic and spectroscopic methods that can interrogate the interaction between the enzyme and a surface.This work is supported by an active, ongoing collaboration with experts in fungal biology. They are currently working on understanding the molecular biology behind laccase, first to mass produce the enzyme, followed by genetic engineering to change laccase's catalytic behaviour, selectivity and surface interactions.In addition to portable fuel cells that work at ambient temperatures, we may also discover more efficient, less expensive catalysts and learn how enzymes are able to carry out the oxygen reduction reaction with copper, a common metal from the first row of the transition metals, rather than platinum, a rare and expensive metal from the third row.