Award details

Rapid electrocatalytic hydrogen cycling by enzymes: establishing the basis for future energy technology

Reference	BB/D52222X/1
Principal Investigator / Supervisor	Professor Fraser Armstrong
Co-Investigators / Co-Supervisors	Professor Kylie Vincent
Institution	University of Oxford
Department	Oxford Chemistry
Funding type	Research
Value (£)	358,442
Status	Completed
Type	Research Grant
Start date	03/10/2005
End date	02/02/2009
Duration	40 months

Abstract

The research involves novel electrochemical experiments on metalloenzymes known as hydrogenases that occur in microbial organisms to produce or oxidise hydrogen. Hydrogenases are important in the organisms because they are energy-producing catalysts. However, they can also be adsorbed on electrodes, in which form they show extremely high electrocatalytic activity, either in hydrogen production or hydrogen oxidation. They therefore offer an important solution to part of the future energy problem, which involves the production of hydrogen from electricity and conversion of hydrogen back to electricity. Indeed, we have been able to construct a fuel cell, with a hydrogenase adsorbed on the anode and a blue copper oxidase adsorbed on the cathode, that powers a light-emitting diode. Hydrogenases contain Fe or Fe and Ni at their active sites along with unusual carbon monoxide and cyanide ligands, and hydrogen is split heterolytically, which means the active site stabilises hydridic and protonic intermediates. Activity is attenuated, often permanently, by oxygen and carbon monoxide. These side reactions are poorly understood. The enzymes also contain Fe-S clusters to carry out long-range electron transfer, so that each enzyme molecule can exhibit several oxidation levels. These factors mean that hydrogenases are extremely complicated catalysts, and specific states that play important roles in catalysis or other transformations are difficult to generate for a spectroscopic or structural investigation. Their reactions will be studied by a suite of electrochemical techniques, known as protein film voltammetry, which has been developed in the Oxford laboratory and elsewhere. These techniques provide a highly detailed picture, both in terms of kinetics and energetics, of the different reactions that hydrogenases undergo, ranging from catalytic hydrogen cycling to inactivation by oxygen and carbon monoxide. We will investigate an important recent discovery of a hydrogenase that exhibits rapid catalytic hydrogen oxidation in the presence of carbon monoxide, and observation that is remarkable both in terms of the mechanistic insight and the technological implications that are highlighted. We will refine details of structurally characterised hydrogenases that are not resolved by conventional investigations. We will commence a program to detect and characterise hydrogenase activities in crude cell samples, identifying microbes that host hydrogenases having particular potential for interesting properties and technological development. This research will underpin the exploitation of hydrogenases as technological catalysts, either directly as stabilised enzyme-electrodes or by providing the knowledge required to design synthetic systems that will achieve high activity, specificity and stability.

Summary

Use of fossil fuels, particularly oil, is such a part of our lives that few realise that these resources are running out rapidly, although most of us are well aware of the greenhouse effect attributed to the release of carbon dioxide from carbon-stores that have rested for over a billion years. In fifty years time there will be little gas or oil left, and our freedom to drive a car or travel in a plane will almost certainly depend on how we develop renewable energy resources. Hydrogen is a crucial component of future energy as it provides the important link between electricity (which will have to come from solar, geo or nuclear primary sources) and chemicals (which are required as stored fuels for combustion and electricity (fuel cells) and for the chemical industry). In electro-hydrogen technology, which can be entirely `green¿, water is converted into hydrogen (electrolysis); the hydrogen is then used directly as a combustion fuel (eg cars) converted into hydrocarbon compounds (to use as a fuel or as a raw material for chemicals) or back into electricity (in a special battery known as a fuel cell). Electrolysis is a particularly useful use of surplus electricity that is generated during low demand (it is not feasible to shut down nuclear reactors and a waste of energy to shut down wind turbines). Electrocatalytic hydrogen cycling requires a catalyst otherwise it is either far too slow to occur or relies on an excessive input of energy (electrolysis) or voltage loss (fuel cell). At present, the electrocatalyst consists of platinum or composites that include platinum metals. These are expensive materials, and platinum is still far from being a perfect catalyst; it is poisoned by carbon monoxide and sulphur-containing chemicals, and it is not a specific catalyses side reactions, including reduction of oxygen. So where do microbes fir in? Microbes use and produce hydrogen, for which they have special catalysts (enzymes) known as hydrogenases. These convert hydrogen into water and electrons and vice versa. The hydrogenases can be extracted from the cells and we have discovered how to attach them to electrodes so that their activity can be harnessed. Thus when hydrogen is present, a current is induced! Conversely, water is converted into hydrogen when we apply a potential. Being on an electrode also provides us with a special way to study these enzymes because we can vary the potential of the electrode to move electrons in or out and measure the rates and energies that are involved. The resulting shape of the current-potential dependence gives important information on how the enzyme works and guides us to make judgments about how we could make improvements by chemical or genetic modification. We can also use this information to help design synthetic catalysts. We are able now to evaluate a whole range of hydrogenases from different organisms, some producing hydrogen and others oxidising hydrogen, some even resistant to poisons such as CO, to learn how to use them as catalysts that will help us to use hydrogen and have a clean, green future.

Committee	Closed Committee - Engineering & Biological Systems (EBS)
Research Topics	Bioenergy, Industrial Biotechnology, Microbiology
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

I accept the terms and conditions of use (opens in new window)

export PDF file

back to list new search