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Developing environmentally friendly fuel

Introduction

My name is Nick and I am a first year PhD student at the Manchester Institute of Biotechnology. At school I studied physics, maths and computing at A-level and then went on to study physics at the University of Manchester (BSc and MSc). My PhD research involves trying to find out how the structure of redox enzymes affects their redox potential. The redox potential is an important factor that needs to be considered in the design of biofuel cells. Biofuel cells use enzymes to help produce electricity from hydrogen and oxygen, with water as a waste product.

In depth

The redox potential (E⁰) tells you how likely a chemical species will accept an electron. When a chemical species accepts and electron, we say it has been reduced. The more positive the redox potential, the more likely it is that a chemical species will accept an electron and be reduced. The below reaction has a positive redox potential, so a copper ion will tend to accept an electron to become a copper atom.  

Cu⁺  +  e^-  ↔  Cu  (E⁰ = +0.52V)

A chemical species may have a negative redox potential. This means it is more likely to lose an electron. When a chemical species loses an electron we say is has been oxidised. The more negative the redox potential, the more likely it is that a chemical species will lose an electron and be oxidised. The below reaction has a negative redox potential, so a sodium atom will tend to lose an electron to become a sodium ion.

Na⁺  +  e^-   ↔  Na    (E⁰ = -2.71V)

Enzymes are a type of biological molecule which catalyse (increase the rate of) the chemical reactions that sustain life. Redox enzymes contain a metal ion which can either be reduced or oxidised. They help control the rate of many different reactions which involve the transfer of electrons. The structure of the enzyme around the metal ion influences the redox potential of the metal ion. Below is an image of an enzyme called Azurin, which has a Cu²⁺ ion in its active site.  The way in which the Azurin is bound to the copper ion affects how easily it can accept an electron.

You might be familiar with the idea that electricity is the flow of charge particles. For example, electrons flow in the wires that make up the electrical devices we use. Electricity can be made in many different ways, some more environmentally friendly than others. Biofuel cells utilise enzymes to help make electricity using hydrogen and oxygen and producing water as the only waste product. The redox enzymes help transfer the electrons through the cell which generates electricity. One enzyme takes electrons from hydrogen and passes them through the cell. The other enzyme collects the electrons and then uses them to make water.