Rational Design of Redox Mediators for Application to Enzymatic Fuel Cells

Enzymatic fuel cells (EFCs) based on mediated electron transfer involve the ‘wiring’ of enzymes at the anode and cathode using redox mediators. The potential difference between the redox mediators used at the anode and cathode can influence the cell voltage and, consequently, the power output of the EFC.^1,2 In addition, the potential difference between the redox mediator and the enzyme binding site can influence the rate of electron transfer (as predicted by Marcus theory) and hence, the catalytic turnover at each electrode. Ideally, for maximum power output, the catalytic reactions at each electrode should occur at low overpotentials (to ensure a large cell voltage) with a high catalytic turnover of substrates. Therefore, judicious choice of enzyme and redox mediator combination at the anode and cathode is essential. For example, it has been proposed that, at the anode, the redox potential of an electron mediator should have a value of about 50 mV downhill of the enzyme active site to generate current with minimal loss in cell voltage.³Although, under physiological conditions, the redox potential of the binding site of a wild type enzyme is, for the most part, fixed there is scope to manipulate the electronic character of the redox mediator. Here, we present an approach for the rational design of metal complexes which possess desirable electrochemical characteristics to act as redox mediators for specific enzymes, such as glucose oxidase, in an effort to maximise EFC power output.

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2. P. Kavanagh, D. Leech, Phys.Chem. Chem. Phys., 2013, 15, 4859-4869

2. A. Heller, AIChE J., 2005, 51, 1054–1066.