TiO2 particles properties

The most common reaction at the anodic side of biofuel cells is the oxidation of sugars which relies on the catalytic properties of oxidases. This class of enzymes has, however, usually poor potential for direct ET. Direct ET on the anodic site was, however, described for a number of hydrogenases [235, 236] and cellobiose dehydrogenase [225, 237, 238]. Enzymatic catalysis by means of direct ET was also realized on conducting graphite or TiO2 particles [239, 240]. 

Okazawa T, Kohyama M, Kido Y. 2006. Electronic properties of Au nano-particles supported on stoichiometric and reduced TiO2(110) substrates. Surf Sci 600 4430-4437. 

On the other hand, the study of CO oxidation performed by Goodman et al. [10] on a Au/TiO2(110) model catalyst, led them to propose that the whole reaction takes place on the gold particles, providing that the latter are small and bi-dimensional they do not exhibit metallic properties any longer due to quantum size effect. 

The study on Au/TiO2(110) model catalyst performed by Goodman et al. [10] is the first study to lead to the proposal of a reaction mechanism on gold particles only . According to these authors when gold metal particles are small enough and bi-dimensional (Section 15.4.1), they lose their metallic properties due to the quantum size effect (band gap of 0.2-0.6eV), and become an active catalyst (Fig. 15.6). The role of the support would be to stabilise the small gold particles. 

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