Complete Oxidation of Glycerol in an Enzymatic Biofuel Cell

Abstract

Glycerol has drawn increasing attention as a prospective fuel because it has many desirable qualities and is abundant due to the fact that it is a by-product of biodiesel production. Qualities such as nontoxicity, extremely low vapour pressure, low flammability and high energy density make glycerol very appealing as an energy source. Previous research has shown that partial oxidation of glycerol can occur at enzymatic bioanodes of biofuel cells utilising PQQ-dependent alcohol dehydrogenase (PQQ-ADH) and PQQ-dependent aldehyde dehydrogenase (PQQ-AldDH). In this paper, we describe the use of glycerol for a fuel in an enzymatic biofuel cell that utilizes a three-enzyme cascade on the anode that can accomplish the complete oxidation of glycerol. The bioanode that was developed contained PQQ-ADH, PQQ-AldDH and oxalate oxidase immobilised within a tetrabutylammonium-modified Nafion membrane. Our previous research has shown that glycerol is an effective fuel with the PQQ-ADH and PQQ-AldDH but still was unable to be fully oxidised. With the addition of oxalate oxidase, these glycerol/air biofuel cells have yielded power densities of up to 1.32 mW cm^–2, and have the ability to operate at high fuel concentrations. The oxidation products were confirmed with ¹³C NMR and comprised mainly ¹³C-labelled carbonate and glycerate.