Efficient electrocatalytic oxygen reduction by the ‘blue’ copper oxidase, laccase, directly attached to chemically modified carbons

Abstract

This discussion describes efforts to produce a stable, efficient electrocatalyst for four-electron O2 reduction through the direct attachment of fungal laccase, a 'blue' copper oxidase, to functionalised carbon electrode materials. Commercially available carbons, including fibrous and porous materials, offer important opportunities for achieving high conductivity over high surface areas that can be chemically functionalised. A promising approach for attaching laccase to a carbon surface is to use the diazonium coupling reaction to generate protrusive aromatic functionalities that can bind to hydrophobic residues close to the 'blue' Cu site: this site provides a fast, intramolecular electron relay into the buried trinuclear Cu active site that converts O2 rapidly and cleanly to H2O. This enhancement procedure makes possible the stable, direct electrocatalytic reduction of O2 at high potential with high efficiency in terms of turnover frequency per enzyme active site engaged with the electrode. The absence of electron-transfer mediators and simplicity of electrode system reveals the more inherent characteristics of the electrocatalytic mechanism that are masked in the waveform when a mediator is used. The study includes experiments to assess the effects of methanol and chloride ions on laccase electrocatalysis, complementing studies carried out by other groups, particularly those in which laccase is embedded in an electron-mediating gel.

Fabrication of high surface area graphene electrodes with high performance towards enzymatic oxygen reduction

“…If we consider the first step of the reaction mechanism as the rate limiting step, where α=β [45], a symmetry factor (β) of 0.5 is obtained, which is the typical value considered in this kind of systems. Therefore, the Tafel plot suggests that DET to the T1 site of the immobilised Lac is the rate determining step of the overall bioelectrocatalysis, in good agreement with previous work by other authors on Lac electrodes 18 [45,50,51]. However, in the case of our BOx-based electrode, α~2/3 is obtained from the Tafel slope value of 84 mV dec -1 .…”

Direct enzymatic bioelectrocatalysis: differentiating between myth and reality

“…Since its conception in 1978 where DET between a multicopper oxidase (MCO) (laccase) and a carbon electrode afforded enzymatic O 2 reduction, DET has evolved into an established ET pathway for many oxidoreductases, most commonly (but not limited to) laccase, bilirubin oxidase (BOx), nitrate reductase, hydrogenase and fructose dehydrogenase [31][32][33][34].…”

Biohydrogen for a New Generation of H2/O2 Biofuel Cells: A Sustainable Energy Perspective

“…[178][179][180][181][182] Following the same idea, graphite electrodes, either bare or modified by CNTs, were modified with aryl diazonium salts, [66] pyrene derivatives, [57,[183][184][185] or benzoic acid derivatives. [186] Accurate observations revealed a decrease in the hysteresis of the onset of O 2 reduction [57] related to the enzyme orientation of Sreptomyces coelicolor (Sc) LAC, which helps in the efficient bioelectrocatalysis in neutral media and in the presence of chloride.…”