O₂Reduction in Enzymatic Biofuel Cells

Abstract

Catalytic four-electron reduction of O to water is one of the most extensively studied electrochemical reactions due to O exceptional availability and high O/HO redox potential, which may in particular allow highly energetic reactions in fuel cells. To circumvent the use of expensive and inefficient Pt catalysts, multicopper oxidases (MCOs) have been envisioned because they provide efficient O reduction with almost no overpotential. MCOs have been used to elaborate enzymatic biofuel cells (EBFCs), a subclass of fuel cells in which enzymes replace the conventional catalysts. A glucose/O EBFC, with a glucose oxidizing anode and a O reducing MCO cathode, could become the in vivo source of electricity that would power sometimes in the future integrated medical devices. This review covers the challenges and advances in the electrochemistry of MCOs and their use in EBFCs with a particular emphasis on the last 6 years. First basic features of MCOs and EBFCs are presented. Clues provided by electrochemistry to understand these enzymes and how they behave once connected at electrodes are described. Progresses realized in the development of efficient biocathodes for O reduction relying both on direct and mediated electron transfer mechanism are then discussed. Some implementations in EBFCs are finally presented.

Controlling Redox Enzyme Orientation at Planar Electrodes

“…Different strategies have been used during maturation to succeed in a fast intramolecular ET, which is not limiting compared with the catalytic efficiency; this is illustrated hereafter by some relevant examples, widely studied in the literature (Figure 3). MCOs [33] such as laccases (LAC), bilirubin oxidases (BOD), or cuprous oxidase (CueO) are copper-containing enzymes that efficiently catalyze oxygen (O2) reduction directly to water [34]. BODs and LACs are found in fungi, plants, and bacteria, where they catalyze the oxidation of bilirubin to biliverdin and the oxidation of polyphenol compounds, respectively.…”

“…O2 reduction requires four copper sites which differ by their ligand coordination and geometry: one T1 Cu, and a trinuclear cluster composed of one T2 Cu center coupled to a binuclear T3 Cu center [34]. Physiologically, electrons are received from the substrate to the T1 Cu, and are transferred through a MCOs [33] such as laccases (LAC), bilirubin oxidases (BOD), or cuprous oxidase (CueO) are copper-containing enzymes that efficiently catalyze oxygen (O 2 ) reduction directly to water [34]. BODs and LACs are found in fungi, plants, and bacteria, where they catalyze the oxidation of bilirubin to biliverdin and the oxidation of polyphenol compounds, respectively.…”

Electrocatalytic Properties of Immobilized Heme Proteins: Basic Principles and Applications

“…[2,33,40,41] In layer-by-layer films (Figure 1), the protein is electroactive for about 5-7 bilayers, which approximately corresponds to the thickness of 40-60 nm. [15,26,29,31] Higher surface concentration of enzyme active sites yields higher rates of substrate turn-over and therefore higher currents: for this reason, small enzymes or mutated ET proteins (which are in general much smaller than enzymes), would be better suited to electrocatalysis as they allow for more active sites per unit electrode surface. For this reason, an electronhopping mechanism has been proposed to explain the electron exchange.…”

“…[1][2][3][4][5][6]9] Insights have been obtained on the role played in this process by the nature and structuring of the electrode surface [10][11][12][13] and the characteristics of the contact solution. [15][16][17][18] Books and book's chapters are available in which the fundamentals and the main applications of bioelectrocatalysis are described, along with the current strategies utilized to improve the electrode response. Bioelectrocatalysis has also found application in fuel cells.…”

In Situ Engineering of Intracellular Hemoglobin for Implantable High‐Performance Biofuel Cells

“…[6] There are two types of EBFCs,w hich differ in the operating mechanism;n amely, mediated electron transfer (MET) [7] and direct electron transfer (DET) [8] EBFCs.M ET EBFCs rely heavily on redox mediators to shuttle electrons between biocatalytic active sites and electrode surfaces,w hereas DET EBFCs enable electron transfer from the enzyme active sites directly to the electrode. [9] In either case,t he other electrode (cathode) requires an oxygen-reduction catalyst, such as laccase [10] or bilirubin oxide (BOD), [11] to facilitate the oxygen reduction reaction (ORR). Unfortunately,i ng eneral, the current catalysts under investigation show very low catalytic performance as well as poor adhesion to the electrode surface.…”