An Oxygen Cathode Operating in a Physiological Solution

Abstract

We report the electroreduction of O(2) to water under physiological conditions (pH 7.4, 0.15 M NaCl, 37.5 degrees C) at a current density of 5 mA cm(-2) and at a potential only 0.18 V reducing versus that of the reversible O(2)/H(2)O electrode at pH 7.4. The immobilized electrocatalyst enabling the reduction is the electrostatic adduct of bilirubin oxidase from Myrothecium verrucaria, a polyanion at pH >4.1, and the polycationic redox copolymer of polyacrylamide and poly (N-vinylimidazole) complexed with [Os (4,4'-dichloro-2,2'-bipyridine)(2)Cl](+/2+), cross-linked on carbon cloth. The current density of the rotating electrodes was O(2) transport limited up to 8.8 mA cm(-2); their kinetic limit was reached at 9.1 mA cm(-2). The operational life of the electrodes depended on their angular velocity, which defined not only the current density but also the mechanical shear stress stripping the electrocatalyst. When the electrodes were rotated at 300 rpm and were poised at -256 mV versus the potential of the reversible O(2)/H(2)O electrode, their 2.4 mA cm(-2) initial current density decreased to 1.3 mA cm(-2) after 6 days of continuous operation at 37.5 degrees C.

Characterization of Nanoporous Gold Electrodes for Bioelectrochemical Applications

“…The mediator Os(bpy) 2 55 The catalytic current will be limited by the enzyme-catalysed rate of O 2 reduction if too little enzyme is present or by increased resistance in the film if too much non-conductive enzyme is present. 55 At 22.8 wt.…”

“…The mediator Os(bpy) 2 55 The catalytic current will be limited by the enzyme-catalysed rate of O 2 reduction if too little enzyme is present or by increased resistance in the film if too much non-conductive enzyme is present. 55 At 22.8 wt. % of cross-linker the films were stable showing no variation in response after 100 scans in the absence of O 2 , while enabling appreciable current densities to be achieved in the presence of O 2 .…”

Analytical Techniques for Characterizing Enzymatic Biofuel Cells

“…If the enzyme is immobilized in a polymer matrix on the RDE, the substrate diffusion coefficient through the polymer membrane can be determined. 19,20 Other types of immobilization materials can also be examined with RDE voltammetry.…”

Enhanced Electrocatalytic Activity for the NADH Oxidation with Oxidatively Treated Carbon Nanotubes Incorporated on a Redox Polymer Modified Electrode

“…16,17 Some oxidase enzymes were "wired" to carbon electrodes and efficient electrocatalytic reactions such as glucose oxidation and O 2 reductions were reported. [16][17][18][19] At an electrode with a hydrogel film of the redox polymer, which is not a quinone-like mediator, catalytic electro-oxidation of NADH, but only a partial fraction, was measured. A composite film of the redox polymer and oxidatively treated single-walled carbon nanotubes (SWNTs) was applied on an edge plane graphite electrode surface.…”