Fuel cells capabable of synthetic glucose catalysis have revolved around the implementation of abiotic catalysts that require extreme acid and alkaline environments. These are not compatible with implantable medical sensor systems, and hence there is a need to develop abiotic catalysts that operate at neutral pH. This paper presents structural and electrochemical characteristics of a nanoporous electrode designed for abiotic glucose oxidation in the presence of oxygen in neutral physiological media. The electrode was fabricated by annealing e-beam deposited thin films of Platinum (Pt) and Nickel (Ni) into a Pt-Ni alloy on a silicon substrate. The porous nature of the alloy enhance electrochemical properties by increasing the real surface area ~ 500 times compared to the geometric surface area of as-prepared multilayer thin films. This was reflected in the exchange current density of the electrode annealed at 800 C being twice that of the electrode annealed at 650 C. The cell voltage increase, due to the addition of dissolved physiological oxygen of 2 ppm, was about 100 ± 8 mV under a load current density of 2 µA cm-2. After running for 72 hours in a physiological saline solution with 5 mM glucose, the increase in the electrode potential was only 23 µV h 1 . These results suggest that the nanoporous Pt-Ni alloy anode offers an improved catalytic stability with time and should be a viable candidate for use in abiotic catalysed glucose fuel cell systems operating under physiological conditions.

The determination of the real, or active, area of a catalytic surface is a key requirement to understand or quantify parameters related to its electrochemical behaviour. There are several experimental methods available, but none of them seems to be universally applied in literature. The choice of method is particularly important when evaluating electrodes made from materials that may interact with the analyte such as gold (Au) and palladium (Pd). A comparable analysis has therefore been made which includes four in situ methods (oxide formation, double layer capacitance, iodine adsorption and electrocatalysis of the Hexacyanoferrate (II/III) reductantoxidant couple), and two ex situ methods (scanning electron microscopy and atomic force microscopy). It was found that measurements of oxide formation and the double layer capacitance gave the largest real surface area whereas scanning electron microscopy gave the smallest. Considering nanoporous Pd electrodes, the surface area ratio (the ratio between the real and geometric surface area) ranged from 0.8 (scanning electron microscopy) to 75.4 (oxide formation) and 76.5 (double layer capacitance). The corroboration between the results suggests that oxide formation and double layer capacitance provide the most accurate way of determining the real surface area for the electrode system investigated in this paper.

Selective reduction of oxygen is an important property of fuel cells designed to operate in a mixed fuel environment containing both oxidizing and reducing reactants. This would be of particular importance in the design of a long lasting energy supply unit powering implantable microsystems and running from exogeneous chemicals that is abundant in the body (such as glucose and oxygen). This paper presents the development of a nanoporous electrode for oxygen reduction in the presence of glucose. The electrode was fabricated by e-beam deposition of palladium thin films on porous ceramic aluminium oxide (AAO) substrates with a pore size of 100 and 200 nm respectively. The porous nature of the electrodes improved the catalytic properties by increasing the real surface area close to 100 times the geometric surface area. At a dissolved physiological oxygen (DO) concentration of 2 ppm, the maximum exchange current density was found to be 2.9×10 −3 ± 0.5×10 −3 µA cm −2 whereas the potential reduction due to the addition of 5 mM glucose was about 20.6 ± 16.1 mV. The Tafel slopes were measured to be about 60 mV per decade. After running for 21 hours in a physiological saline solution with 2 ppm DO and 3 mM glu- cose, the reduction in the electrode operational potential was -0.13 mV h −1 under a load current density of 4.4 µA cm −2 . These results suggest that nanoporous AAO cathodes coated with palladium offers a reasonable catalytic performance with a good selectivity towards oxygen in the presence of glucose.

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