Integration of Glucose Biofuel Cells with a MEMS Diaphragm Micropump

Enzymatic biofuel cells (BFCs) that utilize enzymes as electrocatalysts instead of metals have attracted attention as ubiquitous sustainable power devices that can generate electricity directly from the blood or bodily fluids [1]. A characteristic feature of BFCs is their ability to generate power using various kinds of fuels, such as glucose, lipids, and hydrogen. In other words, a wide range of fuel choices is possible because they do not require an ion-exchange membrane. Many biofuel cells are safe and biocompatible, utilizing enzymes as biological catalysts. In addition, they function under mild conditions from room temperature to human body temperature under neutral pH conditions.

 Microelectromechanical system (MEMS) technologies have been applied to realize compact, high-output power sources toward the commercialization of BFCs. For example, Choban et al. reported a BFC with a Y-shaped channel that used formic acid and oxygen [2]. It utilized laminar flows of the two fuels without mixing for efficient reactions at each electrode. Togo et al. built hydrophobic pillars in a flow path, and fed air individually into three cells [3]. Fukushi et al. reported a flexible biofuel cell equipped with a microchannel which mimicked the blood vessels in the human body [4]. However, these biofuel cells equipped with microchannels require large external flow systems that include tubing and pumps to supply the fuels. Compact fuel transport mechanisms would be more desirable. Micropumps fabricated with MEMS technology have been considered for use in such fuel transport mechanisms [5,6]. Liu et al. reported polyimide (PI) diaphragm micropumps (15 × 15 mm²) fabricated using MEMS technology [7]. Such micropumps should be able to deliver enough glucose fuel solution to continuously generate power in a BFC.

 In this paper, a new BFC equipped in the fluid reservoir of the micropump is reported, and its power generation performance and lifetime are discussed. We fabricated a micropump with a polyimide (PI) diaphragm (53 μm thick, 7 mm diameter) on a silicon chip using microfabrication processes, and a glucose biofuel cell was inserted into the fluid chamber of the micropump. The biofuel cell was fabricated on another PI film, with glucose oxidase immobilized on its porous carbon anode and bilirubin oxidase immobilized on the porous carbon cathode. Each semicircular electrode area was 14.1 mm² with a radius of 3 mm, and the gap between the anode and cathode was 1 mm. The device generated electricity by feeding an aqueous solution of glucose directly onto the electrodes in the micropump chamber. The maximum generated power, 0.076 μW at 98 mV, corresponding to a power density of 0.556 μW/cm², was realized when a 100 mM glucose solution was introduced under diaphragm pressures alternating between 0 and 30 kPa at a pumping frequency of 3 Hz. A longer power generation lifetime was observed under fuel flow driven by micropump operation.

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