Poly(dimethylsiloxane)-based microfluidic electrochemical devices

A novel class of poly(dimethylsiloxane)-based microfluidic electrochemical reactors is described. These devices are comprised of one or more electrodes embedded in poly(dimethylsiloxane) (PDMS)-based microfluidic channels and are fully immersed in liquid electrolyte confined in the channels, while the electroactive species are supplied to the electrodes via permeation through the PDMS channel walls.; In one version of the design, the device architecture is based on a three-electrode electrochemical cell that incorporates a Pt interdigitated array (IDA) working (WE), a Pt counter (CE), and Ag pseudo-reference (RE) electrodes within a microfluidic network in which the WE is embedded and fully immersed in a liquid electrolyte confined in the channels. The PDMS elastomer serves also as a thin gas-permeable membrane through which gaseous reactants in the external ambient environment are supplied to the working electrode by diffusion. Depending on the experimental conditions under which the electrochemical oxygen reduction reaction is performed, the data establish that the device can be operated as both a programmable pH gradient generator and a microfluidic pump. When operated at constant potential under mass transport control, the device can be utilized as a membrane-covered oxygen sensor, the response of which can be tuned by varying the thickness of the PDMS membrane.; In another application, the devices can be operated as passive microfluidic fuel cells incorporating high surface area/porous metal and metal alloy electrodes that are embedded and fully immersed in liquid electrolyte confined in the channels of a PDMS-based microfluidic network. A hydrogen-air fuel cell of the latter design exhibits exceptional durability and high performance, most notably yielding stable output power (>100 days) without the use of an anode-cathode separator membrane. The stability of the device for long-term operation was modeled using a stack of three fuel cells as a power supply for a portable display that otherwise uses a 3 V battery.