An increasing societal demand for a wide range of small, often portable devices that can operate for an extended period of time without recharging has resulted in a surge of research in micropower sources. Most efforts in this area focus on downscaling of existing fuel cell technology such as the well-known proton exchange membrane (PEM) fuel cells. Here we study a novel concept for fuel cells: the use of laminar flow instead of a physical barrier such as a PEM to separate the fuel and oxidant streams. Laminar flow, i.e. low Reynolds number flow, is a property of fluid flow at the microscale: one or more liquid streams that are brought together under low Reynolds number conditions flow in parallel and contact with each other without turbulent mixing. Mass transport transverse to the direction of flow takes place by diffusion only. In our laminar flow-based fuel cell a fuel-containing stream and an oxidant-containing stream are brought together in laminar flow conditions with the electrodes placed on opposite walls within the channel. In un-optimized fuel cell configurations, current densities as high as 10 mA/cm2 are obtained at room temperature using different fuels such as methanol or formic acid vs. oxygen saturated solvents or other oxidants.

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