Microfluidic fuel cells integrating slanted groove micro-mixers to terminate growth of depletion boundary layer thickness

Because of potential high energy densities, microfluidic fuel cells can serve as micro-scale power sources. Because microfluidic fuel cells typically operate in the co-laminar flow regime to enable a membrane-less design, they generally suffer from severe mass transfer limitations with respect to diffusion transport. To address this issue, a novel channel design that integrates slanted groove micro-mixers on the side walls of the channel is proposed. Numerical modeling on the design of groove micro-mixers and grooveless design demonstrates a mass transfer enhancement that has a 115% higher limiting current density and well-controlled convective mixing between the oxidant and the fuel streams with the use of slanted groove micro-mixers. Moreover, the growth of the thickness of the depletion boundary layer is found to be terminated within approximately 2 mm from the channel entrance, which is distinct from the constantly growing pattern in the grooveless design. In addition, a simplified mass transfer model capable of modeling the mass transfer prFocess with the presence of the transverse secondary flow is developed. Further, a dimensionless correlation is derived to analyze the effects of the design parameters on the limiting current density. The present theoretical study paves the way towards an optimal design of a microfluidic fuel cell integrating groove micro-mixers.