Reactant recirculation in electrochemical co-laminar flow cells

• Reactant crossover in co-laminar flow cells is assessed via OCV measurement
• Harvesting reactants through separate outlets leads to unavoidable SOC loss
• A dual-pass cell results in higher reactant utilization and mixing
• Practical conditions for reactant recirculation are demonstrated

Co-laminar electrochemical cells utilize hydrodynamic engineering rather than a physical separator to prevent mixing of reactants. Commonly known as microfluidic fuel cells and batteries, these cells are based on stratified laminar flow of reactants in a microfluidic channel. The objective of the present work is to evaluate the feasibility and effectiveness of reactant recirculation in co-laminar flow cells with flow-through porous electrodes. Two representative device architectures are fabricated with separate outlets for reactant recirculation in Y-junction and dual-pass configurations. It is found that crossover at the electrodes reduces the open circuit potential of both cells and serves as a useful diagnostic method for assessing the degree of crossover at the outlets. Outlet concentration is monitored at a range of flow rates and indicates that asymmetric splitting of the co-laminar interface can lead to a constant 2% loss of state of charge, while the loss due to diffusion ranges from 0-40%. The dual-pass cell is shown to have greater diffusive loss due to deceleration at the splitting junction but also demonstrates better performance due to its higher convective velocity through the porous electrodes. These effects are observed during a series of discharge operations with recirculating reactants, in which the dual-pass cell results in greater reactant utilization despite its higher crossover rates. Overall, the present results demonstrate reactant recirculation as a useful strategy to combine high reactant utilization and high power density in membraneless co-laminar flow cells.

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