Flow Field Effect on the Performance of Direct Formic Acid Membraneless Fuel Cells: A Numerical Study

The performance of both air-breathing and air-feeding direct formic acid membraneless fuel cells (DFAMFCs) possessing different flow fields were numerically investigated in this study at given concentration and flow rate for both fuel and electrolyte. Single serpentine, stepwise broadening serpentine, multi-serpentine and parallel channel were tested as liquid flow field, while single serpentine, stepwise broadening serpentine, multi-serpentine and pin channel were tested as air flow field. The channel width was either 0.8 mm or 1.3 mm. The simulation results showed that the air-breathing DFAMFC having identical flow field for both fuel and electrolyte yielded highest cell output. The air-breathing DFAMFC having SBS liquid flow field yielded a maximum power density of 10.5 mW/cm2, while the air-breathing DFAMFC having S(1.3) liquid flow field produced an open circuit voltage of 1.0 V owing to few formic acid penetration into the cathode. Concerning the air-feeding DFAMFCs, the DFAMFC having SBS liquid flow field and MS(0.8) air flow field yielded highest peak power density, 12 mW/cm2, at an airflow rate of 500 sccm. Considering the power generated by the DFAMFCs together with the power consumed by the air pump, DFAMFC having SBS liquid flow field and Pin(0.8) air flow field could be the preferred design.

Systems of two immiscible liquids for a new type of membraneless fuel cells using renewable fuel

Systems of two immiscible liquids are proposed for a new type of membraneless fuel cells using renewable fuel, in which the stationary phase boundary carries out a role of membrane. These systems consist of water, alcohol (preferable ethanol) and a number of electrolytes (salts and bases) leading to the layering of aqueous alcohol. In such systems top phase has significant alcohol content and insignificant electrolyte content, bottom phase has significant electrolyte content and insignificant alcohol content. To study the layering conditions in these systems, binodal curves were plotted for three two-phase liquid systems (EtOH + K2CO3 + H2O; EtOH + K3PO4 + H2O, EtOH + KOH + H2O), using the cloud point method. Comparison of our experimental data with the results of other authors showed that they are consistent for the first and second systems, and the temperature dependence of the binodal curves is clearly visible for the third system. The specific system EtOH – 30 % m/m; KOH – 40 % m/m; H2O – 30 % m/m was taken as the basis for studies of fuel cells based on two immiscible liquids. A further area of research lies in the field of optimizing the composition of both phases, studying the processes of mass transfer in these systems and their physicochemical characteristics.