| Recently,with the rapid development of high-performance portable electronic device,higher requirements have been put forward for the micro power supply.Among them,the membrane-less microfluidic fuel cell（MMFC）has been widely draw attention.The MMFC utilizes multiple fluids with similar viscosity and density to form a stable co-laminar flow in the microchannel,achieving the natural separation of the oxidant and the fuel.Thereby the proton exchange membrane and membrane-related problems can be eliminated.In addition,there are some critical advantages for the MMFCs such as simple structure,high energy density,convenient integration and greater flexibility reactants.The MMFC is considered as a significantly promising micro power source,but at this stage,it necessitates to further improve cell performance for practical applications.Currently,most MMFCs are based on co-laminar flow of fuel and electrolyte,which means the ions transport to the electrodes surface and participate in electrochemical reaction.Nevertheless,the fuel easily diffuses to the cathode at excessive concentration or slow reactant flow,resulting in serious degradation of the cell performance due to the mixed potential and parasitic current.For the above problem,this work constructed a novel penetrable-flow microfluidic fuel cell with upstream/downstream staggered arrangement of cathode/anode.The fuel crossover can be avoided because the convection transport rate of the electrolyte is much greater than the countercurrent diffusion rate of the fuel.After that,according to the idea of simplifying the cell structure and completely eliminating fuel crossover,a single-stream penetrable-flow microfluidic fuel cell based on carbonaceous catalyst cathode with upstream/downstream staggered arrangement of cathode/anode was proposed.Moreover,the ions transport distance between the electrodes was minimized by the parallel-stacked cathode/anode design to improve the cell power density.Finally,the cell output performance and voltage can scale-up by constructing a microfluidic fuel cell stack.In view of the aforementioned novel structure of MMFC,the flow visualization and performance testing experiment were studied in detail.The main results of this paper were as follows:（1）By flow visualization of the penetrable-flow microfluidic fuel cell with upstream/downstream staggered arrangement of cathode/anode,it was verified that the penetrable-flow structure can avoid the diffusion of fuel to the cathode side.With the increase of fuel concentration in the alkaline media,the open-circuit potential of the cell cathode wasn’t decreased,and its maximum power density can reach 97.6 m W/cm3.Increasing the alkaline electrolyte concentration can enhance the solution conductivity,reducing the ohmic internal resistance of the cell.Compared with the electrolyte concentration of 1 M,the cell performance was improved by 120%at 4 M.The cell exhibited the best performance under the flow rate ratio of electrolyte to fuel（4:1）.Furthermore,the maximum output power density had slightly decreased（only 5%）with the total flow rate reduce to 50μL/min,suggesting the total flow rate of reactants can be appropriately reduced to obtain high fuel utilization.（2）In the acid media,the continuously grew CO2 gas bubbles will produce on the inlet cross-section and the surface of anode.The bubbles in inlet side cannot be effectively removal,which will hinder the mass transport of fuel to the active site of catalyst and reduce the performance and operation stability of the cell.Further increasing fuel and electrolyte concentration,amounts of bubbles generated inside the cell flow channel under high current density,reducing the cell performance.At the electrolyte flow rate of 160μL/min and the fuel flow rate of 40μL/min,the cell performance displayed optimal maximum output power density and limiting current density of 182.6 mW/cm3 and 631.4 mA/cm3,respectively.（3）Physical and electrochemical characterizations were performed on the carbonaceous catalyst,verifying the carbonaceous catalyst had excellent graphitization degree and selective oxygen reduction catalytic activity.A single-stream penetrable-flow microfluidic fuel cell based on carbonaceous catalyst cathode with upstream/downstream staggered arrangement of cathode/anode was constructed.By comparison,the open circuit of the cell decreased significantly under the cathodic Pt catalyst while the carbonaceous catalyst wasn’t affected.In comparison of the reactant flow rate of 400μl/min,the maximum output power density only decreased by 7.2%at1μl/min,while the maximum fuel utilization rate can be increased from 0.87%to100%.（4）Results from the total power output and volume power density of the cell structure with parallel-stacked cathode/anode was increased by 2.4 times and 8.1 times that of the penetrable-flow microfluidic fuel cell with upstream/downstream staggered arrangement of cathode/anode,respectively.The fuel cell can stably run for more than8000 s at the voltage of 0.3 V corresponding maximum power density.However,the carbonate will accumulate in the pores of carbon paper during anodic reaction,resulting in the degradation of anode performance.Moreover,the dynamic behavior of CO2bubbles showed that the structure effectively limited the generation of CO2 bubbles on the electrode surface,ensuring the stable operation of the cell.（5）The output performance and voltage of the cell can scale-up by simply adding multiple reaction units on the main flow channel.The trend of performance change for modes were similar with the two cell stacking under different operating conditions.In addition,the series connection was used to supply power for the timer and calculator,which showed the practical application of the micro power system device. |
