Experimental Study Of Electricity Generation Of Air-breathing Microfluidic Fuel Cells And Stacks With Three-dimensional Flow-through Anodes

With the rapid development of portable electronic devices,the demand for micro power sources becomes higher.However,the current micro power sources cannot meet the need of long-term stable operation.As a new kind of technology of micro power sources,microfluidic fuel cells take advantage of the feature of laminar flow to separate fuel and oxidant,and eliminate the proton exchange membrane,which exits in traditional micro fuel cells.Microfluidic fuel cells have attracted attention from researchers all over the word due to its many advantages such as small volume,light weight,high energy density,flexible reactant,simple structure,easy manufacturing and so on.At present,because of the limitation of mass transport,microfluidic fuel cells face the problems that power density and fuel utilization are not high enough to meet the needs of practical application.Results from previous studies showed that the convection of fuel to the electrode could be realized by a flow-through anode to enhance the mass transfer at the anode.While at the cathode,an air-breathing cathode using the oxidant from the air to react could alleviate the oxidant transfer limitation.In this study,air-breathing microfluidic fuel cells with three-dimensional porous flow-through anodes including carbon felt and Ni foam were fabricated.The mass transfer characteristics and electricity generation of the fuel cells were investigated.Moreover,an air-breathing microfluidic fuel cell stack with one anode fuel flow channel was presented.Through connecting the cells in series and in parallel,higher current,voltage and power output could be obtained to realize the magnification of the microfluidic fuel cell.The experimental results are summarized as follows:1 Results from the air-breathing microfluidic fuel cell with a carbon felt flow-through anode showed that the carbon felt electrode exhibited more electrochemical active surface areas than the carbon paper electrode.The performance of microfluidic fuel cell with carbon felt electrode was better than that with carbon paper electrode in both acidic and alkaline conditions.And the cell performance in alkaline condition was higher than that in acidic condition.In alkaline condition,the microfluidic fuel cell with carbon felt electrode obtained the highest performance.The maximum power density and current density were 35.1 mW/cm~2 and 192.9 mA/cm~2,respectively,at the fuel concentration of 1 M,the electrolyte concentration of 2 M and the flow rate of 5 mL/h.2 Results from the air-breathing microfluidic fuel cell with a Ni foam flow-through anode showed that using alkaline electrolyte at anode and acidic electrolyte at cathode could improve the open circuit voltage.Using the third stream to separate the anolyte and catholyte could reduce the mixing of them,improving the cell performance and operation stability of the fuel cell.The maximum power density and current density of 22.3 mW/cm~2 and 123.4 mA/cm~2 could be achieved at NaCOOH concentration of 1 M,KOH concentration of 2 M,Na2SO4 concentration of 1 M and the flow rate of 7.5 mL/h.Compared with the air-breathing microfluidic fuel cell with carbon felt anode,its cell performance was lower,while no catalyst was loaded at the Ni foam electrode,thus the cost was lower.The performance per unit mass was a little higher.3 The air-breathing microfluidic fuel cell stack with one anode fuel flow channel could realize connection of the cells in series and in parallel.When the cells were connected in parallel,the open circuit voltage was approximately 0.8 V,the maximum power output of 37.8 mW and maximum current of 171.6 mA could be achieved,which were approximately equal to the sum of the two single cells.When the cells were connected in series,the open circuit voltage of 1.52 V,the maximum power 28.9 mW and the maximum current of 81.6 mA were achieved.