Measurement device of the type current scan high res with a 25cm² single cell
The devices of type current scan high res allow:
+ detailed analysis of flow fields
+ detailed analysis of materials
+ optimization of fuel cells
+ fault diagnostics in fuel cells
+ resolution of about 1 x 1 mm
+ current range up to 2A/cm&sub2;
+ standard devices are available
+ special designs on request
With the current scan high res, the current density distribution can be measured with a very high resolution. It is connected via USB to any computer and easy to use. In a fuel cell the local conditions differ, which leads to an inhomogeneous mass conversion resulting in an inhomogeneous current production. One of the keys to a deeper understanding of PEM fuel cells, DMFC and other electrochemical cells is the measurement of the current density distribution. This is important for a save and reliable operation as well as a high lifetime.
The device of type current scan high res, shown befor has a resolution of 32 x 36 measurement cells and an active area of 25cm². The picture below shows a sectional view of the setup.
sectional view of the single cell placed on the segments
If necessary the gas diffusion layer can be placed directly on the segments. Therefore the channels of the flow field can be milled between the segments. The device is usable as anode or cathode of a single cell.
The picture below shows a typical current distribution.
The devices of this series use a segmented electrode with segments of about 1mm² connected to single electronic loads through a multilayered printed circuit board.
An electronic load, connected to a segment, is shown in the following picture.
basic measurement principle
The electronic loads are realized with operational amplifiers which work as current source or sink. So the device can be used on the anode or optionally on the cathode side. The voltage after the resistor R is feed back to the operational amplifier OP. So the voltage Uout at the segment is held constant at the voltage of the input Uin. The voltage Um is measured and the current which flows out of the segment or into the segment is calculated with help of the formula.
Many of these electronic loads are connected with a multiplexer which switches the voltages Um to an Analog-to-Digital converter. The inputs are connected together and the voltage Uin is provided by an Digital-to-Analog converter. This is shown in the following picture.
electronic loads connected to a multiplexer
The size of the device is limited, because the complexity grows quadratically with the size or resolution. For large fuel cells there is another principle available, which is realized in the devices of the series current scan lin.
The available standard device has the same size as the 25cm² ECF 25 single cell fuel cell from Electro Chem. It has 32 x 36 segments of 1.47 x 1.64mm on a base plate. 18 boards with 64 electronic loads and a data-acquisition system with USB interface are pluged into the base plate. The power supply is in a 19" housing.
Nearly any custom made design is possible. The minimal size of the measurement cells is 1 x 1mm. The maximal size is restricted by the current the operational amplifiers are able to deliver. But because of the quadratic complexity the devices of the series current scan high res are restricted to small devices. For large fuel cells or fuel cell stacks please look for a device of the series current scan lin.
|current measurement range||0..20mA/(measurement cell)|
|resolution of current measurement||0.01mA|
|measurement time for current||1.5 seconds for 1000 measurement cells|
|position of measure-ment||at the anode or cathode in a single cell|
|base plate with segments|
|size of measurement cells||typical in the range from 0.01cm² to 0.04cm²|
|maximal current||20mA per measurement cell|
|maximal operating temperature||100°C|
|multiple loads||64 per board|
|power supply||AC Input 110VAC or 230VAC, 50-60Hz|
|operating environment||0-40°C, humidity: no condensation|
|software||user interface and device drivers for
Windows 2000 and Windows XP