Rotating disc and ring-disc electrodes
(rotating unit with speed controller an measuring cell)
The rotating ring-disc electrode allows the testing of end products and intermediates of electrochemical reactions. It consists of a central disc electrode and a concentric ring electrode. Both electrodes lie within one plane on the abutting face of a cylinder and are connected mechanically by a thin, electric isolating coat. The system allows a good controlling of the convection and diffusion conditions in a electrolyte that conform in a wide range by a simple rule.
Ordinary stirring of the electrolyte, for example with a magnetic stirrer, leads to a turbulent flow and as a result it is not suitable to create a defined convection profile on the electrode.
Some very interesting workings with our systems were performed at the University of Vienna (Wien) / Austria.
The rotating disc and ring-disc electrode drive of the Jaissle company is dimensioned for continuous speeds up to 4000 rpm temporary up to 6000 rpm. The electrical connector of the electrodes is ensued by a mercury current collector head that has a consistent contact resistance in the range of Milli-Ohms (mΩ) that is even guaranteed after several 1000 operating hours. A fast responsive drive motor turns the electrode with a concentricity of approximately 1 / 100mm. The motor is equipped with a tachogenerator with the result that a regulation of the speed is ensued.
Especially should be mentioned here that our speed controller can start at 0 RPM. So easily speeds from 0 to 100 RPM can be set (obvious even more). Also can be set in a sequence by means of software, the rotation is stopped and started again. It does not have anything switch off the controller so that the rotation stops.
Rotator with glass vessel (large model)
The electrode is used with a teflon seal in a glass cell that can be thermostated with the result that even an oxygen-free experimental procedure is unproblematically possible.
The power supply of the drive motor is ensued by a RRDE-speed-controller.
Our earlier rotator was equipped with a rigid rectangular spar on the back so that the measuring cell had to be placed on a lifting platform in the right position. But for some time we have a newer model with a round spar on the back so that the head of the rotator including the electrode can be immersed in the glass vessel. Moreover for cleaning purposes the head can be turned to the side so that the glass cell can be easily cleaned.
The controller is assembled with a 4-digit rotation speed indicator. The adjustment of the rotation speed is set by two 10-gear potentiometers, one is for the coarse adjustment, the other one for the fine adjustment. Stepless rotation speed control from 5 up to 6000 rpm. The accuracy of the preset rotation speed lies around 0,5%. For an external control the controller requires 1V / 1000 rpm. To record the rotation speed by a external measuring system there are two BNC-connectors available.
- Connector A supplies 1mV / rpm
- Connector B supplies the square root of rpm
RRDE speed controller
With regard to the use of smaller electrodes, the use of lower amounts of electrolyte and also to reduce the required space on the laboratory bench, we have designed a smaller model yet. The picture Rotator with glass vessel (small model) shows this rotator next to a well-known book, so that the size proportions become clear, the picture Rotator with glass vessel (small model) and RRDE speed controller shows it with the corresponding small speed controller. In this rotator one can use disc-, ring-disc- and cylinder-electrodes, as in the large model also. Thereby the diameter of the discs can be reduced down to 1mm. The measuring cell can either be supplied only as a glass vessel with lid or even complete with counter electrode, intermediate vessel and reference electrode.
Rotator with glass vessel (small model)
Rotator with glass vessel (small model) and RRDE speed controller
In the following some pictures of quick-change electrodes can be seen.
Quick-change electrodes
The delivery program of the ring-disc electrode is complemented by the optional appropriate accessories like quick-change electrodes, assembly tools and a grinding and polish set.
Also a complete device attached in a Faraday cage consisting of rotator, measuring post, electrode, thermostated measuring cell, lifting platform for the measuring cell and a RRDE-speed-controller can be delivered by request.
Software for ring-disc electrode
The measurements on the disc or ring-disc electrode were completely supported by our software EcmWin.
Measuring dialog ring-disc electrode
All relevant parameters can be set up in the measuring dialog. An own scan-file that is being processed parallel to the measurement can be created to control the speed of the electrode. The activation of the controller ensued over the second scan output of the measuring system.
With the first scanner the disc can be polarized. If a ring-disc electrode is used to work with then one electrode will be typically set to a constant potential. This adjustment can be made with the nominal value generator of a potentiostat.
The acquisition of all potentials and currents as well as the rotation speed of the electrode is ensued by the measuring system. If a disc electrode is used, then the measured values with the rotation speed will be saved in a single file. If a ring-disc electrode is used, then the measured values of the ring will be saved in a second file.