This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.
Our protocol further develops an existing approach used over the last four decades, extends the applicability of electrochemical roughening to thin films, and opens the door for miniaturization. By increasing the surface area of platinum electrodes without an additional coating, the devices are more robust and can last longer than a plated device for electrical stimulation. We have worked with many different electrode geometries and found that parameters like electrode size, shape, and layout influence roughening.
We encourage researchers to vary pulsing parameters for their specific electrodes. First, submerge the electrode tip of a device in a 500 millimolar perchloric acid solution that also contains a platinum wire counter electrode and mercury sulfate reference electrode. Connect several short electrodes of a multi-electrode device together as the working electrode.
Then, connect the working, counter, and reference electrodes to a potentiostat. To electrochemically clean the surface of the electrodes by repetitive potential cycling, first open the EC Lab software of the potentiostat. To apply cyclic voltamagrams, or CVs, to the electrodes, press the plus sign to add the electrochemical technique under the Experiment tab.
In the pop-up window, Insert Techniques will appear. Click on Electrochemical Techniques. When that expands, click on Voltamperometric Techniques.
When that expands, click on Cyclic Voltametry. In the experiment window, fill in the appropriate parameters. Under Safety Advanced Settings select the electrode connections as CE to ground.
Press the Run button and select the file name to begin the experiment. Perform repetitive potential cycles until the voltamograms visually appear to overlap from one cycle to the next, which typically occurs after 50 to 200 CVs. To perform the electrochemical characterization, submerge the electrode tip of the device in a beaker of deoxygenated 500 millimolar perchloric acid that also contains a platinum wire counter electrode and mercury sulfate reference electrode.
Under the Experiment tab in the EC Lab software, press the plus sign to add the electrochemical technique. In the pop-up window, Insert Techniques will appear. Click on Electrochemical Techniques.
When that expands, click on Voltamperometric Techniques. When that expands, click on Cyclic Voltametry. In the experiment window, fill in the appropriate parameters.
Under Safety Advanced Settings, select the electrode connections as CE to the ground. Connect the working, counter, and reference electrodes to the instrument leads as shown on the electrode connection diagram. Press the Run button and select the file name to begin the experiment.
Perform repetitive potential cycles until the voltamograms visually appear to overlap from one cycle to the next. If the two cathodic peaks of a platinum CV are poorly resolved, estimate the electrode surface area from the double layer capacitants at the electrode solution interface. To measure the impedance spectra of a single electrode under open circuit conditions, first submerge the electrode tip of the device in PBS that also contains a platinum wire counter electrode and mercury sulfate reference electrode.
Connect one electrode at a time as the working electrode. Under the Experiment tab in the EC Lab software press the plus sign to add the electrochemical technique. In the pop-up window, Insert Techniques will appear.
Click on Electrochemical Techniques. When that expands, click on Impedance Spectroscopy. When that expands, click on Potentioelectrochemical Impedance Spectroscopy.
In the experiment window, fill in the appropriate parameters. Under Advanced Safety Settings, select the electrode connections as CE to the ground. Connect the working, counter, and reference electrodes to the instrument leads as shown on the electrode connection diagram.
Press the Run button and select the file name to begin the experiment. Submerge the electrode tip of the device in a beaker of 500 millimolar perchloric acid that also contains a platinum wire counter electrode and mercury sulfate reference electrode. Then connect an individual electrode as the working electrode and apply the pulsing paradigm to roughen the electrode.
Begin the roughening protocol with a series of oxidation reduction pulses between minus 0.15 volts and 1.9 to 2.1 volts at 250 Hertz with a duty cycle of one to one for 10 to 300 seconds. Open the Versa Studio program for the Par potentiostat. Expand the Experiment menu and select New.
In the Select an Action pop-up window, choose Fast Potential Pulses and enter the desired file name when prompted. The Fast Potential Pulses Line will then appear under the Actions to be Performed tab. Under the Properties for Fast Potential Pulses, enter the number of pulses as 2, potential one as minus 0.59 volts versus reference for 0.002 seconds and potential two as 1.56 volts versus reference for 0.002 seconds.
Under Scan Properties, enter the time per point as one second, the number of cycles as 50, 000 for a 200 second duration. Under Instrument Properties, enter the current range as Auto. Program the potentiostat with the prolonged application of a constant reduction potential by first pressing the plus button to insert a new step.
Click on Chronoamperometry. Enter the potential as minus 0.59 volts, the time per point as one second, and the duration as 180 seconds. Press the Run button to start the roughening.
The program will stop automatically when the roughening procedure is complete. After the roughening is finished, determine the increase in effective surface area of the macroelectrodes as previously described. A schematic showing the voltage application for roughening both macroelectrodes and microelectrodes is shown here.
Optical microscopy can be used to visualize the difference in the appearance of a roughened macroelectrode or microelectrode. In addition, electrochemical characterization of the platinum surface using impedance spectroscopy and cyclic voltametry can clearly show the increased active surface area of a roughened macroelectrode and microelectrode. The relationship between surface roughness and the duration of pulsing applied to macroelectrodes is shown here An example of different roughening parameters to maximally increase electrode active surface area for different electrode geometries is shown here.
Use high purity electrolytes for roughening. Dilute high purity perchloric acid with deionized water and use only dedicated glassware. The procedure will improve techniques that benefit from high surface area, such as enhancing optical spectroscopy signals of surface absorbed species, increasing electrochemical reactant efficiency, and improving by sensors characteristics.
This approach will allow researchers to roughen the surface of thin film electrodes for many different applications without compromising the structural integrity or lifetime of the electrode. Perchloric acid is hazardous. When working with this reagent, use all appropriate personal protective equipment and only handle in a fume hood.
