DE GRUYTER OLDENBOURG tm – Technisches Messen 2017; 84(10): 683–696 Soma Vesztergom*, Noémi Kovács, Mária Ujvári, and Gyözö G. Láng Apparatus and methods for using a rotating ring–disk electrode with potentiodynamic control of both working electrodes Aufbau und Anwendungen einer rotierenden Ringscheibenelektrode mit potentiodynamischer Kontrolle beider Arbeitselektroden https://doi.org/10.1515/teme-2016-0083 Keywords: Electrochemistry, dual cyclic voltammetry, 3D Received December 19, 2017; revised May 17, 2017; accepted map of reaction products, single-frequency capacitance, May 18, 2017 PEDOT. Abstract: When studying electrochemical processes, one of the most widely used methods of determining the reac- Zusammenfassung: Die rotierende Ringscheibenelektro- tion pathway is an electrochemical assay of products using de (rotating ring-disk electrode, RRDE) ist eine der meist a rotating ring–disk electrode (RRDE). An RRDE tip con- genutzten analytischen Methoden zur Ermittlung von Re- sists of two electron conducting parts: a centrally located aktionswegen und Zwischenprodukten elektrochemischer disk and a ring around it. When brought into contact with Umsetzungen. Der planare Aufbau besteht aus einer zen- an electrolyte solution, the disk and the ring both form tral angeordneten Scheibenelektrode und einer sie umge- electrodes, the potentials of which can be independently benden Ringelektrode. Eingetaucht in eine Elektrolytlö- controlled by a bi-potentiostat. When the tip is rotated, sung können mit geeigneten Potentiostaten beide Elektro- reactants from the solution arrive at the disk where they den separat kontrolliert und angesteuert werden. Wird der undergo an electrode reaction (oxidation or reduction) at Elektrodenaufbau in Rotation gebracht, werden die Re- a given rate, depending on the rotation speed. The formed aktanden in Richtung auf die Elektrode bewegt und dort products leave the disk surface and due to forced convec- einer elektrochemischen Reaktion (Oxidation oder Re- tion make their way towards the ring electrode where they duktion) unterworfen. Der Umsatzrate ist von der Rota- can undergo another electrode reaction and can thus be tionsgeschwindigkeit abhängig. Die gebildeten Produkte detected. Normally, one applies potentiostatic control to werden durch die erzwungene Konvektion an die Ring- at least one of the electrodes when carrying out an RRDE elektrode transportiert und können dort einer weiteren experiment; albeit the simultaneous potentiodynamic per- elektrochemischen Umsetzung unterzogen und analysiert turbation of the electrodes offers an increased applicabil- werden. In der Regel wird eine der beiden Elektroden bei ity range. This paper presents the construction of a mea- einem RRDE-Experiment potentiostatisch betrieben, ob- suring system capable for the “bi-potentiodynamic” per- wohl eine simultane potentiodynamische Nutzung beider turbation of two working electrodes, and demonstrates Elektroden eine Erweiterung des elektroanalytischen An- the use of such methods in case of a few chosen example wendungsspektrums erlaubt. Diese Veröffentlichung stellt systems. die Konstruktion eines Messsystems vor, welches für die simultane „bi-potentiometrische“ dynamische Anregung beider Elektroden genutzt werden kann und weist die Eig- nung dieses Aufbaus an einigen exemplarischen Untersu- chungen nach. *Corresponding author: Soma Vesztergom, Eötvös Loránd Schlüsselwörter: Elektrochemie, simultane Voltamme- University, Department of Physical Chemistry, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary, trie, 3D-Karte von Reaktionsprodukten, Einzelfrequenz- e-mail: [email protected]. Kapazität, PEDOT. http://orcid.org/0000-0001-7052-4553 Noémi Kovács, Mária Ujvári, Gyözö G. Láng: Eötvös Loránd University, Department of Physical Chemistry, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary Brought to you by | University of Gothenburg Authenticated Download Date | 10/17/17 8:39 AM 684 | S. Vesztergom et al., RRDEs with bi-potentiodynamic control DE GRUYTER OLDENBOURG 1 Introduction In chemical industry, civil engineering, environmental protection and corrosion testing electrochemical meth- ods [1, 2] are very often used techniques of chemical char- acterization. This is due to the relatively low cost of the measuring equipment and the availability of standard- ized techniques. One of the most often used instruments in both electrochemical research and in applied electro- chemistry is the potentiostat. A potentiostat is a device used for keeping the po- Figure 1: A simplified potentiostat circuit. The operational amplifier tential of a working electrode (the electrode under study) realizes a current flow between the auxiliary and the working electrodes so that the potential difference between the reference at a constant level with respect to a reference electrode and the working electrodes would match the voltage of the control by adjusting the current at an auxiliary electrode. It con- signal. sists of an electric circuit which provides voltage control by the use of operational amplifiers (Figure 1). Depending on their design, potentiostats may be used not only to sta- feature of these methods is that they apply potentiody- bilize a constant potential but also to control the potential namic control to both working electrodes at the same time. of the working electrode according to a time-dependent The advantages of dual potentiodynamic control were voltage waveform. Bi- or multi-potentiostats are similar cir- first made use of for the investigation of gold dissolution cuits that can control the potential of two or more working upon potential excursions to the region of oxide forma- electrodes (with respect to the same reference and by us- tion, for which two techniques —phase-shifted dual cyclic ing one auxiliary electrode). voltammetry [5] and synchronous dual cyclic voltamme- Nowadays potentiostats and galvanostats designed try [7]— have been utilized. The latter technique, as is go- for an everyday laboratory use are commercially avail- ingtobeshown,yieldsresultsthataremoreeasilyquan- able products. These instruments provide a straightfor- tifiable; however both techniques are superior to “stan- ward way of making standard electrochemical and elec- dard” RRDE techniques in terms of reproducibility. While troanalytical measurements, even for an untrained staff. in standard RRDE measurements the surface of the collec- As a result of the fact that the instruments are highly auto- tor electrode loses sensitivity due to long-time condition- mated —controlling the device, as well as visualizing and ing at a certain potential, in case of dual voltammetry the evaluating the measured data can usually be carried out ring potential is continuously scanned, thus the ring sur- by using software—, the job of the operator is simplified to face is under constant “electrochemical polishing”. agreatextent. Dual potentiodynamic control is also expedient in the The advances in electrochemical instrumentation detection of reaction products at a large potential range, as have very significantly improved the reproducibility, accu- it was shown for the case of oxygen reduction occurring on racy and speed with which electrochemical experiments gold [6, 7]. This reaction yields products (primarily H2O2) can be performed. However, in the pursuit of fulfilling that can undergo faradaic reaction at the collector (ring) the needs of applied science, the manufacturers of po- electrode surface. tentiostats often neglect the demands of fundamental re- The original workstation (described in Reference [4]) search [3]. The primary instruments of electrochemical re- has recently undergone serious improvements and —by search more and more become “black boxes” and only the implementation of on-the-fly Fourier analysis— can limited efforts are devoted to the design of new instru- now be used in an essentially non-faradaic detection mode ments. Consequently, methodological developments of- as well, when one carries out single-frequency capacitance ten require the design of new, “home-made” measuring measurements on the ring [8]. systems. The aim of this paper is to review results that became In this paper the construction and application of available by the application of dual potentiodynamic con- a new electrochemical measuring system [4], developed trol to the two working electrodes of an RRDE. For read- in our research group, is described. By the use of the pre- ers who are not familiar with RRDE methods, a short in- sented measuring system, significant improvements [4–8] troduction is given in the next section. For a more ba- have been made to electrochemical methods based on the sic introduction to electrochemistry and electrochemical use of rotating ring–disk electrodes (RRDEs). A common Brought to you by | University of Gothenburg Authenticated Download Date | 10/17/17 8:39 AM DE GRUYTER OLDENBOURG S. Vesztergom et al., RRDEs with bi-potentiodynamic control | 685 measurements in general, the reader is directed to other sources [1, 2]. 1.1 Electrochemical experiments with rotating ring–disk electrodes When studying the mechanisms of electrochemical pro- cesses, one of the most convenient and widely used meth- ods of determining the reaction pathway is an electro- chemical assay of the reaction products using a rotat- ing ring–disk electrode (RRDE) [9, 10]. The first RRDE was developed by Frumkin, Levich and their coworkers in 1959 [11]. As a typical example of so-called generator–collector assemblies, an RRDE tip consists of two electron