Bipolar Electrodes for Rapid Screening of Electrocatalysts

Abstract

We report a method for rapid screening of arrays of electrocatalyst candidates. The approach is based on simultaneous activation of the oxygen reduction reaction (ORR) and Ag electrodissolution at the cathodic and anodic poles, respectively, of bipolar electrodes (BPEs). Because the electrochemical activity of the two poles is directly coupled via the BPE, the extent of Ag electrodissolution is directly related to the ORR activity. The screening process lasts ∼12 min. Because Ag dissolution provides a permanent record of catalyst activity, the screening results can be determined by simple optical microscopy after the electrochemical experiment. The method has the potential to provide quantitative information about electrocatalyst activity.H ere we report a new and potentially powerful method for rapid screening of electrocatalysts. The principle is illustrated in Scheme 1, with specific reference to evaluation of the activity of electrocatalysts for the oxygen reduction reaction (ORR). The top frame of Scheme 1a shows an array of three bipolar electrodes (BPEs). 1 The ORR electrocatalyst candidates are deposited onto the cathodic poles of the BPEs, while the anodic poles are composed of parallel Ag microband electrodes. The Ag microbands of each electrode are in electrical contact with one another and with the ORR catalyst via an underlying indium-doped tin oxide (ITO) contact. When a sufficiently high potential (E tot , Scheme 1b) is applied to the solution in the fluidic channel via a pair of driving electrodes, the ORR proceeds at the cathodic poles and the Ag microbands undergo electrodissolution. 2 The efficiency of the ORR catalyst is then determined by counting the number of dissolved Ag microband electrodes: the more bands that dissolve, the better the catalyst. In fact, as we will show, there is a direct thermodynamic link between the overpotential required for the ORR (Scheme 1c) and the number of Ag microbands remaining after the experiment (Scheme 1a). Although we demonstrate this screening method using just three BPEs, arrays of arbitrary size can be monitored in this way with very little additional technological overhead. This is because it is not necessary to make a direct electrical connection to each electrode, which is an intrinsic property of BPEs and the principal reason for using them in an array format. 3 The basic operating principles of BPEs, along with many interesting applications, have been previously described in the scientific literature. 1−14 A driving voltage E tot applied across a microchannel containing a conductive electrolyte solution (Scheme 1b) is dropped nearly linearly over the length of the microchannel. 6 If a conductive wire of sufficient length is present in the microchannel, it will function as a BPE. 1 Specifically, when the interfacial potential differences between the poles of the BPE and the electrolyte solution (ΔE elec , Scheme 1a) are sufficiently high, faradaic processes occur simultaneously: a reduction at the cathodic pole and an oxidation at the a...

Analytical and Computational Scaling Relationships for the Coupled Phenomena that Control Local Bipolar Electrochemical Behavior

“…For example, the ohmic resistance for rectangular microfluidic channels commonly used for electrocatalysis screening [2][3][4] can be estimated using R ionic = l/κ · A, where l is the length of the bipolar electrode and A is the cross sectional area of the channel above the electrode. In these systems, the kinetics for both the oxidation and reduction reactions must be considered because the anodic and cathodic regions of the bipolar electrode often have similar areas.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] For example, bipolar electrochemistry has been used for screening electrocatalysts, where the hard to detect electrocatalytic rate is visualized by an equal and opposite indicator chemistry such as electrochemiluminescence 1,2 or metal etching. [3][4][5] Bipolar electrochemistry has also proven useful for electrodeposition of material gradients 6,7 and to grow interconnects between electrically isolated conducting posts. 8,9 Previous work by our group experimentally demonstrated localized bipolar electrochemistry using a rastering microjet anode, with a far-field cathode, that we called the scanning bipolar cell (SBC).…”

Probing Local Potentials inside Metallic Nanopores with SERS and Bipolar Electrochemistry

“…Such investigation techniques include electrochemiluminescence, [17] electrochemical corrosion microscopy, [18] epifluoresence, [19] and surface plasmon resonance spectroscopy, [20] which are ultimately restricted by the diffraction of light. Here, working toward subwavelength detection, we propose the use of SERS to study the local potentials.…”

Paper-Based Bipolar Electrochemistry

“…Several examples of sensors using BPEs microfabricated on glass substrates have also been reported in the literature. [23][24][25][26] For example, our group used ECL produced by the co-oxidation of tris(bipyridine)ruthenium(II), Ru(bpy) 3…”