A Compelling Case for Bipolar Electrochemistry

Abstract

Most electrochemists perform experiments with conventional three-electrode set-ups composed of a working electrode, a counter electrode and a reference electrode. The electrode of interest in that case is the working electrode, where, depending on its polarization with respect to the solution, either an oxidation or a reduction reaction occurs. Things are very different for bipolar electrochemistry, because both oxidation and reduction reactions occur simultaneously on the same electrode and that electrode is not physically connected through an electrical contact to a power supply (see also the tutorial article by R. M. Crooks at the beginning of this special issue1). From a historical point of view, the basic concepts associated with bipolar electrochemistry have been known for several decades. With the advent of micro- and nanotechnology, however, there is considerable renewed interest in this approach. This is because, over the last decade or so, it has become apparent that there are extremely attractive features of bipolar electrochemistry for applications in areas ranging from analytical chemistry to materials science. This impressive recent increase in the number of studies, using bipolar electrochemistry as a basis for the development of intriguing new scientific approaches, is mostly due to four main factors: The electrochemical experiments can be carried out in the absence of an ohmic contact. This wireless feature is certainly the most appealing one and opens the door to many experiments that simply cannot be done with a classic electrochemical set-up. A direct consequence of the preceding point is the fact that the technique allows simultaneous control over thousands or millions of electrodes. This provides access to many new types of experiments, including high-throughput screening of materials and mass production of modified particles. Intrinsically, bipolar electrochemistry is a fantastic tool to break the symmetry of a chemical system in a straightforward way, thus opening perspectives in various fields, ranging from the synthesis of graded, asymmetric or multifunctional materials, to the generation of controlled motion. Last but not least, bipolar electrochemistry can be considered as a low-cost method that generally requires only simple instrumentation that can easily be handled, even by inexperienced persons. The direct consequence of these four advantages is that bipolar electrochemistry has experienced an exponential growth in the number of users (and publications, Figure 1), and we believe that this renaissance will continue as more and more scientists and engineers, in disciplines ranging from chemistry, biology, and materials science to device fabrication, take advantage of “wireless” electrochemistry. Citations of publications with the topic “bipolar electrochemistry” over the last two decades. Adapted from Web of Science. For all these reasons, this is a good time to dedicate a special issue of ChemElectroChem to this topic, gathering some of the most recent achievements based on this concept. We hope that after going through this issue (the first dedicated exclusively to bipolar electrochemistry), the reader will share our enthusiasm for this appealing and straight-forward approach and find new and exciting ways to benefit from the power of this interesting electrochemical method. Alexander Kuhn is Full Professor at the Engineering School of Chemistry, Biology and Physics in Bordeaux (France) and also senior member of the Institut Universitaire de France. His main research interests, documented in over 150 publications, are in highly controlled surface modification of electrodes with applications ranging from (bio)electrocatalysis and analytical chemistry to materials science. He became interested in bipolar electrochemistry ten years ago and since then has been exploring its utility in these different areas together with his collaborators. Richard M. Crooks is presently the Robert A. Welch Chair in Materials Chemistry at The University of Texas at Austin. His scientific interests include electrochemistry, chemical sensing, and catalysis. He has published nearly 300 research papers and is the recipient of several awards, including the Carl Wagner Memorial Award of the Electrochemical Society, the American Chemical Society Electrochemistry Award, and the Faraday Medal of the Royal Society of Chemistry. In addition to his scientific interests, he writes detective fiction and enjoys distance running. Shinsuke Inagi received his Ph.D. from Kyoto University in 2007 under the direction of Prof. Yoshiki Chujo. After postdoctoral research at Kyoto University, he joined the group of Prof. Toshio Fuchigami as an Assistant Professor at Tokyo Institute of Technology in 2007. He was promoted to Lecturer in 2011, then to Associate Professor in 2015. His current research interests focus on organic electrochemistry, including electrochemical synthesis of polymeric materials. Bipolar electrochemistry is definitely extending his research field.