A Life in Electrochemistry

Bard, Allen J.

doi:10.1146/annurev-anchem-071213-020227

Cited by 11 publications

(8 citation statements)

References 57 publications

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“…However, with larger RAPs, this mode is replaced by electron transfer at the polymer/electrode interface followed by intraparticle charge transport. When using an insulating backbone, charge propagates pendant-to-pendant through a charge diffusion process mediated by self-exchange reactions, i.e., the hopping of charge between neighboring redox species. − …”

Section: Concepts Of Electron Transfer In Rapsmentioning

confidence: 99%

Redox Active Polymers as Soluble Nanomaterials for Energy Storage

2016

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It is an exciting time for exploring the synergism between the chemical and dimensional properties of redox nanomaterials for addressing the manifold performance demands faced by energy storage technologies. The call for widespread adoption of alternative energy sources requires the combination of emerging chemical concepts with redesigned battery formats. Our groups are interested in the development and implementation of a new strategy for nonaqueous flow batteries (NRFBs) for grid energy storage. Our motivation is to solve major challenges in NRFBs, such as the lack of membranes that simultaneously allow fast ion transport while minimizing redox active species crossover between anolyte (negative electrolyte) and catholyte (positive electrolyte) compartments. This pervasive crossover leads to deleterious capacity fade and materials underutilization. In this Account, we highlight redox active polymers (RAPs) and related polymer colloids as soluble nanoscopic energy storing units that enable the simple but powerful size-exclusion concept for NRFBs. Crossover of the redox component is suppressed by matching high molecular weight RAPs with simple and inexpensive nanoporous commercial separators. In contrast to the vast literature on the redox chemistry of electrode-confined polymer films, studies on the electrochemistry of solubilized RAPs are incipient. This is due in part to challenges in finding suitable solvents that enable systematic studies on high polymers. Here, viologen-, ferrocene- and nitrostyrene-based polymers in various formats exhibit properties that make amenable their electrochemical exploration as solution-phase redox couples. A main finding is that RAP solutions store energy efficiently and reversibly while offering chemical modularity and size versatility. Beyond the practicality toward their use in NRFBs, the fundamental electrochemistry exhibited by RAPs is fascinating, showing clear distinctions in behavior from that of small molecules. Whereas RAPs conveniently translate the redox properties of small molecules into a nanostructure, they give rise to charge transfer mechanisms and electrolyte interactions that elicit distinct electrochemical responses. To understand how the electrochemical characteristics of RAPs depend on molecular features, including redox moiety, macromolecular size, and backbone structure, a range of techniques has been employed by our groups, including voltammetry at macro- and microelectrodes, rotating disk electrode voltammetry, bulk electrolysis, and scanning electrochemical microscopy. RAPs rely on three-dimensional charge transfer within their inner bulk, which is an efficient process and allows quantitative electrolysis of particles of up to ∼800 nm in radius. Interestingly, we find that interactions between neighboring pendants create unique opportunities for fine-tuning their electrochemical reactivity. Furthermore, RAP interrogation toward the single particle limit promises to shed light on fundamental charge storage mechanisms.

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Section: Concepts Of Electron Transfer In Rapsmentioning

confidence: 99%

Redox Active Polymers as Soluble Nanomaterials for Energy Storage

2016

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“…Amperometric techniques can be used to measure electron transfer to and from redox-active mineral phases under defined redox conditions. Amperometric measurements are typically conducted in three-electrode electrochemical cells that contain a working electrode, a reference electrode and a counter (or auxiliary) electrode. , The three electrodes are immersed into a solution, which is commonly pH-buffered and contains an electrolyte. A potentiostat is used to apply defined potentials ( E ) to the working electrode relative to the reference electrode (commonly Ag/AgCl electrodes or saturated calomel electrodes, SCE).…”

Section: Electrochemical Analyses Of Redox-active Mineralsmentioning

confidence: 99%

“…Potentiometric measurements determine the reduction potentials of a sample relative to defined reference states. These potentials are also referred to as “open circuit potentials” (i.e., E OCP ), denoting that a high resistance is placed in the measurement circuit that impedes the exchange of electrons between the working electrode and the redox-active phase(s) during the measurements. , At the E OCP , the rates of oxidation and reduction reactions at the working electrode surface are kinetically balanced, resulting in negligible net current flows. As a consequence, potentiometric measurements do not require a counter electrode and are typically conducted with only a working electrode and a reference electrode.…”

Section: Electrochemical Analyses Of Redox-active Mineralsmentioning

confidence: 99%

Electrochemical Analyses of Redox-Active Iron Minerals: A Review of Nonmediated and Mediated Approaches

Sander

Hofstetter

Gorski

2015

Environ. Sci. Technol.

128

138

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Redox-active minerals are ubiquitous in the environment and are involved in numerous electron transfer reactions that significantly affect biogeochemical processes and cycles as well as pollutant dynamics. As a consequence, research in different scientific disciplines is devoted to elucidating the redox properties and reactivities of minerals. This review focuses on the characterization of mineral redox properties using electrochemical approaches from an applied (bio)geochemical and environmental analytical chemistry perspective. Establishing redox equilibria between the minerals and working electrodes is a major challenge in electrochemical measurements, which we discuss in an overview of traditional electrochemical techniques. These issues can be overcome with mediated electrochemical analyses in which dissolved redox mediators are used to increase the rate of electron transfer and to facilitate redox equilibration between working electrodes and minerals in both amperometric and potentiometric measurements. Using experimental data on an iron-bearing clay mineral, we illustrate how mediated electrochemical analyses can be employed to derive important thermodynamic and kinetic data on electron transfer to and from structural iron. We summarize anticipated methodological advancements that will further contribute to advance an improved understanding of electron transfer to and from minerals in environmentally relevant redox processes.

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“…However, limited by the detection sensitivity of the experiment, the current of single-electron transfer cannot be measured directly. To solve this dilemma, cycling amplification was first raised by using a specially constructed nanotip electrode with a sharp tip of ∼15 nm in a wax sheath in an extremely diluted solution, so that a very limited number of molecules can be trapped between the tip and the substrate electrode − (Figure B). The charge transfer process in which the trapped molecules react multiple times between the electrodes can produce a tiny current to be detected, which is interpreted as cycling amplification of single-molecule electrochemical detection .…”

Section: Single-molecule Electrochemistrymentioning

confidence: 99%