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![Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F55858.jpg&w=3840&q=50)
Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase
Published on: December 4, 2017
Unveiling Anion-Dependent Redox Kinetics of the V4+/V5+ Couple in Acidic Electrolytes: A Combined Powder
Hanbing Liu1,2, Chao Wang2, Min Wu2
1Department of Chemical Physics, University of Science and Technology of China, Hefei, 230026, China.
Abstract:
The redox kinetics of the V4+/V5+ couple govern the power density and stability of all-vanadium redox flow batteries (VRFBs). Using electrolyte additives is the most common strategy to accelerate the kinetics, but their underlying mechanisms remain unclear. Herein, the electrochemical behaviors of the V4+/V5+ couple in sulfuric acid (H2SO4) with phosphoric acid (H3PO4) and perchloric acid (HClO4) as additives were systematically investigated using powder microelectrode (PME) techniques. Based on the in-depth electrochemical analysis using the PME, the electrochemically active species are identified as dimers, whose electron transfer (ET) kinetics can be accelerated by H3PO4 but inhibited by HClO4. Fitting the PME-acquired Tafel plots with the Marcus-Hush-Chidsey (MHC) ET theory demonstrates that H3PO4 reduces the reorganization energy and enhances electronic coupling strength, while HClO4 shows the opposite effect. Furthermore, H3PO4 addition yields a lower-energy intervalence charge transfer (IVCT) absorption band and a higher electronic coupling matrix element, indicating that it not only reduces the formation energy of the dimers but also enhances V4+/V5+ electron transfer kinetics, which is further corroborated by Raman spectroscopy. This work provides a reliable approach to evaluate ET kinetics and offers theoretical guidance for designing high-performance VRFBs.
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