Efficient Edge Plane Exposure on Graphitic Carbon Fiber for Enhanced Flow-Battery Reactions

Abstract

Surface treatments are often applied to carbon materials to impart specific functions to the surface. Surface oxidation is a typical treatment to form oxygen-containing surface functional groups on carbon fiber electrodes of redox flow batteries in order to enhance the performance, which has attracted much attention as a large-scale electric energy storage system. At present, however, little attention has been paid to the effect of the edge plane exposure. In this study, fine etching of the graphitized carbon fiber surface was attained by coating the surface with a metal-containing carbonaceous thin film and thermal oxidation. The etching was caused by the catalysis of the metal species; the mechanism and the effect of the carbonaceous film were demonstrated by in situ X-ray absorption fine structure measurements. The finely etched surface possessed substantially enriched edge planes and an enhanced activity for the positive and negative electrode reactions of the vanadium redox flow battery. The flow cell test with the carbon fiber electrodes after the tuned etching showed a significant decrease in the overpotential and increase in the efficiency as well as stable cycling performance.

Nanoscopic Combination of Edge and Flat Planes in the Active Site for Oxygen Reduction and Evolution

“…The surface etching of the HOPG basal plane was enabled by coating with a carbonaceous thin film derived from cobalt phthalocyanine (CoPc) and thermal oxidation based on our recent study. [12] Co oxide nanoparticles were generated during the thermal oxidation and functioned as a catalyst for the fine carbon surface etching, which were easily removed by an acid treatment afterwards. The Fe-N x unit was imparted by coating the FePc-derived carbonaceous thin film and treating it with an acid to remove the soluble Fe species.…”

Electrocatalysis at Electrodes for Vanadium Redox Flow Batteries

“…Selective etching of graphitic carbon paper assisted by various metal catalysts has been employed by Maruyama et al [316]. Enhanced exposure of edge planes of graphite known to be of higher electrocatalytic activity than basal planes was found.…”

Concurrent nanoscale surface etching and SnO2 loading of carbon fibers for vanadium ion redox enhancement

“…Graphitic carbon paper (TGP-H-090, Toray, abbreviated as TGP) was used as the substrate. The SnPc-derived carbonaceous thin film (CSnPc; obtained thorugh sublimation, deposition, and pyrolysis of SnPc in a single-step heat treatment in an Ar atmosphere at 700 °C) was coated on the carbon fiber surface following the method reported in [15,20]. The obtained sample was labeled TGP-CSnPc.…”

“…Carbon-fiber electrodes are conventionally used in RFBs and surface oxidation is often performed to enhance the redox reactions [7–14], although a sufficient activity has not yet been obtained. Recently, we found a method to efficiently expose the edge planes of the carbon fiber surface by nanoscale etching, which had a significant enhancement effect on the redox reactions of vanadium ions [15]. The reactions shown below are involved in the vanadium redox flow batteries (VRFBs), which are in the most advanced stage of research and development:…”