Flowable Conducting Particle Networks in Redox-Active Electrolytes for Grid Energy Storage

Abstract

This study reports a new hybrid approach toward achieving high volumetric energy and power densities in an electrochemical flow capacitor for grid energy storage. The electrochemical flow capacitor suffers from high self-discharge and low energy density because charge storage is limited to the available surface area (electric double layer charge storage). Here, we examine two carbon materials as conducting particles in a flow battery electrolyte containing the VO 2+ /VO 2 + redox couple. Highly porous activated carbon spheres (CSs) and multi-walled carbon nanotubes (MWCNTs) are investigated as conducting particle networks that facilitate both faradaic and electric double layer charge storage. Charge storage contributions (electric double layer and faradaic) are distinguished for flow-electrodes composed of MWCNTs and activated CSs. A MWCNT flow-electrode based in a redox-active electrolyte containing the VO 2+ /VO 2 + redox couple demonstrates 18% less self-discharge, 10 X more energy density, and 20 X greater power densities (at 20 mV s −1 ) than one based on a non-redox active electrolyte. Furthermore, a MWCNT redox-active flow electrode demonstrates 80% capacitance retention, and >95% coulombic efficiency over 100 cycles, indicating the feasibility of utilizing conducting networks with redox chemistries for grid energy storage. Grid energy storage is a critical component toward the integration of renewable energy technologies and ensuring reliable distribution of electricity.1,2 Numerous flow-assisted electrochemical systems (FAESs) based on different active materials are being pursued including redox flow batteries (RFB), 3-5 semi-solid flow batteries, 6,7 organic-redox flow batteries, [8][9][10] and the electrochemical flow capacitor (EFC).11,12 A flow-architecture provides for scalable and modular systems, decoupled power and energy densities, and a potentially low-cost means for storing energy at the grid level (Fig. 1a).All FAESs utilize active materials either dissolved in an electrolyte solution or suspended in an electrically conductive flow-electrode for scalable energy storage (Fig. 1). Redox-flow batteries and organicredox flow batteries both utilize soluble redox species as the active materials (Figs. 1c and 1d). In traditional RFBs, soluble metal ions (vanadium, cerium, iron, etc.) are used, while organic RFBs utilize soluble organic compounds (e.g. quinones) as active material. Metal ions have been widely studied in commercial RFBs and are the closest technology to be widely used. FAESSs based on organic compounds are new and promising for grid energy storage applications because they do not rely on precious metals, have tunable properties based on their chemical structure, 13,14 and have the potential to be low-cost, durable, environmentally friendly, and scalable. Both of these systems rely on chemical reactions based on heterogeneous charge transfer for charge storage. Vanadium compounds have been known to have sluggish kinetics when compared to quinone-based molecules, which undergo rapid t...

3D-printed conductive static mixers enable all-vanadium redox flow battery using slurry electrodes

“…However, the polarization curves show a significantly lower cutoff current density of AC slurries compared to the GF electrode. This phenomenon may be explained by the high porosity of the AC particles which adsorbs redox active species, thus resulting in lower current densities due to internal mass transport limitations [19]. Therefore, graphite powder is used as alternative to AC.…”

“…AC was was identified as unsuitable due to the adsorptive surface properties. In contrast, CNT resulted in improved electrode characteristics [19]. However, CNTs may be expensive in such large-capacity batteries.…”

Pseudocapacitive Electrodes Produced by Oxidant‐Free Polymerization of Pyrrole between the Layers of 2D Titanium Carbide (MXene)

“…To determine the charge storage ability of the PPy/Ti 3 C 2 T x films, we conducted cyclic voltammetry (CV) experiments ( Figure a) in 1 m H 2 SO 4 at various sweep rates in the potential window from −0.2 to 0.35 V versus Ag/AgCl. The acidic electrolyte was chosen due to its high conductivity and because it promotes surface redox reactions for PPy . Across all scan rates, CVs of the PPy/Ti 3 C 2 T x (1:2) remained pseudorectangular with no peaks due to redox processes in a narrow range of potentials.…”

Waste Tire Derived Carbon–Polymer Composite Paper as Pseudocapacitive Electrode with Long Cycle Life

“…[28,[31][32][33] The GCPL of PANI/TC electrodes (Figure 4d)a tv ariousc urrent densities (3,5,8,10, and 15 Ag À1 )s howedt wo distinct voltage stages between + 0.8 Vt o+ 0.5 Va nd + 0.5 Vt o À0.2 V. The first linear potential stage of the dischargep lot can be assignedt ot he double-layerc apacitance from TC, while the other can be ascribed to the combinedd ouble-layer and faradicc ontribution of the PANI. [34,35] The discharge time of the PANI/TC electrodes was increased by decreasing the current density,i ndicating good ion accessibility at low current densities, and vice versa. The symmetric charge/discharge curves reveal highe lectrochemical reversibility and satisfactory coulombice fficiency (80 %a t1 5Ag…”