Mass Transfer and Reaction Kinetic Enhanced Electrode for High‐Performance Aqueous Flow Batteries

Abstract

A scalable and efficient process to modify electrodes with enhanced mass transfer and reaction kinetics is critical for redox flow batteries (RFBs). For the first time, this work introduces electrochemical exfoliation as a surface modification method of graphite felt (GF) to enhance the mass transfer and reaction kinetics in RFBs. Anion intercalation and subsequent gas evolutions at room temperature for one minute expand the graphite layers that increase the electrode surface area. Meanwhile, sufficient oxygen functional groups are introduced to the electrode, resulting in enhanced reaction kinetics and improved hydrophilicity. Further, spin-polarized density functional theory is employed to reveal the role of oxygen functional groups in accelerating the vanadium redox reaction. Benefitting from sufficient oxygen groups, larger surface area, and superior wettability, the as-prepared exfoliated GF (E-GF) shows exceptional electrocatalytic activity with minimized overpotential, higher volumetric capacity, and improved energy efficiency. The redox flow battery assembled with the E-GF electrode delivers voltage and energy efficiencies of 89.72% and 86.41% at the current density of 100 mA cm −2 , respectively. Remarkably, compared to the traditional GF treatment method, the elimination of the high temperature and long-time treatment processes make this approach much more energy and time efficient, scalable, and affordable for large-scale manufacturing.

The effect of plasma treated carbon felt on the performance of aqueous quinone‐based redox flow batteries

“…According to Figure S5, the nitrogen groups formed on CF surface make the CF surface more hydrophilic, and this increases the frequency of contact between CF surface and the molecules of TironA due to the improved mass transfer and reduced charge transfer resistance. Such benefits can induce the reduction in over‐potential of QRFB full cells 16,41,42 …”

“…Such benefits can induce the reduction in over-potential of QRFB full cells. 16,41,42 3.4 | Performance evaluations of QRFB full cells using N 2 plasma-treated CF According to the optimized plasma conditions and kinetic property data, it is expected the optimized N 2 plasma-treated CF will be useful as the positive electrode of QRFB full cells. With this anticipation, its effects on the performance of QRFB full cell is investigated (Figure 8).…”

Versatile zero‐ to three‐dimensional carbon for electrochemical energy storage

“…In summary, 0D sphere carbonous materials improve active materials' contact and electron transportation in the electrode. Moreover, the sphere structures, such as core-shell and yolk-shell structures, enable blocking or minimizing the active materials' loss caused by phase Bifunctional and tunable mesoporous carbon sphere for Li-sulfur battery [33] Nanostructured Si/porous carbon spherical composite as an anode for Li-ion battery [34] Sandwich-like hollow sphere anode for Li-ion battery [35] 1D carbon fiber • Low percolation threshold • Excellent electrical conductivity Carbon fiber prepared by electrospinning as an anode for Li-ion battery [36] Sulfur@carbonized mesoporous wood fiber as cathode [37] Exfoliated graphite fiber for electrode in flow battery [38] Carbon nanofiber foam pyrolyzing bacterial cellulose [39] 2D layered carbon Stacked graphene used as an anode for Li-ion battery [40] Corrugated graphene sheets as electrodes in a supercapacitor [41] LiNi 0.5 Mn 0.5 O 4 /graphene composites as cathodes for lithium-ion batteries [42] Caterpillar-like and reconfigurable graphene as a sulfur host in Li-sulfur battery [43] 3D bulky carbon • Ordered and interconnected porous structures • Free-standing strucrure • Good electrical conductivity Activated wood carbon and MnO 2 /wood carbon in an asymmetric supercapacitor [44] Freestanding wood-based carbon electrode for vanadium flow battery [45] Wood-derived carbon with a hierarchical porous structure as a gas diffusion layer in Li-O 2 battery [46] F I G U R E 2 (See caption on next page) change, volume expansion, shuttle effect, or pulverization. The excellent electrical conductivity and protection of active materials significantly improve the reversible capacity, rate performance, and cycling stability.…”

“…Reproduced with permission: Copyright 2009, Wiley 59 However, the small surface area and the low surface hydrophilicity limit its effectiveness. 70 Mukhopadhyay et al 38 proposed a fast, scalable, and environmentally friendly method to fabricate a hierarchical core-shell framework of graphite fibers to obtain ultrahigh surface areas, as shown in Figure 4D. The surface properties of the graphite fiber were significantly modified by treatment with a controlled electrochemical exfoliation in 0.1 M (NH 4 ) 2 SO 4 by applying a 10 V positive bias voltage, which conducted a high specific surface area and functionalized oxygen groups on the surface.…”

Densely Populated Bismuth Nanosphere Semi‐Embedded Carbon Felt for Ultrahigh‐Rate and Stable Vanadium Redox Flow Batteries

“…[ 18,19 ] To date, several approaches have been developed to improve the electrode kinetics, mainly including introducing functional groups, carbon, and metal or metal oxide/carbide/nitride nanomaterials onto the carbon surfaces. [ 20–40 ] Although oxygen containing functional groups have been demonstrated to function as active sites to bridge the active vanadium species and catalyze the electron‐transfer processes, immobilizing the functional groups in a wide potential range (−0.5–1.4 V vs SHE) during VRFB operations remained a challenging issue in practical applications. In this sense, more attentions should be paid to electrocatalysts that have good electrochemical and chemical stabilities in the VRFB environment.…”