A Comprehensive Study on Hydroxyl Multiwalled Carbon Nanotubes Used as Catalysts for VO₂⁺/VO²⁺ Reaction in Vanadium Redox Flow Battery

Abstract

A comprehensive study on the hydroxyl multiwalled carbon nanotubes (hydroxyl MWCNTs) as catalysts in a positive reaction was performed to improve the efficiency of the vanadium redox flow battery (VRFB). e physicochemical properties of the hydroxyl MWCNT-modified electrode were characterized by using a scanning electron microscope (SEM), conductivity measurement, Brunner-Emmet-Teller (BET) measurement, X-ray photoelectron spectroscopy (XPS) analysis, cyclic voltammetry (CV) tests, electrochemical impedance spectroscopy (EIS) analysis, and charge-discharge tests. e prepared composite electrode possesses a huge amount of oxygen-containing groups, high-specific surface area, high electrical conductivity, and high catalytic activity towards the VO 2 + /VO 2+ reaction based on physicochemical characterization. e hydroxyl MWCNT-modified graphite felt (hydroxyl MWCNTs/GF) shows the best cell performance with the energy efficiency of 79.74% and remains in high stability after 50 cycles. e improved cell performance is probably ascribed to the increase in active sites, fast charge transfer, and mass transfer rate of the introduced hydroxyl MWCNTs.

Recent progress on carbon and metal based electrocatalysts for vanadium redox flow battery

“…The CE, VE, and EE are 97.5%, 91.2%, and 88.9%, respectively, at the current density of 20 mA cm −2 . Li et al (2019) also reported the performance of hydroxyl MWCNT‐modified graphite felt. The cell using hydroxyl MWCNTs/GF electrodes showed CE ~96.01, VE ~83.05, and EE ~79.74, and remained stable up to 50 cycles.…”

“…As a result, the performance of VRFB cells in term of VE and EE were measured, and found that POH‐CNT/GF (VE: 83.79% and EE: 79.74%) exhibited highest performance compared to pristine CNT/GF (78.13% and 73.98%) and CR‐CNT/GF (81.21% and 77.26%) based VRFB. Influenced by the efficacy of CNT, multi‐walled CNT (MWCNT) were tested as a electrocatalyst on carbon felt and graphite felt electrode for VRFB (Li et al, 2011, 2019). Three forms of MWCNT that is, carboxyl and hydroxyl functionalized, and pristine MWCNT were tested.…”

Recent Development of Carbon-based Electrode for Vanadium Redox Flow Battery

“…[13][14][15] The large surface area introduced by chemical treatment and the deposition of carbon nanomaterials are also enhanced reaction points for the vanadium species on the electrodes. [22][23][24][25][26][27][28][29] In recent research, the optimal combination of thermally activated and nonactivated carbon felts in VO 2+ /VO 2 + and V 2+ /V 3+ redox couples showed the most efficient configuration. 31 The electron transfer was found to occur by an inner-sphere process in VO 2+ /VO 2 + redox couple, whereas redox reaction of V 2+ /V 3+ progressed an outer-sphere electron transfer.…”

“…15 With some of metal and metal oxide additions, the chemical stability of the electrode surface remains poor, and the introduction is not inexpensive. Carbon-based nanostructured materials include carbon nanofibers (CNFs), 22 carbon nanotubes (CNTs), [23][24][25][26] and graphene (graphene oxide, nanowalls), 27,28 carbon nanosheets and nanorods. 29 These modification, deposition and growth techniques with carbon nanomaterials introduce enhanced wettability, a much larger surface area, and higher conductivity for vanadium RFBs.…”

Sustainable electrodes for the next generation of redox flow batteries

“…A schematic synthesis route of the process is shown in figure 2. These carbon-based electrocatalysts include activated carbon (AC) [36], carbon nanofibers (CNFs) 37], carbon aerogels [38, [39], graphene [40][41][42], graphene oxide (GO) [43], reduced GO (rGO) [44,45], carbon nanotubes [46,47], carbon microspheres [48], or carbon nanorods [49]. AC has been widely researched as electrode because of its high porosity, electrical conductivity, and stability in acidic media, enabling it to provide more active sites for electrocatalytic reactions [50,51].…”