Xinzhuang Fan - Academia.edu (original) (raw)

Papers by Xinzhuang Fan

Research paper thumbnail of Numerical Modeling of a Convection-Enhanced Flow Field for High-Performance Redox Flow Batteries

Research paper thumbnail of A Secondary-Doped Polybenzimidazole Membrane with High Proton Conductivity and Ion Selectivity for Vanadium Redox Flow Batteries

Journal of The Electrochemical Society, Nov 1, 2022

Polybenzimidazole (PBI)-based membranes are one of the most promising proton exchange membranes f... more Polybenzimidazole (PBI)-based membranes are one of the most promising proton exchange membranes for vanadium redox flow batteries (VRFBs) due to their excellent ion selectivity. However, the relatively lower proton conductivity limits their application. Herein, a PBI membrane with both high proton conductivity and ion selectivity is prepared through a secondary phosphoric acid-doping method. The secondary-doped PBI membrane has a lower doping level in the surface layer while a higher doping level at the inner layer, forming a significant gradient-doped structure. In this structure, the former ensures an excellent ion selectivity while the latter enables a preferable proton conductivity. As a result, the VRFB with the secondary-doped PBI membrane exhibits an ultrahigh coulombic efficiency (CE) of 99.2% at the operating current density of 200 mA cm−2, which is significantly higher than that of the Nafion 212 membrane (97.7%), signifying an excellent ion selectivity. Meanwhile, the corresponding voltage efficiency (VE) is high up to 87.1%, which is also better than that of the Nafion 212 membrane (84.8%), indicating a high proton conductivity. Therefore, the secondary-doped PBI membrane might be a promising candidate for the highly efficient membrane for VRFB, and the secondary-doping method is simple and facile to realize engineering applications.

Research paper thumbnail of A response time-based method to operando decouple the polarizations in redox flow batteries

Cell reports physical science, May 1, 2023

Research paper thumbnail of Numerical modeling of interdigitated flow fields for scaled-up redox flow batteries

International Journal of Heat and Mass Transfer, Feb 1, 2023

Research paper thumbnail of Thermal issues of vanadium redox flow batteries

International Journal of Heat and Mass Transfer, Apr 1, 2023

Research paper thumbnail of A convection-enhanced flow field for aqueous redox flow batteries

International Journal of Heat and Mass Transfer, Nov 1, 2021

Research paper thumbnail of Enhanced cycle life of vanadium redox flow battery via a capacity and energy efficiency recovery method

Journal of Power Sources, Dec 1, 2020

Cycle life of VRFB is extended by recovering energy efficiency and capacity. • Capacity is restor... more Cycle life of VRFB is extended by recovering energy efficiency and capacity. • Capacity is restored by balancing electrolyte concentration, volume and valence. • Energy efficiency is restored by interchanging positive and negative terminals. • The method is effective with no need to replace electrolytes and electrodes.

Research paper thumbnail of A gradient porous electrode with balanced transport properties and active surface areas for vanadium redox flow batteries

Journal of Power Sources, Nov 1, 2019

Cadmium selenide (CdSe) quantum dots (QDs) were synthesized by water phase synthesis method using... more Cadmium selenide (CdSe) quantum dots (QDs) were synthesized by water phase synthesis method using 3-mercaptopropionic acid (3-MPA) as a stabilizer, and they were applied to the detection of copper ions (Cu 2+). The results showed that CdSe QDs have excellent selectivity and sensitivity toward Cu 2+. The fluorescence intensity of CdSe QDs decreased with the increase of Cu 2+ concentration. The linear range was from 30 nM to 3 µM, and the detection limit was 30 nM. Furthermore, CdSe QDs were used for detecting the concentration of Cu 2+ in oysters. The content of Cu 2+ was 40.91 mg/kg, which was close to the one measured via flame atomic absorption spectrometry (FAAS), and the relative error was 1.81%. Therefore, CdSe QDs have a wide application prospect in the rapid detection of copper ions in food.

Research paper thumbnail of Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries

Energy Storage Materials, Mar 1, 2020

Developing electrodes with high catalytic activity and cycling stability is essential to make van... more Developing electrodes with high catalytic activity and cycling stability is essential to make vanadium redox flow batteries (VRFBs) viable on a commercial level. In this work, hollow Ti 3 C 2 T x spheres, in the form of 3D nanostructured MXene, are investigated as electrocatalysts for V 3þ /V 2þ redox reactions. The first-principles study demonstrates that Ti 3 C 2 exhibits a metallic behavior with a high electrical conductivity. The catalytic effect of the material is then verified experimentally by cyclic voltammetry and electrochemical impedance spectra test. The hollow Ti 3 C 2 T x spheres decorated graphite felt electrodes are finally prepared and tested in the VRFB. It is shown that the prepared electrode enables the electrolyte utilization efficiency and energy efficiency to be as high as 80.1% and 81.3% at 200 mA cm À2 , which are 41.7% and 15.7% higher than that of the battery with the pristine electrode. At the current density of 300 mA cm À2 , the electrolyte utilization efficiency and energy efficiency can be still maintained at 62.9% and 75.0%, which are 44.5% and 12.8% higher than the battery with the XC-72 carbon nanoparticle decorated electrode. More impressively, the battery exhibits excellent stability with a high capacity retention rate and no energy efficiency decay over 500 charge-discharge cycles at a current density of 200 mA cm À2. The superior performance is ascribed to significant improvement in the electrochemical kinetics and enlarged active sites towards V 3þ /V 2þ redox reactions by the decoration of hollow MXene spheres.

Research paper thumbnail of Advanced dual-gradient carbon nanofibers/graphite felt composite electrode for the next-generation vanadium flow battery

Journal of Materials Science & Technology

Research paper thumbnail of Improvement of the Battery Performance of Vanadium Flow Battery by Enhancing the Specific Surface Area of the Carbon Felt Electrodes: II. Digging Effect

Journal of The Electrochemical Society, 2021

Aiming at the shortcoming of low specific surface area of the most commonly used carbon felt (CF)... more Aiming at the shortcoming of low specific surface area of the most commonly used carbon felt (CF) electrodes in vanadium flow battery (VFB), there are mainly two approaches to enhancing its specific surface area: anchoring effect and digging effect. Based on the digging effect, the CO2-etched CF has been fabricated by a simple heat treatment under the CO2atmosphere. As expected, lots of etch pits are formed and evenly distribute on the fiber surface, indicating a greatly enhanced surface area. Meanwhile, the content of O in the CO2-etched CF increases obviously, meaning the formation of more oxygen-containing groups, which are conducive to the improvement of hydrophilicity and electrochemical surface area. Furthermore, the oxygen-containing groups newly generated during the CO2etching process not only improve the hydrophilicity, but also enhance the electrocatalytic activity toward to the V3+/V2+redox couples. Consequently, VFB with CO2-etched CF as its electrodes presents significa...

Research paper thumbnail of A feasible strategy to enhance mass transfer property of carbon nanofibers electrode in vanadium redox flow battery

Electrochimica Acta, 2021

Abstract Carbon nanofibers (ECNFs) electrode possess good electrochemcial reactivity towards the ... more Abstract Carbon nanofibers (ECNFs) electrode possess good electrochemcial reactivity towards the V3+/V2+ and VO2+/VO2+ redox couples in vanadium redox flow battery (VRFB), while its inferior mass transfer property limits the cell power density seriously due to the lower porosity and poorer permeability. In order to improve the mass transfer property, starch based carbon microsphere (SCMS) of a few micrometers is synthesized by a green hydrothermal method and introduced into the electrospun precursor solution. Subsequently, a novel spherical-filament binary carbon nanofibers electrode (ECNFs-SCMS) is constructed by the controllable electrospining technique along with the subsequent heat treatment processes. The novel binary carbon nanofibers exhibits more loose structure, improved hydrophilia, increased oxygen contents and more defects, which result in the simultaneous improvement of electrochemical reaction area, electrocatalytic activity and mass transfer kinetics. The single VRFB cell with ECNFs-SCMS as electrodes shows higher energy efficiency and maximun power density as compared to the one with pure ECNFs electrodes. The results in this work suggest that improving permeability is a feasible strategy to enhance the mass transfer property of carbon nanofibers electrode.

Research paper thumbnail of Electrocatalytic Performance and Pseudo-Capacitive Characteristics of Modified Graphite Electrode with Fe3+/Fe2+ in H2SO4 Solution

Acta Physico-Chimica Sinica, 2012

The electrocatalytic performance and pseudocapacitive characteristics of a modified graphite elec... more The electrocatalytic performance and pseudocapacitive characteristics of a modified graphite electrode (MGE) with Fe 3+ /Fe 2+ in H2SO4 solution were studied by cyclic voltammetry (CV), constant current charge-discharge measurements, and electrochemical impedance spectroscopy (EIS). The results showed that the MGE had high electrocatalytic activity and good reversible characteristics for the redox reaction of Fe 3 + /Fe 2 + because of a large quantity of oxygen-containing functional groups on the MGE surface. The apparent area-specific capacitance of the MGE in 2.0 mol •L-1 H2SO4 solution containing 0.5 mol •L-1 Fe 3 + and 0.5 mol •L-1 Fe 2+ reached 2.157 F•cm-2 , which was almost double that in 2.0 mol •L-1 H2SO4 without Fe 3+ / Fe 2 +. Meanwhile, increasing the concentration of iron ions increased the capacitance of the MGE. The addition of Fe 3 + /Fe 2 + made the charge-discharge curves more symmetric and change more slowly, which increases the charge-discharge time, and effectively improves the capacitive energy storage and high power performance for an electrochemical capacitor (EC). The obvious capacitive characteristics were confirmed by EIS, and are attributed to the oxygen-containing functional groups on the MGE and the [Article]

Research paper thumbnail of Analyses and optimization of electrolyte concentration on the electrochemical performance of iron-chromium flow battery

Applied Energy, 2020

Effect of FeCl 2 , CrCl 3 and HCl concentration on the electrochemical performance of iron-chromi... more Effect of FeCl 2 , CrCl 3 and HCl concentration on the electrochemical performance of iron-chromium flow battery is systematically investigated, and the optimized electrolyte exhibits excellent battery efficiency (energy efficiency: 81.5%) at 120 mA cm −2 .

Research paper thumbnail of Enhanced electrochemical performance of the activated carbon electrodes with a facile and in-situ phosphoric acid modification

Journal of Energy Storage, 2019

A facile and in-situ modification approach is proposed to significantly improve the electrochemic... more A facile and in-situ modification approach is proposed to significantly improve the electrochemical performance of the commercial activated carbon (AC) electrode used in supercapacitor. After the phosphoric acid modification, the pore structure, specific surface area and conductivity of the AC electrode are almost unchanged, while the percentage composition of O and P is apparently increased, consequently the corresponding wettability and effective surface area are significantly improved. Electrochemical measurements show that the specific capacitance of the modified AC electrode is high up to 249 F g −1 , almost increasing 35% compared with that of the commercial AC electrode, and the capacitance retention after 10,000 cycles at 4 A g −1 still can reaches up to 97%, indicating a preferable cycling stability. Most importantly, the simple phosphoric acid modification used in this work results in such a significant improvement in the electrochemical performance on the premise of the commercial AC electrode, so the facile and in-situ modification method might be a promising approach to improving the electrochemical performance of the commercial AC electrode for the supercapacitor in the future.

Research paper thumbnail of The reduction reaction kinetics of vanadium(V) in acidic solutions on a platinum electrode with unusual difference compared to carbon electrodes

Electrochimica Acta, 2018

With the consideration of understanding the interplays between the electrolyte and electrode for ... more With the consideration of understanding the interplays between the electrolyte and electrode for the VO 2 þ /VO 2þ redox reactions at various electrodes and developing high-activity electrode materials for an all-vanadium redox flow battery, the reduction reaction kinetics of vanadium(V) ions on a platinum (Pt) electrode in comparison with that on carbon electrodes is investigated by steady-state potentiodynamic polarization and impedance spectroscopy measurements in sulfuric acid solutions with various pH and vanadium concentrations. No abnormal increase is observed neither in the cathodic Tafel slope nor the charge transfer resistance (R ct) at a transition potential (E K) on the Pt electrode. However, an abrupt change in the Tafel slope and R ct of vanadium(V) ions is observed on carbon electrodes. The above results indicate that the reduction reaction kinetics of vanadium(V) ions in acidic solutions on the Pt electrode show some unusual difference with that on carbon electrodes, and this is the first study to report such a new phenomenon. Additionally, possible mechanism pathways for the reduction reaction of vanadium(V) ions in acidic solutions are proposed for the above-mentioned carbon and Pt electrodes in this work.

Research paper thumbnail of A gradient bi-functional graphene-based modified electrode for vanadium redox flow batteries

Energy Storage Materials, 2018

Vanadium redox flow batteries (VRFBs) are an ideal choice for large-scale energy storage because ... more Vanadium redox flow batteries (VRFBs) are an ideal choice for large-scale energy storage because they have the advantages of long cycle life, flexible design and high safety. However, the poor electrocatalytic activity of carbon-based materials results in a large polarization resistance and energy loss during charge/discharge that greatly limits their commercial viability. Here we report a hybrid electrode with a gradient bi-functional oxygen-containing groups for VRFBs. It consists of a hybrid material of graphene oxide (GO), reduced graphene oxide (rGO) and graphene foam (GF) that combines materials with a high electrocatalytic activity (GO) and a high electrical conductivity (GF). One side is enriched with functional groups and provides preferential redox reversibility for VO 2+ /VO 2 + and V 3+ /V 2+ redox couples because of the electrocatalytic nature of the many oxygen functional groups. The side with the

Research paper thumbnail of CeO 2 embedded electrospun carbon nanofibers as the advanced electrode with high effective surface area for vanadium flow battery

Electrochimica Acta, 2016

Abstract Although electrospun carbon nanofibers (ECNFs) possess excellent conductivity, high surf... more Abstract Although electrospun carbon nanofibers (ECNFs) possess excellent conductivity, high surface area and good electrochemical activity toward vanadium redox couples, much surface area of ECNFs was still unutilized because of its poor hydrophilicity. CeO2 nanoparticles as an excellent hydrophilic agent are embedded in polyacrylonitrile (PAN) based carbon nanofibers by a simple electrospinning and subsequent carbonization process. The physicochemical characterizations show that the introduction of CeO2 nanoparticles slightly changes the structure and compositions of ECNFs, while the corresponding wettability is greatly improved. It is worth noting that the electrochemical surface area (ECSA) of CeO2/ECNFs is more than four times of that for ECNFs. According to the cyclic voltammograms (CV) and electrochemical impedance spectra (EIS) results, the addition of CeO2 improves the electrocatalytic activity toward the negative reaction of vanadium flow battery (VFB) to some extent while has less effect on that toward the positive reaction, the significant improvement in the electrochemical performance of CeO2/ECNFs might be mostly ascribed to the remarkable enhancement in ECSA. In addition, the charge/discharge tests further verify that CeO2/ECNFs with high ECSA could significantly reduces the electrochemical polarization during the discharging process and results in an enhanced discharge capacity and energy efficiency. The accomplishment of this work provides a new concept that it might be more convenient and effective to improve the electrochemical performance of the electrode materials for VFB by increasing their ECSA.

Research paper thumbnail of Improved electrochemical performance for vanadium flow battery by optimizing the concentration of the electrolyte

Journal of Power Sources, 2016

h i g h l i g h t s This work is developed based on physical property, half-cell and cell perform... more h i g h l i g h t s This work is developed based on physical property, half-cell and cell performance. Electrolyte of 1.6 M VOSO 4 and 2.8 M H 2 SO 4 exhibits the best performance. This work can provide direct guidance to the engineering application of VFB.

Research paper thumbnail of Kinetic investigation of vanadium (V)/(IV) redox couple on electrochemically oxidized graphite electrodes

Electrochimica Acta, 2016

The morphology, surface composition, wettability and the kinetic parameters of the electrochemica... more The morphology, surface composition, wettability and the kinetic parameters of the electrochemically oxidized graphite electrodes obtained under different anodic polarization conditions have been examined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, steady-state polarization and cyclic voltammetry (CV) tests, with an attempt to investigate the inherent correlation between the physicochemical properties and the kinetic characteristics for carbon electrodes used in an all-vanadium redox flow battery (VRFB). When the anodic polarization potential raises up to 1.8 V vs. SCE, the anodic corrosion of the graphite might happen and a large number of oxygen-containing functional groups generate. The VO 2 + /VO 2+ redox reaction can be facilitated and the reaction reversibility tends to become better with the increasing anodic potential, possibly owing to the increased surface oxides and the resulting improved wettability of the electrode. Based on this, a real reaction kinetic equation for the oxidation of VO 2+ has been obtained on the electrode polarized at 1.8 V vs. SCE and it can be also well used to predict the polarization behavior of the oxidized electrode in vanadium (IV) acidic solutions.

Research paper thumbnail of Numerical Modeling of a Convection-Enhanced Flow Field for High-Performance Redox Flow Batteries

Research paper thumbnail of A Secondary-Doped Polybenzimidazole Membrane with High Proton Conductivity and Ion Selectivity for Vanadium Redox Flow Batteries

Journal of The Electrochemical Society, Nov 1, 2022

Polybenzimidazole (PBI)-based membranes are one of the most promising proton exchange membranes f... more Polybenzimidazole (PBI)-based membranes are one of the most promising proton exchange membranes for vanadium redox flow batteries (VRFBs) due to their excellent ion selectivity. However, the relatively lower proton conductivity limits their application. Herein, a PBI membrane with both high proton conductivity and ion selectivity is prepared through a secondary phosphoric acid-doping method. The secondary-doped PBI membrane has a lower doping level in the surface layer while a higher doping level at the inner layer, forming a significant gradient-doped structure. In this structure, the former ensures an excellent ion selectivity while the latter enables a preferable proton conductivity. As a result, the VRFB with the secondary-doped PBI membrane exhibits an ultrahigh coulombic efficiency (CE) of 99.2% at the operating current density of 200 mA cm−2, which is significantly higher than that of the Nafion 212 membrane (97.7%), signifying an excellent ion selectivity. Meanwhile, the corresponding voltage efficiency (VE) is high up to 87.1%, which is also better than that of the Nafion 212 membrane (84.8%), indicating a high proton conductivity. Therefore, the secondary-doped PBI membrane might be a promising candidate for the highly efficient membrane for VRFB, and the secondary-doping method is simple and facile to realize engineering applications.

Research paper thumbnail of A response time-based method to operando decouple the polarizations in redox flow batteries

Cell reports physical science, May 1, 2023

Research paper thumbnail of Numerical modeling of interdigitated flow fields for scaled-up redox flow batteries

International Journal of Heat and Mass Transfer, Feb 1, 2023

Research paper thumbnail of Thermal issues of vanadium redox flow batteries

International Journal of Heat and Mass Transfer, Apr 1, 2023

Research paper thumbnail of A convection-enhanced flow field for aqueous redox flow batteries

International Journal of Heat and Mass Transfer, Nov 1, 2021

Research paper thumbnail of Enhanced cycle life of vanadium redox flow battery via a capacity and energy efficiency recovery method

Journal of Power Sources, Dec 1, 2020

Cycle life of VRFB is extended by recovering energy efficiency and capacity. • Capacity is restor... more Cycle life of VRFB is extended by recovering energy efficiency and capacity. • Capacity is restored by balancing electrolyte concentration, volume and valence. • Energy efficiency is restored by interchanging positive and negative terminals. • The method is effective with no need to replace electrolytes and electrodes.

Research paper thumbnail of A gradient porous electrode with balanced transport properties and active surface areas for vanadium redox flow batteries

Journal of Power Sources, Nov 1, 2019

Cadmium selenide (CdSe) quantum dots (QDs) were synthesized by water phase synthesis method using... more Cadmium selenide (CdSe) quantum dots (QDs) were synthesized by water phase synthesis method using 3-mercaptopropionic acid (3-MPA) as a stabilizer, and they were applied to the detection of copper ions (Cu 2+). The results showed that CdSe QDs have excellent selectivity and sensitivity toward Cu 2+. The fluorescence intensity of CdSe QDs decreased with the increase of Cu 2+ concentration. The linear range was from 30 nM to 3 µM, and the detection limit was 30 nM. Furthermore, CdSe QDs were used for detecting the concentration of Cu 2+ in oysters. The content of Cu 2+ was 40.91 mg/kg, which was close to the one measured via flame atomic absorption spectrometry (FAAS), and the relative error was 1.81%. Therefore, CdSe QDs have a wide application prospect in the rapid detection of copper ions in food.

Research paper thumbnail of Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries

Energy Storage Materials, Mar 1, 2020

Developing electrodes with high catalytic activity and cycling stability is essential to make van... more Developing electrodes with high catalytic activity and cycling stability is essential to make vanadium redox flow batteries (VRFBs) viable on a commercial level. In this work, hollow Ti 3 C 2 T x spheres, in the form of 3D nanostructured MXene, are investigated as electrocatalysts for V 3þ /V 2þ redox reactions. The first-principles study demonstrates that Ti 3 C 2 exhibits a metallic behavior with a high electrical conductivity. The catalytic effect of the material is then verified experimentally by cyclic voltammetry and electrochemical impedance spectra test. The hollow Ti 3 C 2 T x spheres decorated graphite felt electrodes are finally prepared and tested in the VRFB. It is shown that the prepared electrode enables the electrolyte utilization efficiency and energy efficiency to be as high as 80.1% and 81.3% at 200 mA cm À2 , which are 41.7% and 15.7% higher than that of the battery with the pristine electrode. At the current density of 300 mA cm À2 , the electrolyte utilization efficiency and energy efficiency can be still maintained at 62.9% and 75.0%, which are 44.5% and 12.8% higher than the battery with the XC-72 carbon nanoparticle decorated electrode. More impressively, the battery exhibits excellent stability with a high capacity retention rate and no energy efficiency decay over 500 charge-discharge cycles at a current density of 200 mA cm À2. The superior performance is ascribed to significant improvement in the electrochemical kinetics and enlarged active sites towards V 3þ /V 2þ redox reactions by the decoration of hollow MXene spheres.

Research paper thumbnail of Advanced dual-gradient carbon nanofibers/graphite felt composite electrode for the next-generation vanadium flow battery

Journal of Materials Science & Technology

Research paper thumbnail of Improvement of the Battery Performance of Vanadium Flow Battery by Enhancing the Specific Surface Area of the Carbon Felt Electrodes: II. Digging Effect

Journal of The Electrochemical Society, 2021

Aiming at the shortcoming of low specific surface area of the most commonly used carbon felt (CF)... more Aiming at the shortcoming of low specific surface area of the most commonly used carbon felt (CF) electrodes in vanadium flow battery (VFB), there are mainly two approaches to enhancing its specific surface area: anchoring effect and digging effect. Based on the digging effect, the CO2-etched CF has been fabricated by a simple heat treatment under the CO2atmosphere. As expected, lots of etch pits are formed and evenly distribute on the fiber surface, indicating a greatly enhanced surface area. Meanwhile, the content of O in the CO2-etched CF increases obviously, meaning the formation of more oxygen-containing groups, which are conducive to the improvement of hydrophilicity and electrochemical surface area. Furthermore, the oxygen-containing groups newly generated during the CO2etching process not only improve the hydrophilicity, but also enhance the electrocatalytic activity toward to the V3+/V2+redox couples. Consequently, VFB with CO2-etched CF as its electrodes presents significa...

Research paper thumbnail of A feasible strategy to enhance mass transfer property of carbon nanofibers electrode in vanadium redox flow battery

Electrochimica Acta, 2021

Abstract Carbon nanofibers (ECNFs) electrode possess good electrochemcial reactivity towards the ... more Abstract Carbon nanofibers (ECNFs) electrode possess good electrochemcial reactivity towards the V3+/V2+ and VO2+/VO2+ redox couples in vanadium redox flow battery (VRFB), while its inferior mass transfer property limits the cell power density seriously due to the lower porosity and poorer permeability. In order to improve the mass transfer property, starch based carbon microsphere (SCMS) of a few micrometers is synthesized by a green hydrothermal method and introduced into the electrospun precursor solution. Subsequently, a novel spherical-filament binary carbon nanofibers electrode (ECNFs-SCMS) is constructed by the controllable electrospining technique along with the subsequent heat treatment processes. The novel binary carbon nanofibers exhibits more loose structure, improved hydrophilia, increased oxygen contents and more defects, which result in the simultaneous improvement of electrochemical reaction area, electrocatalytic activity and mass transfer kinetics. The single VRFB cell with ECNFs-SCMS as electrodes shows higher energy efficiency and maximun power density as compared to the one with pure ECNFs electrodes. The results in this work suggest that improving permeability is a feasible strategy to enhance the mass transfer property of carbon nanofibers electrode.

Research paper thumbnail of Electrocatalytic Performance and Pseudo-Capacitive Characteristics of Modified Graphite Electrode with Fe3+/Fe2+ in H2SO4 Solution

Acta Physico-Chimica Sinica, 2012

The electrocatalytic performance and pseudocapacitive characteristics of a modified graphite elec... more The electrocatalytic performance and pseudocapacitive characteristics of a modified graphite electrode (MGE) with Fe 3+ /Fe 2+ in H2SO4 solution were studied by cyclic voltammetry (CV), constant current charge-discharge measurements, and electrochemical impedance spectroscopy (EIS). The results showed that the MGE had high electrocatalytic activity and good reversible characteristics for the redox reaction of Fe 3 + /Fe 2 + because of a large quantity of oxygen-containing functional groups on the MGE surface. The apparent area-specific capacitance of the MGE in 2.0 mol •L-1 H2SO4 solution containing 0.5 mol •L-1 Fe 3 + and 0.5 mol •L-1 Fe 2+ reached 2.157 F•cm-2 , which was almost double that in 2.0 mol •L-1 H2SO4 without Fe 3+ / Fe 2 +. Meanwhile, increasing the concentration of iron ions increased the capacitance of the MGE. The addition of Fe 3 + /Fe 2 + made the charge-discharge curves more symmetric and change more slowly, which increases the charge-discharge time, and effectively improves the capacitive energy storage and high power performance for an electrochemical capacitor (EC). The obvious capacitive characteristics were confirmed by EIS, and are attributed to the oxygen-containing functional groups on the MGE and the [Article]

Research paper thumbnail of Analyses and optimization of electrolyte concentration on the electrochemical performance of iron-chromium flow battery

Applied Energy, 2020

Effect of FeCl 2 , CrCl 3 and HCl concentration on the electrochemical performance of iron-chromi... more Effect of FeCl 2 , CrCl 3 and HCl concentration on the electrochemical performance of iron-chromium flow battery is systematically investigated, and the optimized electrolyte exhibits excellent battery efficiency (energy efficiency: 81.5%) at 120 mA cm −2 .

Research paper thumbnail of Enhanced electrochemical performance of the activated carbon electrodes with a facile and in-situ phosphoric acid modification

Journal of Energy Storage, 2019

A facile and in-situ modification approach is proposed to significantly improve the electrochemic... more A facile and in-situ modification approach is proposed to significantly improve the electrochemical performance of the commercial activated carbon (AC) electrode used in supercapacitor. After the phosphoric acid modification, the pore structure, specific surface area and conductivity of the AC electrode are almost unchanged, while the percentage composition of O and P is apparently increased, consequently the corresponding wettability and effective surface area are significantly improved. Electrochemical measurements show that the specific capacitance of the modified AC electrode is high up to 249 F g −1 , almost increasing 35% compared with that of the commercial AC electrode, and the capacitance retention after 10,000 cycles at 4 A g −1 still can reaches up to 97%, indicating a preferable cycling stability. Most importantly, the simple phosphoric acid modification used in this work results in such a significant improvement in the electrochemical performance on the premise of the commercial AC electrode, so the facile and in-situ modification method might be a promising approach to improving the electrochemical performance of the commercial AC electrode for the supercapacitor in the future.

Research paper thumbnail of The reduction reaction kinetics of vanadium(V) in acidic solutions on a platinum electrode with unusual difference compared to carbon electrodes

Electrochimica Acta, 2018

With the consideration of understanding the interplays between the electrolyte and electrode for ... more With the consideration of understanding the interplays between the electrolyte and electrode for the VO 2 þ /VO 2þ redox reactions at various electrodes and developing high-activity electrode materials for an all-vanadium redox flow battery, the reduction reaction kinetics of vanadium(V) ions on a platinum (Pt) electrode in comparison with that on carbon electrodes is investigated by steady-state potentiodynamic polarization and impedance spectroscopy measurements in sulfuric acid solutions with various pH and vanadium concentrations. No abnormal increase is observed neither in the cathodic Tafel slope nor the charge transfer resistance (R ct) at a transition potential (E K) on the Pt electrode. However, an abrupt change in the Tafel slope and R ct of vanadium(V) ions is observed on carbon electrodes. The above results indicate that the reduction reaction kinetics of vanadium(V) ions in acidic solutions on the Pt electrode show some unusual difference with that on carbon electrodes, and this is the first study to report such a new phenomenon. Additionally, possible mechanism pathways for the reduction reaction of vanadium(V) ions in acidic solutions are proposed for the above-mentioned carbon and Pt electrodes in this work.

Research paper thumbnail of A gradient bi-functional graphene-based modified electrode for vanadium redox flow batteries

Energy Storage Materials, 2018

Vanadium redox flow batteries (VRFBs) are an ideal choice for large-scale energy storage because ... more Vanadium redox flow batteries (VRFBs) are an ideal choice for large-scale energy storage because they have the advantages of long cycle life, flexible design and high safety. However, the poor electrocatalytic activity of carbon-based materials results in a large polarization resistance and energy loss during charge/discharge that greatly limits their commercial viability. Here we report a hybrid electrode with a gradient bi-functional oxygen-containing groups for VRFBs. It consists of a hybrid material of graphene oxide (GO), reduced graphene oxide (rGO) and graphene foam (GF) that combines materials with a high electrocatalytic activity (GO) and a high electrical conductivity (GF). One side is enriched with functional groups and provides preferential redox reversibility for VO 2+ /VO 2 + and V 3+ /V 2+ redox couples because of the electrocatalytic nature of the many oxygen functional groups. The side with the

Research paper thumbnail of CeO 2 embedded electrospun carbon nanofibers as the advanced electrode with high effective surface area for vanadium flow battery

Electrochimica Acta, 2016

Abstract Although electrospun carbon nanofibers (ECNFs) possess excellent conductivity, high surf... more Abstract Although electrospun carbon nanofibers (ECNFs) possess excellent conductivity, high surface area and good electrochemical activity toward vanadium redox couples, much surface area of ECNFs was still unutilized because of its poor hydrophilicity. CeO2 nanoparticles as an excellent hydrophilic agent are embedded in polyacrylonitrile (PAN) based carbon nanofibers by a simple electrospinning and subsequent carbonization process. The physicochemical characterizations show that the introduction of CeO2 nanoparticles slightly changes the structure and compositions of ECNFs, while the corresponding wettability is greatly improved. It is worth noting that the electrochemical surface area (ECSA) of CeO2/ECNFs is more than four times of that for ECNFs. According to the cyclic voltammograms (CV) and electrochemical impedance spectra (EIS) results, the addition of CeO2 improves the electrocatalytic activity toward the negative reaction of vanadium flow battery (VFB) to some extent while has less effect on that toward the positive reaction, the significant improvement in the electrochemical performance of CeO2/ECNFs might be mostly ascribed to the remarkable enhancement in ECSA. In addition, the charge/discharge tests further verify that CeO2/ECNFs with high ECSA could significantly reduces the electrochemical polarization during the discharging process and results in an enhanced discharge capacity and energy efficiency. The accomplishment of this work provides a new concept that it might be more convenient and effective to improve the electrochemical performance of the electrode materials for VFB by increasing their ECSA.

Research paper thumbnail of Improved electrochemical performance for vanadium flow battery by optimizing the concentration of the electrolyte

Journal of Power Sources, 2016

h i g h l i g h t s This work is developed based on physical property, half-cell and cell perform... more h i g h l i g h t s This work is developed based on physical property, half-cell and cell performance. Electrolyte of 1.6 M VOSO 4 and 2.8 M H 2 SO 4 exhibits the best performance. This work can provide direct guidance to the engineering application of VFB.

Research paper thumbnail of Kinetic investigation of vanadium (V)/(IV) redox couple on electrochemically oxidized graphite electrodes

Electrochimica Acta, 2016

The morphology, surface composition, wettability and the kinetic parameters of the electrochemica... more The morphology, surface composition, wettability and the kinetic parameters of the electrochemically oxidized graphite electrodes obtained under different anodic polarization conditions have been examined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, steady-state polarization and cyclic voltammetry (CV) tests, with an attempt to investigate the inherent correlation between the physicochemical properties and the kinetic characteristics for carbon electrodes used in an all-vanadium redox flow battery (VRFB). When the anodic polarization potential raises up to 1.8 V vs. SCE, the anodic corrosion of the graphite might happen and a large number of oxygen-containing functional groups generate. The VO 2 + /VO 2+ redox reaction can be facilitated and the reaction reversibility tends to become better with the increasing anodic potential, possibly owing to the increased surface oxides and the resulting improved wettability of the electrode. Based on this, a real reaction kinetic equation for the oxidation of VO 2+ has been obtained on the electrode polarized at 1.8 V vs. SCE and it can be also well used to predict the polarization behavior of the oxidized electrode in vanadium (IV) acidic solutions.