Cyclic Stability Test Research Articles

Anomalous increase in specific capacitance in MXene during galvanostatic cycling studies

Layered Ti3C2 is attracting much attention as a promising electrode material for energy storage devices due to its excellent electrical conductivity and electrochemical properties due to its surface functional groups. Though various methods have been used to etch Ti3AlC2, the energy storage performance of Ti3C2 mainly depends on exfoliation of aluminium, surface functional groups and intercalation of potassium. Hence, the optimization of Ti3AlC2 etching process has been done by hydrothermal, stirring, and ultra-sonication methods which exhibits a different specific capacitance of 8.7 F g−1, 23.75 F g-1, and 141.45 F g−1 respectively in 3 M KOH electrolyte at 2 mA constant current galvanostatic charge/discharge (GCD) analysis even though same etching time and quantity of MAX materials used. Surprisingly, all the samples show an increased specific capacitance up to 2000th cycles and a maximum value of around 170 % is reached and this value is maintained until 5000 charge-discharge cycle at 10 mA by GCD analysis. These electrochemical differences are investigated in terms TiAl bond termination and formation of O-Ti-O bonds due to the removal by Al during etching process. It is found from XPS analysis that -OH surface termination has occurred with F desorption and the interaction of K+ ion has increased the interlayer space between the individual layers. Moreover, the material has been phase transformed from Ti3C2 to TiO2/Ti3C2 hybrid crystal structure during the cycling stability test. The high dipole moment in TiO2/Ti3C2 hybrid structure due to the decreased work function has increased the specific capacitance of MXene electrode material. To the best of the authors' knowledge, this has not been observed previously and reported.

Few-layered nitrogen-doped graphene wrapped three-dimensional titanium oxide flower as a robust support for Pt nanoparticles in catalyzing oxygen reduction reaction

• Few-layered nitrogen-doped graphene wrapped 3D flower-like TiO 2 is synthesized. • The anti-corrosion support has a high surface area and electronic conductivity. • Pt-TiO 2 @N-Gr-800 exhibits superior ORR activity, stability, and CO tolerance. • Pt-TiO 2 @N-Gr-800 shows a strong metal and support interaction. Carbon materials are commonly used as electrocatalyst supports in fuel cells. Nevertheless, carbon corrosion is a severe concern under strong acidic and oxidizing environments. Hence, developing a robust catalyst support is critical to ensuring fuel cells stability. Herein, we report a unique support of few-layered nitrogen-doped graphene wrapped three-dimensional (3D) flower-like anatase TiO 2 (TiO 2 @N-Gr) via in-situ polymerizing dopamine on the surface of a 3D-TiO 2 flower precursor, followed by pyrolysis. After loading Pt nanoparticles, Pt-TiO 2 @N-Gr-800 exhibits comparable ORR activity to the commercial Pt/C catalyst (E 1/2 = 0.91 V RHE ), superior stability in a 30 K cycling stability test and strong CO resistance capability. The outstanding performance of the Pt-TiO 2 @N-Gr-800 catalyst is attributed to the strong anti-corrosion property and high electronic conductivity of the nanocomposite support, as well as a strong metal and support interaction. The unique flower-like scaffold is also of great advantage for mass transfer. This work provides a facile strategy to synthesize robust nanocomposite supports for fuel cells.

Electrophoretic co‐deposition of Bi2O3–multiwalled carbon nanotubes coating as supercapacitor electrode

AbstractNafion is suggested as an efficient assistant in preparing supercapacitor by employing nanoparticles. In this work, using a bi‐additive of 0.10‐mM NaOH + 0.10 g L−1 Nafion, Nafion‐assisted electrophoretic co‐deposition of Bi2O3–multiwalled carbon nanotubes (MWCNTs) coating is successfully realized in ethanol solvent. The capacitance performances of the electrophoretic coatings in 6.0‐M KOH electrolyte are investigated by cyclic voltammetry and galvanostatic charge–discharge techniques. Comparing with Bi2O3 coating prepared with electrophoretic deposition (EPD) by employing other additive (such as polyethyleneimine), the Bi2O3 coating prepared by Nafion‐assisted EPD shows a better capacitance performance. Benefiting from the improvement in coating conductivity caused by MWCNTs, with a small additional amount of 4.0 wt.%, the Bi2O3–MWCNTs coating exhibits an amazing 164% increase of mass‐specific capacitance (473 F g−1 at the current density of 1.0 A g−1) in comparison with pure Bi2O3 coating (179 F g−1 at the current density of 1.0 A g−1). The cyclic stability test exhibits excellent capacitance retention of 88.7% over 3000 cycles at a constant current density of 10.0 A g−1. This work combines the advantages of MWCNTs, Nafion, and EPD to provide a facile route for preparing Bi2O3‐based coating as a high‐performance supercapacitor electrode.

A novel lattice-embedded ZnO@TiO2(B) nanoflowers promotes photocatalytic production of H2

Traditional surface-to-surface contact heterojunctions suffer from poor stability and low electron-hole separation efficiency, which has become a crucial limiting the further improvement of photocatalytic property. Therefore, improving the combination of heterogeneous materials will become a new attempt. In this work, a novel lattice embedded ZnO@TiO2(B) nanoflowers was prepared by combining electrodeposition method combined with hot solvent method. The hetero interface of the ZnO@TiO2(B) nanoflowers is distributed in the phase of TiO2(B), which drives high-efficiency charge separation. The sample Zn:Ti 1:4 has the highest photocatalytic property, and the H2 generation efficiency under the full spectrum is 1.695 mmol g−1 h−1, which is 3.5 times that of TiO2(B). After 36 h cycle stability test, its stability is as high as 90%. According to results, the possible mechanism of ZnO@TiO2(B) photocatalytic hydrogen production is proposed. These findings may provide new strategies for the preparation of high-efficiency heterojunction photocatalysts with special structures.

Performance improvement of poly(acrylic acid) binder-based silicon/graphite composite anodes by room temperature electron beam irradiation-induced crosslinking

In this study, we demonstrated that the enhanced performance of poly(acrylic acid) binder-based silicon/graphite composite anode (c-PAA-Si/C) can be achieved by a quick, scalable, and solid-state electron beam irradiation-induced crosslinking in the presence of methylenebisacrylamide (MBA) as a water-soluble crosslinker. The result from analysis of an irradiated PAA binder film revealed that the PAA was completely crosslinked by the electron beam irradiation at the absorbed dose of 30 kGy in the presence of 10 wt% MBA, thereby leading to the much reduced swelling degree and improved tensile strength. Likewise, the c-PAA-Si/C-30 anode (irradiated at absorbed dose of 30 kGy) possessed higher hardness than the non-irradiated PAA-Si/C-0 probably due to the effective formation of the crosslinked structure. Moreover, based on the coin-type half cell performance and cycle stability test, the c-PAA-Si/C-30 anode-based cell exhibited the better retention capacity at 100 cycles than that of the PAA-Si/C-0-based one. The EIS and FE-SEM results showed that this better cycling performance could be ascribed to the crosslinked structure-induced structural stability.

A Cu/CuFe2O4-OVs two-electron centre-based synergistic photocatalysis-Fenton system for efficient degradation of organic pollutants

To promote the separation of photogenerated carriers, break through the bottleneck of classical Fenton reaction, and achieve the efficient degradation of organic pollutants, a two-electron centre Cu/CuFe2O4 with oxygen vacancies (Cu/CuFe2O4-OVs)11Cu/CuFe2O4 with oxygen vacancies, Cu/CuFe2O4-OVs. was synthesised by citric acid complexation and ascorbic acid (Vc)22ascorbic acid, Vc.in-situ reduction. Under visible light irradiation, H2O2 was added to form a two-electron centre synergistic photocatalysis-Fenton degradation system that could degrade 100 ppm of phenol by 92.72% in 18 min. The degradation efficiency constant was 8165 and 4.35 times that of photocatalysis and Fenton oxidation, respectively. Such excellent degradation activity is attributed to the synergistic effect of the two-electron centre and photocatalysis-Fenton. Cu0 has two functions: (1) it acts as an electronic bridge of Fe and Cu in Fenton and accelerates the separation of photogenerated carriers; (2) it acts as the transfer channel of the two-electron centre. Oxygen vacancies are electron-rich centres that activate H2O2, while the electron-poor centre Cu(II) captures photogenerated electrons and phenol electrons. Quenching experiments and EPR results indicated that OH, O2− and h+ are the main active species. The synergistic degradation mechanism was proposed based on experiments and theoretical calculations. Through further optimization of the conditions and cyclic regeneration stability test, the system was extended to degrade different dyes, phenolic organic pollutants and coking wastewater.

Molten Salt Thermal Treatment Synthesis of S-Doped V2CTx and Its Performance as a Cathode in Aqueous Zn-Ion Batteries.

The lack of suitable cathode materials with a high capacity and good stability is a crucial problem affecting the development of aqueous Zn-ion batteries. Herein, a novel strategy for the modification of V2CTx through molten salt thermal treatment is proposed. In the novel route, S heteroatoms were introduced into V2CTx through a substitution reaction during the dissolution of Li2S in LiCl-KCl molten salts. Then, surface V2O5 was obtained through the in situ electrochemical charging/discharging of the S-doped V2CTx (MS-S-V2CTx) cathode. The assembled Zn/MS-S-V2CTx battery showed a high reversible discharge capacity of 411.3 mAh g-1 at a current density of 0.5 A g-1, an 80% capacitance retention after long cycle stability tests at 10 A g-1 for 3000 cycles, and a high energy density of 375.5 Wh kg-1 in 2M ZnSO4. Density functional theory calculations demonstrate that the improved electrochemical performance of the cathode can be attributed to the introduced S heteroatoms, which considerably reduced the ion diffusion energy barrier for Zn2+ ions and improved the stability of V2O5. This work provides a novel method to produce highly active and stable vanadium-based cathodes for aqueous Zn-ion batteries.

Strain-Assisted Single Pt Sites on High-Curvature MoS 2 Surface for Ultrasensitive H 2 S Sensing

Strain-Assisted Single Pt Sites on High-Curvature MoS ₂ Surface for Ultrasensitive H ₂ S Sensing

Integration of fully printed and flexible organic electrolyte-based dual cell supercapacitor with energy supply platform for low power electronics

We report the fabrication of flexible, printed dual cell supercapacitors (DCSCs) and their implementations in energy storage units providing peak power to portable devices. The use of organic electrolytes enhances higher capacity in both potential windows (2.5 V/cell) and the temperature ranges than the aqueous electrolytes, while propylene carbonate retains the advantages of low cost and low toxicity. The device delivered capacitance value between 3 and 4 mF, equivalent series resistance < 2 Ω, and very low leakage current of about 0.1 µA. We demonstrated the integration of an organic photovoltaic module (OPV) with an energy supply platform (ESP) and DCSCs for indoor light energy harvesting and storage. The maximum harvested energy was about 39 mJ. The energy is sufficient to provide peak power to portable devices and sensors. This was confirmed by powering an LED with our energy harvesting system. Mechanical deformation testing of DCSCs shows excellent mechanical stability, so that the device is well suited for flexible energy storage units. In a long-term cyclic stability test, the decrease in capacitance value was only 1% of the initial value after 10,000 cycles, indicating good durability and performance.

Enhanced thermal energy storage performance of hydrous salt phase change material via defective graphene

Structural modification of two-dimensional materials has a significant influence on performance. In this work, a novel preparation method is presented to get defective graphene and the as-obtained defective graphene shows great benefits for the thermal energy storage performance of phase change material (PCM). Based on the experimental results, we found the structure of few-layer graphene becomes weak at high temperatures (1200 °C) under the protection of N2, and then some micro-defects could be formated in the surface of graphene at a suitable thermal treatment schedule in air atmosphere. Owing to the unique nature of defective graphene, the PCM/defective graphene composite showed a higher thermal conductivity than barium hydroxide octahydrate (Ba(OH)2·8H2O) as the pure PCM. Scanning electron microscopy (SEM) and thermal cycling tests revealed that the defective graphene can be acted as the nucleating agent, which reduced the supercooling degree of Ba(OH)2·8H2O. Furthermore, thermal cycle stability tests showed the composite PCM had outstanding thermal cycling stability, and the defective graphene can also be acted as a kind of stabilizer. We showed the excellent application values of defective graphene in the PCM field for energy storage. This work is beneficial to the development of graphene and PCM composites.

Comparative study on pilot-scale production of CuO-loaded activated biochar and hydrochar from oil-palm empty fruit bunches for high-performance symmetric supercapacitor application

• Pilot-scale slow pyrolysis or HTC were used to produce carbon electrodes from EFB. • CuO/ABC electrodes exhibited high specific capacitance of up to 495.4F/g. • CuO/ABC electrodes produced energy density of 22.83 Wh/kg at power density of 1,200 W/kg. • CuO/ABC electrodes had capacitance retention rate of 92.4% after 5,000 cycles. • CuO/AC is a promising electrode which can be mass produced from pilot-scale production. This study reports a comparative study on the integration of double-layer capacitive activated carbon with CuO, which imposes pseudocapacitive activity to the electrode materials, for supercapacitor application in the presence of different electrolytes. The activated carbon was prepared from different pilot-scale char production procedures. The CuO/activated char (CuO/AC) electrode material with an exceptional electrochemical performance was efficiently produced by slow pyrolysis or by hydrothermal carbonization through the chemical activation to produce activated biochar (ABC) or activated hydrochar (AHC). The specific surface area and total pore volume of the produced ABC was 810–1008 m 2 g −1 and 0.53–0.79 cm 3 g −1 , respectively. In a three-electrode cell, the CuO/ABC electrode material exhibited superior specific capacitances of 495 and 274F g −1 in 2 M KOH and 1 M Na 2 SO 4 electrolytes, respectively. The energy density of the symmetric supercapacitor produced in KOH electrolyte was 11.42 Wh kg −1 with power density of 600 W kg −1 and could maintain up to 6.17 Wh kg −1 at 6,000 W kg −1 . In Na 2 SO 4 aqueous electrolyte, the cells achieved the maximum energy density of 6.01 Wh kg −1 at 700 W kg −1 . In the cyclic stability test, the initial capacitance was retained at 92.7% after 5,000 cycles by using Na 2 SO 4 as the electrolyte, signifying that CuO/ABC is a promising electrode material which can be mass production from pilot-scale to perform the excellent electrochemical energy storage capacity with outstanding long-cycling life.

Polyethylene glycol/silica and carbon black/silica xerogel composites as an adsorbent for CO2 capture.

Mesoporous polyethylene glycol (PEG)/silica and carbon black (CB)/silica xerogel composites were prepared by the sol-gel method as an adsorbent for CO2 adsorption. The CO2 adsorption process was carried out under pure CO2 atmosphere at room temperature in addition to ambient air. The xerogel composites with high surface area and pore volume showed better CO2 adsorption capacity than the pure silica xerogel. After modifying samples with propylene diamine using the wet impregnation method, an increase in CO2 adsorption capacity was observed for the samples except CB/silica xerogel composite. The highest CO2 adsorption capacity was determined as approximately 0.80 mmol/g for amine modified PEG/silica xerogel composite under pure CO2 exposure. According to the adsorption-desorption cyclic stability test, it was clear that the stable samples were obtained, which is a desirable property for all CO2 adsorbents. The promising findings revealed that the xerogel composites can be efficiently used as a CO2 adsorbent instead of conventional materials in many CO2 adsorption applications. Additionally, it can be expected that the xerogel composites can provide an effective adsorption process without high-cost, complexity, corrosion, and toxicity problems.

Increase of Cycling Stability in Pilot-Scale 21700 Format Li-Ion Cells by Foil Tab Design

Li-ion cells of the industrially-relevant 21700 format were built on pilot-scale with tabs made from (a) the electrodes’ current collecting foils (Al and Cu, “foil tabs”) in comparison with (b) conventional tabs (Al and Ni) welded to the electrodes’ current collecting foils (“welded tabs”). Both cell types use the same anode (graphite), cathode (NMC622), separator, electrolyte, as well as the same tab positions. This allows a direct comparison of welded tabs and foil tabs regarding formation, C-rate capability, cell electrical resistance, and long-term cycling stability tests. Our data reproducibly shows 14.4% longer cycling stability and 11.2% increased total charge throughput in the case of the cells with foil tabs until 80% SOH, which is likely due to less inhomogeneities in the case of the foil tab design.

1T-2H MoSe2 modified MAPbI3 for effective photocatalytic hydrogen evolution

Organic-inorganic perovskites such as iodine methylamine lead (MAPbI3) shows superb photocatalytic prospect in the field of solar energy driven photocatalysis. However, its catalytic performance is insufficient due to serious charge recombination. In this article, 1T-2H MoSe2/MAPbI3 composites were obtained by simple electrostatic adsorption method. The results of photocatalytic hydrogen production showed that 10 wt% 1T-2H MoSe2/MAPbI3 performed the best hydrogen evolution rate of 552.93 μmol·h−1·g−1, which was 23 times than that of pure MAPbI3 (23.13 μmol·h−1·g−1). The long-term cyclic stability test also indicated that 1T-2H MoSe2/MAPbI3 composites have good stability. The excellent hydrogen evolution rate activity is thoroughly investigated by optical/optoelectrochemical measurements, showing that 1T-2H MoSe2 as a co-catalyst can effectively transfer electrons and promote the separation of photogenerated charge. This study provided a reference for further exploration of MAPbI3-based catalysts with excellent catalytic activity.

Prolonged-Photoresponse-Lifetime Ni2P Nanocrystalline with Highly Exposed (001) for Efficient Photoelectrocatalytic Hydrogen Evolution.

Seeking highly efficient non-preference electrocatalytic materials that serve photoelectrochemical (PEC) water splitting in acidic systems is expectant in the context of environmentally friendly production. We designed Ni2P electrocatalysts synthesized in oil phases via the hot-bubbling method with superb stability in air and sulfuric acid solution for PEC, which were found with excellent hydrogen evolution performance. A tunable particle size and highly exposed (001) planes of Ni2P nanocrystals were achieved. The designed catalysts achieved a notable promotion in the hydrogen evolution reaction activity compared to that of Ni2P synthesized in the water phase. More specifically, the electrode prepared by self-assembled Ni2P nanoparticles was found to have decent over-potential of η10 = 164 mV in darkness and was further decreased to 129 mV with irradiation of visible light. The cyclic stability tests manifested brilliant durability in 0.5 M H2SO4. Measurement of the transient photocurrent response and PEC water splitting catalytic performance indicated that the Ni2P had high carrier concentration upon irradiation, lower carrier recombination probability, and prolonged photo-response lifetime (3.03-3.14 s).

Amorphous Porous Molybdenum Dioxide as an Efficient Supercapacitor Electrode Material

AbstractMolybdenum dioxide (MoO2) with amorphous and porous nanostructure is synthesized via a facile hydrothermal methodology in a short reaction time and used as a supercapacitors electrode material. X‐ray diffraction, transmission electron microscopy and cyclic voltammetry, galvanostatic charge–discharge measurements, and cycle stability tests of the amorphous and porous MoO2 are investigated. The novel‐innovative structure conduces to the high specific capacity of 444.7 F g−1 at 1 A g−1 in 0.5 m H2SO4 solution. After 1000 cycles, 92% capacity is retained, indicating that the as‐prepared electrodes possess excellent stabilities. Furthermore, at a high current density of 8 A g−1, the capacity can reach 210.67 F g−1, exhibiting outstanding rate characteristics. The amorphous and porous MoO2 achieves preeminent electrochemical performance, which can be attributed to the short ion diffusion routes and can provide reversible and fast faradic reactions and the porous structure will increase the utilization of the electrode materials. Besides that, the amorphous and porous MoO2 will let each MoO2 nanoparticles to participate in electrochemical reactions due to the full contact between electrolyte and MoO2. Therefore, MoO2 will be a promising anode material for aqueous supercapacitors.

A facile green synthesis of porous hexagonal cobalt pyrovanadate electrode for supercapacitors by deep eutectic solvent

Cobalt vanadate is a kind of promising electrode material for pseudo-supercapacitors because of their higher electrical conductivity, better electrochemical activity, and prominent specific capacitance than single metal oxides. In this paper, cobalt pyrovanadate (Co2V2O7) was primarily fabricated by a facile environment-friendly ionothermal method using a green deep eutectic solvent (DES) and followed the heat treatment in the air. The eutectic mixture discussed here was consisted of a hydrogen bond donor (urea) and acceptor (ChCl) in a 2:1 molar ratio. The as-prepared Co2V2O7 was porous hexagonal nanoplatelets, and its electrochemical performances were characterized by cycle voltammetry, galvanostatic charge/discharge and cycling stability tests in a three-electrode system with 2 M KOH electrolyte solution. The specific capacitance of the synthesized Co2V2O7 revealed 304 F g−1 at the current density of 1 A g−1. Surprisingly, it remained an excellent cycle performance with 103% in 100 charge/discharge cycles. Therefore, we have successfully presented a deep eutectic solvent derived routine to prepare porous hexagonal Co2V2O7 nanoplatelets electrode material.

Origin of capacitance decay for a flower-like δ-MnO2 aqueous supercapacitor electrode: The quantitative surface and electrochemical analysis

Herein, we report the electrochemical energy storage performance of δ-MnO2 (K-birnessite MnO2) as supercapacitor electrode material in Na2SO4 aqueous electrolyte. The electrode exhibited considerable electrochemical performances due to the fast intercalation/deintercalation reactions of Na+ on the pseudocapacitive MnO2 surface. However, a long-term cyclic stability test of the electrode at a low specific current (1 A g−1) demonstrated a decline in its initial capacitance value to the tune of ~ 21%. To quantify the above discrepancy, the electrochemical intercalation of Na+ ions on the electrode surface was quantitatively studied employing electrochemical impedance spectroscopy, EDAX analysis and X-ray photoelectron spectroscopy. Further, the surface of the electrode was analyzed by performing complete charge and charge/discharge measurements at a low specific current of 0.1 A g−1. These results disclosed that, besides the surface intercalation/deintercalation reactions, some Na+ ions have permanently substituted into the bulk (layer) of δ-MnO2 by replacing the host K ions from the layered nanostructure. Thus, this finding suggests that Na+ ions replaced in the site of K in δ-MnO2 considerably affect the electrochemical properties of the supercapacitor electrode.

Hierarchical N-doped holey three-dimensional reduced graphene oxide with high performance capacitive deionization

In this study, a novel three-dimensional reduced graphene oxide (NHGH-0.2) was synthesized via one-step hydrothermal treatment based on nitrogen doped and hydrogen peroxide etching. The preparation of NHGH-0.2 showed a hierarchical holey structure with high specific surface area of 874.9 m2/g, resulted from the synergistic effect of the N-doped and chemical etching. Electrochemical analysis showed ultrahigh specific capacitance of 303.1 F/g at a current density of 1 A/g and low charge transfer resistance, due to the excellent wettability and conductivity, which was help for rapidly diffuse and transfer of ions on the electrode surface. Capacitance was still maintained at 92.8% by the cycling stability test after 1000 charge–discharge cycles. The desalination performance applied for capacitive deionization (CDI) displayed the salt adsorption capacitive as high as 22.14 mg/g at the voltage of 1.6 V in the initial concentration of 500 mg/L NaCl solution. Therefore, the NHGH-0.2 electrode could be a promising CDI material for water treatment.

High-performance of quasi-solid-state complementary electrochromic devices based on Al3+/Li+ dual-ion electrolyte

Monovalent lithium ion has been successfully employed in quasi-solid-state electrochromic devices (ECDs), but it still needs to be optimized in terms of cost, life stability and so on. Herein, a novel electrolyte containing multivalent Aluminum ion (Al 3+ ) was introduced into the ECDs and compared with Lithium ion ECDs. With acrylate-based UV curable glue as the gel electrolyte curing adhesive, WO 3 and NiO x films as the complementary counter electrode layers, Li + (ECD-1), Al 3+ (ECD-2) and Al 3+ /Li + double ion (ECD-3) as the electrolyte ions, three types of quasi-solid-state ECDs were prepared as Glass/ITO/WO 3 /polymer electrolyte/NiO x /ITO/Glass. The results showed that the optical modulation amplitude ΔT of three devices is 54.3%, 51.6%, and 53.2%, respectively, while the coloring efficiency (CE) is 62.2, 64.6, and 62.2 cm 2 /C. The cycle stability test results displayed that during 2000 CA cycles (lasting for 40,000 s, 20 s for one cycle), the optical modulation amplitude ΔT of the Al 3+ /Li + devices only decays 16%, which has the excellent cycle durability compared with Li + devices. This article is an effective attempt to expand the quasi-solid-state electrochromic electrolyte with multivalent ions species, which can broaden the application range of the devices. • WO 3 //NiO x complementary quasi-solid-state electrochromic devices based on Al 3+ /Li + dual-ion electrolyte. • UV curing adhesive as the gel electrolyte carrier for ECDs. • Al 3+ /Li + dual-ion devices achieve better electrochemical cycle stability.