Facile synthesis of PEDOT-rGO/HKUST-1 for high performance symmetrical supercapacitor device

A novel poly(3,4-ethylenedioxythiophene)-reduced graphene oxide/copper-based metal–organic framework (PrGO/HKUST-1) has been successfully fabricated by incorporating electrochemically synthesized poly(3,4-ethylenedioxythiophene)-reduced graphene oxide (PrGO) and hydrothermally synthesized copper-based metal–organic framework (HKUST-1). The field emission scanning microscopy (FESEM) and elemental mapping analysis revealed an even distribution of poly(3,4-ethylenedioxythiophene) (PEDOT), reduced graphene oxide (rGO) and HKUST-1. The crystalline structure and vibration modes of PrGO/HKUST-1 were validated utilizing X-ray diffraction (XRD) as well as Raman spectroscopy, respectively. A remarkable specific capacitance (360.5 F/g) was obtained for PrGO/HKUST-1 compared to HKUST-1 (103.1 F/g), PrGO (98.5 F/g) and PEDOT (50.8 F/g) using KCl/PVA as a gel electrolyte. Moreover, PrGO/HKUST-1 composite with the longest charge/discharge time displayed excellent specific energy (21.0 Wh/kg), specific power (479.7 W/kg) and an outstanding cycle life (95.5%) over 4000 cycles. Thus, the PrGO/HKUST-1 can be recognized as a promising energy storage material

Development of high-performance electrochromic supercapacitors using copper-based metal-organic framework/reduced graphene oxide composites

Supercapacitors (SCs) are promising energy storage devices with tremendous specific capacitance, fast rate for charging/discharging, high specific power and long-life cycle. It is difficult to estimate the state-of-charge of the existing supercapacitors, which leads to excessive charging/discharging. Hence, supercapacitors with more functions and novel features are fabricated to widen the energy storage applications. The electrochromic (EC) materials are able to exhibit visual color changes upon an applied potential. Therefore, it is highly attractive to combine SC and EC characteristics into one device for bifunctional applications namely electrochromic supercapacitor (EC-SC). The EC-SCs can function as a normal supercapacitor to store energy, at the same time, the energy level of the devices can be sensed by observing the changes in visual colors. In this work, copper-based metal-organic framework/reduced graphene oxide (HKUST-1/rGO) composites were successfully developed as high-performance EC-SC devices via hydrothermal and electrochemical deposition. The asfabricated composites were characterized via X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), Raman spectroscopy, field emission scanning microscopy (FESEM) and electrochemical impedance spectroscopy (EIS). Initially, poly(3,4-ethylenedioxythiophene)-reduced graphene oxide/copper-based metal-organic framework (PEDOT-rGO/HKUST-1) was prepared and electrochromic performance was evaluated. PEDOTrGO/ HKUST-1 exhibited a high coloration efficiency of 176.8 cm2/C with high optical contrast. An electrochromic coloration and bleaching times of 1.1 s and 1.3 s were recorded at 500 nm which proved excellent switching kinetics of PEDOT-rGO/HKUST-1. The similar composite also depicted promising supercapacitive properties with remarkable specific energy and specific capacitance of 21.0 Wh/kg and 360.5 F/g, respectively. The HKUST-1/rGO composite was designed as a negative electrode of an asymmetrical supercapacitor (ASC) device. A vanadium oxide/reduced graphene oxide//copper-based metal-organic framework/reduced graphene oxide (V2O5/rGO//HKUST-1/rGO) ASC device successfully delivered enormous specific energy (31.2 Wh/kg) at a specific power of 656.4 W/kg. Nickel oxide/vanadium oxide/reduced graphene oxide//HKUST-1/rGO (NiO/V2O5/rGO//HKUST-1/rGO) and manganese oxide/ vanadium oxide/reduced graphene oxide//HKUST-1/rGO (MnO2/V2O5/rGO//HKUST- 1/rGO) devices were developed for bifunctional asymmetrical electrochromic supercapacitor (EC-SC) devices. The designed PEDOT-rGO/HKUST-1, V2O5/rGO//HKUST-1/rGO, NiO/V2O5/rGO//HKUST-1/rGO and MnO2/V2O5/rGO//HKUST-1/rGO depicted outstanding specific capacitance of 360.5, 483.9, 500 and 652.7 F/g, respectively. Both bifunctional asymmetric ECSC devices (NiO/V2O5/rGO//HKUST-1/rGO and MnO2/V2O5/rGO//HKUST- 1/rGO) were also demonstrated green and orange color at the discharged and charged state, respectively. These results proved that the successfully prepared asymmetrical EC-SC devices with both excellent charge storage capability and outstanding electrochromic properties are promising candidates for bifunctional application

Recent advances in development of electroactive composite materials for electrochromic and supercapacitor applications

Supercapacitors are outstanding energy storage devices with remarkable electrochemical properties i.e., enormous specific capacitance, rapid charge/discharge rate, great specific power and long-life cycle. Researchers have been developing the supercapacitor application by including smart functions such as electrochromic. The bifunctional devices with both electrochromic and supercapacitive properties are highly explored as the environmentally friendly supercapacitors are able to depict visual color changes upon applied potential. Hence, the excessive charging issue in the supercapacitors can be overcome and the energy level of the device can be also determined qualitatively, observing the color of the material. Numerous electroactive materials such as carbon-based materials, conductive polymers (CPs), transition metal oxides (TMOs) and metal-organic frameworks (MOFs) have been greatly investigated in supercapacitor applications. This review mainly emphasizes and elaborates on the electrochromic and supercapacitive performance of CP/TMO-, graphene- and MOF-based materials. At the same time, the criteria and the challenges for bifunctional electrochromic supercapacitors are also addressed in this review

Bifunctional ternary manganese oxide/vanadium oxide/reduced graphene oxide as electrochromic asymmetric supercapacitor

A bifunctional ternary manganese oxide/vanadium oxide/reduced graphene oxide (MnO2/V2O5/rGO) was developed for asymmetric electrochromic supercapacitor (EC-SC) application. The elemental mapping revealed uniformly distributed MnO2, V2O5 and rGO, depicting homogenous synthesis of the hybrid composite. The phase composition, vibration modes and valance state of the ternary composite were analyzed via X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis, respectively. Interestingly, the as-prepared MnO2/V2O5/rGO composite disclosed tremendous Csp of 1403.5 F/g, which was higher compared to MnO2/V2O5 (801.1 F/g), V2O5 (613.1 F/g), MnO2 (126.7 F/g) and rGO (60.7 F/g). MnO2/V2O5/rGO that appeared in dark green switched its visual color to orange at the charged state, confirming the electrochromic property. The bifunctional manganese oxide/vanadium oxide/reduced graphene oxide//copper-based metal-organic framework/reduced graphene oxide (MnO2/V2O5/rGO//MrGO) asymmetrical EC-SC device revealed outstanding cycling stability (90.3% charge retention over 5000 cycles), tremendous specific capacitance (652.7 F/g) and maximum specific energy (60.4 Wh/kg). MnO2/V2O5/rGO//MrGO asymmetrical EC-SC device demonstrated reversible color changes from dark green to orange at the discharged and charged states, respectively. The significantly great electrochromic and supercapacitive performance revealed that MnO2/V2O5/rGO//MrGO is an outstanding electroactive candidate for the next generation of electrochromic supercapacitors

A promising negative electrode of asymmetric supercapacitor fabricated by incorporating copper-based metal-organic framework and reduced graphene oxide

A hybrid negative electrode was developed by combining a hydrothermally prepared copper-based metal-organic framework (Cu-MOF) and electrochemically synthesized reduced graphene oxide (rGO), which was labeled as MrGO. The MrGO composite was characterized using field emission scanning microscopy, Raman spectroscopy, Fourier transform infrared spectrometry and X-ray diffraction to confirm the presence of both Cu-MOF and rGO. Cyclic voltammetry, galvanostatic charge discharge and electrochemical impedance spectroscopy (EIS) were carried out to study the electrochemical properties of the MrGO negative electrode for asymmetric supercapacitor (ASC) application. The EIS analysis of the MrGO electrode revealed the lowest charge transfer resistance of 0.95 Ω compared to rGO (23.73 Ω) and Cu-MOF (10.23 Ω). The electrochemical measurements were performed on the MrGO electrode at a negative operating potential (−0.4 to 0 V) to emphasize the hybrid MrGO as a high-performance negative electrode. The novel ASC was then constructed utilizing the vanadium oxide/reduced graphene oxide (VrGO) as the positive electrode and the hybrid MrGO as the negative electrode. The VrGO//MrGO ASC device was successfully delivered a superior specific capacitance (483.9 F/g) and enormous specific energy (31.2 Wh/kg). The inclusion of incredibly conductive rGO in the MrGO electrode could synergistically enhance the cycling stability (92% over 4000 CV cycles) of the VrGO//MrGO ASC device

A Comparison between Various Polymeric Membranes for Oily Wastewater Treatment via Membrane Distillation Process

Oily wastewater (OW) is detrimental towards the environment and human health. The complex composition of OW needs an advanced treatment, such as membrane technology. Membrane distillation (MD) gives the highest rejection percentage of pollutants in wastewater, as the membrane only allows the vapor to pass its microporous membrane. However, the commercial membranes on the market are less efficient in treating OW, as they are prone to fouling. Thus, the best membrane must be identified to treat OW effectively. This study tested and compared the separation performance of different membranes, comparing the pressure-driven performance between the membrane filtration and MD. In this study, several ultrafiltration (UF) and nanofiltration (NF) membranes (NFS, NFX, XT, MT, GC and FILMTEC) were tested for their performance in treating OW (100 ppm). The XT and MT membranes (UF membrane) with contact angles of 70.4 ± 0.2° and 69.6 ± 0.26°, respectively, showed the best performance with high flux and oil removal rate. The two membranes were then tested for long-term performance for two hours with 5000 ppm oil concentration using membrane pressure-filtration and MD. The XT membrane displayed a better oil removal percentage of >99%. MD demonstrated a better removal percentage; the flux reduction was high, with average flux reduction of 82% compared to the membrane pressure-filtration method, which experienced a lower flux reduction of 25%. The hydrophilic MT and XT membranes have the tendency to overcome fouling in both methods. However, for the MD method, wetting occurred due to the feed penetrating the membrane pores, causing flux reduction. Therefore, it is important to identify the performance and characteristics of the prepared membrane, including the best membrane treatment method. To ensure that the MD membrane has good anti-fouling and anti-wetting properties, a simple and reliable membrane surface modification technique is required to be explored. The modified dual layer membrane with hydrophobic/hydrophilic properties is expected to produce effective separation in MD for future study