Polystyrene activated linear tube carbon nanofiber for durable and high-performance supercapacitors

With increasing demand for sustainable energy, it is essential to develop low cost, high performance, and environment-friendly materials for energy storage application. Metal oxides and sulfides are mostly being used as electrode materials for energy storage devices. However, their wide applications are precluded due to their higher cost, low stability, and adverse effect on the environment. Therefore, development of environment-friendly supercapacitors with low cost, high performance, and stable performance is a big challenge. Here, we report surface engineered carbon nanofibers for durable and high-performance supercapacitor. Surface engineered carbon nanofibers showed the highest specific capacitance of 277 F/g (at 1 mV/s), along with superior flexibility and cyclic stability. Moreover, they showed high energy and power density of 30.5 Wh/kg and 8.3 kW/kg, respectively. The cyclic stability showed almost 100% retention in charge storage capacity up to 5000 cycles. Electrochemical properties of a fabricated symmetrical supercapacitor device using these carbon nanofibers showed improved charge storage capacity at elevated temperatures. The charge storage capacity improved by over 150% by increasing temperature from 10 to 60 °C. Our results suggest that surface engineered carbon nanofibers could be a potential candidate for higher performance and durable supercapacitors

A facile preparation of sulfur doped nickel–iron nanostructures with improved HER and supercapacitor performance

Since the use of diverse synthesis approaches can induce the variation in the density of active sites, which impacts electrocatalytic performance, the strategy utilized to fabricate the electrode materials for energy devices is just as important as the materials themselves. Herein, porous NiFe-oxide nanoflowers (NiFe-NFs) and macroparticles (NiFe-MPs) and corresponding S-doped NiFe-oxide nanoflowers (NiFeS-NFs) and macroparticles (NiFeS-MPs) were fabricated using facile co-precipitation and hydrothermal-sulfurization strategies, respectively. The prepared NiFe-NFs, NiFeS-NFs, NiFe-MPs, and NiFeS-MPs materials were investigated for their electrocatalytic HER in 1 M KOH electrolyte. The results indicated that NiFe-NFs displayed an overpotential of 177 mV @ 10 mA/cm2 for HER, whereas the NiFe-MPs, having similar composition, exhibited a high HER overpotential of 187 mV @ 10 mA/cm2. The enhanced HER catalytic performance of NiFe-NFs was attributed to the extensive exposure of active sites at the edges and vertices of nanocubes in the NFs-architecture. Moreover, after sulfurization, NiFeS-NFs and NiFeS-MPs demonstrated a considerable enhancement in their HER activity (54 mV and 152 mV @ 10 mA/cm2, respectively) as compared to un-sulfurized materials, which can be attributed to the enhanced conductivity of materials after S-doping, as supported by theoretical studies. Further, the capacitance experiments showed a significant increment in specific capacitances of NFs and MPs after sulfurization, from 69 to 604 F/g and from 185 to 514 F/g, respectively. This work shows that morphological and compositional changes in metal oxide-based materials may considerably enhance their catalytic activity and capacitance

Tuning the electrochemical properties of nanostructured CoMoO4 and NiMoO4 via a facile sulfurization process for overall water splitting and supercapacitors

In contemporary society, there are many different ways that energy is used in daily life. From applications that require a high energy density to long-term storage in a stable manner, the requirements for energy usage are diverse. Therefore, the greater the number of uses a designed material exhibits, the more practical it may be for wide-scale manufacture. Two areas of particular interest for energy applications are fuel cells (to generate energy) and supercapacitors (to store energy). To provide cheaper and more durable alternatives for energy storage, electrodes containing CoMoO4, NiMoO4, CoMoS4, and NiMoS4 were synthesized. The electrodes were synthesized through a hydrothermal method using Ni-foam as the substrate then tested as electrocatalysts for water splitting and electrodes for supercapacitor. As an electrocatalyst for hydrogen evolution reaction, NiMoS4 displayed the lowest overpotential of 148 mV with a Tafel slope of 159 mV/dec. On the other hand, CoMoS4 showed the lowest overpotential of 189 mV with a Tafel slope of 78 mV/dec among all four samples for oxygen evolution reactions. In terms of energy storage, the CoMoO4 had the highest specific capacitance of 2652 F/g at a current density of 0.5 A/g with an averaged charge retention of 91% and a Coulombic efficiency of 99% after 10,000 cycles

Electrochemical energy storage performance of electrospun CoMn2O4nanofibers

Nanofibers of cobalt manganese oxide (CoMn2O4) were grown using an electrospun technique. Structural and microstructural characterizations confirm the formation of phase pure CoMn2O4with high porosity. The potential application of CoMn2O4nanofibers as an electrode material for energy storage device was studied using cyclic voltammetry and galvanostatic charge-discharge measurements. A specific capacitance of 121 F/g was observed with enhanced cyclic stability. Furthermore, an energy storage device was fabricated by sandwiching two electrodes separated by an ion transporting layer. The device showed a specific capacitance of 241 mF/cm2in 3 M NaOH electrolyte. The effect of temperature on the charge storage properties of the device was also investigated for high temperature applications. The device showed about 75% improvement in the charge storage capacity when the temperature was increased from 10 to 70 °C. This research suggests that nanofibers of CoMn2O4could be used for fabrication of energy storage devices which could operate in a wide temperature range with improved efficiency

Pomegranate: An eco-friendly source for energy storage devices

With an increasing demand for energy and concerns about the environment, scientists are trying to find a better way to generate green energy and store the generated energy efficiently. Biowaste could be an attractive source for the preparation of active materials for energy storing devices. In this project, a shell of pomegranate was used to prepare high surface area carbon for supercapacitor applications. The dry powder of pomegranate was chemically activated using various ratios of pomegranate and activating agent to produce carbon with a range of properties. The unactivated pomegranate-based carbon\u27s surface area was 40 m2/g, which improved to 1459, 1737, and 2189 m2/g upon chemical activation using 1:1, 1:2, and 1:3 ratios of pomegranate: activating agent, respectively. The energy storage capacity was calculated using galvanostatic charge-discharge measurements, and the highest specific capacitance of 190 F/g at 1 A/g was observed for PG-2 (1:2 ratio of pomegranate: activating agent) carbon. Using the electrode, the symmetric supercapacitor devices were fabricated utilizing various electrolytes (aqueous, organic, and ionic liquid electrolytes). The highest energy density of 8.8, 39, and 68 Wh/kg were obtained for aqueous, organic, and ionic liquid electrolytes, respectively. On the other hand, the highest power density of 3950, 8943, and 11,316 W/kg have been achieved for the pomegranate-based carbon in aqueous, organic, and ionic liquid electrolytes, respectively. Our research suggests that pomegranate-based carbon could be an attractive material for the fabrication of energy storage devices

Flower-shaped cobalt oxide nano-structures as an efficient, flexible and stable electrocatalyst for the oxygen evolution reaction

The industrial application of water splitting for oxygen evolution requires low cost, high performance and stable electrocatalysts which can operate at low overpotential. Here, we develop a high performance and stable electrocatalyst for the oxygen evolution reaction (OER) using earth abundant materials. A binder free approach for the synthesis of flower-shaped cobalt oxide (Co3O4) composed of nanosheets showed high OER catalytic activity. The Co3O4 electrode requires a low overpotential of 356 mV to achieve a current density of 10 mA cm-2 with a low onset potential of 284 mV. The electrode showed outstanding flexibility and stability. The catalytic activity of the Co3O4 electrode was very stable up to the 2000th cycle of the polarization study. The high catalytic activity and structural stability arise due to efficient and fast charge transportation through the nanosheets of Co3O4 which are in direct contact with the conducting nickel of the electrode. The porous structure of Co3O4 allows easy access of the electrolyte and escape of generated oxygen without damaging the structure. Collectively, the flower-shaped nanostructured Co3O4 electrode can be used as a flexible and high performance electrode for the OER in an industrial setup

Optimum iron-pyrophosphate electronic coupling to improve electrochemical water splitting and charge storage

Abstract Tuning the electronic properties of transition metals using pyrophosphate (P2O7) ligand moieties can be a promising approach to improving the electrochemical performance of water electrolyzers and supercapacitors, although such a material’s configuration is rarely exposed. Herein, we grow NiP2O7, CoP2O7, and FeP2O7 nanoparticles on conductive Ni-foam using a hydrothermal procedure. The results indicated that, among all the prepared samples, FeP2O7 exhibited outstanding oxygen evolution reaction and hydrogen evolution reaction with the least overpotential of 220 and 241 mV to draw a current density of 10 mA/cm2. Theoretical studies indicate that the optimal electronic coupling of the Fe site with pyrophosphate enhances the overall electronic properties of FeP2O7, thereby enhancing its electrochemical performance in water splitting. Further investigation of these materials found that NiP2O7 had the highest specific capacitance and remarkable cycle stability due to its high crystallinity as compared to FeP2O7, having a higher percentage composition of Ni on the Ni-foam, which allows more Ni to convert into its oxidation states and come back to its original oxidation state during supercapacitor testing. This work shows how to use pyrophosphate moieties to fabricate non-noble metal-based electrode materials to achieve good performance in electrocatalytic splitting water and supercapacitors

Nanostructured nickel-cobalt oxide and sulfide for applications in supercapacitors and green energy production using waste water

With the advancement in technology, the demand for green energy production and storage is increasing year by year. To meet the increasing demand for green energy, there has been continuous research in a bid to find better materials and efficient ways to store energy. Supercapacitors continue to show a promising green energy storage capacity with their modified and improved electrode materials, which show better electrochemical properties. Transition metals such as Fe, Mo, Ni, etc. based materials have shown great potential for electrode materials in supercapacitors, electrocatalysts for water splitting, and urea oxidation reaction (UOR). In this work, nanostructured nickel‑cobalt oxide and nickel‑cobalt sulfide were synthesized using a facile hydrothermal method for their applications in a supercapacitor, water splitting, and urea oxidation reaction. It was observed that the properties of nickel‑cobalt oxide improved significantly after converting it to nickel‑cobalt sulfide. The energy storage capacity of nickel‑cobalt sulfide was significantly enhanced compared to nickel‑cobalt oxide. Additionally, nickel‑cobalt sulfide showed an overpotential of 282 mV, while nickel‑cobalt oxide displayed an overpotential of 379 mV to generate a current density of 10 mA/cm2, towards oxygen evolution reaction. After the introduction of 0.33 M urea, the potential for oxidation of urea for both nickel‑cobalt oxide and nickel‑cobalt sulfide was reduced significantly

Highly Efficient and Durable Electrocatalyst Based on Nanowires of Cobalt Sulfide for Overall Water Splitting

Water electrolysis to generate hydrogen and oxygen at low overpotential is one of the main requirements for clean and renewable energy technology. Currently, precious-metal-based catalysts such as Pt, IrO2, and RuO2 are being used for water electrolysis limiting its wide range of applicability due to their high cost and rare-earth abundance. In this research, we have used nanowires of cobalt sulfide as an efficient electrocatalyst for overall water splitting. Directly grown nanowires of cobalt sulfide on nickel foam provided superior electrocatalytic activities favoring electron transfer. High surface area and porosity of the nanowires allowed easy escape of the generated oxygen and hydrogen. Cobalt sulfide nanowires required an overpotential of 299 and 217 mV to achieve a current density of 10 mA/cm2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Furthermore, nanowires of cobalt sulfide required a low cell voltage of 1.66 V to achieve a current density of 10 mA/cm2 which is among the best-reported value. A facile preparation method, outstanding bi-functionality, and electrochemical stability of cobalt sulfide as both HER and OER electrocatalyst, suggest that cobalt sulfide could be a promising material for commercial applications in water electrolysis