A high energy density asymmetric supercapacitor utilizing a nickel phosphate/graphene foam composite as the cathode and carbonized iron cations adsorbed onto polyaniline as the anode

This work presents the effect of different contents of graphene foam (GF) on the electrochemical capacitance of nickel phosphate Ni₃(PO₄)₂ nano-rods as an electrode material for hybrid electrochemical energy storage device applications. Pristine Ni₃(PO₄)₂ nano-rods and Ni₃(PO₄)₂/GF composites with different GF mass loadings of 30, 60, 90 and 120 mg were synthesised via a hydrothermal method. The electrochemical behavior of pristine Ni₃(PO₄)₂ and Ni₃(PO₄)₂/GF composites were analysed in a three-electrode cell configuration using 6 M KOH electrolyte. The Ni₃(PO₄)₂/90 mg GF composite sample exhibited the highest specific capacity of 48 mA h g⁻¹ at a current density of 0.5 A g⁻¹. The electrochemical behavior of the Ni₃(PO₄)₂/90 mg GF composite was further analysed in a two-electrode hybrid asymmetric device. A hybrid asymmetric device was fabricated with Ni₃(PO₄)₂/90 mg GF as the cathode and carbonized iron cations (Fe³⁺) adsorbed onto polyaniline (PANI) (C-FP) as the anode material (Ni₃(PO₄)₂/90 mg GF//C-FP) and tested in a wide potential window range of 0.0–1.6 V using 6 M KOH. This hybrid device achieved maximum energy and power densities of 49 W h kg⁻¹ and 499 W kg⁻¹, respectively, at 0.5 A g⁻¹ and had long-term cycling stability.

This work presents the effect of different contents of graphene foam (GF) on the electrochemical capacitance of nickel phosphate Ni₃(PO₄)₂ nano-rods as an electrode material for hybrid electrochemical energy storage device applications.     

Correction: A high energy density asymmetric supercapacitor utilizing a nickel phosphate/graphene foam composite as the cathode and carbonized iron cations adsorbed onto polyaniline as the anode

Correction for ‘A high energy density asymmetric supercapacitor utilizing a nickel phosphate/graphene foam composite as the cathode and carbonized iron cations adsorbed onto polyaniline as the anode’ by A. A. Mirghni et al., RSC Adv., 2018, 8, 11608–11621.

Sekhar C. Ray was incorrectly spelled in the published article; the corrected version is shown above.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Bullet-like microstructured nickel ammonium phosphate/graphene foam composite as positive electrode for asymmetric supercapacitors

Unique microstructured nickel ammonium phosphate Ni(NH₄)₂(PO₃)₄·4H₂O and Ni(NH₄)₂(PO₃)₄·4H₂O/GF composite were successfully synthesized through the hydrothermal method with different graphene foam (GF) mass loading of 30, 60 and 90 mg as a positive electrode for asymmetric supercapacitors. The crystal structure, vibrational mode, texture and morphology of the samples were studied with X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis and scanning electron microscopy (SEM). The prepared materials were tested in both 3-and 2-electrode measurements using 6 M KOH electrolyte. The composite material Ni(NH₄)₂(PO₃)₄·4H₂O/60 mg exhibited a remarkable gravimetric capacity of 52 mA h g⁻¹, higher than the 34 mA h g⁻¹ obtained for the Ni(NH₄)₂(PO₃)₄·4H₂O pristine sample, both at 0.5 A g⁻¹. For the fabrication of the asymmetric device, activated carbon from pepper seed (ppAC) was used as a negative electrode while Ni(NH₄)₂(PO₃)₄·4H₂O/60 mg GF was adopted as the positive electrode. The Ni(NH₄)₂(PO₃)₄·4H₂O/60 mg GF//ppAC asymmetric device delivered a specific energy of 52 Wh kg⁻¹ with an equivalent specific power of 861 W kg⁻¹ at 1.0 A g⁻¹ within a potential range of 0.0–1.5 V. Moreover, the asymmetric device displayed a capacity retention of about 76% for over 10 000 cycles at a high specific current of 10.0 A g⁻¹.

Unique morphology of (Ni(NH₄)₂(PO₃)₄·4H₂O/60GF) as a positive electrode for high-performance asymmetric supercapacitors.     

Electrochemical analysis of Na–Ni bimetallic phosphate electrodes for supercapacitor applications

Bimetallic sodium–nickel phosphate/graphene foam composite (NaNi₄(PO₄)₃/GF) was successfully synthesized using a direct and simple precipitation method. The hierarchically structured composite material was observed to have demonstrated a synergistic effect between the conductive metallic cations and the graphene foam that made up the composite. The graphene served as a base-material for the growth of NaNi₄(PO₄)₃ particles, resulting in highly conductive composite material as compared to the pristine material. The NaNi₄(PO₄)₃/GF composite electrode measured in a 3-electrode system achieved a maximum specific capacity of 63.3 mA h g⁻¹ at a specific current of 1 A g⁻¹ in a wide potential range of 0.0–1.0 V using 2 M NaNO₃ aqueous electrolyte. A designed and fabricated hybrid NaNi₄(PO₄)₃/GF//AC device based on NaNi₄(PO₄)₃/GF as positive electrode and activated carbon (AC) selected as a negative electrode could operate well in an extended cell potential of 2.0 V. As an assessment, the hybrid NaNi₄(PO₄)₃/GF//AC device showed the highest energy and power densities of 19.5 W h kg⁻¹ and 570 W kg⁻¹, respectively at a specific current of 0.5 A g⁻¹. The fabricated device could retain an 89% of its initial capacity with a coulombic efficiency of about 94% over 5000 cycling test, which suggests the material''s potential for energy storage devices applications.

CV curve of the hybrid device as reflection of the conductive NaNi₄(PO₄)₃/GF composite and AC.     

Onion-derived activated carbons with enhanced surface area for improved hydrogen storage and electrochemical energy application

High surface area activated carbons (ACs) were prepared from a hydrochar derived from waste onion peels. The resulting ACs had a unique graphene-like nanosheet morphology. The presence of N (0.7%) and O content (8.1%) in the OPAC-800 °C was indicative of in situ incorporation of nitrogen groups from the onion peels. The specific surface area and pore volume of the best OPAC sample was found to be 3150 m² g⁻¹ and 1.64 cm³ g⁻¹, respectively. The hydrogen uptake of all the OPAC samples was established to be above 3 wt% (at 77 K and 1 bar) with the highest being 3.67 wt% (800 °C). Additionally, the OPAC-800 °C achieved a specific capacitance of 169 F g⁻¹ at a specific current of 0.5 A g⁻¹ and retained a capacitance of 149 F g⁻¹ at 5 A g⁻¹ in a three electrode system using 3 M KNO₃. A symmetric supercapacitor based on the OPAC-800 °C//OPAC-800 °C electrode provided a capacitance of 158 F g⁻¹ at 0.5 A g⁻¹. The maximum specific energy and power was found to be 14 W h kg⁻¹ and 400 W kg⁻¹, respectively. Moreover, the device exhibited a high coulombic efficiency of 99.85% at 5 A g⁻¹ after 10 000 cycles. The results suggested that the high surface area graphene-like carbon nanostructures are excellent materials for enhanced hydrogen storage and supercapacitor applications.

Graphene-like activated carbons (ACs), with excellent properties for enhanced hydrogen storage and supercapacitor applications, were prepared from waste onion peels.     

Green and scalable synthesis of 3D porous carbons microstructures as electrode materials for high rate capability supercapacitors

Porous carbon nanostructures have long been studied because of their importance in many natural phenomena and their use in numerous applications. A more recent development is the ability to produce porous carbon materials with tuneable properties for electrochemical applications, which has enabled new research directions towards the production of suitable carbon materials for energy storage applications. Thus, this work explores the activation of carbon from polyaniline (PANI) using a less-corrosive potassium carbonate (K₂CO₃) salt, with different mass ratios of PANI and the activating agent (K₂CO₃ as compared to commonly used KOH). The obtained activated carbon exhibits a specific surface area (SSA) of up to ∼1700 m² g⁻¹ for a carbon derived PANI : K₂CO₃ ratio of 1 : 6. Moreover, the prepared samples were tested as electrode materials for supercapacitors with the results showing excellent electrical double layer capacitor behavior. Charge storage was still excellent for scan rates of up to 2000 mV s⁻¹, and a capacitance retention of 70% at a very high specific current of 50 A g⁻¹ was observed. Furthermore, the fabricated device can deliver an energy density of 25 W h kg⁻¹ at a specific current of 0.625 A g⁻¹ and a power density of 260 W kg⁻¹ in 1-ethyl-3-methylimidazolium bistrifluorosulfonylimide (EMIM-TFSI) ionic liquid, with excellent rate capability after cycling for 16 000 cycles at 3.0 V with ∼98% efficiency. These results are promising and demonstrate the electrode''s potential for energy storage, leading to the conclusion that K₂CO₃ is a very good alternative to corrosive activation agents such as KOH in order to achieve high electrochemical performance.

Porous carbon nanostructures have long been studied because of their importance in many natural phenomena and their use in numerous applications.