Kabir O. Oyedotun

Hydrothermal synthesis of manganese phosphate/graphene foam composite for electrochemical supercapacitor applications

Manganese phosphate (Mn3(PO4)2 hexagonal micro-rods and (Mn3(PO4)2 with different graphene foam (GF) mass loading up to 150mg were prepared by facile hydrothermal method. The characterization of the as-prepared samples proved the successful synthesis of Mn3(PO4)2 hexagonal micro-rods and Mn3(PO4)2/GF composites. It was observed that the specific capacitance of Mn3(PO4)2/GF composites with different GF mass loading increases with mass loading up to 100mg, and then decreases with increasing mass loading up to 150mg. The specific capacitance of Mn3(PO4)2/100mg GF electrode was calculated to be 270Fg-1 as compared to 41Fg-1 of the pristine sample at a current density of 0.5Ag-1 in a three-electrode cell configuration using 6M KOH. Furthermore, the electrochemical performance of the Mn3(PO4)2/100mg GF electrode was evaluated in a two-electrode asymmetric cell device where Mn3(PO4)2/100mg GF electrode was used as a positive electrode and activated carbon (AC) from coconut shell as a negative electrode. AC//Mn3(PO4)2/100mg GF asymmetric cell device was tested within the potential window of 0.0-1.4V, and showed excellent cycling stability with 96% capacitance retention over 10,000 galvanostatic charge-discharge cycles at a current density of 2Ag-1.

Exploring the stability and electronic structure of beryllium and sulphur co-doped graphene: a first principles study

The South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation (NRF) of South Africa (Grant No. 97994). O. Okikiola acknowledges the financial support from NRF and the University of Pretoria for his PhD studies. Remove selected

Enhanced electrochemical response of activated carbon nanostructures from tree-bark biomass waste in polymer-gel active electrolytes

Activated carbon (ACB) obtained from tree bark waste biomass was obtained by adopting an optimized activation and carbonization route using potassium hydroxide (KOH) pellets. The morphological and structural characteristics of the optimized carbon material revealed a porous network suitable for charge storage. The potential of the ACB material as a suitable supercapacitor electrode was investigated in a symmetric two electrode cell configuration using a polymer-gel/KOH active electrolyte. The KOH was included to improve ionic mobility within the polyvinyl alcohol (PVA) gel, while carbon acetylene black and a polymer-fullerene blend acted as the conductive additives. The cell exhibited an EDLC behaviour in all electrolytes with the PVA/KOH/carbon black (PKCB) electrolyte portraying the best electrochemical response with a 1.4 V voltage window. A specific capacitance (CSP) of ∼227 F g−1 was obtained with a corresponding energy density of 15.5 W h kg−1 and power density of 700 W kg−1 at a current density of 0.5 A g−1. An excellent stability was exhibited with a coulombic efficiency of 98% after 5000 continuous cycles at 5.0 A g−1 and a slight deterioration of the ideal electrochemical behavior was observed after further subjecting the electrode to a floating test for 120 h (5 days) at 1.4 V. Interestingly, the gel-based electrolyte showed a peculiar “recuperating behavior” after further floating process and negligible charge loss after a self-discharge process for 30 h at 1.0 A g−1 which demonstrates the viability for adopting gel-electrolytes in SC devices from plant biomass waste.

Nanostructured porous carbons with high rate cycling and floating performance for supercapacitor application

Biomass-derived activated carbon from cork (Quercus Suber) (ACQS) was prepared via a two-step environment-friendly route using mild KHCO3 as the activating agent. This synthesis route makes the material produced less toxic for usage as electrode material for energy storage application. The ACQS has well-defined microporous and mesoporous structures and a specific surface area of 1056.52 m2 g-1 and pore volume of 0.64 cm3 g-1. Three-electrode tests were performed in 6 M KOH, 1 M H2SO4 and 3 M KNO3 aqueous electrolytes, to analyse the material performance in acidic, basic, and neutral media. Specific capacitance values (Cs) of 133 F g-1/167 F g-1 at 1.0 A g-1 was obtained in 3 M KNO3 in the positive/negative potential windows. Due to the observed best performance in neutral 3 M KNO3, further electrochemical analysis of the symmetric device was carried out using the same electrolyte. The device displayed a Cs value of 122 F g-1, energy and power densities of ∼14 W h kg-1 and 450 W kg-1 respectively; at 0.5 A...