h i g h l i g h t sHigh surface area activated carbon was synthesized from orange peel (OP-AC). OP-AC showed high porous structure and rich oxygen-containing functional groups. OP-AC coated electrode showed less contact resistance and good catalytic activity. OP-AC coated electrode enhanced voltage and energy efficiency in VRB static cell. a b s t r a c t Activated carbon (AC) with high surface area (1901 m 2 g À1 ) is synthesized from low cost bio-waste orange (Citrus sinensis) peel for vanadium redox flow battery (VRB). The composition, structure and electrochemical properties of orange peel derived AC (OP-AC) are characterized by elemental analyzer, field emission-scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy. CV results show that OP-AC coated bipolar plate demonstrates improved electro-catalytic activity in both positive and negative side redox couples than the pristine bipolar plate electrode and this is ascribed to the high surface area of OP-AC which provides effective electrode area and better contact between the porous electrode and bipolar plate. Consequently, the performance of VRB in a static cell shows higher energy efficiency for OP-AC electrode than the pristine electrode at all current densities tested. The results suggest the OP-AC to be a promising electrode for VRB applications and can be incorporated into making conducting plastics electrode to lower the VRB cell stack weight and cost.

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In this work, β-Co(OH) nanosheets are explored as efficient pseudocapacitive materials for the fabrication of 1.6 V class high-energy supercapacitors in asymmetric fashion. The as-synthesized β-Co(OH) nanosheets displayed an excellent electrochemical performance owing to their unique structure, morphology, and reversible reaction kinetics (fast faradic reaction) in both the three-electrode and asymmetric configuration (with activated carbon, AC). For example, in the three-electrode set-up, β-Co(OH) exhibits a high specific capacitance of ∼675 F g at a scan rate of 1 mV s . In the asymmetric supercapacitor, the β-Co(OH) ∥AC cell delivers a maximum energy density of 37.3 Wh kg at a power density of 800 W kg . Even at harsh conditions (8 kW kg ), an energy density of 15.64 Wh kg is registered for the β-Co(OH) ∥AC assembly. Such an impressive performance of β-Co(OH) nanosheets in the asymmetric configuration reveals the emergence of pseudocapacitive electrodes towards the fabrication of high-energy electrochemical charge storage systems.

Activated carbon (AC) with high surface area (1,901 m 2 g À1 ) is synthesized from bio-waste orange (Citrus sinensis) peel for fabrication of high specific energy lithium ion capacitors (LICs). The composition, structure and electrochemical properties of orange peel derived AC (OP-AC) are characterized by elemental analyzer, field emission-scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammogram, charge-discharge and impedance studies. Fabricated LIC using the high surface area OP-AC with pre-lithiated graphite (LiC 6 ) delivered specific energy of~106Wh kg À1 . In addition, LIC configuration with Li 4 Ti 5 O 12 was also fabricated and observed to be capable of delivering the specific energy of~35 Wh kg À1 . Symmetric configuration of OP-AC with aqueous and organic solutions was also made for comparison purpose. A systematic improvement from the specific energy of 7 to 106 Wh kg À1 is noted from aqueous to LIC assembly. The findings open up the possibility of developing high specific energy LICs from abundant, low-cost, sustainable biomass waste.

Improved electrocatalytic activity via facile surface modification of waste derived activated carbon as electrodes for all vanadium redox flow battery, Applied Surface Science, under review. [4] M. Maharjan, M. Ulaganathan, T. M. Lim, High surface area activated carbon for high energy aqueous supercapacitor, ACS Applied Energy Materials, under review.