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This study reports the preparation of a set of hybrid materials consisting of molybdenum disulfide (MoS2) nanopatches on reduced graphene oxide (rGO) nanosheets by microwave specific heating of graphene oxide and molecular molybdenum precursors followed by thermal annealing in 3% H2 and 97% Ar. The microwave process converts graphene oxide to ordered rGO nanosheets that are sandwiched between uniform thin layers of amorphous molybdenum trisulfide (MoS3). The subsequent thermal annealing converts the intermediate layers into MoS2 nanopatches with two-dimensional layered structures whose defect density is tunable by controlling the annealing temperature at 250, 325 and 600 °C, respectively. All three MoS2/rGO samples and the MoS3/rGO intermediate after the microwave step show a high Li-ion intercalation capacity in the initial 10 cycles (over 519 mA h gMoSx−1, ∼3.1 Li+ ions per MoS2) which is attributed to the small MoS2 nanopatches in the MoS2/rGO hybrids while the effect of further S-rich defects is insignificant. In contrast, the Zn-ion storage properties strongly depend on the defects in the MoS2 nanopatches. The highly defective MoS2/rGO hybrid prepared by annealing at 250 °C shows the highest initial Zn-ion storage capacity (∼300 mA h gMoSx−1) and close to 100% coulombic efficiency, which is dominated by pseudocapacitive surface reactions at the edges or defects in the MoS2 nanopatches. The fast fading in the initial cycles can be mitigated by applying higher charge/discharge currents or extended cycles. This study validates that defect engineering is critical for improving Zn-ion storage.

Highly conducting freestanding graphene (FSG) was synthesized by the simple vacuum filtration method and utilized as a cathode current collector for (fluorine doped tin oxide) FTO free quasi-dye sensitized solar cell (q-DSSC). Subsequently,conducting polymers (CPs) viz., polyaniline (PANI) and poly(3,4-ethylene-di-oxythiophene) (PEDOT) was decorated on FSG surface by electrochemical polymerization which acts as a electrocatalytst for Pt free q-DSSC. Entirely, the FSG/CPs affords as a novel cathode architecture for FTO/Pt free electrode for q-DSSCs. Remarkably, the FSG paper electrode exhibits lower sheet resistance (9-11 Ω sq-1) than the FTO which was directly utilized as current collector. Interestingly, the FSG/CPs based cathode shows an improved electro-catalytic behaviour towards tri-iodide reduction and in particularly, the photovoltaic performance of FSG/PEDOT shows power conversion efficiency (PCE) of 5.4 % compared with Pt/FTO of 5.1 %. It can be stated that synergetic effect of FSG/PEDOT proves to be a cost effective and efficientsubstitute for cathodes in q-DSSC.

Rechargeable aqueous zinc ion batteries are an emerging topic in the battery research due to its high volumetric capacity (5855 mAh/cm3), low cost, environmental friendliness and safety. But the development of the zinc ion batteries have been seriously hindered by the slow insertion/extraction kinetics of the multivalent Zn2+ ions in the host structure. Two-dimensional (2D) transition metal oxides are intensely studied for various energy storage applications such as batteries and supercapacitors but controlled synthesis and tunable nanoscale properties are still a challenge. Herein we present and discuss the self-assembly of a hybrid material of microwave-exfoliated Vanadium pentoxide (V2O5) nanoribbons (NRs) on graphene oxide (GO) nanosheets as a potential host for zinc ion storage. Vanadium pentoxide have several advantages such as high discharge capacity (294 mAhg-1) and large abundance but suffers from low electrical conductivity and poor stability. Using a thermal treatment, the GO template is converted to reduced graphene oxide (rGO) which improves the electrical conductivity of the hybrid. Multiple divalent cations such as Zn2+ and Mn2+ have been used in the self-assembly process to bind the negatively charged V2O5 NRs and GO nanosheets to improve the stability of the hybrid and accommodate the intercalation/deintercalation of the Zn2+ ions. Incorporation of 0.0357 M Mn2+ along with 0.10 M Zn2+ in the assembly process has been found to form a stoichiometric composition of Mn0.15Zn0.08V2O5 by XPS, which provides the high specific capacity of 295 mAh g-1 at 0.5 A g-1 and a high stability with the capacity retention of ~81.3% after 500 cycles at 4 A g-1.

Ultrathin 2D transition metal oxide materials have great advantages as electrical energy storage materials. At present, improving the yield and processing techniques is one of the top priorities to push these materials for scalable applications. Here, a novel microwave-assisted technique is presented to exfoliate crystalline α-V2O5 powder into wrinkled nanoribbons. The yield of the V2O5 nanoribbons can reach up to 20% after 40 min of microwave treatment. The as-exfoliated V2O5 nanoribbons are further used to form a strongly bound hybrid material with larger graphene oxide (GO) nanosheets through a simple cation-mediated self-assembly process, and the 2D GO template is converted into highly conductive reduced graphene oxide (rGO) nanosheets by thermal annealing treatment. The obtained V2O5/rGO hybrid material exhibits typical capacitive behavior with a specific capacitance of 423.6 F g−1 at 1 A g−1, an excellent high-rate capability and good cycling stability. These results suggest the exciting potential of the microwave-assisted technique for high-yield exfoliation of V2O5 nanoribbons toward future electrical energy storage applications.