Aerogels are 3-D nanostructures of non-fluid colloidal interconnected porous networks consisting of loosely packed bonded particles that are expanded throughout its volume by gas and exhibit ultra-low density and high specific surface area. Aerogels are normally synthesized through a sol-gel method followed by a special drying technique such as supercritical drying or ambient pressure drying. The fascinating properties of aerogels like high surface area, open porous structure greatly influence the performances of energy conversion and storage devices and encourage the development of sustainable electrochemical devices. Therefore, this review describes on the applications of inorganic, organic and composite aerogel nanostructures to dye-sensitized solar cells, fuel cells, batteries and supercapacitors accompanied by the significant steps involved in the synthesis, mechanism of network formation and various drying techniques.

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Hybrid dual-network membranes comprising chitosan (CS)-polyvinyl alcohol (PVA) networks crosslinked with sulfosuccinic acid (SSA) and glutaraldehyde (GA) and modified with stabilized silicotungstic acid (SWA) are reported for their application in direct methanol fuel cells (DMFCs). Physico-chemical properties of these membranes are evaluated using thermo-gravimetric analysis and scanning electron microscopy in conjunction with their mechanical properties. Based on water sorption and proton conductivity measurements for the membranes, the optimum content of 10 wt.% SWA in the membrane is established. The methanol crossover for these membranes are studied by measuring the mass balance of methanol using density meter and are found to be lower compared to Nafion-117 membrane. The membrane-electrode assembly with 10 wt.% stabilized SWA-CS-PVA hybrid membrane with SSA and GA as crosslinking agent delivers a peak power density of 156 mW cm −2 at a load current density of 400 mA cm −2 and 88 mW cm −2 at a load current density of 300 mA cm −2 , respectively, in DMFC at 70°C.

Nanocomposite polymer electrolytes (NCPEs) have been playing a considerable role in the development of alternative clean and sustainable energy technologies. This review article summarizes the recent research progress on the synthesis and characterization of NCPEs and its application in lithium ion battery based energy storage devices. First, an introduction on the properties, synthesis strategies and use of NCPEs is briefly given, followed by a state-of-the-art review on the preparation of NCPEs and their electrochemical properties in lithium ion battery (LIB) applications. Finally, the prospects and future challenges of NCPEs for energy storage are discussed

TiO 2 aerogel-metal organic framework (MOF) nanocomposite was synthesized using sol-gel method followed by subcritical drying technique and employed as a photoanode material in quasi-solid dye-sensitized solar cells (DSSCs). The nanocomposite material showed a BET surface area of 250 m 2 g −1 with an average pore size of 5 nm. Field emission scanning electron microscopic images revealed the continuous arrangement of pore-solid network structure. Energy-dispersive X-ray analysis shows the presence of MOF clusters on TiO 2 aerogel network. X-ray photoelectron spectroscopic analysis also supports the presence of MOF clusters in the aerogel network and indicates the presence of some oxygen vacancies in the nanocomposite material. The TiO 2 aerogel-MOF nanocomposite was used as photoanode in DSSC and an overall power conversion efficiency 2.34% along with a short-circuit current density 6.22 mA cm −2 was achieved.

The polyvinylidene fluoride ͑PVDF͒ membrane is modified by the chemical etchant-route employing a sodium naphthalene charge-transfer complex followed by impregnation with Nafion ionomer or polyvinyl alcohol ͑PVA͒-polystyrene sulfonic acid ͑PSSA͒ polymeric blend solutions by a dip-coating technique to form pore-filled-membrane electrolytes for application in direct methanol fuel cells ͑DMFCs͒. The number of coatings on the surface-modified PVDF membrane is varied between 5 and 15 and is found to be optimum at 10 layers both for Nafion and PVA-PSSA impregnations for effective DMFC performance. Hydrophilicity of the modified-membrane electrolytes is studied by determining average contact angle and surface-wetting energy. Morphology of the membranes is analyzed by a cross-sectional scanning electron microscope. The modified PVDF membrane electrolytes are characterized for their water-methanol sorption in conjunction with their mechanical properties, proton conductivity, and DMFC performance. Air permeability for the modified membranes is studied by a capillary-flow porometer. Methanol crossover flux across modified-PVDF-membrane electrolytes is studied by measuring the mass balance of methanol using a density meter. DMFCs employing membrane electrode assemblies with the modified PVDF membranes exhibit a peak powerdensity of 83 mW/cm 2 with Nafion impregnation and 59 mW/cm 2 for PVA-PSSA impregnation, respectively. Among the membranes studied here, stabilities of modified-pore-filled PVDF-Nafion and PVDF-PVA-PSSA membranes with 10-layers coat are promising for application in DMFCs.Direct methanol fuel cells ͑DMFCs͒ have advanced substantially and are now almost universally referred to as the sixth-fuel-cell type. DMFCs are attracting commercial interest particularly because methanol has higher volumetric energy-density than hydrogen. 1,2 Besides, the promise of DMFCs to complement/substitute the existing batteries is being realized along with their potential as the future technology for mobile and portable-power applications. 3,4 Currently, perfluoro sulfonic acid membranes trade marked as Nafion are being used as polymer electrolyte in DMFCs. Nafion membranes have excellent ionic conductivity, long-term durability, and good mechanical stability. 5,6 However, Nafion membranes are expensive and suffer from high methanol crossover that not only results in wastage of the fuel but also vitiates the platinum catalyst on the cathode. 7 Accordingly, efforts are being expended to fabricate cost-effective alternative membranes to help reduce methanol crossover in DMFCs. 8,9 Polymer electrolyte blend membranes of polyvinyl alcohol ͑PVA͒ with different proton conducting agents, namely sulfosuccinic acid ͑SSA͒, polystyrene sulfonic acid ͑PSSA͒, and poly ͑sty-rene sulfonic acid-co-maleic anhyride͒, have been successfully employed in DMFCs. 10-12 Composite membranes with phosphotungstic acid-doped PVA, mordenite-incorporated PVA-PSSA, and heteropolyacid ͑HPA͒-incorporated chitosan ͑CS͒ are also found to restrict methanol crossover ...