Herein, very recent advances in polymer, peptide, and hybrid hydrogels for uses in photovoltaics, supercapacitor, organic electronics, drug delivery, tissue engineering, biosensing, cell culture, and different optoelectronic materials are discussed.

We have synthesized a ternary rGO/Fe3O4/PANI (rGFP) composite for binder-free, semiflexible, thin, all-solid-state supercapacitor device fabrication. A scalable soft-template technique has been adopted for the preparation of three-dimensional Fe3O4-decorated reduced graphene oxide (rGO)-doped polyaniline (PANI) nanorods that are unambiguously investigated under electron microscopes (FESEM and HRTEM). The presence of PANI in the nanocomposite is overwhelmingly supported by the absorption and vibration studies. Raman spectra convincingly show the presence of rGO in the nanocomposites, and the formation of Fe3O4 nanoparticles is confirmed by XRD and XPS results. The specific capacitance value that has been achieved for synthesized ternary rGFP nanocomposite is ∼283.4 F/g at 1.0 A/g current density and exhibited a maximum energy density of 47.7 W h/kg at a power density of 550 W/kg. Interestingly, after 5000 cycles the composite shows excellent life stability that is a 78% retention of the electrochemical property. To demonstrate the portable energy storage applicability, a binder-free rGFP-based supercapacitor device was fabricated, which illustrated the operation of an LED bulb for 30 min when fully charged. These results indicate that synthesized ternary nanocomposites are worth their potential as an electrode material and would be used in next-generation high-rate energy storage systems.

Graphene quantum dot-doped polyaniline composites have been prepared by the chemical oxidation of aniline. Synthesized novel fibrous composites show an excellent specific capacitance value of ∼1044 F g(-1) at a current density of 1 A g(-1) as well as moderate cyclic stability with a retention of life time of 80.1% after 3000 cycles.

Facile synthesis of polyaniline@Ag composite has been successfully demonstrated by a simple solution-dipping method using high-aspect-ratio benzene tetracarboxylic acid-doped polyaniline (BDP) fiber as a nontoxic reducing agent as well as template cum stabilizer. In BDP@Ag composite, BDP fibers are decorated with spherical Ag nanoparticles (Ag NPs), and the population of Ag NPs on BDP fibers is controlled by changing the molar concentration of AgNO3. Importantly, Ag-NP-decorated BDP fibers (BDP@Ag composites) have been evolved as a sensitive materials for the detection of trace amounts of 4-mercaptobenzoic acid and rhodamine 6G as an analyte of surface-enhanced Raman scattering (SERS), and the detection limit is down to nanomolar concentrations with excellent recyclability. Furthermore, synthesized BDP@Ag composites are applied simultaneously as an active SERS substrate and a superior catalyst for reduction of 4-nitrothiophenol.

Electrically conductive hydrogels are a fascinating class of materials that exhibit multifarious applications such as photoresponse, energy storage, etc., and the three-dimensional micro- and nanofibrillar structures of the gels are the key to those applications. Herein, we have synthesized a hybrid hydrogel based on folic acid (F) and polyaniline (PANI) in which F acts as a supramolecular cross-linker of PANI chains. The gels are mechanically robust and are characterized by field-emission scanning electron microscopy, transmission electron microscopy, and spectroscopic, rheological, and universal testing measurements. The hybrid xerogel exhibit a BET surface area 238 m g-, conductivity of 0.04 S/cm, specific capacitance of 295 F/g at a current density of 1A/g, and photocurrent of ∼2 mA under white-light illumination. Silver nanoparticles (AgNPs) are in situ grown to elegantly improve the conductivity, energy storage, and photoresponse capability of the gels. The formation of AgNPs drastically improves the specific capacitances up to 646 F/g (at current density 1A/g), excellent rate capability (403 F/g at 20 A/g), and stable cycling performance with a retention ratio of 74% after 5000 cycles. The AgNPs embedded gel exhibits dramatic enhancement of photocurrent to 56 mA, and its time-dependent photoillumination corroborates faster rise and decay of current compared to those of folic acid-polyaniline hydrogel.