Research on solid supercapacitors over the last few years has aimed to provide high performing and safely operating energy storage solutions for the fast growing application areas of consumer and micro-electronics, providing printable, flexible and wearable devices. Most of the reported research has leveraged proton conducting polymer electrolytes for electrochemical double layer capacitors and pseudo-capacitors. In this paper, we provide an overview of the state-of-the-art solid supercapacitors enabled by proton-conducting polymer electrolytes. After a short overview of the types and configurations of solid supercapacitors, this review introduces proton-conducting polymers electrolytes and the mechanisms of proton conduction in a polymer matrix. Based on their chemistry, synthesizing method, and the nature of proton conduction, proton-conducting polymer electrolytes and the resultant supercapacitors are discussed in two categories: polymeric proton-conducting electrolytes and inorganic/polymer proton-conducting electrolytes. The performance and the technology gaps of the solid supercapacitors enabled by the presented polymer electrolytes are reviewed and compared. The review concludes with an outlook of future advancements required and the key research directions to achieving these.

Proton-conducting polymer electrolytes and their applications in solid supercapacitors: a review

A novel flexible, ultra-sensitive, selective, and room temperature operable polyaniline/iron-oxide (PAni/α-Fe2O3) nanocomposite ammonia (NH3) gas sensor was developed onto a flexible polyethylene terephthalate (PET) substrate by in situ polymerization process. The observations were recorded to 100 ppm fixed level for various gases including NO2, CH3OH, C2H5OH, NH3, and H2S through monitoring the change in resistance of the developed sensor. The flexible PAni/α-Fe2O3 nanocomposite sensor demonstrated better selectivity towards NH3 (response = 39% and stability = 74%). The synergistic response of the flexible PAni/α-Fe2O3 sensor was remarkable than that of the PAni and α-Fe2O3 alone; indicating the effective improvement in the performance of PAni flexible sensor on nanocomposite process. Moreover, the flexible sensor detected NH3 at low concentration (5 ppm) with a fast response (27 s) and very short recovery time (46 s). Further, PAni/α-Fe2O3 flexible sensor films were characterized by X-ray diffraction, field-emission scanning electron microscopy, UV-visible and Raman spectroscopy, Fourier transform infrared and X-ray photoelectron for structural analysis, morphological evolution, optical and surface related studies.

Ultra-sensitive polyaniline–iron oxide nanocomposite room temperature flexible ammonia sensor

While today’s lithium-ion batteries offer acceptable energy storage capability, they lack the ability to be cycled repeatedly more than a couple thousand times. Electrochemical capacitors, i.e., supercapacitors, are being developed whose lifetimes exceed 1 × 106 cycles and power densities surpass those of batteries by several times. Here, we present an all-solid-state supercapacitor using a Li2S-P2S5 glass-ceramic electrolyte as both separator and ion conductor. Three device architectures are examined including two with nanostructured electrodes which incorporate multi-walled carbon nanotubes (MWCNTs). Cyclic voltammograms and electrochemical impedance measurements demonstrate that these devices develop reversible double layer capacitance, and a maximum of 7.75 F/g is achieved in the device constructed by mechanically mixing the nanostructured electrodes. Electrochemical impedance spectroscopy explains non-idealities observed when MWCNTs are incorporated in the electrode layers.

Nanostructured all-solid-state supercapacitor based on Li2S-P2S5 glass-ceramic electrolyte

For high-performance energy-storage devices, three-dimensional (3D) designs with diverse configurations are demonstrated to provide highly qualified electrodes and efficient device integration. From a microscope to a macroscope view, this review summarizes the recent advances in electrochemically active nanomaterials, novel current collectors, and integrations of the devices in 3D configurations.

Three‐Dimensional Structural Engineering for Energy‐Storage Devices: From Microscope to Macroscope

The use of photodynamic therapy (PDT) in the treatment of brain cancer has produced exciting results in clinical trials over the past decade. PDT is based on the concept that a photosensitizer exposed to a specific light wavelength produces the predominant cytotoxic agent, to destroy tumor cells. However, delivering an efficient light source to the brain tumor site is still a challenge. The light source should be delivered by placing external optical fibers into the brain at the time of surgical debulking of the tumor. Consequently, there exists the need for a minimally invasive treatment for brain cancer PDT. In this study, we investigated an attractive non-invasive option on glioma cell line by using Tb3+-doped LaF3 scintillating nanoparticles (LaF3:Tb) in combination with photosensitizer, meso-tetra(4-carboxyphenyl)porphyrin (MTCP), followed by activation with soft X-ray (80 kVp). Scintillating LaF3:Tb nanoparticles, with sizes of approximately 25 nm, were fabricated. The particles have a good dispersibility in aqueous solution and possess high biocompatibility. However, significant cytotoxicity was observed in the glioma cells while the LaF3:Tb nanoparticles with MTCP were exposed under X-ray irradiation. The study has demonstrated a proof of concept as a non-invasive way to treat brain cancer in the future.

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Non-invasive Photodynamic Therapy in Brain Cancer by Use of Tb3+-Doped LaF3 Nanoparticles in Combination with Photosensitizer Through X-ray Irradiation: A Proof-of-Concept Study.

Growth and characterisation of new non linear optical material α-glycine sulpho-nitrate (GLSN) with stable dielectric and light dependent properties

A 5 F–5 V prototype of solid state supercapacitor based on polymer electrolyte (PANI) and XSPEEK composing of six single cells stacked in series has been fabricated. The scale-up from a small single cell to a larger stack prototype of a solid-state electrochemical supercapacitor is discussed in this paper. The developed prototype showed a higher series resistance than estimated in our previous study on individual cell supercapacitor. The fabricated prototype achieved a specific capacitance of 480 F/g. The assembled capacitor has been characterized by cyclic voltammetry, impedance spectroscopy and galvanostatic charging/discharging. The performances of the electrodes have been compared with that of the single cell electrodes of area 4 cm 2 .

Design, fabrication, and evaluation of a 5 F–5 V prototype of solid-state PANI based supercapacitor

Avalanche breakdown in a p-n junction can generate rf negative resistance due to twin delay mechanism (Avalanche Delay associated with growth of charge bump and transit time delay caused due to time elapsed for the grown charge bump drifting through the depletion zone) leading to generation of high frequency power in IMPATT mode. With the advancement of device technology and with the motive of furtherance of device performance, replacement of homo junction of single elemental semiconductor with hetero junction, hetero structure junctions from lattice matched pair of elemental semiconductors is now being explored as supported by recent reports. The introduction of an n-Ge and p-Ge impurity bumps on either side of junction interface of a Si p-n junction, results in the formation of a n-Si-Ge/p-Ge-Si hetero structure p-n junction. The analysis of such hetero structure Impatt diode for generation of micro/mm-wave power at designed atmospheric window frequencies of 15 and 94 GHz becomes the scope of the study of this paper. The results are computed through three tier sophisticated computer algorithm indicate efficiency enhancement in case of proposed hetero structure to nearly 29% (at X-band) as against only 14% for the corresponding the homo junction diodes associated with increase of diode negative conductance by nearly two fold which in turn could enhance the rf power delivery from the hetero structure diode by many fold. Presence of low BG Ge near high field junction interface and its order high carrier ionization rate (compared to Si) localizes the avalanche zone to below 10% of the depletion zone and thereby pushes the device efficiency and value of negative conductance. However the performance of complementary n-Ge-Si/p-Si-Ge hetero structure remains close to Si or Ge homo junction. The results are highly encouraging which may make Si-Ge-Si Hetero Structure Diode as a prospective microwave generator.

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S. P. Pati

Papers

Growth and characterisation of new non linear optical material α-glycine sulpho-nitrate (GLSN) with stable dielectric and light dependent properties

Design, fabrication, and evaluation of a 5 F–5 V prototype of solid-state PANI based supercapacitor

Possible Realization of Near Optimum Efficiency from n-Si-Ge/p-Ge-Si DDR Hetero Structure IMPATT Diode

Growth, structural, optical and mechanical studies on acid mixed glycine metal salt (GABN) crystal as potential NLO material

Growth, characterization, non-linear optical properties and dislocation studies in new GCF crystals