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.

Results of computer aided studies on mm-wave performance of GaAs (narrow band gap, E g = 1.42 eV) and zinc-blende (ZB) phase GaN (wide band gap, E g = 3.2 eV) double drift IMPATT diode for frequencies of operation in the range of 35 to 140 GHz indicate avalanche breakdown at very high electric field for ZB-GaN diode with exhibition of seven times higher breakdown voltage for ZB-GaN (331V) compared to GaAs (45.4 V) making it possible to realize high RF power. However the values of device efficiency and value of diode negative resistance remains high for GaAs diodes.

Prospects of wide band gap material ZB-GaN over low band gap GaAs-based IMPATT Devices

A method for design of high frequency IMPATT, operating in MITATT mode is presented which can compensate for the deterioration in device performance due to loss of carrier build up phase delay caused by tunneling current. The results for 94 GHz Si DDR indicate that the device performance of MITATT diodes would be improved considerably with the modulation of diode design parameters based on phase distortion. The suggested method would provide a realistic approach for design consideration of any form of high frequency IMPATTs operating in mixed tunneling and avalanche mode.

Phase Distortion Assisted MITATT Design for Compensation of Performance Deterioration due to Tunnel Current

The fundamental problem in the investigation of the properties of a quantum dot is the calculation of the energy eigen
values of its confined charge carriers and evaluation of their corresponding wave functions. The quantum dots may be
approximated as spheres whose surfaces constitute infinite potential barriers for carriers. Consequently, the motion of
electrons and holes (which are confined inside the dot) can be analyzed by effective mass approximation applied to noninteracting
particles. An attempt has been made here to solve the Schrodinger’s equation for particles inside the infinite
spherical potential well to determine their allowed energy eigen values and eigen functions.

On the calculation of energy eigenstates of electrons in a spherical quantum dot

Wide band gap semiconductor SiC with their superior electrical properties are likely candidates to replace conventional low band gap materials like Si and GaAs in the near future for RF power applications. The authors have therefore studied this prospects through advanced computer simulation experiment on hexagonal (both 4H and 6H) SiC based double drift region IMPATT diodes. The study indicates that around 300GHz, 4H-SiC based Impatt devices is capable of generating high microwave power with efficiency as compared to 6H-SiC based IMPATT diodes for the same frequency of operation.

MM-wave characteristics of SiC-based IMPATT oscillators

A recent report on realization/studies of Si-SiC hetero junction has given impetus to explore them for generation of rf
power in double drift impact ionization avalanche transit time (IMPATT) mode. MM-wave properties of this hetero
junction are compared with corresponding Si and SiC homo .junction. Interesting feature of ionization free n-SiC zone
localizes the avalanche zone to less than 10% of depletion zone resulting in diode efficiency around 27% (against only
10-15% for both homo junctions Si and SiC) and three fold high rf negative resistance, which can be therefore termed as
promising high rf power source.

S. P. Pati

Papers

Prospects of wide band gap material ZB-GaN over low band gap GaAs-based IMPATT Devices

Phase Distortion Assisted MITATT Design for Compensation of Performance Deterioration due to Tunnel Current

On the calculation of energy eigenstates of electrons in a spherical quantum dot

MM-wave characteristics of SiC-based IMPATT oscillators

Si, SiC homo junctions and n-SiC/p-Si hetero junction: MM-wave performance characteristics