Electrochemical performance of activated carbon fiber with hydrogen bond-induced high sulfur/nitrogen doping

Graphene oxide-based materials as proton-conducting membranes for electrochemical applications

The rapid advancements of graphene oxide (GO)-based membranes necessitate the understanding of their properties and application potential. Generally, proton (H+)-conducting membranes, including GO-based ones, are crucial components in various energy-relevant devices, significantly determining the transport process, selectivity, and overall efficiency of these devices. Particularly, GO-based membranes exhibit great potential in electrochemical applications owing to their remarkable conductivity and ease of undergoing further modifications. This review is aimed at highlighting recent functionalization strategies for GO with diverse substrates. It is also aimed at emphasizing how these modifications can enhance the electrochemical performances of GO-based membranes. Notably, key aspects, such as the enhanced H+-transfer kinetics, improved conductivity, functionalities, and optimization, of these membranes for specific applications are discussed. Additionally, the existing challenges and future directions for the field of functionalized GO are addressed to achieve precise control of the functionalities of these membranes as well as advance next-generation electrochemical devices.

In-situ detoxification of schedule-I chemical warfare agents utilizing Zr(OH)4@W-ACF functional material for the development of next generation NBC protective gears

Chemical warfare agents (CWAs) have become a pivotal concern for the global community and spurred a wide spectrum of research for the development of new generation protective materials. Herein, a highly effective self-detoxifying filter consisting of in-situ immobilized Zirconium hydroxide [Zr(OH)4] over woven activated carbon fabric [Zr(OH)4@W-ACF] is presented for the removal of CWAs. It was prepared to harness the synergistic effect of high surface area of W-ACF, leads to high dispersion of CWAs and high phosphilicity and reactivity of [Zr(OH)4]. The synthesized materials were characterized by ATR-FTIR, EDX, SEM, TEM, XPS, TGA, and BET surface area analyzer. The kinetics of  in-situ degradation of CWAs over Zr(OH)4@W-ACF were studied and found to be following the first-order reaction kinetics. The rate constant was found to be 0.244 min-1 and 2.31 × 10-2 min-1 for sarin and soman, respectively over Zr(OH)4@W-ACF. The potential practical applicability of this work was established by fabricating Zr(OH)4@W-ACF as reactive adsorbent layer for protective suit, and found to be meeting the specified criteria in terms of air permeability, tearing strength and nerve agent permeation as per TOP-08-2-501A:2013 and IS-17380:2020. The degradation products of CWAs were analyzed with NMR and GC-MS. The combined properties of dual functional textile with reactive material are expected to open up new exciting avenues in the field of CWAs protective clothing and thus find diverse application in defence and environmental sector.

Boosting supercapacitive performance of flexible carbon via surface engineering

The relatively low specific capacitance of flexible carbons hinders their practical application for fabricating high-performance flexible supercapacitors. In this work, a surface engineering method is proposed to boost the supercapacitive performance of the flexible carbon. In this method, a flexible carbon was fabricated from carbon felt via co-activation with potassium argininate and potassium hydroxide (KOH) as activators, and the resulting material is abbreviated as AKCF. Unlike traditional KOH activation processes, the addition of potassium argininate can produce a micro-graphitized carbon layer to be the outer layer of AKCF fibers for achieving better electronic transfer. Due to the improved conductivity and lower charge transfer resistance endowed by a thin micro-graphitized carbon layer, the capacitance of the AKCF-0.1 (0.1 M arginine was used) electrode obtained by the co-activation process is elevated to a 1.8-fold higher value of 403 C·g^-1 (2583 mC·cm^-2) relative to the AKCF-0 (0 M arginine was used) electrode prepared by KOH activation alone (222 C·g^-1 or 1369 mC·cm^-2). Moreover, this AKCF-0.1 electrode also displays satisfactory rate capability (66% capacitance retention after a 20-fold current increase) and highly stable cycling performance (no capacitance decline after 20,000 cycles). In addition, the asymmetric supercapacitors constructed with this AKCF-0.1 electrode as the flexible negative electrode expresses high energy densities of 68.4 Wh·kg^-1 and 0.139 mWh·cm^-2 in aqueous and gel electrolytes, respectively.

Porous 3D graphene aerogel co-doped with nitrogen and sulfur for high-performance supercapacitors

Heteroatom-doped carbon materials with a high specific area, a well-defined porous structure is important to high-performance supercapacitors (SCs). Here, S and N co-doped three-dimensional porous graphene aerogel (NS-3DPGHs) have been synthesized in a facile and efficient self-assembly process with thiourea acting as the reducing and doping agent solution. Operating as a SC electrode, fabricated co-doping graphene, i.e. the sample of NS-3DPGH-150 exhibits the highest specific capacitance of 412.9 F g^-1 under 0.5 A g^-1 and prominent cycle stabilization with 96.4% capacitance retention in the back of 10 000 cycles. Furthermore, based on NS-3DPGH-150, the symmetrical supercapacitor as-prepared in 6 M KOH displays a superior energy density of 12.9 Wh kg^-1 under the power density of 249 W kg^-1. Hence, NS-3DPGHs could be considered as an excellent candidate for SCs.

Synthesis and electrochemical performance of an electroactive nitrogen-doping SnO2 nanoarray supported on carbon fiber

An electroactive nitrogen-doping tin dioxide nanorod array (N-SnO2 NRA) is designed as an effective energy-storage electrode material for supercapacitor applications. N-SnO2 supported on a carbon fiber substrate is prepared using SnCl4 as a precursor through hydrolysis, hydrothermal growth, and an NH3-nitriding process. Electroactive N-SnO2 is formed by an N-doping reaction between Sn(OH)4 and NH3, revealing a high nitrogen-doping level of 12.5% in N-SnO2. N-SnO2/carbon fiber reveals a lower ohmic resistance and charge transfer resistance than SnO2/carbon fiber, which is consistent with its higher current response and lower voltage drop in electrochemical measurements. N-SnO2 NRA has an independent nanoarray structure and a small side length of a quadrangular nanorod, contributing to a more accessible interspace, reactive sites, and feasible electrolyte ion diffusion. The N-SnO2/carbon fiber NRA electrode shows higher specific capacitance (105.4 F g−1 at 0.5 A g−1) and rate capacitance retention (45.0% from 0.5 to 5 A g−1) than a SnO2/carbon fiber NRA electrode (58.6 F g−1, 38.4%). Significantly, the cycling capacitance retention after 2000 cycles increases from 78.1% of SnO2/carbon fiber to 98.8% of N-SnO2/carbon fiber, presenting a superior electrochemical cycling stability. The N-SnO2 supercapacitor maintains stable power working at an output voltage of 1.6 V. The specific capacitance decreases from 75.2 to 55.1 F g−1 when the current density increases from 1 to 10 A g−1. The corresponding energy density decreases from 24.23 to 9.81 Wh kg−1, presenting a reasonable rate capability. So, the prepared N-SnO2 nanorod array demonstrates superior capacitance performance for energy-storage applications.

Electrochemical performance of the homologous molybdenum(vi) redox-active gel polymer electrolyte system

PVA–H₃PO₄–Na₂MoO₄ and PVA–H₃PO₄–PMo₁₂ are assembled into a single solid-state supercapacitor to improve the specific capacitance. Homologous molybdenum (vi) of PMo₁₂ and Na₂MoO₄ provides synergistic effect to improve faradaic capacitance performance.

Fabrication of Highly Ordered Ag/TiO2 Nanopore Array as a Self-Cleaning and Recycling SERS Substrate

Silver nanoparticles deposited on a titania nanopore array (Ag/TiO2 NPA) has been designed as a surface-enhanced Raman scattering (SERS) substrate for sensitive and recycling application of organic molecule detection. A TiO2 NPA was fabricated by a surface oxidization reaction of a titanium sheet by a double anodization process. A Ag/TiO2 NPA was then formed by depositing silver nanoparticles onto the TiO2 NPA by a cycling chemical reduction deposition process. The Ag/TiO2 NPA has a uniform mono-layer dispersion of Ag nanoparticles with a size of 30–50 nm on TiO2 nanopores with a diameter of 100–110 nm. The Ag/TiO2 NPA SERS substrate could facilitate interfacial adsorption of Rhodamine 6G (R6G), which achieves a sensitive detection limit of 10−8 M R6G through SERS spectrum measurement. The Ag/TiO2 NPA SERS substrate achieves an analytical enhancement factor value of 2.6 × 105. The Ag/TiO2 NRA could promote the UV light-excited photocatalytic degradation reaction of R6G adsorbed on its surface which gives rise to a refreshed Ag/TiO2 NRA under UV irradiation for 60 min and accordingly behave as a self-cleaning and recycling SERS substrate. The Ag/TiO2 NPA exhibits a much higher R6G degradation reaction rate constant (0.05764 min−1) than the TiO2 NPA (0.02600 min−1), indicating its superior photocatalytic activity and self-cleaning activity. The refreshed Ag/TiO2 NPA was able to be recycled for the Raman detection of R6G, maintaining a high stability, reproducibility, and cyclability. The highly ordered Ag/TiO2 NPA with well controlled Ag nanoparticle dispersion and TiO2 nanopore shape could act as a suitable SERS substrate for recycling and self-cleaning application for stable and sensitive molecule detection.

Fabrication and charge storage capacitance of PPY/TiO2/PPY jacket nanotube array

A PPY/TiO2/PPY jacket nanotube array was fabricated by coating PPY layer on the external and internal surface of a tube wall-separated TiO2 nanotube array. It shows coaxial triple-walled nanotube structure with two PPY nanotube layers sandwiching one TiO2 nanotube layer. PPY/TiO2/PPY reveals much higher current response than TiO2. The theoretical calculation indicates PPY/TiO2/PPY reveals higher density of states and lower band gap, accordingly presenting higher conductivity and electroactivity, which is consistent with the experimental result of a higher current response. The electroactivity is highly enhanced in H2SO4 rather than Na2SO4 electrolyte due to feasible pronation process of PPY in an acidic solution. PPY/TiO2/PPY could conduct the redox reaction in H2SO4 electrolyte which involves the reversible protonation/deprotonation and HSO4 − doping/dedoping process and accordingly contributes to Faradaic pseudocapacitance. The specific capacitance is highly enhanced from 1.7 mF cm−2 of TiO2 to 123.4 mF cm−2 of PPY/TiO2/PPY at 0.1 mA cm−2 in H2SO4 electrolyte. The capacitance also declines from 123.4 to 31.7 mF cm−2 when the current density increases from 0.1 to 1 mA cm−2, presenting the rate capacitance retention of 26.7% due to the semiconductivity of TiO2. A PPY/TiO2/PPY jacket nanotube with high charge storage capacitance is regarded as a promising supercapacitor electrode material.