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1. Electrochemically Stable Carbazole-Derived Polyaniline for Pseudocapacitors

   https://doi.org/10.1021/acsapm.1c01616  

   Almtiri, Mohammed; Dowell, Timothy J.; Giri, Hari; Wipf, David O.; Scott, Colleen N. (March 2022, ACS Applied Polymer Materials)

   Supercapacitor energy storage devices are well suited to meet the rigorous demands of future portable consumer electronics (PCEs) due to their high energy and power densities (i.e., longer battery-life and rapid charging, respectively) and superior operational lifetimes (10 times greater than lithium-ion batteries). To date, research efforts have been narrowly focused on improving the specific capacitance of these materials; however, emerging technologies are increasingly demanding competitive performance with regards to other criteria, including scalability of fabrication and electrochemical stability. In this regard, we developed a polyaniline (PANI) derivative that contains a carbazole unit copolymerized with 2,5-dimethyl-p-phenylenediamine (Cbz-PANI-1) and determined its optoelectronic properties, electrical conductivity, processability, and electrochemical stability. Importantly, the polymer exhibits good solubility in various solvents, which enables the use of scalable spray-coating and drop-casting methods to fabricate electrodes. Cbz-PANI-1 was used to fabricate electrodes for supercapacitor devices that exhibits a maximum areal capacitance of 64.8 mF cm–2 and specific capacitance of 319 F g–1 at a current density of 0.2 mA cm–2. Moreover, the electrode demonstrates excellent cyclic stability (≈ 83% of capacitance retention) over 1000 CV cycles. Additionally, we demonstrate the charge storage performance of Cbz-PANI-1 in a symmetrical supercapacitor device, which also exhibits excellent cyclic stability (≈ 91% of capacitance retention) over 1000 charge–discharge cycles. 

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2. Detection of Diclofenac and Carbamazepine using Voltammetry and Flow Injection Analysis at Boron‐Doped Diamond Thin‐Film Electrodes

   https://doi.org/10.1002/elan.202400157  

   Jacobs, Aaron I; Zwane, Simphiwe; Jarošová, Romana; Zamora, Marissa D; Kuvarega, Alex T; Swain, Greg (December 2024, Electroanalysis)

   Abstract The electrochemical detection of two pharmaceuticals, diclofenac (DCF) and carbamazepine (CBZ), was investigated as an oxidation current using boron‐doped nanocrystalline diamond (BDD) thin‐film electrodes. Both voltammetry and flow injection analysis with amperometric detection (FIA‐EC) were used to measure the drugs in standard solutions and a urine simulant. The oxidation potential for DCF wasca. 0.7 V vs. Ag/AgCl (3 M KCl) in 0.1 M phosphate buffer (pH 7.2) and wasca. 1.2 V for CBZ in 0.1 M perchloric acid. The DCF oxidation reaction was diffusion controlled at the detection potential with evidence of some surface fouling by reaction products. The CBZ oxidation reaction was also controlled by diffusion at the detection potential, but with no surface fouling. The voltammetric peak currents for both drugs increased linearly with the concentration in the micromolar range (r²≥0.994). FIA‐EC analysis of DCF and CBZ revealed a linear dynamic range from at least 0.1 to 100 μM with the actual minimum concentration detectable (S/N=3) being less than the lowest concentration measured. The recovery percentage for DCF in the urine simulant ranged from 94–108% and from 97–100% for CBZ, both assessed using square wave voltammetry. FIA‐EC data revealed that the BDD electrodes offer excellent intra and inter‐electrode repeatability with an RSD for DCF and CBZ of 4.90% and 3.81%, respectively. The BDD electrode provided good reproducibility and response stability over eight days of continuous use detecting both DCF and CBZ. Overall, BDD electrodes are a viable material  for the sensitive, selective, and reproducible electrochemical detection of these two pharmaceuticals. 

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3. MoS ₂ Nanoflakes based Kilohertz Electrochemical Capacitors

   https://doi.org/10.1002/batt.202300363  

   Bal, Sourayan; Baranwal, Rishav; Lin, Xueyan; Li, Wenyue; Yang, Shize; Islam, Nazifah; Fan, Zhaoyang (November 2023, Batteries & Supercaps)

   Abstract An ultra‐fast electrochemical capacitor (EC) designed for efficient ripple current smoothing was fabricated using vertically oriented MoS₂(VOM) nanoflakes deposited on freestanding carbonized cellulose (CC) sheets as electrodes. The daily used cellulose tissue sheets were transformed into electrode scaffolds through a rapid pyrolysis process within a preheated furnace, on which VOM nanoflakes were formed in a conventional hydrothermal process. With these ~10 μm thick VOM‐CC electrodes, ultrafast ECs with tunable frequency response and specific capacitance density were fabricated. The ECs with a cell‐level areal capacitance density of 0.8 mF/cm²at 120 Hz were demonstrated for ripple current filtering from 60 Hz to 60 kHz. At a lower frequency response level, EC cell with a large capacitance density of 4.8 mF/cm²was also demonstrated. With the facile and easily scaled up process to producing the nanostructured electrode, the miniaturized VOM‐CC based ECs have the potential to substitute the bulky aluminum electrolytic capacitors for current smoothing and pulse power applications. 

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4. Carbon–titanium dioxide (C/TiO ₂ ) nanofiber composites for chemical oxidation of emerging organic contaminants in reactive filtration applications

   https://doi.org/10.1039/D0EN00975J  

   Greenstein, Katherine E.; Nagorzanski, Matthew R.; Kelsay, Bailey; Verdugo, Edgard M.; Myung, Nosang V.; Parkin, Gene F.; Cwiertny, David M. (March 2021, Environmental Science: Nano)

   null (Ed.)

   The recalcitrance of some emerging organic contaminants through conventional water treatment systems may necessitate advanced technologies that use highly reactive, non-specific hydroxyl radicals. Here, polyacrylonitrile (PAN) nanofibers with embedded titanium dioxide (TiO 2 ) nanoparticles were synthesized via electrospinning and subsequently carbonized to produce mechanically stable carbon/TiO 2 (C/TiO 2 ) nanofiber composite filters. Nanofiber composites were optimized for reactivity in flow through treatment systems by varying their mass loading of TiO 2 , adding phthalic acid (PTA) as a dispersing agent for nanoparticles in electrospinning sol gels, comparing different types of commercially available TiO 2 nanoparticles (Aeroxide® P25 and 5 nm anatase nanoparticles) and through functionalization with gold (Au/TiO 2 ) as a co-catalyst. High bulk and surface TiO 2 concentrations correspond with enhanced nanofiber reactivity, while PTA as a dispersant makes it possible to fabricate materials at very high P25 loadings (∼80% wt%). The optimal composite formulation (50 wt% P25 with 2.5 wt% PTA) combining high reactivity and material stability was then tested across a range of variables relevant to filtration applications including filter thickness (300–1800 μm), permeate flux (from 540–2700 L m −2 h), incident light energy (UV-254 and simulated sunlight), flow configuration (dead-end and cross-flow filtration), presence of potentially interfering co-solutes (dissolved organic matter and carbonate alkalinity), and across a suite of eight organic micropollutants (atrazine, benzotriazole, caffeine, carbamazepine, DEET, metoprolol, naproxen, and sulfamethoxazole). During cross-flow recirculation under UV-irradiation, 300 μm thick filters (30 mg total mass) produced micropollutant half-lives ∼45 min, with 40–90% removal (from an initial 0.5 μM concentration) in a single pass through the filter. The initial reaction rate coefficients of micropollutant transformation did not clearly correlate with reported second order rate coefficients for reaction with hydroxyl radical ( k OH ), implying that processes other than reaction with photogenerated hydroxyl radical ( e.g. , surface sorption) may control the overall rate of transformation. The materials developed herein represent a promising next-generation filtration technology that integrates photocatalytic activity in a robust platform for nanomaterial-enabled water treatment. 

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5. High stability SrTi _1−x Fe _x O _3−δ electrodes for oxygen reduction and oxygen evolution reactions

   https://doi.org/10.1039/c9ta07548h  

   Zhang, Shan-Lin; Cox, Dalton; Yang, Hao; Park, Beom-Kyeong; Li, Cheng-Xin; Li, Chang-Jiu; Barnett, Scott A. (September 2019, Journal of Materials Chemistry A)

   Sr(Ti 1−x Fe x )O 3−δ (STF) has recently been explored as an oxygen electrode for solid oxide electrochemical cells (SOCs). Model thin film electrode studies show oxygen surface exchange rates that generally improve with increasing Fe content when x < 0.5, and are comparable to the best Co-containing perovskite electrode materials. Recent results on porous electrodes with the specific composition Sr(Ti 0.3 Fe 0.7 )O 3−δ show excellent electrode performance and stability, but other compositions have not been tested. Here we report results for porous electrodes with a range of compositions from x = 0.5 to 0.9. The polarization resistance decreases with increasing Fe content up to x = 0.7, but increases for further increases in x . This results from the interaction of two effects – the oxygen solid state diffusion coefficient increases with increasing x , but the electrode surface area and surface oxygen exchange rate decrease due to increased sinterability and Sr surface segregation for the Fe-rich compositions. Symmetric cells showed no degradation during 1000 h life tests at 700 °C even at a current density of 1.5 A cm −2 , showing that all the STF electrode compositions worked stably in both fuel cell mode and electrolysis modes. The excellent stability may be explained by X-ray Photoelectron Spectroscopy (XPS) results showing that the amount of surface segregated Sr did not change during the long-term testing, and by relatively low polarization resistances that help avoid electrode delamination. 

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