Poly Hydroquinone Research Articles

Controlling Electronic and Ionic Conductivity in oMLD Polymer Coatings

Thin film polymer coatings formed by oxidative molecular layer deposition (oMLD) are of interest as ion-selective membranes for electrochemical sensors, and as protective coatings for lithium ion batteries. In both of these applications, it is critical to control the electronic conductivity, the ionic conductivity, and the ion selectivity of the MLD coatings. Recent understanding of the oMLD mechanism reveals this synthesis method as a path to control the molecular sequence of conjugated heteroatom-containing copolymers. We employ oMLD to reveal fundamental insights into how the molecular sequence of these copolymers influences conductivity, shifting the electronic conductivity by more than three orders of magnitude by altering the molecular sequence. We also summarize the development of new oMLD chemistries including polythiourea (PTU), polyhydroquinone (PHQ), and poly(2,5‐Dimercapto‐1,3,4‐Thiadiazole) (PDMCT). We employ in-situ quartz crystal microbalance (QCM) studies during oMLD growth to understand the chemical growth mechanisms, as well as ex-situ spectroscopic ellipsometry (SE), electrical impedance spectroscopy (EIS), and electrical Van der Pauw measurements, and electrochemical characterization to identify material properties. We examine PTU as an anion-selective membrane for ion sensor applications, and PHQ and PDMCT as protective coatings for lithium-ion battery applications that provide enhanced Li+-ion conductivity with control over electronic conductivity.

4D-STEM of LGPS and NMC Interfaces Reveal Interphase Formation Mechanism

Solid-state lithium-ion batteries (SS-LIBs) are a cutting-edge technology that will enhance safety and energy density compared to traditional LIBs. However, the rapid degradation of SS-LIBs upon charge-discharge cycling is a current barrier to commercialization. This degradation primarily stems from the formation of undesirable compounds at the electrode-electrolyte interfaces, which impede Li+ transport and lead to a reduction in charge capacity. Understanding the reactions occurring at the electrode-electrolyte interface is critical to mitigate this degradation and enhance battery performance. Here, we employ cryogenic four-dimensional STEM (4D-STEM) including energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and electron diffraction pair distribution function analysis (ePDF) at ~1 nm spatial resolution to inspect the cathode-electrolyte interfaces in SS-LIBs and study the reaction mechanisms driving interphase formation. For this study we employed Nickel rich LiNi0.6Co0.2Mn0.2O2 (NMC 622) as the cathode electrode material and Li10GeP2S12 (LGPS) as the solid electrolyte. We report a simplified process to measure interphase formation using chemical delithiation of NMC with MoCl5 in ethanol, followed by physical mixing of NMC and LGPS powder before STEM imaging. STEM measurement at the NMC-LGPS interface reveal that anion migration through the interface is a key driver for interphase formation. We also describe the development of a thin-film polyhydroquinone (PHQ) coating formed by oxidative molecular layer deposition (oMLD) as a candidate to encapsulate NMC and mitigate interface formation issues in SS-LIBs. The PHQ coating is expected to act as a selective conductor for cations and electrons, ensuring electrochemical operation of the battery while preventing anion transport. Our latest results showing assembly of SS-LIB cells with and without the oMLD barrier coatings will be discussed to reveal how the oMLD coating influence interface reactions and overall battery performance. Figure 1

Mechanism of polyhydroquinone coating iron/copper oxides for enhanced catalytic activity

In this study, Polyhydroquinone (PHQ) coated eight kinds of iron/copper oxides (CuO, Cu2O, Fe3O4, Fe2O3, C-CuFe2O4, T-CuFe2O4, 3R-CuFeO2, 2H-CuFeO2) to enhance their catalytic activity. As evidenced by the characterization results, PHQ was coated at Cu(I), Cu(II), and Fe(II) sites rather than Fe(III) sites by forming metal-organic complexes at the catalyst surface. These results were supported by catalytic experiments of Persulfate (PS) activation for 1,4-dioxane degradation. Based on the normalized pseudo-first-order kinetics constant, PHQ enhanced iron/copper sites in the order of Cu(I) > Fe(II) ≈ Cu(II). Interestingly, in contrast to the general agreement, the Hard and Soft Acids and Bases (HSAB) Principle indicated that the benzene ring (soft base) rather than the phenolic hydroxyl group (hard base) was the reactive site between Fe/Cu and PHQ. Six of the above eight iron/copper oxides (CuO, Cu2O, Fe3O4, C-CuFe2O4, 3R-CuFeO2, 2H-CuFeO2) displayed improved catalytic performance. The other two catalysts (Fe2O3 and T-CuFe2O4) showed no improvement in activity after PHQ coating. Among all the catalysts, PHQ/2H-CuFeO2 showed the best catalytic performance, which was also able to activate Hydrogen peroxide (HP) and Peroxymonosulfate (PMS) for 1,4-dioxane degradation by a radical pathway. However, radical process caused the decomposition of PHQ at the catalyst surface, leading to a dramatic drop (from 100% to approximately 30%) in catalyst activity. In contrast, PHQ/2H-CuFeO2 activated PS by a nonradical pathway where Cu(III) was likely responsible for 1,4-dioxane degradation. PHQ/2H-CuFeO2 was more stable after activating PS.

New insight for simultaneous determination of hazardous di-hydroxybenzene isomers at crown ether modified polymer/carbon nanotubes composite sensor

A new insight is presented in the fabrication of a reliable electrochemical sensor for di-hydroxybenzene isomers; hydroquinone (HQ), catechol (CC), and resorcinol (RC) which have been considered as common pollutants in environment and water samples. The sensor is based on modifying the glassy carbon electrode (GC) with successive layers, multi-walled carbon nanotubes (CNT), poly-hydroquinone (PHQ) and benzo-12-crown-4 (CE); GC/CNT/PHQ/CE. CE is introduced for the first time as a receptor for the di-hydroxybenzene isomers based on host-guest size matching. Other cycling compound with different cavity diameter as β-cyclodextrin (β-CD) (6.0–6.5 Å) was examined displaying lower current responses. CE exhibited “fit” cavity size (1.20–1.50 Å). Thus, the inclusion complexes formed between β-CD and di-hydroxybenzene isomers are less stable. The layered sensor showed highly electro-catalytic activity for simultaneous determination of isomers; HQ, CC and RC in the concentration ranges of 0.03–100 μM, 0.01–100 μM and 0.05–100 μM with low detection limit values of 0.156 nM, 0.118 nM and 0.427 nM, respectively. The practical impact of the sensor was illustrated for determination of di-hydroxybenzene isomers in real water matrices from two different sources. Moreover, anti-interference ability of the layered sensor for determination of di-hydroxybenzene isomers was successfully achieved in presence of common interfering ions and organic pollutants.

The Adsorption of Malachite Green on Graphene Nanocomposites: A Study on Kinetics Under Dynamic Conditions

The present paper examines the kinetics of the adsorption of the cationic dye, malachite green (MG), on polyhydroquinone (PHQ)/graphene and polyamine cumulene (PAC)/graphene nanocomposites representing graphene-oxide-based hybrid materials, in which p-benzoquinone and hexamethylenetetramine were used as modifier, respectively. Kinetic studies were carried out under dynamic conditions with a setup designed by the authors. The solution to be purified was continuously circulated through an adsorption cell, and its optical density was measured every 180 s using a spectrophotometer. The adsorption capacity of PHQ/graphene and PAC/graphene for MG was experimentally found to be 688.1 and 1,862.6 mg g-1, respectively Equilibrium in the systems was achieved in 57 min (PHQ/graphene) and 135 min (PAC/graphene). Results of the experimental studies were processed using diffusion models and chemical kinetic equations. Mathematical descriptions allowed establishing that the dye molecules are adsorbed on both materials by a complex mechanism - along with mixed diffusion adsorption, the molecules chemically interact with functional groups on the adsorbent surface.

Adsorption of the Methylene Blue Dye on Carbon Nanocomposites Under Dynamic Conditions: A Kinetic Study

The present paper describes kinetic regularities of the removal of the typical synthetic dye, methylene blue (MB), from aqueous solutions by two graphene-organic composites, polyhydroquinone (PHQ)/graphene and polyamine-cumulene (PAC)/carbon nanotubes (CNTs). To study the adsorption kinetics under dynamic conditions simulating the real industrial environment, a column method was implemented using the facility developed. The MB adsorption capacity of the studied nanocomposites was found to be very high (2,938 mg g−1 for the PAC/CNTs at the contact time of 75 min, and 2,610 mg g−1 for PHQ/graphene at 40 min). Finally, the kinetic parameters of the process were determined, and the mechanisms proceeding during the dye adsorption on the carbon nanocomposites were elucidated.

Electroactive Polyhydroquinone Coatings for Marine Fouling Prevention-A Rejected Dynamic pH Hypothesis and a Deceiving Artifact in Electrochemical Antifouling Testing.

Nanometer-thin coatings of polyhydroquinone (PHQ), which release and absorb protons upon oxidation and reduction, respectively, were tested for electrochemically induced anti-biofouling activity under the hypothesis that a dynamic pH environment would discourage fouling. Antifouling tests in artificial seawater using the marine, biofilm-forming bacterium Vibrio alginolyticus proved the coatings to be ineffective in fouling prevention but revealed a deceiving artifact from the reactive species generated at the counter electrode (CE), even for electrochemical bias potentials as low as |400| mV versus Ag|AgCl. These findings provide valuable information on the preparation of nanothin PHQ coatings and their electrochemical behavior in artificial seawater. The results further demonstrate that it is critical to isolate the CE in electrochemical anti-biofouling testing.

Electrochemical Polymerization of Hydroquinone on Graphite Felt as a Pseudocapacitive Material for Application in a Microbial Fuel Cell.

Here we reported the use of electropolymerization to achieve the transformation of aqueous hydroquinone to solid-phase polyhydroquinone (PHQ) with pseudocapacitive characteristics, and the application of this redox-active product to shuttle electron transfer in the anode system of a microbial fuel cell (MFC). The microscopic and spectroscopic results showed that the treatment of the graphite felt (GF) substrate with acids was effective in improving the amounts of surface-bound oxygen-containing groups, enabling better adhesion of PHQ onto the GF surfaces. The electrochemical measurements indicated that the resulting PHQ–AGF (acid treated GF) possessed high pseudocapacitance due to the fast and reversible redox cycling between hydroquinone and benzoquinone. The MFC equipped with the PHQ–AGF anode achieved a maximum power density of 633.6 mW m−2, which was much higher than 368.2, 228.8, and 119.7 mW m−2 corresponding to the MFC with the reference PHQ–GF, AGF, and GF anodes, respectively. The increase in the power performance was attributed to the incorporation of the redox-active PHQ abundant in C–OH and C=O groups that were beneficial to the increased extracellular electron transfer and enhanced bacterial adhesion on the anode.

Modification of an enzyme electrode by electrodeposition of hydroquinone for use as the anode of a glucose fuel cell

An electrode having immobilized glucose oxidase (GOx) was modified with polyhydroquinone (PHQ), which was employed as an electron-transferring mediator, by a simple electrochemical method and used as the anode of a glucose fuel cell. The GOx-immobilized electrode was fabricated by attaching polyallylamine (PAAm) and then GOx covalently onto a gold electrode covered with a monolayer formed with 3-mercaptopropionic acid. Subsequently, the GOx-immobilized electrode (GOx/PAAm electrode) was modified with PHQ by electrodeposition of hydroquinone. The cyclic voltammogram of the modified electrode (PHQ/GOx/PAAm electrode) in a phosphate buffer solution (0.10M, pH 7.0) showed redox peaks due to the electrodeposited PHQ, whereas no redox peaks were found for the GOx/PAAm electrode in the buffer solution containing p-benzoquinone (BQ). The onset potential of glucose oxidation with the PHQ/GOx/PAAm electrode became ca. 0.2V more negative than that observed with the GOx/PAAm electrode in the presence of BQ. The glucose fuel cell equipped with the PHQ/GOx/PAAm electrode as an anode gave a 3 times larger power output than the cell with the GOx/PAAm electrode using dissolved quinone as the mediator.

Oxidative polymerization of hydroquinone using deoxycholic acid supramolecular template

Polyhydroquinone (PHQ) is a redox-active polymer with quinone/hydroquinone redox active units in the main chain and may have potential applications as a mediator in biosensors and biofuel cells. By the oxidative polymerization of hydroquinone (HQ), PHQ can be easily synthesized, but the reaction lacks control over the structure of the product. Deoxycholic acid (DCA) was introduced as a supramolecular template to control the reaction. The reaction rate is 14 times of that in deionized water and twice of that in buffer. The DCA template increases not only the reaction rate, but also the molecular weight of the polymer obtained. The template effect of DCA was attributed to the supramolecular assemblies of DCA formed in the solution. Cyclic voltammetry study indicated the resulting PHQ was redox-active. While the supramolecular assemblies of DCA provided a template for the oxidative polymerization of HQ, the protons released as a by-product of the oxidative polymerization of HQ in turn enhanced the self-assembly of DCA. As a result, DCA microfibers form and separate out of the solution.