Quinone Hydroquinone Research Articles

Control of the Hydroquinone/Benzoquinone Redox State in High-Mobility Semiconducting Conjugated Coordination Polymers.

Conjugated coordination polymers (c-CPs) are unique organic-inorganic hybrid semiconductors with intrinsically high electrical conductivity and excellent charge carrier mobility. However, it remains a challenge in tailoring electronic structures, due to the lack of clear guidelines. Here, we develop a strategy wherein controlling the redox state of hydroquinone/benzoquinone (HQ/BQ) ligands allows for the modulation of the electronic structure of c-CPs while maintaining the structural topology. The redox-state control is achieved by reacting the ligand TTHQ (TTHQ=1,2,4,5-tetrathiolhydroquinone) with silver acetate and silver nitrate, yielding Ag4TTHQ and Ag4TTBQ (TTBQ=1,2,4,5-tetrathiolbenzoquinone), respectively. In spite of sharing the same topology consisting of a two-dimensional Ag-S network and HQ/BQ layer, they exhibit different band gaps (1.5 eV for Ag4TTHQ and 0.5 eV for Ag4TTBQ) and conductivities (0.4 S/cm for Ag4TTHQ and 10 S/cm for Ag4TTBQ). DFT calculations reveal that these differences arise from the ligand oxidation state inhibiting energy band formation near the Fermi level in Ag4TTHQ. Consequently, Ag4TTHQ displays a high Seebeck coefficient of 330 μV/K and a power factor of 10 μW/m ⋅ K2, surpassing Ag4TTBQ and the other reported silver-based c-CPs. Furthermore, terahertz spectroscopy demonstrates high charge mobilities exceeding 130 cm2/V ⋅ s in both Ag4TTHQ and Ag4TTBQ.

Control of the Hydroquinone/Benzoquinone Redox State in High‐Mobility Semiconducting Conjugated Coordination Polymers

Conjugated coordination polymers (c‐CPs) are unique organic‐inorganic hybrid semiconductors with intrinsically high electrical conductivity and excellent charge carrier mobility. However, it remains a challenge in tailoring electronic structures, due to the lack of clear guidelines. Here, we develop a strategy wherein controlling the redox state of hydroquinone/benzoquinone (HQ/BQ) ligands allows for the modulation of the electronic structure of c‐CPs while maintaining the structural topology. The redox‐state control is achieved by reacting the ligand TTHQ (TTHQ = 1,2,4,5‐tetrathiolhydroquinone) with silver acetate and silver nitrate, yielding Ag4TTHQ and Ag4TTBQ (TTBQ = 1,2,4,5‐tetrathiolbenzoquinone), respectively. In spite of sharing the same topology consisting of two‐dimensional Ag‐S network and HQ/BQ layer, they exhibit different band gaps (1.5 eV for Ag4TTHQ and 0.5 eV for Ag4TTBQ) and conductivities (0.4 S/cm for Ag4TTHQ and 10 S/cm for Ag4TTBQ). DFT calculations reveal that these differences arise from the ligand oxidation state inhibiting energy band formation near the Fermi level in Ag4TTHQ. Consequently, Ag4TTHQ displays a high Seebeck coefficient of 330 μV/K and a power factor of 10 μW/m·K2, surpassing Ag4TTBQ and the other reported silver‐based c‐CPs. Furthermore, terahertz spectroscopy demonstrates high charge mobilities exceeding 130 cm2/V·s in both Ag4TTHQ and Ag4TTBQ.

Assessing fresh water acute toxicity with Surface-Enhanced Raman Scattering (SERS)

It's well known that the toxicity of chemicals in the environment depends not only their concentrations, but more importantly, their bio-availability. Thus, the acute toxicity test of environmental water samples is of great importance in water quality evaluation. In this work, water acute toxicity was determined via SERS approach for the first time based on the reaction between Escherichia coli (E. coli) and p-benzoquinone (BQ). The E. coli was used as the subject of toxicity assay. Under normal conditions, the BQ molecules can be transformed into Hydroquinone (HQ) by the E. coli bacteria; subsequently, the BQ will continue to react with the resulting HQ to form Quinone hydroquinone (QHQ). This process could be impaired in the presence of many toxic chemicals. Bromide modified Ag NPs was then introduced for the highly sensitive SERS detection of the product (HQ and QHQ). Several key factors that may affect water acute toxicity evaluation have been explored, which include the initial BQ and E. coli concentration, the incubation time with BQ, and the sodium chloride concentration. Later, the established system was applied for the toxicity evaluation of Cu2+. It was found that the IC50 value of Cu2+ was 0.94 mg/L, which is superior compared with literature report. This study provides a promising SERS method for assessing acute toxicity in water bodies with high sensitivity and short detection time.

A bacteriorhodopsin-based biohybrid solar cell using carbon-based electrolyte and cathode components

There is currently a high demand for energy production worldwide, mainly producing renewable and sustainable energy. Bio-sensitized solar cells (BSCs) are an excellent option in this field due to their optical and photoelectrical properties developed in recent years. One of the biosensitizers that shows promise in simplicity, stability and quantum efficiency is bacteriorhodopsin (bR), a photoactive, retinal-containing membrane protein. In the present work, we have utilized a mutant of bR, D96N, in a photoanode-sensitized TiO2 solar cell, integrating low-cost, carbon-based components, including a cathode composed of PEDOT (poly(3,4-ethylenedioxythiophene) functionalized with multi-walled carbon nanotubes (CNT) and a hydroquinone/benzoquinone (HQ/BQ) redox electrolyte. The photoanode and cathode were characterized morphologically and chemically (SEM, TEM, and Raman). The electrochemical performance of the bR-BSCs was investigated using linear sweep voltammetry (LSV), open circuit potential decay (VOC), and impedance spectroscopic analysis (EIS). The champion device yielded a current density (JSC) of 1.0 mA/cm2, VOC of −669 mV, a fill factor of ~24 %, and a power conversion efficiency (PCE) of 0.16 %. This bR device is one of the first bio-based solar cells utilizing carbon-based alternatives for the photoanode, cathode, and electrolyte. This may decrease the cost and significantly improve the device's sustainability.

Reactivities of 1,2-, 1,3-, and 1,4-dihydroxynaphthalenes toward electrogenerated superoxide in N,N-dimethylformamide through proton-coupled electron transfer

We have carried out an electrochemical and theoretical study on the reactivity of 1,2-, 1,3-, and 1,4-dihydroxynaphthalenes (1nH2NQ, n = 2, 3, 4) toward electrogenerated superoxide radical anion (O2•−) in N,N-dimethylformamide. Cyclicvoltammetry and in situ electrolytic electron spin resonance measurements revealed that the quinone–hydroquinone π-conjugation plays an important role in a successful O2•− scavenging by 12H2NQ and 14H2NQ through proton-coupled electron transfer (PCET) reaction. The reactivities of 12H2NQ and 14H2NQ toward O2•− were mediated by the ortho- (catechol) or para-diphenol (hydroquinone) moieties, as experimentally confirmed in comparative analyses with catechol, hydroquinone, and 13H2NQ, aided by density functional theory (DFT) calculations. The electrochemical and DFT results suggested that a concerted PCET mechanism involving two-proton transfers and one-electron transfer proceeds, demonstrating a successful O2•− scavenging by 12H2NQ and 14H2NQ. Furthermore, a subsequent electron transfer between molecular dioxygen and product-naphthoquinone-radicals was observed, where O2•− was regenerated. The DFT analysis suggested that the spin distribution on the planar naphthalene ring embodies the superior kinetics of the PCET and the subsequent generation of O2•− from dioxygen demonstrated in the electrochemical results.

Microwave-Assisted Scalable Synthesis of Pt/C: Impact of the Microwave Irradiation and Carrier Solution Polarity on Nanoparticle Formation and Aging of the Support Carbon

Microwave-assisted (MW-assisted) synthesis of nanomaterials is a facile method for material development studies involving small-scale synthesis. The method is being explored further toward industrial scale production of nanoparticle catalyst. Here, optimization of the process parameters for a scalable synthesis of Pt/C through a MW-assisted polyol route using (NH4)2PtCl6 as the Pt precursor has been presented. Further, the impact of MW-irradiation on the carbon support surface structure and its effect on the electrochemical stability of the synthesized Pt/C have been explored. Pt/C electrocatalysts were synthesized using a MW synthesizer in an open system configuration. Effects of different process parameters, namely, solvent composition and hence solvent polarity, reaction time, and Pt precursor concentration on the structure and the electrochemical performance of the synthesized Pt/C catalysts were studied. A mixture of water and ethylene glycol with a water content of 30% v/v was found appropriate for achieving Pt nanoparticles with a particle size of ∼2 nm, suitable for a high electrochemically active surface area (ECSA) of ∼75 m2/gPt. Pt concentrations higher than 5 mM were found unsuitable due to incomplete reduction of the Pt precursor. The minimum reaction time for complete reduction of the Pt precursor was observed to be 400 s. However, increasing the MW treatment time beyond 400 s leads to growth of the Pt nanoparticles and hence reduction in ECSA. Porosity and surface area analysis suggests decreased pore size and surface area of the carbon support by the MW-irradiation during Pt/C synthesis. Hence, the initial electrochemical double layer capacitance (DLC) decreases with increasing MW-irradiation time, leading to the increased surface corrosion and the decreased bulk corrosion of the support carbon, monitored respectively through the relative change in DLC and the evolution of the quinone–hydroquinone redox peak during an accelerated stress test meant for durability assessment of the electrocatalysts.

Modifying Carbon Supports of Catalyst for the Oxygen Reduction Reaction in Vehicle PEMFCs

For current carbon-supported Pt catalysts in vehicle proton exchange membrane fuel cells (PEMFCs), the insufficient stability and durability of carbon supports are severe limitations under operating conditions. This paper adopts the accelerated stress test (AST) method to study the carbon corrosion of catalysts, which is significant to efficiently select the catalysts supports in fuel cells. Graphitized carbon blacks with various surface properties are heated under different conditions, followed by evaluation of their antioxidation capacity with the AST. It is shown that optimally graphitized carbon blacks demonstrate superior stability, retaining a constant quinone/hydroquinone (QH) transition peak potential for over 70,000 AST cycles. A Pt catalyst supported on the selected graphitized carbon exhibits excellent durability at both the rotating disk electrode (RDE) and membrane electrode assembly (MEA) levels. The final specific mass activity (MA) of the optimum catalyst is 47.87 mA/mgPt, which is 2.06 times that of commercial Pt/C (23.31 mA/mgPt) in the RDE tests. The final maximum power density of the optimum catalyst is 525.68 mW/cm2, which is 305.52 mW/cm2 higher than that of commercial Pt/C after undergoing the AST during the MEA measurements. These results prove that the rational surface features of carbon supports play a vital role in improving the overall fuel cell performance by realizing uniform dispersion of Pt nanoparticles, resisting corrosion, and reinforcing metal–support interactions.

In Situ Determination of pH at Nanostructured Carbon Electrodes Using IR Spectroscopy

Changes in pH at electrode surfaces can occur when redox reactions involving the production or consumption of protons take place. Many redox reactions of biological or analytical importance are proton-coupled, resulting in localized interfacial pH changes as the reaction proceeds. Other important electrochemical reactions, such as hydrogen and oxygen evolution reactions, can likewise result in pH changes near the electrode. However, it is very difficult to measure pH changes located within around 100 µm of the electrode surface. This paper describes the use of in situ attenuated total reflectance (ATR) infrared (IR) spectroscopy to determine the pH of different solutions directly at the electrode interface, while a potential is applied. Changes in the distinctive IR bands of solution phosphate species are used as an indicator of pH change, given that the protonation state of the phosphate ions is pH-dependent. We found that the pH at the surface of an electrode modified with carbon nanotubes can increase from 4.5 to 11 during the hydrogen evolution reaction, even in buffered solutions. The local pH change accompanying the hydroquinone–quinone redox reaction is also determined.

A Stereodynamic Redox‐Interconversion Network of Vicinal Tertiary and Quaternary Carbon Stereocenters in Hydroquinone–Quinone Hybrid Dihydrobenzofurans

AbstractReversible redox processes involving hydroquinones and quinones are ubiquitous in biological reaction networks, materials science, and catalysis. While extensively studied in intermolecular settings, less is known about intramolecular scenarios. Herein, we report hydroquinone–quinone hybrid molecules that form two‐stereocenter dihydrobenzofurans via intramolecular cyclization under thermodynamic control. A π‐methylhistidine peptide‐catalyzed kinetic resolution allowed us to study the stereodynamic behavior of enantio‐ and diastereo‐enriched dihydrofurans. In the course of this study, it was revealed that a reversible intramolecular redox‐interconversion network connects all four possible stereoisomers via inversion of a quaternary carbon stereocenter without achiral intermediates. As a result, these findings on hydroquinone‐quinone hybrid molecules provide insights into potential natural origin and synthetic access of the common dihydrobenzofuran motif.

A Stereodynamic Redox-Interconversion Network of Vicinal Tertiary and Quaternary Carbon Stereocenters in Hydroquinone-Quinone Hybrid Dihydrobenzofurans.

Reversible redox processes involving hydroquinones and quinones are ubiquitous in biological reaction networks, materials science, and catalysis. While extensively studied in intermolecular settings, less is known about intramolecular scenarios. Herein, we report hydroquinone-quinone hybrid molecules that form two-stereocenter dihydrobenzofurans via intramolecular cyclization under thermodynamic control. A π-methylhistidine peptide-catalyzed kinetic resolution allowed us to study the stereodynamic behavior of enantio- and diastereo-enriched dihydrofurans. In the course of this study, it was revealed that a reversible intramolecular redox-interconversion network connects all four possible stereoisomers via inversion of a quaternary carbon stereocenter without achiral intermediates. As a result, these findings on hydroquinone-quinone hybrid molecules provide insights into potential natural origin and synthetic access of the common dihydrobenzofuran motif.

Ab initio computational modeling of the electrochemical reactivity of quinones on gold and glassy carbon electrodes

We propose electronic structure modeling, in accordance with the Gerischer conceptualization, to explain the electrochemical response of the benzoquinone/hydroquinone (BQ/HQ) redox couple on gold and glassy carbon (GC) electrodes. Specifically, coupling differed to gold compared to GC; this is of interest because BQ/HQ are representative of a promising class of molecules used in redox flow batteries (RFBs). We calculated the energy difference between the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO), Fermi levels (EF), and density of states (DOS) of the electrode materials via density functional theory in periodic systems. The Au (111) surface was considered for gold modeling, whereas graphite and graphene were used for GC. We compared these results with experimental data to explain the differences in the reversible behavior of the BQ/HQ couple in both electrode materials, setting the pH, electrolyte composition, and electrode geometry equal in both electrodes. The loss of reversibility in GC can be attributed to the anodic branch of the cyclic voltammetry response, which is consistent with the larger energetic distance found for the HQ–HOMO from the EF of the electrode compared to BQ–LUMO. In contrast, the energetic distances in gold are similar in both cases and agree with the symmetry of the experimental current–potential response for both the anodic and cathodic branch. To validate the model, we calculated the total DOS and projected DOS for different quinone molecules—such as 2,5-dichloro-1,4-benzoquinone, 2-hydroxy-1,4-naphthoquinone, and 1,2,4-trihydroxynaphtalene—adsorbed on gold and GC. The experimental findings support our hypothesis. Additionally, graphite and graphene models equivalently described GC electrodes; both models showed a similar trend in adsorption energy for quinone molecules [due to van der Waals (VDW) interactions], DOS, and partial charge density. For the gold electrode, we found a similar trend in adsorption energy to the graphite and graphene, also attributable to VDW interactions. Our results indicate that theoretical modeling can explain electrochemical principles which underpin quinone-based energy storage systems and RFBs.

Durability of Electrocatalysts for ORR: Pt on Nanocomposite of Reduced Graphene Oxide with FTO versus Pt/C

Catalyst degradation results in performance losses of proton exchange membrane fuel cells (PEMFC) and is caused by electrochemical instability of commonly used platinum on carbon black (Pt/C). In this study, a comparison in durability of commercial Pt/C with a new Pt catalyst on a nanocomposite of fluorine-doped SnO2 (FTO) and reduced graphene oxide (rGO) is carried out. Transmission electron microscopy (TEM) shows similar Pt distributions on support surfaces and Pt particle sizes so that a high comparability of support materials during durability investigation is ensured. High resolution TEM with EDS reveals dispersed Pt anchored at FTO–rGO interfaces. During stripping voltammetry Pt/FTO–rGO provides weaker CO sorption than Pt/C, indicating higher CO tolerances. Accelerated stress testing (0.05–1.47 VRHE) provokes Pt degradation on both supports in comparable rates. However, the FTO–rGO nanocomposite presents the more stable substrate in this study compared to carbon black. Identical location TEM illustrates stable FTO particles in size and position on rGO surface. Moreover, unchanged hydroquinone/quinone (HQ/Q) amounts and double layer capacitance in case of Pt/FTO–rGO were revealed by cyclic voltammetry. On the contrary, standard Pt/C shows significantly more generation of HQ/Q functionalities by a factor of 25 and thus higher carbon corrosion.

Strongly enhanced Fenton degradation of organic pollutants by cysteine: An aliphatic amino acid accelerator outweighs hydroquinone analogues

Quinone–hydroquinone analogues have been proven to be efficient promoters of Fenton reactions by accelerating the Fe(III)/Fe(II) redox cycle along with self-destruction. However, so far there is little information on non-quinone–hydroquinone cocatalyst for Fenton reactions. This study found that cysteine, a common aliphatic amino acid, can strongly enhance Fenton degradation of organic pollutants by accelerating Fe(III)/Fe(II) redox cycle, as quinone–hydroquinone analogues do. Further, cysteine is superior to quinone–hydroquinone analogues in catalytic activity, H2O2 utilization and atmospheric limits. The cocatalysis mechanism based on the cycle of cysteine/cystine was proposed.

A simple method for estimating the electrochemical stability of the carbon materials

The corrosion stability of a series of carbon supports of various porous structure and morphology: commercial carbon blacks, carbon–carbon composite, and multiwall carbon nanotubes was studied using start-stop protocol cycling (1–1.5 V vs reversible hydrogen electrode (RHE) potential range with 0.5 V/s of scan rate) in an electrochemical cell at 25 °C using 0.1 M HClO4 as electrolyte. Two stability regions were revealed for the first time depending on the cycle number. The first one is characterized by a constant value of quinone/hydroquinone (QH) transition potential. In the second part anode and cathode QH peaks gradually shift toward higher and lower potentials respectively, which is due most likely to a complete degradation of the supports. We proposed an effective resistance (Reff) as the corrosion stability parameter that can be easily obtained from the cyclic voltammetry (CV) data. Based on these results, a model of corrosion of porous carbon materials supported on glassy carbon rod was proposed. It was shown that the decrease in the Reff of the samples in the initial stages of degradation is due to the increase in the number of QH groups on the surface, while a sharp increase in the Reff upon further cycling can be explained by a decrease in the number of contacts between the carbon grains.

Characterization of a zeolite-templated carbon by electrochemical quartz crystal microbalance and in situ Raman spectroscopy

Electrochemical quartz crystal microbalance was used to monitor the mass changes during the electrochemical characterization of a zeolite-templated carbon (ZTC) in 1M H2SO4 medium. Under electrochemical oxidation conditions, a high anodic current and a net mass increase were recorded, resulting in the increase of the specific capacitance owing to the contribution of the pseudocapacitance, mainly derived from the hydroquinone–quinone redox couple. Under more severe electrochemical conditions, a net mass loss was observed, revealing that electrochemical gasification took place. Surface chemistry, before and after the electrochemical treatments, was analyzed through temperature programmed desorption experiments. Furthermore, in situ Raman spectroscopy was used to further characterize the structural changes produced in ZTC under the electrochemical conditions applied, supporting that high potential values produce the electrochemical oxidation and degradation of the carbon material.

Deleterious effects of interim cyclic voltammetry on Pt/carbon black catalyst degradation during start-up/shutdown cycling evaluation

We investigated the deleterious effects of the common practice of measuring cyclic voltammetry (CV) on Pt/CB catalysts during long-term start-up/shutdown cycling longevity evaluation of the type used in standard protocols used in the fuel cell automotive industry. These “interim” CV measurements, which are generally conducted after a certain number of potential cycles to evaluate the electrochemically active surface area (ECSA) of Pt catalysts, result in depassivation of the passive layer formed on Pt particles during the cycling tests; this allows the platinum to again catalyze the carbon corrosion effectively during the potential cycling. This phenomenon causes additional corrosion of the CB support. The measured ECSA loss, cycle half-life N1/2 (N value at which the ECSA value was estimated to reach 1/2 of the initial value) and IR-free polarization curves show that the potential cycling, followed by intermittent CV measurements on the same electrode, termed consecutive cycling, brings about severe lifetime reduction and cell performance degradation of the Pt/CB catalyst. The quinone-hydroquinone (Q-HQ) oxidation current supports the idea that this degradation can be ascribed to severe corrosion of the CB support by the consecutive cycling. In addition, SEM and TEM images confirm that the interim CV measurements lead to severe degradation of the Pt/CB catalyst due to dissolution of platinum and carbon support corrosion. Thus, from the viewpoint of practical operation, the catalyst degradation is overestimated with this testing protocol.

Kinetic studies of hydroxyquinone formation from water soluble benzoquinones

The kinetics and mechanisms of the redox reactions between hydrogen peroxide and 1,4-benzoquinone, 2-methyl-1,4-benzoquinone, 2,6-dimethyl-1,4-benzoquinone, 2-chloro-1,4-benzoquinone and 2,6-dichloro-1,4-benzoquinone were studied in aqueous media using spectrophotometric monitoring. The formation and decay of a hydroxylated 1,4-benzoquinone was detected. The formation of the intermediate was first order with respect to the parent 1,4-benzoquinone and hydrogen peroxide, whereas inverse first order dependence was revealed with respect to the hydrogen ion. The decomposition reaction had two parallel pathways: one was first order with respect to the intermediate, while the other showed second-order dependence. The values of the rate constant measured for the formation step were successfully correlated with both the redox potentials of the substituted quinone–hydroquinone systems and the pKa values of the hydroxylated quinone derivatives. Therefore, electronic effects govern the reactivity of the quinones in this process. NMR and GC-MS measurements were carried out to identify the products in the system. Quantum mechanical calculations were also carried out in these systems.

Monitoring hydroquinone-quinone redox cycling by single molecule fluorescence spectroscopy.

Current research in the field of single-molecule chemistry is increasingly focused on the development of reliable experimental approaches for investigating chemical processes on a molecular level using single-molecule fluorescence spectroscopy (SMFS). Herein, we report on single-molecule observations of the copper(II)/air mediated oxidation of fluorescently labeled hydroquinone-based probe molecules followed by their reduction with cysteine. The redox cycle is signaled by quenching/recovery of fluorescence emission after addition of the oxidant/reductant, respectively. The experiments were realized by immobilizing the probe on a glass cover slide to allow single-molecule observation by means of total-internal-reflection fluorescence microscopy. Besides detection of successful oxidation and reduction events on single probe molecules, individual molecular intensity trajectories revealed dynamic processes and formation of intermediate states upon reaction. For the experimental design presented, we envision further reaction studies of catalytic redox-processes of single hydroquinone-moieties by means of SMFS.

Electrochemical manipulation of adhesion strength of polybenzoxazines on metal surfaces: from strong adhesion to dismantling

A novel electrochemical redox process for the manipulation of adhesion of polybenzoxazine thermosets on metal surfaces is reported. The method pertains to the electrochemically driven hydroquinone–quinone redox couple. Several antraquinone based bisbenzoxazines possessing phenyl, benzyl and methyl furfuryl substituents were synthesized and characterized. The antraquinone bisbenzoxazines were shown to readily undergo thermally activated ring-opening polymerization in the absence of a catalyst forming cross-linked networks on metal surfaces. The substituent effect on thermal curing behaviour and thermal stability of the cured polymers were investigated. The strong binding affinities of phenolic hydroxyl groups of the anthraquinone moiety in the cured polymers promote adhesion on the metal surface. Electrochemical oxidation converts hydroquinone groups into quinone moieties resulting in the dismantling of the coated films. The generality of this electrochemical method is demonstrated by initial results on platinum electrodes as well as steel plates.

Electrocatalysis of the hydroquinone/benzoquinone redox couple at platinum electrodes covered by a thin film of poly(3,4-ethylenedioxythiophene)

The hydroquinone/benzoquinone (HQ/BQ) redox reaction is studied on platinum electrodes coated by poly(3,4-ethylenedioxythiophene) (PEDOT) thin films using cyclic voltammetry and chronocoulometry. It was found that HQ is weakly adsorbed on PEDOT and that the HQ/BQ redox reaction is well described by a reversible diffusion-governed charge transfer on platinum electrodes coated by a thin film of PEDOT and in the presence of very low HQ concentration, indicating that the modification of PEDOT on Pt can greatly accelerate the electron transfer rate and that PEDOT seems to be the best electrocatalyst for this reaction reported until know. The reaction kinetics is very sensitive to the local environment around the active sites of the electrocatalyst, which is affected by the amount of adsorbed HQ and the PEDOT film thickness. Finally, the porous nature of PEDOT films, which have a high internal surface area, allows the HQ adsorption, deep inside the PEDOT film. In this sense, we suggest that the first step of hydroquinone oxidation is the formation of an acid–base complex between HQ and PEDOT.