Redox Pair Research Articles

Efficient removal of tetracycline hydrochloride by high entropy oxides in visible photo-Fenton catalytic process

ABSTRACT A novel type of oxide material, high entropy oxide (Mn0.2Fe0.2Co0.2Ni0.2Cu0.2)3O4 (MFO) composites with spinel structure were successfully synthesized by a simple solution combustion in this paper, and it was first applied to the degradation of antibiotic organic pollutants in water by photo-Fenton. SEM and BET characterization showed that the composite was porous and had a large specific surface area. XPS results showed that Fe, Mn, Cu, Co and Ni all participated in the redox reaction of the catalytic process. The redox pairs of Mn2+/Mn3+, Cu+/Cu2+, Co2+/Co3+, Ni2+/Ni3+ can accelerate the Fe2+/Fe3+ redox cycling in MFO to activate H2O2 and produce more reactive oxygen species. The catalytic performance of MFO composite was investigated using tetracycline hydrochloride (TC-HCl) as a model pollutant. The results displayed that the degradation rate of TC-HCl by MFO was 92.9% when the initial pH was 4, the dose of H2O2 was 50 mM, and the irradiation time was 60 min. The high entropy oxide MFO composites could build up an internal electric field, which restrains electron–hole recombination, improves the transfer of photogenerated charge carriers and maximize photocatalytic property. In addition, the free radical capture experiment determined that the main active species of the degradation reaction were e−, •O2 − and •OH. The synergistic effect of the five components in the high entropy oxide strengthens lattice distortion and defects, increases oxygen vacancies, and thus has enhanced catalytic effect for TC-HCl degradation. This work shows that high entropy oxides have excellent catalytic performance for tetracycline organic pollutants, and it is speculated that high entropy oxides have good application prospects in the field of advanced oxidation technology for the degradation of organic pollutants.

Metal–organic framework–derived CeO2 catalyst supported by carboxyl–functionalized MXene for oxidative coupling of benzyl alcohol with aniline

Direct oxidative coupling of alcohols and amines is a highly sought–after method for imine synthesis, and non–precious metal catalysts have been identified as essential components for their efficient production. Here, we report a CeO2 catalyst that is supported by carboxyl–functionalized MXene (CFMX). The catalyst, referred to as CeO2–C@CFMX–T (where T is the pyrolysis temperature), was prepared by high–temperature pyrolysis of a Ce–based metal–organic framework (MOF) and MXene composite (MOF@MXene) in a nitrogen flow environment. The MOF@MXene composite was synthesized by directly assembling Ce–MOF on the outer surface of MXene, which was pre–functionalized with terminal carboxylated aryl diazonium salts. The developed CeO2–C@CFMX–873 exhibited outstanding catalytic behavior in the oxidative coupling of benzyl alcohol and aniline, without the need for any basic additives. The catalyst achieved high benzyl alcohol conversion (98.9 %), desirable imine selectivity (97.7 %), good recyclability (5 cycles), and broad substrate tolerance (22 examples) under mild conditions (353 K, air atmosphere). It was found that the CFMX support improved the dispersion of CeO2 nanoparticles and alleviated the problem of CeO2 aggregation during pyrolysis. The remarkable activity of CeO2–C@CFMX–873 was attributed to reversible Ce3+/Ce4+ redox pairs, abundant oxygen vacancies, and an appropriate number of acid–base sites.

Quantitative analysis of the glutathione pathway cellular metabolites by targeted liquid chromatography-tandem mass spectrometry.

Glutathione, its biosynthesis intermediates, and other thiol metabolites are of central relevance for the redox homeostasis of cells. Their analysis is critical due to the facile interconversion of redox pairs during sampling, sample preparation, and data acquisition, in particular in the electrospray ionization interface. In this work, we propose a fast-targeted liquid chromatography-tandem mass spectrometry method to accurately analyze 14 metabolites from the glutathione pathway. N-Ethylmaleimide reagent is added with the extraction solvent and instantly stabilizes the thiol-redox state by derivatization. Liquid chromatographic separation of the analytes was performed on a sub-2μm superficially porous hydrophilic interaction liquid chromatography column with sulfobetaine chemistry. Tandem mass spectrometry with triple-quadrupole mass spectrometry in multiple-reaction monitoring acquisition mode allowed sensitive detection of the targeted metabolites with limits of quantification in the range of 5-25nM. Run times of 3min enable a high throughput analysis of cellular samples. For calibration, a 13 C-labelled cell extract was used as an internal standard. The method was validated and the concentrations of glutathione and its biosynthesis intermediates were determined in HeLa cells.

Surface motifs regulated aggregation induced emission in AuAg nanoclusters combined with Ce(III)/Ce(IV) catalytic cyclic amplification strategy for sensitive bioanalysis

Achieving high luminescence intensity in electrochemiluminescence biosensors is a challenge for metal nanoclusters (MNCs) due to their non-radiative relaxation-mediated self-quenching tendency. Here, the surface motifs [M(I)-SR] of MNCs were regulated based on aggregation-induced emission (AIE) strategy was proposed to mitigate non-radiative relaxation vibrations, and an efficient luminescent AuAg NCs was designed via host-guest assembly as a signal probe. The Au(I)-SR of AuAg NCs used glutathione (GSH) as a template and reducing agent, and the introduction of Ag(I) made the Au(I)-SR of AuAg NCs cross-linked and interlocked, resulting in AuAg NCs with denser surface patterns. The aggregation of surface motifs limited the ligand movement to reduce the non-radiative energy dissipation. Furthermore, the spontaneous catalytic cycle amplification strategy of Ce(III)/Ce(IV) redox pairs in the matrix material of Ce-MOF promoted the reaction of more co-reactants triethylamine (TEA), obtaining potent reducing radicals TEA* for further improving the ECL efficiency of AuAg NCs. Using cardiac troponin I (cTnI) as the analytical model, the biosensor exhibited a wide linear relationship range (50 fg·mL−1 - 500 ng·mL−1) and a low detection limit (4.77 fg·mL−1). The breakthrough in surface motifs regulation of MNCs guides a new way to design high luminiferous MNCs, and further expands the application potential of MNCs.

Laser Thermal Shock Enabling Ultrafast Spin Regulation of MnO2 for Robust Pseudocapacitive Energy Storage

AbstractThe pseudocapacitive performance of MnO2 is intrinsically determined by its electronic structure, especially the spin state. However, the correlation between the electrochemical behavior and the spin state of electrode materials remains ill‐defined, and efficient spin regulation strategies for MnO2 are thus lacking. Herein, the study reports laser thermal shock of electrochemically deposited MnO2 for efficient spin regulation. The combined use of theoretical calculation and experimental investigation indicates that the thermal shock induces oxygen vacancy in MnO2 to reduce spin polarization and delocalize electron distribution. As a result, the electrical conductivity largely increases and the Na+ adsorption is reasonably optimized. By lasering an integrated electrode for only 83 s, a 54% increase of the specific capacitance is observed. For the first time, the pseudocapacitive capability of MnO2 is revealed by in situ electron paramagnetic resonance where the enhanced redox pair is correlated with evolution of Mn2+ during charge/discharge. Moreover, the commercial‐level mass‐loaded electrode also offers a decent performance enhancement after laser treatment, indicating the great prospect of this technology for real applications. This work innovatively correlates the pseudocapacitive performance of MnO2 with its spin state and offers a new avenue to optimize the electrochemical capability through spin regulation.

Impact of water on structure stabilization in layered manganese-oxide for high-voltage zinc storage in non-aqueous electrolyte: Experimental and theoretical aspects

In this work, we suggest layered K0.32MnO2·0·15H2O as a promising high-energy cathode material for non-aqueous zinc-ion batteries (ZIBs). Electrochemical cycling tests indicate acceptable electrode performance with a capacity of 194 mAh (g-oxide)−1 at 0.2 C (40 mA g−1) in the voltage range of 0.6 – 2 V. This performance is achieved via a single-phase reaction accompanied by a Mn4+/Mn3+ redox pair. Further tests validate the availability of the reaction at higher currents, namely, capacity retention of 88% after 200 cycles at 0.5 C and 54% after 700 cycles at 2 C. Structural analysis using operando X-ray diffraction confirms a small volume change of ∼1.1 % during de/zincation, of which water molecules act as pillars that support the layered structure for long-term cycling stability. The beneficial impact of water within the K0.32MnO2·0·15H2O structure has been validated through density functional theory calculation. Accordingly, the use of a non-aqueous electrolyte yields not only widening of the operating window compared with conventional aqueous solutions but also, more importantly, prevention of cell swelling and bulging caused by H2 generation in an aqueous system. The above findings provide possible solutions toward the practical application of non-aqueous rechargeable ZIBs with high energy.

Highly-efficient natural gas desulfurization and simultaneous H2O2 synthesis based on the electrochemical coupling reaction strategy

Hydrogen sulfide (H2S) generated by natural gas exploitation is a dangerous and harmful gas that needs to be purified. Electrochemical Natural Gas Desulfurization offers a promising way for H2S purification and resource utilization in ambient conditions. However, poor energy efficiency and low resource value limit the prospective application in the industry. Herein, we propose a gas-liquid flow electrocatalysis system that couples H2S oxidation and O2 reduction processes to effectively recover sulfur and H2O2 with low energy consumption. Gas diffusion and mass transfer are accelerated by gas-liquid flow cells, which also significantly decrease the resistance. Besides, I-/I3- redox pairs promote selective H2S oxidation while inhibiting water decomposition, resulting in a 56% reduction in oxidation potential. Moreover, the surface proton concentration is elevated by employing a modified carbon gas diffusion electrode (GDE), which assists to maintains a high H2O2 faradic efficiency. The system is able to operate at a high current density of 102 mA/cm2 at an Ecell voltage of 3.5 V, yielding S and H2O2 at rates of 60 mg cm−2 h−1 and 50 mg cm−2 h−1 respectively. A techno-economic model forecasts the effects of system efficiency and energy prices on operational costs and illustrates potential routes to a plant-gate levelized application in the petrochemical industry.

Ce4+/Ce3+ Redox Effect-Promoted CdS/CeO2 Heterojunction Photocatalyst for the Atom Economic Synthesis of Imines under Visible Light.

The employment of stoichiometric alcohols and amines for imine synthesis under mild and green reaction conditions is still a challenge in the field. In this work, based on our research foundation in the thermocatalytic synthesis of imines over ceria, a CdS/CeO2 heterojunction photocatalyst was constructed and successfully realized the atom-economic synthesis of imines under visible light without additives at room temperature. Mechanistic experiments and corresponding characterizations indicated that the CdS/CeO2 heterojunction can improve the separation efficiency of photogenerated carriers, which can be further enhanced by the Ce4+/Ce3+ redox pair by rapidly combining photogenerated e-. The in situ-reduced Ce3+ can better activate O2 to form Ce-O-O·, which, together with h+, efficiently accelerates alcohol oxidation, which is the rate-determined step for the synthesis of imines via oxidative coupling reaction of alcohol and amine. In addition, our photocatalyst exhibited fairly decent reusability and substrate universality. This work solves problems of using base additives and excess amine or alcohol in the reported photocatalytic systems and provides new insight for designing CeO2-based photocatalytic oxidation catalysts.

Experimental screening of metal nitrides hydrolysis for green ammonia synthesis via solar thermochemical looping

Ammonia is a fundamental chemical commodity for fertilizers and as a novel energy vector. Solar-driven ammonia synthesis is proposed as a sustainable alternative to the catalytic energy-intensive and CO2-emitting Haber-Bosch process. The considered thermochemical process aims to produce ammonia from nitrogen and water (N2 + 3H2O → 2NH3 + 1.5O2) via redox cycles using a solar heat source, thus bypassing the supply of H2 or electricity. Metal oxide/nitride redox pairs can be employed for this cyclic process. The exothermal hydrolysis reaction of nitrides produces ammonia (MxNy + 3H2O → 2NH3 + Mx’Oy’), and is followed by one or several regeneration steps (Mx’Oy’+N2 → MxNy+3/2O2) requiring a heat supply from concentrated solar energy. This study aims to experimentally identify the most suitable metal nitrides in the hydrolysis step for ammonia synthesis based on solar-driven chemical-looping. As a result, FeN, CrN, BN, and Si3N4 turned out to be irrelevant candidates for NH3 production, as the hydrolysis yield was poor up to 1000 °C. In contrast, AlN, Li3N, Ca3N2, Mg3N2, TiN, and ZrN exhibited noteworthy reactivity depending on the temperature. The hydrolysis rate of AlN was significantly enhanced only above 1100 °C, TiN showed an increasing NH3 production rate with temperature (reaching 3.4 mmol/min/g at 1000 °C), while an optimum at 750 °C was unveiled for complete ZrN conversion (corresponding to the highest rate of 34.2 mmol/min/g). Hydrolysis of Li3N, Ca3N2, and Mg3N2 was complete at lower temperatures (∼200 °C), with NH3 yields of 5.9, 4.9, and 18.6 mmol/g, respectively. Solar-driven regeneration of metal nitrides at high temperature will be then necessary to demonstrate the complete feasibility of thermochemical cycles for green ammonia synthesis.

Isopropylthiol emission by bloom-forming Microcystis: Biochemistry, ecophysiology and semiochemistry of a volatile organosulfur compound

Microcystis species not only produce toxic cyanobacterial blooms, but can be a significant source of taste and odour. Previous studies have associated foul-smelling volatile organic sulfur compounds (VOSCs) with Microcystis blooms, but have largely attributed these compounds to bacterial bloom decomposition. However, earlier reports of the production of isopropylthio compounds by several Microcystis strains suggests that these cyanobacteria may themselves be a source of these VOSCs. Sulphur compounds have been shown to play important semiochemical roles in algal cell protection and grazer interactions in marine systems, but little is known about the production and chemical ecology of freshwater cyanobacterial VOSCs. To address this knowledge gap, we undertook the first detailed investigation of the biochemistry, ecophysiology and semiochemistry of these compounds and their production by Microcystis, and tested the hypothesis that they act as multifunctional semiochemicals in processes related to cell protection and grazer defence. Using short-term incubations and an adapted headspace-GC–MS technique, we investigated VOSC production by axenic and non-axenic strains, and verified that isopropylthio compounds are in fact produced by these cyanobacteria, identifying 5 isopropyl moiety-containing VOSCs (isopropylthiol (ISH), isopropylmethyl sulfide, isopropyl methyl disulfide, diisopropyl disulfide (ISSI) and diisopropyl trisulfide) as well as methanethiol in three strains. Further studies with the axenic strain Microcystis PCC 7806 using different light regimes, metabolic inhibitors (sodium azide, DCMU), the antioxidant enzyme catalase and stable labelled precursors (hydrogencarbonate, acetates and sulfate) demonstrated that ISH is a true exo-metabolite, synthesized via the acetate pathway. It is actively produced and continuously excreted by the cyanobacteria during growth, with minimal internal storage or post-lysis catalytic generation. The molar ratios of the redox pair ISH/ISSI are not directly involved in the photosynthetic and respiratory electron transport chains, but dependant on the redox state of the cell - likely mediated by reactive oxygen species (ROS), as shown by a marked effect of catalase. These results, along with toxicological and behavioural assays using the two aquatic invertebrates Thamnocephalus platyurus and Daphnia magna indicate that ISH plays multiple important physiological and ecological roles. It acts as an effective antioxidant against high ROS levels, as often experienced in surface blooms, it elicits avoidance-related behavioural responses in grazer communities and at high levels, it can be toxic to some invertebrates.

Enhancing pseudocapacitive intercalation in Ti3C2T x MXene with molecular crowding electrolytes

The growing demand for safe, cost-efficient, high-energy and high-power electrochemical energy storage devices has stimulated the development of aqueous-based supercapacitors with high capacitance, high rate capability, and high voltage. 2D titanium carbide MXene-based electrodes have shown excellent rate capability in various dilute aqueous electrolytes, yet their potential window is usually narrower than 1.2 V. In this study, we show that the potential window of Ti3C2T x MXene can be efficiently widened to 1.5 V in a cost-effective and environmentally benign polyethylene glycol (PEG) containing molecular crowding electrolyte. Additionally, a pair of redox peaks at −0.25 V/−0.05 V vs. Ag (cathodic/anodic) emerged in cyclic voltammetry after the addition of PEG, yielding an additional 25% capacitance. Interestingly, we observed the co-insertion of the molecular crowding agent PEG-400 during the Li+ intercalation process based on in-situ x-ray diffraction analysis. As a result, Ti3C2T x electrodes presented an interlayer space change of 4.7 Å during a complete charge/discharge cycle, which is the largest reversible interlayer space change reported so far for MXene-based electrodes. This work demonstrates the potential of adding molecular crowding agents to improve the performance of MXene electrodes in aqueous electrolytes and to enlarge the change of the interlayer spacing.

Doping of molecular semiconductors through proton-coupled electron transfer.

The chemical doping of molecular semiconductors is based on electron-transfer reactions between the semiconductor and dopant molecules; here, the redox potential of the dopant is key to control the Fermi level of the semiconductor1,2. The tunability and reproducibility of chemical doping are limited by the availability of dopant materials and the effects of impurities such as water. Here we focused on proton-coupled electron-transfer (PCET) reactions, which are widely used in biochemical processes3,4; their redox potentials depend on an easily handled parameter, that is, proton activity. We immersed p-type organic semiconductor thin films in aqueous solutions with PCET-based redox pairs and hydrophobic molecular ions. Synergistic reactions of PCET and ion intercalation resulted in efficient chemical doping of crystalline organic semiconductor thin films under ambient conditions. In accordance with the Nernst equation, the Fermi levels of the semiconductors were controlled reproducibly with a high degree of precision-a thermal energy of about 25 millielectronvolts at room temperature and over a few hundred millielectronvolts around the band edge. A reference-electrode-free, resistive pH sensor based on this method is also proposed. A connection between semiconductor doping and proton activity, a widely used parameter in chemical and biochemical processes, may help create a platform for ambient semiconductor processes and biomolecular electronics.

Enhancing Oxygen Evolution Reaction by Simultaneously Triggering Metal and Lattice Oxygen Redox Pair in Iridium Loading on Ni‐Doped Co3O4

AbstractSince the active sites in catalytic systems are either metal sites or lattice oxygen, simultaneously triggering metal and lattice oxygen redox pair with low energy barriers is expected to provide diversified and efficient sites to accelerate oxygen evolution reaction (OER) kinetics, but this is a great challenge. Herein, Ir species (Ir clusters and Ir single atoms) loaded on Ni‐doped Co3O4 is designed (Ir/Ni‐Co3O4), where metallic Ir clusters downsize to spread into high‐density Ir single atoms to load on reconstruction‐derived Ni‐doped CoOOH. In situ spectroscopy, isotope‐labeled, and chemical probe experiments demonstrate that metal site and lattice oxygen are simultaneously activated to participate in the OER. Further theoretical studies demonstrate that the Co site is the most favorable site to promote the OER through an adsorbate evolution mechanism with a low energy barrier of 1.69 eV. The Ni cooperating with Ir atoms synergistically upshifts energy positions of the O p band centers. Thus, the lattice O that bridges Ni and Ir atoms is activated to participate in the OER via coupling with adsorbed O on the Ir site to fulfill O─O bond formation. Benefiting from the conjoint participation of the metal and lattice oxygen redox pair, Ir/Ni‐Co3O4 affords extremely low OER overpotentials of 177 and 263 mV at corresponding 10 and 500 mA cm−2.

Preparation and characterization of molybdenum trioxide/poly(3,4-ethylenedioxythiophene): Polystyrene sulphonate nanocomposites for electrochromic application.

Electrochromic processes are mostly characterized by colour change arising from the energy of a chemical reaction involving electron transfer. Transition metal oxides of tungsten, molybdenum, iridium, and nickel show the most intense Electrochromic colour changes and photochemical stability of about 100 cycles compared to organic electrochromes which are susceptible to photochemical degradation. The prospect of conjugated polymers (comprising of metal oxides and polymers) has opened a new dimension on improving the Electrochromic performance of the transition metal oxides. In this work, solution growth methods were employed in preparing a MoO3/PEDOT: PSS composite layer by adding PEDOT: PSS into MoO3 aqueous dispersion resulting in an electrostatic interaction between MoO3 and PEDOT: PSS for electrochromic application. This composite has shown a long-term stability up to more than 550 cycles which shows higher potential specific capacitance than WO3/PEDOT: PSS. This approach has significantly improved the stability issue of MoO3 and enhances the potential of MoO3-based materials for electrochromic applications. The semi crystalline nature of MoO3-300 °C was further proved by FE-SEM observation of the MoO3 nanoparticles. The particle size shown in the images corresponds with FE-SEM result and polycrystalline structure was observed under high magnification. The polycrystalline nature of the MoO3 particles favors their electrochemical stability, while their small size facilitates their effective interactions with PEDOT: PSS. The electrochemical properties of MoO3, PEDOT: PSS and composite were further studied by cyclic voltammetry (CV) from -1 V to +1 V. MoO3 has a broad oxidation peak at -0.43 V and no obvious reduction peak in this range. PEDOT: PSS has an oxidation peak at -0.02 V and a reduction peak at -0.55 V. In the composite, the peak at -0.43 V becomes a shoulder and a new pair of redox peaks appear at -0.18 V/-0.09 V.

Adsorption of Thymol Blue dye from Aqueous solution using modified Chitosan

The main objective of this research project is to perform some experimental procedures to study the ability of the novel adsorbent used in this project. The chemical modification of the adsorbent is the chemical oxidation of pure powder chitosan using some specific redox pairs which are potassium dichromate and sodium bisulphite. After preparing the modified chitosan, there are some parameters that must be discussed during the adsorption process. The first parameter is the time parameter, showing experimentally the optimum time for adsorption under certain conditions by collecting values of absorbance and concentration of thymol blue adsorbed after the process from the spectrophotometer showing that the optimum time is 120 minutes. While for the optimum pH experiment, it is shown that optimum pH is 4, 0.5% v/v is optimum concentration and 0.05 grams is the optimum dose for the adsorbent. Then after computing these conditions and values of absorbance, some mathematical calculations and classifications are done to show the reaction kinetics classification of the process. By performing some equations using mathematical rules it is provided that the reaction is not a first order reaction, showing by calculations and graphs that the reaction is a second order reaction.

A novel Co–CoAl2O4/exfoliated montmorillonite composite with improved nanoparticle dispersion for methyl orange removal via coupling peroxydisulfate

The degradation of refractory pollutants via the activation of peroxydisulfate (PDS) by Co-based nanostructures as catalysts has been gaining significant attention. However, most cobalt-based catalysts suffer from severe aggregation and metal ion leakage, resulting in a loss of activity and potential environmental threats. In this study, exfoliated montmorillonite (EMMT) loaded Co–CoAl2O4 composites were elaborately constructed through a facile coprecipitation-reduction method. The effects of the calcination temperature, the EMMT addition content, the pH of the precursor, and the reduction temperature on the microstructure of the Co–CoAl2O4/EMMT composites were investigated, and the optimum synthesis conditions were determined. In the optimal sample, well-crystallized CoAl2O4 nanoparticles were uniformly deposited onto the EMMT nanosheets with a considerably large specific surface area, while ultrafine metallic Co nanoparticles were homogeneously immobilized on the CoAl2O4 surface. This sample exhibited a superior activity (90% within 70 min) and reusability during methyl orange (MO) degradation. In the catalytic reaction, the superior adsorption property of EMMT facilitated the rapid transfer of MO molecules to the catalytically active sites. Moreover, CoAl2O4 acted as a transition layer which provided a cobalt source for the subsequent reduction process and regulated the growth of metallic Co nanoparticles, which increased the number of active sites for catalysis. Simultaneously, the metallic Co can not only activate PDS by being an electron donor, but also initiate the formation of Co-based redox pairs. This study offers new insights into the synthesis of efficient and cost-effective supported Co-based catalysts.

An Aqueous Redox Flow Battery Using CO2 as an Active Material with a Homogeneous Ir Catalyst**

AbstractFor the application of CO2 as an energy storage material, a H2 storage system has been proposed based on the interconversion of CO2 and formic acid (or formate). However, energy losses are inevitable in the conversion of electrical energy to H2 as chemical energy (≈70 % electrical efficiency) and H2 to electrical energy (≈40 % electrical efficiency). To overcome these significant energy losses, we developed a system based on the interconversion of CO2 and formate for the direct storage and generation of electricity. In this paper, we report an aqueous redox flow battery system using homogeneous Ir catalysts with CO2‐formate redox pair. The system exhibited a maximum discharge capacity of 10.5 mAh (1.5 Ah L−1), capacity decay of 0.2 % per cycle, and total turnover number of 2550 after 50 cycles. During charging‐discharging, in situ fluorescence X‐ray absorption fine structure spectroscopy based on an online setup indicated that the active species was in a high valence state of IrIV.

An Aqueous Redox Flow Battery Using CO2 as an Active Material with a Homogeneous Ir Catalyst.

For the application of CO2 as an energy storage material, a H2 storage system has been proposed based on the interconversion of CO2 and formic acid (or formate). However, energy losses are inevitable in the conversion of electrical energy to H2 as chemical energy (~70% electrical efficiency) and H2 to electrical energy (~40% electrical efficiency). To overcome these significant energy losses, we developed a system based on the interconversion of CO2 and formate for the direct storage and generation of electricity. In this paper, we report an aqueous redox flow battery system using homogeneous Ir catalysts with CO2-formate redox pair. The system exhibited a maximum discharge capacity of 10.5 mAh (1.5 Ah L-1), capacity decay of 0.2% per cycle, and total turnover number of 2550 after 50 cycles. During charging-discharging, in situ fluorescence X-ray absorption fine structure spectroscopy based on an online setup indicated that the active species was in a high valence state of Ir4+.

Electrochemical sensing platform based on screen-printed carbon electrode modified with plasma polymerized acrylonitrile nanofilms for determination of bupropion

A original electrochemical sensing platform, based on screen-printed electrodes modification with plasma polymerized acrylonitrile (pp-AN) nanofilms is proposed. For that purpose, plasma-enhanced chemical vapor deposition (PECVD) process was conducted in a parallel plate (13.56 MHz) plasma reactor for 2 min with discharge power of 10 W. The surface topography and electrochemical properties of prepared sensors were investigated by X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersion spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The electrochemical characteristics of pp-AN/SPCE and pp-AN/SPAuE sensors was investigated for model redox pair [Fe(CN)6]4−/3−. Conducted research confirmed the excellent chemical stability, durability, wide potential window, high signal-to-noise (S/N) ratio, and, most importantly, the ability to standardize the sensors. The pp-AN/SPCE sensor was applied to the determination of bupropion, an antidepressant drug whose intake has increased dramatically during the COVID-19 pandemic. The voltammetric response of pp-AN/SPCE for BUP was linear in two concentration ranges of 0.63–10.0 and 10.0–50.0 μmol L−1, with a detection limit of 0.21 μmol L−1. Satisfactory recoveries (96.2–102%) and good precision (RSD below 4.1%) obtained for environmental and biological samples confirmed the usefulness of the sensor for the analysis of various kinds of samples.Graphical

Reversible Fe3+/Fe2+ and Ti4+/Ti3+ redox couple in Fe-substituted LiTi2O4 ramsdellite and its electrochemical properties as electrode material in lithium ion batteries

Ti/Fe substitution in ramsdellite LiTi2O4, an attractive insertion material for lithium-ion battery applications, has been performed by the ceramic method yielding electrode materials with general stoichiometry LiFexTi2−xO4. Samples with 0 ≤ x ≤ 0.5 resulted in well crystallized orthorhombic ramsdellite phases, space group Pbnm, while samples with x > 0.5 formed spinel, space group Fd-3m, as revealed by powder X-ray diffraction. The ramsdellites were further investigated with X-EDS microanalysis, 57Fe Mössbauer spectroscopy and electrochemical discharge-charge cycling in lithium cells. This provided a comprehensive insight into the Ti/Fe substitution mechanism, which turned out to be rather more complex than the predicted simple M3+ isovalent substitution, with participation of Fe3+/Fe2+ and Ti4+/Ti3+. Upon testing against lithium in the low voltage range (ocv-1 V), ramsdellite with low Ti/Fe substitution, namely LiFe0.125Ti1.875O4, outperformed undoped LiTi2O4 electrochemically, delivering a 1st cycle capacity of 180 mAh g−1 at C/30 (5.3 mA g−1) stabilized at 140 mAh g−1 upon cycling, compared to 120 and 80 mAh g−1, respectively, in LiTi2O4. Two active redox pairs, Ti4+/Fe3+ and Fe3+/Fe2+, combined with better electrical properties due to the presence of metallic iron, boosting farther electronic conductivity in LiFe0.125Ti1.875O4, allow a noticeable capacity of 71 mAh g−1 still to be held at a high current of 2 C (320 mA g−1). In the high voltage range (ocv-4 V), LiFe0.125Ti1.875O4 electrochemically outmatched the higher Fe-substituted ramsdellites, which were characterized by a high irreversible capacity ascribed to the unavailability of Fe3+/Fe4+ redox couple and electrolyte decomposition.