Perylenetetracarboxylic Diimide Composite Electrodes as Organic Cathode Materials for Rechargeable Sodium-Ion Batteries: A Joint Experimental and Theoretical Study.

The organic semiconductor 3,4,9,10-perylenetetracarboxylic diimide (PTCDI), a widely used industrial pigment, has been identified as a diffusion-less Na-ion storage material, allowing for exceptionally fast charging/discharging rates. The elimination of diffusion effects in electrochemical measurements enables the assessment of interaction energies from simple cyclic voltammetry experiments through the theoretical work of Laviron and Tokuda. In this work, the two N-substituted perylenes, N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic diimide (Me2PTCDI) and N,N'-diphenyl-3,4,9,10-perylenetetracarboxylic diimide (Ph2PTCDI), as well as the parent molecule 3,4,9,10-perylenetetracarboxylic diimide (H2PTCDI) are investigated as thin-film composite electrodes on carbon fibers for sodium-ion batteries. The composite electrodes are analyzed with Raman spectroscopy. Interaction parameters are extracted from cyclic voltammetry measurements. The stability and rate capability of the three PTCDI derivatives are examined through galvanostatic measurements in sodium-ion half-cell batteries and the influence of the interactions on those parameters is evaluated. In addition, self-consistent charge density function tight binding calculations of the different PTCDI systems interacting with graphite have been carried out. The results show that the binding motif displays notable deviations from an ideal ABA stacking, especially for the neutral state. In addition, data obtained for the electron-transfer integrals show that the difference in performance between different PTCDI thin-film batteries cannot be solely explained by the electron-transfer properties and other factors such as H-bonding have to be considered.

Titanium Oxycarbide as Platinum-Free Electrocatalyst for Ethanol Oxidation.

The compound material titanium oxycarbide (TiOC) is found to be an effective electrocatalyst for the electrochemical oxidation of ethanol to CO2. The complete course of this reaction is one of the main challenges in direct ethanol fuel cells (DEFCs). While TiOC has previously been investigated as catalyst support material only, in this study we show that TiOC alone is able to oxidize ethanol to acetaldehyde without the need of expensive noble metal catalysts like Pt. It is suggested that this behavior is attributed to the presence of both undercoordinated sites, which allow ethanol to adsorb, and oxygenated sites, which facilitate the activation of water. This is a milestone in DEFC research and development and opens up innovative possibilities for the design of catalyst materials for intermediate temperature fuel cells.

A laboratory-based multifunctional near ambient pressure X-ray photoelectron spectroscopy system for electrochemical, catalytic, and cryogenic studies.

A versatile multifunctional laboratory-based near ambient pressure x-ray photoelectron spectroscopy (XPS) instrument is presented. The entire device is highly customized regarding geometry, exchangeable manipulators and sample stages for liquid- and solid-state electrochemistry, cryochemistry, and heterogeneous catalysis. It therefore delivers novel and unique access to a variety of experimental approaches toward a broad choice of functional materials and their specific surface processes. The high-temperature (electro)catalysis manipulator is designed for probing solid state/gas phase interactions for heterogeneous catalysts including solid electrolyzer/fuel cell electrocatalysts at pressures up to 15 mbar and temperatures from room temperature to 1000 °C. The liquid electrochemistry manipulator is specifically designed for in situ spectroscopic investigations of polarized solid/liquid interfaces using aqueous electrolytes and the third one for experiments for ice and ice-like materials at cryogenic temperatures to approximately -190 °C. The flexible and modular combination of these setups provides the opportunity to address a broad spectrum of in situ and operando XPS experiments on a laboratory-based system, circumventing the limited accessibility of experiments at synchrotron facilities.

Substantial Na-Ion Storage at High Current Rates: Redox-Pseudocapacitance through Sodium Oxide Formation.

Batteries and supercapacitors, both governed by electrochemical processes, operate by different electrochemical mechanisms which determine their characteristic energy and power densities. Battery materials store large amounts of energy by ion intercalation. Electrical double-layer capacitors store charge through surface-controlled ion adsorption which leads to high power and rapid charging, but much smaller amounts of energy stored. Pseudocapacitive materials offer the promise to combine these properties by storing charge through surface-controlled, battery-like redox reactions but at high rates approaching those of electrochemical double-layer capacitors. This work compares the pseudo-capacitive charge storage characteristics of self-organized titanium dioxide (TiO2-x) nanotubes (NTs) to flat TiO2-x surface films to further elucidate the proposed charge storage mechanism within the formed surface films. By comparing TiO2-x NTs to flat TiO2-x surface films, having distinctively different oxide mass and surface area ratios, it is shown that NaO2 and Na2O2 formation, which constitutes the active surface film material, is governed by the metal oxide bulk. Our results corroborate that oxygen diffusion from the lattice oxide is key to NaO2 and Na2O2 formation.

Direct Electrochemical CO2 Capture Using Substituted Anthraquinones in Homogeneous Solutions: A Joint Experimental and Theoretical Study.

Electrochemical capture of carbon dioxide (CO2) using organic quinones is a promising and intensively studied alternative to the industrially established scrubbing processes. While recent studies focused only on the influence of substituents having a simple mesomeric or nucleophilicity effect, we have systematically selected six anthraquinone (AQ) derivatives (X-AQ) with amino and hydroxy substituents in order to thoroughly study the influence thereof on the properties of electrochemical CO2 capture. Experimental data from cyclic voltammetry (CV) and UV-Vis spectroelectrochemistry of solutions in acetonitrile were analyzed and compared with innovative density functional tight binding computational results. Our experimental and theoretical results provide a coherent explanation of the influence of CO2 on the CV data in terms of weak and strong binding nomenclature of the dianions. In addition to this terminology, we have identified the dihydroxy substituted AQ as a new class of molecules forming rather unstable [X-AQ-(CO2) n ]2- adducts. In contrast to the commonly used dianion consideration, the results presented herein reveal opposite trends in stability for the X-AQ-CO2 •- radical species for the first time. To the best of our knowledge, this study presents theoretically calculated UV-Vis spectra for the various CO2-AQ reduction products for the first time, enabling a detailed decomposition of the spectroelectrochemical data. Thus, this work provides an extension of the existing classification with proof of the existence of X-AQ-CO2 species, which will be the basis of future studies focusing on improved materials for electrochemical CO2 capture.

Anthraquinone and its derivatives as sustainable materials for electrochemical applications - a joint experimental and theoretical investigation of the redox potential in solution.

Anthraquinone (AQ) has long been identified as a highly promising lead structure for various applications in organic electronics. Considering the enormous number of possible substitution patterns of the AQ lead structure, with only a minority being commercially available, a systematic experimental screening of the associated electrochemical potentials represents a highly challenging and time consuming task, which can be greatly enhanced via suitable virtual pre-screening techniques. In this work the calculated electrochemical reduction potentials of pristine AQ and 12 hydroxy- or/and amino-substituted AQ derivatives in N,N-dimethylformamide have been correlated against newly measured experimental data. In addition to the calculations performed using density functional theory (DFT), the performance of different semi-empirical density functional tight binding (DFTB) approaches has been critically assessed. It was shown that the SCC DFTB/3ob parametrization in conjunction with the COSMO solvation model provides a highly adequate description of the electrochemical potentials also in the case of the two-fold reduced species. While the quality in the correlation against the experimental data proved to be slightly inferior compared to the employed DFT approach, the highly advantageous cost-accuracy ratio of the SCC DFTB/3ob/COSMO framework has important implications in the formulation of hierarchical screening strategies for materials associated with organic electronics. Based on the observed performance, the low-cost method provides sufficiently accurate results to execute efficient pre-screening protocols, which may then be followed by a DFT-based refinement of the best candidate structures to facilitate a systematic search for new, high-performance organic electronic materials.

Analysis of the Ordering Effects in Anthraquinone Thin Films and Its Potential Application for Sodium Ion Batteries.

The ordering effects in anthraquinone (AQ) stacking forced by thin-film application and its influence on dimer solubility and current collector adhesion are investigated. The structural characteristics of AQ and its chemical environment are found to have a substantial influence on its electrochemical performance. Computational investigation for different charged states of AQ on a carbon substrate obtained via basin hopping global minimization provides important insights into the physicochemical thin-film properties. The results reveal the ideal stacking configurations of the individual AQ-carrier systems and show ordering effects in a periodic supercell environment. The latter reveals the transition from intermolecular hydrogen bonding toward the formation of salt bridges between the reduced AQ units and a stabilizing effect upon the dimerlike rearrangement, while the strong surface-molecular interactions in the thin-film geometries are found to be crucial for the formed dimers to remain electronically active. Both characteristics, the improved current collector adhesion and the stabilization due to dimerization, are mutual benefits of thin-film electrodes over powder-based systems. This hypothesis has been further investigated for its potential application in sodium ion batteries. Our results show that AQ thin-film electrodes exhibit significantly better specific capacities (233 vs 87 mAh g-1 in the first cycle), Coulombic efficiencies, and long-term cycling performance (80 vs 4 mAh g-1 after 100 cycles) over the AQ powder electrodes. By augmenting the experimental findings via computational investigations, we are able to suggest design strategies that may foster the performance of industrially desirable powder-based electrode materials.

Perylenetetracarboxylic Diimide as Diffusion-Less Electrode Material for High-Rate Organic Na-Ion Batteries.

In this work 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) is investigated as electrode material for organic Na-ion batteries. Since PTCDI is a widely used industrial pigment, it may turn out to be a cost-effective, abundant, and environmentally benign cathode material for secondary Na-ion batteries. Among other carbonyl pigments, PTCDI is especially interesting due to its high Na-storage capacity in combination with remarkable high rate capabilities. The detailed analysis of cyclic voltammetry measurements reveals a diffusion-less mechanism, suggesting that Na-ion storage in the PTCDI film allows for exceptionally fast charging/discharging rates. This finding is further corroborated by galvanostatic sodiation measurements at high rates of 17 C (2.3 A g-1 ), showing that 57 % of the theoretically possible capacity of PTCDI, or 78 mAh g-1 , are attained in only 3.5 min charging time.

Substantially Improved Na-Ion Storage Capability by Nanostructured Organic-Inorganic Polyaniline-TiO2 Composite Electrodes.

Developing sodium (Na)-ion batteries is highly appealing because they offer the potential to be made from raw materials, which hold the promise to be less expensive, less toxic, and at the same time more abundant compared to state-of-the-art lithium (Li)-ion batteries. In this work, the Na-ion storage capability of nanostructured organic-inorganic polyaniline (PANI) titanium dioxide (TiO2) composite electrodes is studied. Self-organized, carbon-coated, and oxygen-deficient anatase TiO2-x -C nanotubes (NTs) are fabricated by a facile one-step anodic oxidation process followed by annealing at high temperatures in an argon-acetylene mixture. Subsequent electropolymerization of a thin film of PANI results in the fabrication of highly conductive and well-ordered, nanostructured organic-inorganic polyaniline-TiO2 composite electrodes. As a result, the PANI-coated TiO2-x -C NT composite electrodes exhibit higher Na storage capacities, significantly better capacity retention, advanced rate capability, and better Coulombic efficiencies compared to PANI-coated Ti metal and uncoated TiO2-x -C NTs for all current rates (C-rates) investigated.

Photoelectrocatalytic Synthesis of Hydrogen Peroxide by Molecular Copper-Porphyrin Supported on Titanium Dioxide Nanotubes.

We report on a self-assembled system comprising a molecular copper-porphyrin photoelectrocatalyst, 5-(4-carboxy-phenyl)-10,15,20-triphenylporphyrinatocopper(II) (CuTPP-COOH), covalently bound to self-organized, anodic titania nanotube arrays (TiO2 NTs) for photoelectrochemical reduction of oxygen. Visible light irradiation of the porphyrin-covered TiO2 NTs under cathodic polarization up to -0.3 V vs. Normal hydrogen electrode (NHE) photocatalytically produces H2O2 in pH neutral electrolyte, at room temperature and without need of sacrificial electron donors. The formation of H2O2 upon irradiation is proven and quantified by direct colorimetric detection using 4-nitrophenyl boronic acid (p-NPBA) as a reactant. This simple approach for the attachment of a small molecular catalyst to TiO2 NTs may ultimately allow for the preparation of a low-cost H2O2 evolving cathode for efficient photoelectrochemical energy storage under ambient conditions.

Synthesis and investigation of tetraphenyltetrabenzoporphyrins for electrocatalytic reduction of carbon dioxide.

We report the synthesis and electrochemical properties of freebase tetraphenyltetrabenzoporphyrin and its complexes of Zn(ii), Co(ii), Ni(ii), Cu(ii) and Sn(iv) towards electrochemical reduction of carbon dioxide (CO2). Based on cyclic voltammetry, it is shown that central metals significantly affect the electrocatalytic performance in the reduction of CO2 in terms of reduction potential and catalytic current enhancement. At an applied potential of -1.90 V vs. an Ag/AgCl quasi reference electrode for 20 h, the electrocatalytic reduction of CO2 realized by Zn(ii)- and Cu(ii)-tetraphenyltetrabenzoporphyrins to carbon monoxide resulted in faradaic efficiencies of around 48% and 33%, respectively.

Preferentially Oriented TiO2 Nanotubes as Anode Material for Li-Ion Batteries: Insight into Li-Ion Storage and Lithiation Kinetics.

Self-organized TiO2 nanotubes (NTs) with a preferential orientation along the [001] direction are anodically grown by controlling the water content in the fluoride-containing electrolyte. The intrinsic kinetic and thermodynamic properties of the Li intercalation process in the preferentially oriented (PO) TiO2 NTs and in a randomly oriented (RO) TiO2 NT reference are determined by combining complementary electrochemical methods, including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic cycling. PO TiO2 NTs demonstrate an enhanced performance as anode material in Li-ion batteries due to faster interfacial Li insertion/extraction kinetics. It is shown that the thermodynamic properties, which describe the ability of the host material to intercalate Li ions, have a negligible influence on the superior performance of PO NTs. This work presents a straightforward approach for gaining important insight into the influence of the crystallographic orientation on lithiation/delithiation characteristics of nanostructured TiO2 based anode materials for Li-ion batteries. The introduced methodology has high potential for the evaluation of battery materials in terms of their lithiation/delithiation thermodynamics and kinetics in general.

Electrochemical Capture and Release of CO2 in Aqueous Electrolytes Using an Organic Semiconductor Electrode.

Developing efficient methods for capture and controlled release of carbon dioxide is crucial to any carbon capture and utilization technology. Herein we present an approach using an organic semiconductor electrode to electrochemically capture dissolved CO2 in aqueous electrolytes. The process relies on electrochemical reduction of a thin film of a naphthalene bisimide derivative, 2,7-bis(4-(2-(2-ethylhexyl)thiazol-4-yl)phenyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NBIT). This molecule is specifically tailored to afford one-electron reversible and one-electron quasi-reversible reduction in aqueous conditions while not dissolving or degrading. The reduced NBIT reacts with CO2 to form a stable semicarbonate salt, which can be subsequently oxidized electrochemically to release CO2. The semicarbonate structure is confirmed by in situ IR spectroelectrochemistry. This process of capturing and releasing carbon dioxide can be realized in an oxygen-free environment under ambient pressure and temperature, with uptake efficiency for CO2 capture of ∼2.3 mmol g-1. This is on par with the best solution-phase amine chemical capture technologies available today.

Organic, Organometallic and Bioorganic Catalysts for Electrochemical Reduction of CO2.

A broad review of homogeneous and heterogeneous catalytic approaches toward CO2 reduction using organic, organometallic, and bioorganic systems is provided. Electrochemical, bioelectrochemical and photoelectrochemical approaches are discussed in terms of their faradaic efficiencies, overpotentials and reaction mechanisms. Organometallic complexes as well as semiconductors and their homogeneous and heterogeneous catalytic activities are compared to enzymes. In both cases, their immobilization on electrodes is discussed and compared to homogeneous catalysts in solution.

Electrochemical Reduction of Carbon Dioxide to Methanol by Direct Injection of Electrons into Immobilized Enzymes on a Modified Electrode.

We present results for direct bio-electrocatalytic reduction of CO2 to C1 products using electrodes with immobilized enzymes. Enzymatic reduction reactions are well known from biological systems where CO2 is selectively reduced to formate, formaldehyde, or methanol at room temperature and ambient pressure. In the past, the use of such enzymatic reductions for CO2 was limited due to the necessity of a sacrificial co-enzyme, such as nicotinamide adenine dinucleotide (NADH), to supply electrons and the hydrogen equivalent. The method reported here in this paper operates without the co-enzyme NADH by directly injecting electrons from electrodes into immobilized enzymes. We demonstrate the immobilization of formate, formaldehyde, and alcohol dehydrogenases on one-and-the-same electrode for direct CO2 reduction. Carbon felt is used as working electrode material. An alginate-silicate hybrid gel matrix is used for the immobilization of the enzymes on the electrode. Generation of methanol is observed for the six-electron reduction with Faradaic efficiencies of around 10%. This method of immobilization of enzymes on electrodes offers the opportunity for electrochemical application of enzymatic electrodes to many reactions in which a substitution of the expensive sacrificial co-enzyme NADH is desired.

Photoinduced energy transfer from poly(N-vinylcarbazole) to tricarbonylchloro-(2,2'-bipyridyl)rhenium(I).

This work investigates the photoinduced energy transfer from poly(N-vinylcarbazole) (PVK), as a donor material, to fac-(2,2'-bipyridyl)Re(CO)3Cl, as a catalyst acceptor, for its potential application towards CO2 reduction. Photoluminescence quenching experiments reveal dynamic quenching through resonance energy transfer in solid donor/acceptor mixtures and in solid/liquid systems. The bimolecular reaction rate constant at solution-film interfaces for the elementary reaction of the excited state with the quencher material could be determined as 8.8(±1.4)×10(11) L mol(-1) s(-1) by using Stern-Volmer analysis. This work shows that PVK is an effective and cheap absorber material that can act efficiently as a redox photosensitizer in combination with fac-(2,2'-bipyridyl)Re(CO)3Cl as a catalyst acceptor, which might lead to possible applications in photocatalytic CO2 reduction.

Direct electrochemical capture and release of carbon dioxide using an industrial organic pigment: quinacridone.

Limiting anthropogenic carbon dioxide emissions constitutes a major issue faced by scientists today. Herein we report an efficient way of controlled capture and release of carbon dioxide using nature inspired, cheap, abundant and non-toxic, industrial pigment namely, quinacridone. An electrochemically reduced electrode consisting of a quinacridone thin film (ca. 100 nm thick) on an ITO support forms a quinacridone carbonate salt. The captured CO2 can be released by electrochemical oxidation. The amount of captured CO2 was quantified by FT-IR. The uptake value for electrochemical release process was 4.61 mmol g(-1). This value is among the highest reported uptake efficiencies for electrochemical CO2 capture. For comparison, the state-of-the-art aqueous amine industrial capture process has an uptake efficiency of ca. 8 mmol g(-1).

Two-electron carbon dioxide reduction catalyzed by rhenium(I) bis(imino)acenaphthene carbonyl complexes.

Rhenium(I) carbonyl complexes carrying substituted bis(arylimino)acenaphthene ligands (BIAN-R) have been tested as potential catalysts for the two-electron reduction of carbon dioxide. Cyclic voltammetric studies as well as controlled potential electrolysis experiments were performed using CO2-saturated solutions of the complexes in acetonitrile and acetonitrile-water mixtures. Faradaic efficiencies of more than 30 % have been determined for the electrocatalytic production of CO. The effects of ligand substitution patterns and water content of the reaction medium on the catalytic performance of the new catalysts are discussed.

Electrocatalytic Reduction of Carbon Dioxide to Carbon Monoxide by a Polymerized Film of an Alkynyl-Substituted Rhenium(I) Complex.

The alkynyl-substituted ReI complex [Re(5,5'-bisphenylethynyl-2,2'-bipyridyl)(CO)3Cl] was immobilized by electropolymerization onto a Pt-plate electrode. The polymerized film exhibited electrocatalytic activity for the reduction of CO2 to CO. Cyclic voltammetry studies and bulk controlled-potential electrolysis experiments were performed by using a CO2-saturated acetonitrile solution. The CO2 reduction, determined by cyclic voltammetry, occurs at approximately -1150 mV versus the normal hydrogen electrode (NHE). Quantitative analysis by GC and IR spectroscopy was used to determine a Faradaic efficiency of approximately 33 % for the formation of CO. Both values of the modified electrode were compared to the performance of the homogenous monomer [Re(5,5'-bisphenylethynyl-2,2'-bipyridyl)(CO)3Cl] in acetonitrile. The polymer formation and its properties were studied by using SEM, AFM, and attenuated total reflectance (ATR) FTIR and UV/Vis spectroscopy.