Charge Transfer Reactions Research Articles

Faradaic deionization technology: Insights from bibliometric, data mining and machine learning approaches

Faradaic deionization (FDI) is an emerging water treatment technology based on electrodes able to remove ionic species from water by charge transfer reactions. It is a young and promising technology that has attracted much attention due to its large capacity to store ions and the high selectivity of the faradaic electrode materials. This study reviews published papers on FDI from different angles: data mining, bibliometric and machine learning. Metrics such as annual growth rate, most important journals, relevant authors, collaborations maps, sentiment and subjectivity analysis, similarity and clustering analysis were performed. The results indicated that the strong interest in FDI really started in 2016, China is the most active country in FDI, and Desalination is the most important journal publishing FDI articles. The word cloud method showed that the most preferred adopted words are deionization, capacitive, electrode, material. Sentiment analysis results indicated that most of the researchers are optimistic about FDI technology. The title similarity method revealed that FDI researchers were successful in proposing unique and appropriate titles. The clustering approach stressed that FDI literature is concentrated on electrode material production, desalination application, lithium recovery and comparison with CDI.

As(III) removal of aqueous solutions using zerovalent iron nanoparticles: The role of the UVA-Vis irradiation wavelength

Arsenic contamination in drinking water is dramatic in many countries, particularly in Asia and Latin America. Arsenic removal from water can be achieved through some conventional technologies but some of them have drawbacks or are very expensive, especially in developing countries, where the population uses groundwater for drinking purposes. Therefore, the need of searching for new and low-cost methodologies for As removal from water is mandatory. Because As(V) is removed more easily than As(III), oxidation of this species, when present, is needed as the first step. The use of zerovalent iron nanoparticles (nZVI), particularly reactive due to their extremely small particle size and large surface area can be proposed at a household scale and in isolated regions. The effect of UV–Vis irradiation on the removal of arsenical species using nZVI presents scarce reports in the literature. In the present work, experiments of As(III) removal with commercial nZVI under UVA-Vis irradiation (λem = 300–800 nm) are described. The effect of the As(III) concentration, the As:nZVI molar ratio (MR = [As(III)]:[FeTOTAL]), and the irradiation wavelength on the As(III) removal were analyzed. Two initial As(III) concentrations, 1 and 10 mg L−1, and different MR in the range 1:10–1:100 were tested at pH 6–6.8. The increase of the nZVI amount and the use of UV–Vis irradiation enhanced the As removal under all conditions. The optimal MR for the As(III) removal after 60 min of irradiation at both initial concentrations was 1:30, being 85% for [As(III)]0 = 10 mg L−1, and 92% for [As(III)]0 = 1 mg L−1. By the use of chemical optical filters, it was determined that the most efficient wavelengths to improve the As(III) removal were those lower than 450 nm. All experimental data were adjusted to a biexponential decay suggesting the occurrence of two removal processes, one faster than the other. It was proposed that the main mechanisms under UVA-Vis irradiation were the action of oxides and oxyhydroxides already present or formed on the surface of nZVI during the reaction as semiconductors originating oxidative species and a ligand-to-metal charge-transfer reaction on As(III)-Fe(III) complexes formed in the system with simultaneous As(III) oxidation and Fe(III) reduction. It was concluded that the effect of the light depends on the pollutant and not on the iron material.

Cathode reaction models for Braga-Goodenough Na-ferrocene and Li-MnO2 rechargeable batteries

Braga-Goodenough all-solid-state Na-Fc and Li-MnO2 batteries demonstrate deposition of Na and Li on the cathode during discharge. These reaction mechanisms were investigated in light of the generalized charge neutrality level and the experimental results of Braga et al., and two new types of mechanisms were proposed. The Na-Fc mechanism is represented by a multi-step C[(CE)cC]n mechanism where C is the chemical step, E is the electrochemical step, c is the catalytic (CE) step, and n denotes the number of [(CE)cC] part cycles. The nth cycle corresponds to n moles of Na and Li deposition. For Li-MnO2, two mechanisms were considered. One is the C[(CE)cC]n mechanism which is the same as Na-Fc, and the other is the C[2(CE)cC]n mechanism, which involves two consecutive (CE)c steps. In the C step of (CE)c of both mechanisms, Fc and MnO2 reduce Na+(sf) and Li+(sf) (sf - surface states) to deposit Na and Li, respectively, which are intramolecular charge transfer reactions within the adsorbed molecules. Fc and MnO2 are oxidized to inter­mediates immediately reduced to Fc and MnO2 by their anodes in the subsequent E step. Based on these mechanisms, these batteries' discharge capacity and cathode alkali metal deposition were examined in detail.

Revealing the effects of microstructural changes of graphite anodes during cycling on their lithium intercalation kinetics utilizing operando XRD

Concerning cell ageing and lithium plating, electrode kinetics – in particular the one of the anode - plays an important role. In our study, we applied a holistic physicochemical post-mortem analysis including operando XRD and SEM-studies as well as electrochemical analysis to get deeper insights into the changes of the microstructure and phase composition of graphite anodes from LiNi0.6Co0.2Mn0.2O2//Graphite pouch cells during cyclic ageing and their influence on the lithium intercalation kinetics. The key findings are as follows: Li plating and loss of cyclable lithium is the main source of capacity fade of the investigated cells. Cycling causes pore clogging of the anode leading to an increased transport resistance for Li-ions and slower charge transfer reactions. Visual inspections and operando XRD measurements in turn indicate an inhomogeneous Li intercalation over the thickness of the electrode resulting in a Li gradient. In the cycled electrode LiC6 forms in surface-near regions, whereas in deeper regions LiC12 formation has not finished yet. As a result, Li plating occurs as the surface-near graphite is already fully intercalated and Li-ion transport to deeper regions is hindered due to pore clogging. By combining complementary methods we could consistently prove the hypothesis of pore clogging, deterioration of anode kinetics and subsequent inhomogeneous lithiation which is supposed to trigger the observed Li-plating.

A Comparative Study of the Performance and Electrode Processes of Solid Oxide H2O Electrolysis and CO2 Electrolysis

Solid oxide CO2 electrolysis was less studied compared with H2O electrolysis and the relevant reaction mechanism and electrode processes were poorly understood. This paper investigated the performance and electrode processes differences between CO2 electrolysis and H2O electrolysis. The shape of j-V curves, electrochemical impedance spectroscopy data and calculated distribution relaxation time results were analyzed. It was found that the performance of CO2 electrolysis degraded the most compared with that in SOFC mode and for H2O electrolysis after a 65 h’ operation. Meanwhile, j-V curve of CO2 electrolysis changed a lot and finally showed a convex total resistance pattern with applied current. It was also found that the characteristic frequency of charge transfer reaction and diffusion process for CO2 electrolysis was much lower than that of H2O electrolysis. A thermal activated peak at 10-100 Hz which was not noted for H2O electrolysis was considered to be CO2 adsorption and dissociation process in fuel electrode. Besides, diffusion process for H2O-H2 and CO2-CO mixture also differed. Finally, it was indicated that the different performance degradation may be due to different suppressed degree of charge transfer reaction in fuel electrode for H2O electrolysis and CO2 electrolysis and additional suppressed adsorption or dissociation process of CO2 for CO2 electrolysis.

Auto-selective reaction mechanism on Al-substituted ZnFe2O4 spinel electrode and sustainable water oxidation by oxygen vacancy transition

This study aims to optimize the oxygen evolution reaction (OER) by maximizing OH– adsorption on the mixed spinel ZFAO surface, in which Al3+ is substituted for Fe3+ in the ZnFe2O4 (ZFO) spinel structure composed of inexpensive transition metals. The substituted Al3+ ions simultaneously occupy the tetrahedral and octahedral sites of Fe in the ZFO spinel lattice. As the amount of substituted Al3+ increases, the amount of OH– adsorbed on the crystal surface increases significantly, and the OER activity is maximized at the ZFA0.75O/NF electrode, in which 0.75 M of Al is substituted. The overpotential is greatly reduced to 270 mV at 10 mA cm−2, and the Tafel slope is very low at 79 mA dec−1. These results were constant even after 10 d, which means that the charge transfer reaction proceeds rapidly between the ZFAO spinel catalyst and aqueous solution during the OER without side reactions. In particular, this study confirms that the main OER active sites of the ZFAO catalyst are the Al-tetrahedral and Fe-octahedral sites, and oxygen through the lattice vacancies rapidly transfers, maintaining a stable spinel structure. This study also reveals that the OER selectively pursues two mechanisms: an adsorbate evolution mechanism (AEM) on the Al-tetrahedral site and a lattice oxygen participation mechanism (LOPM) on the Fe-octahedral site. This study contributes to making the catalyst cost-effective, which has been an obstacle to the commercialization of water electrolysis technology, and securing its long-term durability, thereby opening the door to the mass production of clean hydrogen energy.

Spectroelectrochemical sensing of reaction intermediates and products in an affordable fully 3D printed device

Recent advances in fused deposition modelling 3D printing (FDM 3DP) and synthesis of printable electrically conductive materials enabled the manufacture of customized electrodes and electrochemical devices by this technique. The past couple of years have seen a boom in applying approaches of FDM 3DP in the realm of spectroelectrochemistry (SEC). Despite significant progress, reported designs of SEC devices still rely on conventionally manufactured optical components such as quartz windows and cuvettes. To bridge this technological gap, in this work we apply bi-material FDM 3DP combining electrically conductive and optically translucent filaments to manufacture working electrodes and cells, constituting a fully integrated microfluidic platform for transmission absorption UV–Vis SEC measurements. The cell design enables de-aeration of samples and their convenient handling and analysis. Employing cyclic voltammetric measurements with ruthenium(III) acetylacetonate, ethylviologen dibromide and ferrocenemethanol redox-active probes as model analytes, we demonstrate that the presented platform allows SEC sensing of reactants, intermediates and products of charge transfer reactions, including the inspection of their long-term stability. Approaches developed and presented in this work pave the way for manufacturing customized SEC devices with dramatically reduced costs compared to currently available commercial platforms.

Synergistic Coupling of CoFe-LDH Nanosheets with Cu3P Nanoarrays for Efficient Water Splitting

A crucial requirement for overall water splitting (OWS) is the creation of highly active bifunctional electrocatalysts. In this study, a CoFe-LDH (LDH = layered double hydroxide) nanosheet is integrated on a Cu3P nanowire to form heterogeneous structure Cu3P@CoFe-LDH/CF. Studies prove that the formation of a p–n heterojunction between Cu3P and CoFe-LDH promotes the charge-transfer reaction. Due to the synergistic contribution of the heterogeneous structure, Cu3P@CoFe-LDH/CF displays promising electrocatalytic activity. The overpotentials of 293 mV at 100 mA cm–2 for oxygen evolution reaction and 181 mV at 100 mA cm–2 for hydrogen evolution reaction are achieved in 1 M KOH. In addition, the alkaline electrolyzer of Cu3P@CoFe-LDH/CF||Cu3P@CoFe-LDH/CF shows a low cell voltage of 1.45 V at 10 mA cm–2 as well as great stability for OWS. This work provides a facile method to enhance the electrocatalytic activity by constructing heterogeneous structures with p–n heterojunctions, which holds significant promise for application in renewable energy technology.

Impedance of a tubular electrochemical cell with BZCY electrolyte and Ni-BZCY cermet electrodes for proton ceramic membrane reactors

In this work, impedance spectroscopy has been employed to explore the electrochemical behaviour of a 15 cm2 complete tubular cell with BaZr0.8Ce0.1Y0.1O3-δ (BZCY) electrolyte and two asymmetric Ni-BCZY cermet electrodes for hydrogen separation. Analyses of impedance spectra at different temperatures and gas compositions reveal that the thick inner electrode contributes most to the total polarisation resistance (Rp). For Rp there are four contributions with well-separated time constants of which gas phase hydrogen diffusion within the porous Ni-BZCY anode is predominant. The other three can be ascribed to proton migration through the space charge layer of the BZCY electrolyte adjacent to the Ni electrode, hydrogen redox charge transfer reactions, and hydrogen diffusion within Ni bulk. The present study guides the way to parameterise and, on this basis, optimise electrodes for scalable proton ceramic electrochemical cells.

A theoretical study of the time-resolved x-ray absorption spectrum of the photoionized BT-1T cation.

The time-resolved x-ray absorption spectrum of the BT-1T cation (BT-1T+) is theoretically simulated in order to investigate the charge transfer reaction of the system. We employ both trajectory surface hopping and quantum dynamics to simulate the structural evolution over time and the changes in the state populations. To compute the static x-ray absorption spectra (XAS) of the ground and excited states, we apply both the time-dependent density functional theory and the coupled cluster singles and doubles method. The results obtained are in good agreement between the methods. It is, furthermore, found that the small structural changes that occur during the reaction have little effect on the static XAS. Hence, the tr-XAS can be computed based on the state populations determined from a nuclear dynamics simulation and one set of static XAS calculations, utilizing the ground state optimized geometry. This approach can save considerable computational resources, as the static spectra need not to be calculated for all geometries. As BT-1T is a relatively rigid molecule, the outlined approach should only be considered when investigating non-radiative decay processes in the vicinity of the Franck-Condon point.

A kinetic perspective of charge transfer reactions: the downfall of hard/soft acid/base interactions

A kinetic perspective of charge transfer reactions: the downfall of hard/soft acid/base interactions

Construction of adiabatic vis-á-vis quasi-diabatic surfaces of He+ + CO system for the investigation of charge transfer reaction

The charge transfer process, He+ + CO → He + CO+, is one of the often-seen events in high energy collisions that correspond to typical solar wind conditions. At MRCI/aug-cc-pVQZ level of theory, an elaborate ab initio analysis involving the lowest nine electronic states for the system has been conducted to identify and investigate the involved potential energy surfaces for the charge transfer process. The reaction is caused by non-adiabatic interactions among all the nine electronic states. The nonadiabatic couplings and the associated quasi-diabatic surfaces have also been computed using ab initio procedure. The strength of the non-adiabatic couplings corroborates the experimental findings on different probable charge transfer channels.

Advanced electrocatalytic activity of praseodymium-deficient copper-based oxygen electrodes for solid oxide fuel cells

Herein praseodymium-deficient Pr1.90−xCe0.1CuO4 oxides are evaluated as potential oxygen electrodes for solid oxide fuel cells (SOFCs). Introducing Pr-deficiency promotes the oxygen vacancy concentration, further improving electrocatalytic activity of the Pr1.90−xCe0.1CuO4 electrodes towards oxygen reduction reaction (ORR). The Pr1.75Ce0·.1CuO4 (P1·75CC) component exhibits outstanding electrode performance, as supported by a polarization resistance as low as 0.025 Ω cm2 and high peak power density of the single cell (1.11 W cm−2) at 700 °C. In addition, the rate-limiting steps for ORR kinetics are determined to be the charge transfer reaction and oxygen adsorption/diffusion process on the electrode surface. This work highlights an effective way for developing the cathode candidates with high electrocatalytic activity and superior stability.

Development of spectrophotometric method for the determination of catecholamines in pure and pharmaceutical formulations, using pyromellitic dianhydride reagent by charge transfer reaction

Development of spectrophotometric method for the determination of catecholamines in pure and pharmaceutical formulations, using pyromellitic dianhydride reagent by charge transfer reaction

Sulfonamide derived Schiff base Mn (II), Co (II), and Ni (II) complexes: Crystal structures, density functional theory and Hirshfeld surface analysis

The three transition metal complexes of the ligand named as 2,4‐dibromo‐6‐{[2‐(1,1‐dioxo‐1H‐benzoisothiazole‐3‐yl‐amino)‐ethylimino]‐methyl}‐phenol 3 were synthesized with divalent manganese, cobalt and nickel metal ions and characterized by employing different analytical methods including UV–visible, FT‐IR and elemental analyses. The crystal structures of Mn (II) complex 4, Co (II) complex 5, and Ni (II) complex 6 are determined by single beam X‐rays crystallography, which confirm the distorted octahedral coordination of the complexes 4–6. The non‐covalent interactions of the complexes 4–6 are investigated by the Hirshfeld surface analysis. The tendency of the pair of chemical species to form crystal packing interactions are computed, which provide the favorable contacts in the crystal packing for the complexes 4–6. For the sake of computing strength of the crystal packing, void analysis is performed for the complexes 4–6. The non‐electrolytic nature of synthesized metal complexes was confirmed by molar conductance. The spectral analyses suggested that sulfonamide functionalized Schiff base behaves as bidentate ligand and coordinates with the metal center through phenolic oxygen and iminic nitrogen atoms. The density functional theory (DFT) studies were performed for the Mn (II), Co (II), and Ni (II) metal complexes at the B3LYP/LANL2DZ level of theory. The structural characteristics, vibrational analysis (IR), NMR analysis, UV–Vis, natural bonding orbital (NBO), frontier molecular orbital (FMO), charges (Mulliken and NPA), global reactivity descriptors, molecular electrostatic potential (MEP), and dipole moments were investigated using this method. The large values of stabilization energy, that is, 12.02, 15.25, and 23.81 kcal/mol were found for the complexes Mn (II) 4, Co (II) 5, and Ni (II) 6, respectively by NBO analysis. The global reactivity findings suggested the positive values of electron affinity for all complexes, which indicate the involvement of charge transfer reaction. Among these complexes, complex 6 is the most stable and complex 4 is the least. Further, FMO analysis indicated large HOMO‐LUMO gap (3.85–3.97 eV) with higher LUMO values for all metal complexes.

Crystalline silica particle functionalized by PEG for its collision-enhanced detection at ultramicroelectrode

Detecting individual particulate matter is highly significant in many areas, such as mine safety, environment, and human health. The analytical method based on single entity electrochemistry (SEE) has shown great potential in detecting, counting, and measuring individual particles, especially conductive metals or carbon particles, based on their unique charge transfer reactions at an ultramicroelectrode (UME). In this study, we report an innovative SEE method for improving the sensitivity of the detection of electrochemical inert crystalline silica particles by functionalizing silica particles with polyethylene glycol (PEG) molecules. The PEG surface functionalization of the silica was characterized by Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The morphology of silica particles was characterized by a scanning electron microscope (SEM), and a transmission electron microscope (TEM) was employed to calibrate size distribution and determine the elemental composition of silica particles. The surface charges of silica particles were measured by dynamic light scattering techniques. The collision behaviors of crystalline silica particles with UME were investigated by cyclic voltammetric experiments, which are rarely reported in the literature. The crystalline silica particles were detected based on electrochemically blocking the flux of the redox mediator at the surface of UME, which showed significant signal amplification in the proposed method. Our method was demonstrated for detecting crystalline silica functionalized with or without PEG, acquiring the limit of quantification (LOQ) values of 0.391 μM (23.45 μg/L) and 0.824 μM (49.45 μg/L), respectively, which confirmed that a more than two times improvement in LOQ could be achieved over the PEG functionalized silica particles. We further presented a theoretical model using finite element simulations with COMSOL Multiphysics. We deduced a quantitative relation between the distribution of the current step size and the size distribution of silica particles. Therefore, the reported method here provides a paradigm for SEE-based detection of electrochemically inert crystalline silica particles, which extends the previous report substantially concerning particle detection.

Solar Wind Protons in the Diamagnetic Cavity at Comet 67P/Churyumov-Gerasimenko.

The plasma environment at a comet can be divided into different regions with distinct plasma characteristics. Two such regions are the solar wind ion cavity, which refers to the part of the outer coma that does not contain any solar wind ions anymore; and the diamagnetic cavity, which is the region of unmagnetized plasma in the innermost coma. From theory and previous observations, it was thought that under usual circumstances no solar wind ion should be observable near or inside of the diamagnetic cavity. For the first time, we report on five observations that show that protons near solar wind energies can also be found inside the diamagnetic cavity. We characterize these proton signatures, where and when they occur, and discuss possible mechanisms that could lead to protons penetrating the inner coma and traversing the diamagnetic cavity boundary. By understanding these observations, we hope to better understand the interaction region of the comet with the solar wind under nonstandard conditions. The protons detected inside the diamagnetic cavity have directions and energies consistent with protons of solar wind origin. The five events occur only at intermediate gas production rates and low cometocentric distances. Charge transfer reactions, high solar wind dynamic pressure and a neutral gas outburst can be ruled out as causes. We suggest that the anomalous appearance of protons in the diamagnetic cavity is due to a specific solar wind configuration where the solar wind velocity is parallel to the interplanetary magnetic field, thus inhibiting mass-loading and deflection.

Boosting charge separation and transfer at the boron-triggered BiVO4 interface for efficient and stable solar water splitting

Photoelectrochemical (PEC) water splitting is a promising strategy for solar energy conversion and storage. However, poor charge transfer and sluggish water oxidation reaction restrain the PEC performance. Herein, we propose a simple and effective interface etching strategy on the semiconductor surface to modulate the photoanode/cocatalyst interface, following by the decoration of NiFeBi oxygen evolution catalyst (OEC) for significantly improved oxygen evolution activity and stability of the BiVO4 photoanode. The resultant photoanode achieves a record photocurrent density of 6.33 mA cm−2 at 1.23 VRHE under one sun illumination, over approximately 3.63 times higher than that of the pristine BiVO4. The applied bias photon-to-current efficiency of 2.3% can be attained with showing a good durability of 40 h. Systematic studies have demonstrated that the introduction of electron-deficient state of B accelerates the surface trapping hole and the charge transfer, which enhances the interfacial coupling between BiVO4 and NiFeBi OEC, and strongly drives the hole from the BiVO4 to the NiFeBi surface for capable water oxidation. Density functional theory calculations prove that the surface B treatment increases the effective number of reaction paths of OER and the density of electronic states near the Fermi energy level, which improves the electrical conductivity of the BiVO4/OEC interface. This work provides a feasible strategy for tailoring the interface engineering to significantly enhance the PEC activity and stability of the photoanodes.

Fe-doped Co3O4 nanostructures prepared via hard-template method and used for the oxygen evolution reaction in alkaline media

Low-cost and highly efficient anode catalysts are required for the oxygen evolution reaction (OER), which is integral to the commercialization of alkaline-based water electrolysis. Herein, pore size-controlled Fe-doped Co3O4 nanostructures are prepared as non-precious metal anode catalysts using a hard-template method with silica beads of different sizes, ranging from 20 to 1000 nm in diameter. The pore size distribution and specific surface area of the catalysts are measured by nitrogen adsorption/desorption analysis and mercury intrusion porosimetry. The electrochemical properties and OER performances of the catalysts are evaluated in half and unit cells, respectively. Among the catalysts studied, FCO-T-500 synthesized using 500 nm-sized silica beads exhibits the best OER activity and stability, given by a high current density of 847 mA cm−2 at 1.8 V and superior 100 h-stability during single cell test of anion exchange membrane water electrolysis. The improved OER performance of FCO-T-500 can be attributed to the optimal pore size favorable for gas diffusion and mass transport, sufficient surface OH and H2O groups produced via KOH leaching, the largest number of electrocatalytic active sites, and the fastest charge-transfer reaction.

Determining single Electrode Entropies via a novel indirect Measuring Method

The entropy is a fundamental thermodynamic parameter to describe the working principle of a battery. Its value can be determined on a full cell level, describing the entropy differences between anode and cathode. However, its origin is based on individual effects occurring on each half-cell. Here, the entropy of a single electrode towards the used electrolyte can be measured. On this level, the effect describes the heat flux at the charge transfer reaction and the temperature induced potential difference of the electrode–electrolyte interface. In this paper, a new method to determine those entropies is developed and is described in detail. As a main advantage of this method, neither half-cell temperatures differences, nor half-cell heat flows need to be identified. Instead, an unknown but equal temperature gradient is generated between two identical electrodes resulting in a voltage difference. Through the comparison of the voltage progressions of electrodes with different entropies, their individual entropy is determined, by comparing its value towards a reference. The used experimental set-up is based on common experimental cells, making it widely accessible.