Charge Transfer Reactions Research Articles

Development of Fuel Electrode Supported Solid Oxide Cell with Ni/CGO Active Layer

Increasing the current density, at which substantial lifetime can be achieved, is one way to lower the cost of solid oxide electrolysis cell (SOEC) technology. Many state-of-the-art fuel electrode supported SOECs employ Ni/8YSZ fuel electrodes. These degrade at high current density because the increased fuel electrode overpotential accelerates Ni depletion/migration and loss of percolation in the Ni/8YSZ structure. This limits maximum current density. The stability for Ni/CGO (Ce0.9Gd0.1O1.95) fuel electrodes is not documented quite as well, but several reports show very stable fuel electrode performance for Ni/CGO in electrolyte supported cells. Good fuel electrode stability with Ni/CGO was also found in our tests at 750°C above -1.1 A/cm2 as shown in Figure b). To exploit this high current density performance stability at intermediate SOEC operating temperatures (~750ºC) we are working to incorporate Ni/CGO in a co-sintered thin electrolyte cell.This contribution will give select results from our ongoing efforts to incorporate a Ni/CGO active layer into a fuel electrode supported SOEC consisting of a Ni/3YSZ support and a thin stabilized zirconia electrolyte. Half cells consisting of Ni/3YSZ support, Ni/CGO fuel electrode, zirconia electrolyte and CGO barrier layer have been successfully co-sintered, as shown in Figure a). Results from full cell tests based on these architectures will be reported.To evaluate the general feasibility of the cell concept in parallel with cell manufacturing, supporting studies have been carried out. The chemical expansion of CGO caused by strongly reducing conditions at the fuel electrode is a potential mechanical threat to the cell concept. Initial modelling has shown a technologically relevant operating range with respect to gas composition, temperature and current density where the cell is predicted by modelling to stay intact. As shown in Figure c) thermoneutral operation falls well within the boundaries of mechanically safe operation. Subsequent experimental testing has even showed that the model gave a conservative estimate of the safe range, as we were unable to enforce a mechanical failure by testing under conditions of very strong chemical expansion (predicted expansion of 2%). In-situ XRD studies revealing strain levels and phases present have been performed to elucidate why mechanical failure does not occur, even under very strong reduction.Beyond that, we are also testing the durability of Ni/CGO electrodes on commercial electrolyte supported cells to verify that stable electrode performance can be achieved under conditions relevant to fuel electrode supported SOECs with a thin electrolyte. So far these tests show no change in the polarization resistance contribution from the charge transfer reaction denoted Rp,lf, after operation at 0.5-1.3 A/cm2 regardless of current density. Figure 1

Inkjet Printing of PrBa0.5Sr0.5Co1.5Fe0.5O5+ δ Cathode for High-Performance Proton Ceramic Fuel Cells

Ceramic fuel cells have been actively studied and are in the commercialization stage because of their economic and efficiency advantages, including the lack of precious metal catalysts, including Pt, fuel flexibility, and high efficiency. Solid oxide fuel cells (SOFCs) are the most typical type of ceramic fuel cell that conduct oxide ions. However, the operating temperature of SOFCs is high (>700 °C) owing to the high activation energy required for ion conduction. Prolonged operation at high temperatures can cause chemical and mechanical degradation in materials and peripheral parts, discouraging their use as long-time stationary generators, which is the main target market for SOFCs. For these reasons, expectations and interest in proton ceramic fuel cells (PCFCs) have recently increased owing to excellent power and durability exhibited at intermediate temperatures (<600 °C). According to recent reports, the durability of PCFC is superior to that of SOFC, even when methane fuel or city gas is used. The cathode reaction accounts for the highest resistance in PCFC operation. Therefore, the development of a high-performance cathode is the biggest factor for the success of PCFCs. To develop a high-performance cathode, the following factors must be optimized: 1) surface and interface shapes and components that can maximize the charge transfer reaction, and 2) porous microstructure that can effectively deliver oxygen gas to the reaction sites, and 3) electrolyte-electrode adhesion at the interface. The potential of inkjet printing (IJP) as a fabrication technology capable of optimizing these structures and components was recently confirmed by our group. IJP has attracted attention as a thin-film deposition technology that can produce complex and sophisticated microstructures, such as various multi-component ceramic materials, while controlling them at the nano-level. Recently, solution processes such as spin coating, tape casting, and screen printing have been frequently adopted in device manufacturing owing to their advantages such as simple accessibility and convenient management. However, fabricating films with nanoscale thickness is very difficult. Moreover, the precision with which a microstructure with the desired shape can be fabricated is limited. Conventional thin-film processes, such as physical vapor deposition and chemical vapor deposition, require complex and difficult deposition conditions, such as high-temperature or high-vacuum maintenance. In addition, equipment management is difficult, a large number of parts and a large system are required, and large-area deposition is highly challenging. Meanwhile, in the case of IJP technology, it is feasible to deposit high-quality nanoscale thin films relatively conveniently without requiring vacuum or temperature maintenance. Furthermore, they can be manufactured over large areas. IJP can be used to conveniently fabricate various patterns in the desired shape without masking or lithography. Moreover, it can precisely control the concentration and combination of printing inks to produce thin films with desired material compositions and microstructures. We successfully fabricated perovskite-type PBSCF cathodes for PCFCs using thermal inkjet printing (T-IJP) on a BaZrxCe0.8-xY0.1Yb0.1O3-δ electrolyte using an inexpensive desktop printer. Ceramic ink solutions were formulated using PBSCF nanopowder as a solid material and dispersed in anhydrous ethanol/propylene glycol methyl ether (PGME)-based solvents. The ink properties were improved by adding various polymers such as surfactants and dispersants. Printability was verified by analyzing the viscosity, surface tension, and particle size of the pigments. The shape and microstructure of the PBSCF cathode layer were successfully adjusted by controlling the number of printing cycles and grayscale value (color level) using commercial printing software. We verified the tendency of these specimens by observing the images using a scanning electron microscope (SEM) equipped with energy dispersive spectra. We also conducted performance evaluations and electrochemical impedance spectroscopy (EIS). Finally, we obtained an optimized PBSCF cathode (G-80) with adequate thickness and a favorable number of pores and cracks. The samples had identical thicknesses of 6–7 μm. This enabled a more reliable and accurate comparison and examination of the tendencies of the specimen microstructures by using grayscale values. We enhanced the performance compared to that of our previous T-IJP work. Among the four specimens measured in this study, G-80 attained a high power output of 728 mWcm-2 in the sub-IT regime (< 600 °C). This performance is higher than that achieved in previous similar studies.

Tunable Conformal Electrodeposition of Ultra-Thin Polymeric Films for Electrolyte Interphases

Functional coatings and interphases influence the stability and performance parameters of electrodes in various applications. Polymer thin films offer a wide range of molecular structures and compositions for tunable functionalities that can be custom designed to the needs of an application. In solid-state energy storage devices in particular, electrolyte-type polymeric interfaces between battery components and materials with disparate functions, such as the active electrode material and solid electrolyte could overcome some of these incompatibility detriments and the increase in contact resistance over long-term operation. In high-performance micro scale power sources, 3D thin-film all-solid-state batteries show great potential as they take advantage of both short ion diffusion distances for high-rate capability with low heat generation, as well as the third dimension for high material loading and energy density. Therefore, conformal deposition methods for ultra-thin polymeric electrolyte interphases on the interior surface of electrodes with mesoscale 3D architectures and complex porosity are in demand. Here, we report a molecular design concept of dual-functional molecules that contain electrochemically active end groups for self-limiting electropolymerization, and a core molecular motif that determines the thin film functionality. The electrodeposition of this monomer represents a non-line-of-sight coating method for polymer thin films with independently tailorable functionalities and tunable properties on conductive substrates with arbitrary shape. We exemplify this method using monomers with poly(ethylene glycol) (PEG) as the core motif for lithium-ion transport and phenol as electrochemically active end groups. We studied the electrodeposition of the monomers, poly(ethylene glycol) diphenol (PEGDP), and demonstrate their self-limiting film formation mechanism (Figure 1a) which originates from the insulating nature of resulting poly(PEGDP) film that confines the charge transfer reaction. We present an exhaustive exploration of their material-processing-structure-property relationships that reveals the multi-scale control over the ultrathin-film properties. For example, the uniform film thickness is tunable from 10 to 100s of nanometer through electrodeposition conditions and molecular design, while their molecular permeability and electronic resistance can be tailored from pervious to fully blocking. We show that the electrodeposited functional interphases fully coat complex 3D electrode architectures (Figure 1b top: uncoated carbon electrode, bottom: film coated carbon electrode) with retention of their functionality in a battery. This work demonstrates that rational molecular design enables the conformal electrodeposition of ultrathin functional coatings with solid polymer electrolyte properties on 3D structured electrodes that will enable designer interphases in various solid-state battery architectures and chemistries. Figure 1

Operando odd random phase electrochemical impedance spectroscopy (ORP-EIS) for in-situ monitoring of the Zr-based conversion coating growth in the presence of (in)organic additives

Operando odd random phase electrochemical impedance spectroscopy (ORP-EIS) is introduced as an in-situ monitoring tool to directly monitor the conversion treatment of zinc in a hybrid Zr-based solution containing aminosilane and Cu additives. SEM and EDX are applied to investigate the morphology and elemental composition of the oxide film. Results show that the operando ORP-EIS provides an opportunity to investigate the growth of the conversion layer and its surface homogeneity as well as the charge transfer reaction during conversion. Moreover, the presence of aminosilane in the Zr solution containing Cu improves the morphology and barrier properties of the conversion film.

Switching mechanisms of CMOS-compatible ECRAM transistors—Electrolyte charging and ion plating

To elucidate the internal chemical physics of measured CMOS-compatible electrochemical random-access memory (ECRAM) devices, we constructed a 2D semiconductor device simulation, including ions and electrochemical reactions, and used it to fit measured devices. We present the results of a device simulation model that includes Cu+ ions’ diffusion and the charge transfer reaction between the WOx conduction band electron and Cu+ (i.e., “Cu plating”). Reproducing the linear response of ECRAM devices, the effect of charging HfOx by the Cu+ ions is sufficient, and WOx is not being doped by the Cu+ ions. While potentiation is supported by the formation of an electron channel, an efficient depression requires the formation of high positive charge density at the channel material. At higher Cu+ flux, Cu+ reaches and penetrates the WOx layer. While this effect enhances the potentiation response, it also initiates the “plating” reactions. Including this reaction is essential to reproducing the data of devices exhibiting sub-linear responses. We suggest that electron trapping by ions (i.e., plating) would constitute a long-term degradation process even for H+ based devices.

Corrosion behavior of Zn in electrolyte during the charge and discharge process and its influence on the electrochemical performance of zinc doped Mg2Ni1-xZnx rapidly quenched alloys

In the electrochemical process, a continuous passivation layer of Mg(OH)2 is formed on the surface of Mg2Ni alloy particles and prevents the penetration of hydrogen atoms, which have a negative impact on the discharge capacity. In this work, Mg2Ni1-xZnx (x = 0, 0.17, or 0.33) rapid quenching alloys were prepared by partially replacing Ni with Zn in order to modify the surface of the alloy with the corrosiveness of Zn in alkaline solution. The microstructure results indicate that Zn doping promotes the corrosion of Mg2Ni alloy in the electrolyte, and many corrosion holes are formed on the surface after the electrochemical process. With the increase of Zn, the charge-transfer reaction resistance (Rct) and polarization resistance (Rp) of the alloy electrode increase from 306.24 and 366.41 mΩ to 508.76 and 526.57 mΩ, respectively, and the corrosion current density (Io) decreases from 70.08 to 48.77 mA/g. The appropriate amount of Zn atoms increases the discharge capacity, and the highest value can reach 92.94 mAh/g at x = 0.33. This reveals that corrosion holes are formed on the surface of Zn-doped alloys during the electrochemical process and destroy the continuity of the passivation layer on the Mg2Ni surface, which facilitate the penetration of hydrogen atoms.

Electron and Ar+ interaction with Mo(CO)6 at thermal energies; energetic limit on removal of 5 ligands from Mo(CO)6.

The rate constant for electron attachment to Mo(CO)6 was determined to be ka = 2.4 ± 0.6 × 10-7cm3s-1 at 297K in a flowing-afterglow Langmuir-probe experiment. The sole anion product is Mo(CO)5-. A small decline in ka was observed up to 450K, and decomposition was apparent at higher temperatures. The charge transfer reaction of Ar+ with Mo(CO)6 is exothermic by 7.59 ± 0.03eV, which appears to be sufficient to remove the first 5 ligands from Mo(CO)6+.

Imaging of the charge-transfer reaction of spin-orbit state-selected Ar+(2P3/2) with N2 reveals vibrational-state-specific mechanisms.

Charge-transfer reactions are ubiquitous and play important roles in various gaseous environments, but, despite a long history of extensive research, our understanding of their dynamics at the quantum state-to-state level is still lacking. Here we report quantum-state-resolved experiments for the paradigmatic charge-transfer reaction Ar+ + N2 → Ar + N2+ using a three-dimensional velocity-map imaging crossed-beam apparatus with the Ar+ beam prepared exclusively in the spin-orbit state 2P3/2. High-resolution scattering images show strong dependence of rotational and angular distributions on the vibrational quantum number of the N2+ product. Trajectory surface-hopping calculations, which semi-quantitatively reproduce the experimental observations, support the existence of two distinct charge-transfer mechanisms. One of these, in the dominant N2+(v' = 1) channel, is the well-known long-distance harpooning mechanism. However, the highly rotationally excited products in the forward direction are attributed to a hard-collision glory scattering mechanism, which occurs on account of the strong attraction between the collisional partners counterbalanced by the short-range repulsive interaction.

Assessing the role of asymmetric charge transfer reactions in analytical glow discharges in argon

Charge transfer reactions between argon ions and analyte atoms occur at a much higher rate in analytical glow discharges than in other similar plasmas, as follows from experimental Boltzmann plots of glow discharge emission spectra and the spectra generated by an inductively coupled plasma. A simple model of a Grimm-type discharge suggests that charge transfer-excited emission of the analyte elements comes largely from the cathode sheath, due to a high collision rate between the sputtered analyte atoms and argon ions accelerated in the cathode fall. The contribution to this radiation from the negative glow is several times lower. The mentioned enhancement of the charge transfer-excited emission in the cathode sheath is, however, not sufficiently high to explain the anomalously high rates of those charge transfer reactions relative to other plasmas. The different characteristics of emission from the cathode sheath and the negative glow also means that Boltzmann plots of glow discharge spectra cannot be interpreted in the conventional way. Further work is needed to explain the observed features of glow discharge excitation, as reflected in the emission spectra.

Molecular level interaction of solvents (water, benzene and DMSO) analysis of the 2-Bromo-6-nitrotoluene's reactive charge transfer, docking, and spectroscopic properties

The chemical structure of 2-Bromo-6-nitrotoluene was optimized using the B3LYP/6–311++G (d, p) basis set and density functional theory. Calculations were made on the molecules of the substance 2-Bromo-6-nitrotoluene's geometrical-parameters. A variety of DFT techniques, including border atomic orbitals, essential binding orbitals, local reaction descriptors, and molecular electrostatic potentials, are worn to test the reactivity of molecules. Several solvents (water, benzene and DMSO) were examined by UV–vis spectroscopy and vapor phase electronic transition. Estimated efficiency for the most heavily inhabited molecular orbital and even the least vacant molecular orbital describes electron excitation properties. Environmental toxicity, pharmacological similarity, localized orbital location, and electron localized function were assessed. To evaluate the material's metabolic processes, chemical interaction modelling was used. In conclusion, this paper offers a thorough investigation combining spectroscopic and quantum computational methods to evaluate the metabolic function and solvation impact of selected therapeutic substances. The information gathered is therefore very useful in planning for future study.

Tuning the Electronic Structures of TMNs‐Modified Ni‐Based Catalysts to Enhance the Performance for MOR in Alkaline Media

AbstractTransition metal nitrides are considered as the promising materials in the energy conversion processes due to the similar electronic structures to Pt. In this work, a series of Ni/TMN−C (TM=V, Mo, Nb, Ta) catalysts were synthesized and investigated the catalytic performance for methanol oxidation reaction in alkaline media. The electrochemical measurements indicated that the TNNs‐modified Ni/C catalysts exhibited higher activity, kinetics, charge transfer and stability for alkaline MOR compared with Ni/C. It was found that the incorporation of TMNs improved the activity and stability for MOR in various degree. Specially, Ni/VN−C showed the highest catalytic activity, nearly three times higher than that of Ni/C due to the highest coverage of the surface component NiOOH, consistent with the Tafel and EIS results that it exhibited the fastest charge transfer kinetics and reaction rate. XPS characterization indicated that the obvious electron interaction occurred between the TMNs and Ni species and Ni would transfer electrons to the transition metal nitrides, resulting in the electron‐rich states of TMNs. Interestingly, combining the d‐band center and activity of the corresponding catalysts, it could be found that a volcano plot existed between them, suggesting that the introduction of appropriate nitrides would change the electronic structure of Ni and enhance the catalytic performance for MOR in alkaline media.

Computer-simulated degradation of CF3Cl, CF2Cl2, and CFCl3 under electron beam irradiation

Abstract Electron beam treatment technologies should be versatile in the removal of chlorofluorocarbons (CFCs) owing to their exceptional cross sections for the thermal electrons generated in the radiolysis of air. Humidity, dose rates, O2 concentration, and CFC concentration influence the efficiency of the destruction process under electron beam treatment. Computer simulations have been used to theoretically demonstrate the destruction of chlorotrifluoromethane (CF3Cl), dichlorodifluoromethane (CF2Cl2), and trichlorofluoromethane (CFCl3) in the air (N2 + O2: 80% + 20%) in room temperature up to a dose of 13 kGy. Under these conditions, it is predicted that the removal efficiency is in the order CF3Cl (0.1%) &lt; CF2Cl2 (7%) &lt; CFCl3 (34%), which shows the dependence of the process on the number of substituted Cl atoms. Dissociative electron attachment with the release of Cl– is the primary process initiating the destruction of CFCs from the air stream. Reactions with the first excited state of oxygen, namely, O(1D), and charge-transfer reactions further promote the degradation process. The degradation products can be further degraded to CO2, Cl2, and F2 by prolonged radiation treatment. Other predicted products can also be removed through chemical processes.

Thiols as Powerful Atom Transfer Catalyst: Opportunities in Photoredox‐Mediated Reactions

AbstractThe employing visible light to drive organic transformations is the most promising choice to meet the needs for green synthesis, in which the reactions promoted by visible light may provide a more efficient and greener method. Currently, the most abundant methods for activation and functionalization of reaction substrates have relied on the direct single‐electron transfer (SET) between the excited photocatalyst and substrates, and these wonderful works were summarized and docoumented in many reviews. As a complement to the above reactions, the photoredox‐mediated atom transfer transformations (photocatalyst‐to‐HAT catalyst‐to‐substrates) to generate radical species are showing an explosively growing trend. In this review, we highlight recent significant developments in this rapidly growing area, mainly focusing on the photoinduced base‐to‐substrates charge transfer reactions.

Highly active Co2P/2H-1T MoS2 cocatalyst with fast charge transfer and H2 production reaction toward effective photocatalytic activity of P-TiO2

Cobalt phosphide (Co2P) and molybdenum sulfide (MoS2) have been shown to be efficient cocatalysts for photocatalytic H2O splitting reactions in hydrogen (H2) production. However, maintaining remarkable stability while obtaining high photocatalytic efficiency remains challenging due to the limited optical absorption. Herein, Co2P and MoS2 nanospecies were securely mounted as cocatalysts on phosphorous-titanium dioxide (TiO2) nanobelts to achieve increased activity and stability for photocatalytic H2 evolution. The photocatalytic H2 yield of the 2Co2P/P-TiO2/2H-1T MoS2 material driven by visible light was 4156 μmol/g, which was 129 and 2.3 times higher compared to those of TiO2 (32 μmol/g) and 2H-1T MoS2/TiO2 (1800 μmol/g), respectively. In particular, 2Co2P/P-TiO2/2H-1T MoS2 exhibited consistently stable photocatalytic H2 evolution while undergoing more than eight cycles of reactions for a total of 8 h. A thorough understanding of the modification effect of the Co2P and 2H-1T MoS2 nanospecies reveals that the modification strongly promotes the migration and separation of photoinduced electron-hole pairs and increases the interaction at the heterointerfaces between the Co2P and 2H-1T MoS2 nanospecies and P-TiO2 nanobelts. This study broadens the potential use of Co2P and 2H-1T MoS2 as co-catalysts for the photocatalytic conversion of solar energy to chemical energy.

Engineering surficial atom arrangement on α-SnWO4 film for efficient photoelectrochemical water splitting

Achieving high-efficient photoelectrochemical (PEC) water splitting requires great charge transfer and excellent surficial reaction activity. To improve the PEC performance of α-SnWO4 photoanode, the atomic ratio of Sn and W on the surface of the α-SnWO4 photoanode is subtly adjusted by exposing the α-SnWO4 photoanode to a Sn2+ or H+-rich microenvironment, which is considered to determine the coordination environment of active sites. Increasing the content of tin on the surface can shift the work function to vacuum level and up-regulate the band-edge position, and the difference between the energy band of bulk and surface facilitates transferring photo-generated carriers to the surface. Besides, the tin atom as the actives sites is in favor of the water oxidation reaction compared to the W atom as termination. Thus, the faster charge separation and enhanced hole injection ability lead to the 1st-order reaction behavior of water oxidation on the tin-rich surface, while the tin-poor surface presents 2nd-order behavior. As a result, the Tin-rich SnWO4 photoanode (1.05 mA cm−2 at 1.23 V vs. RHE in 0.2 M KPi) shows 2 folds photocurrent of Tin-poor SnWO4 photoanode, which is the state-of-the-art photocurrent density of the material so far. This study provides a path for understanding the effect of surface termination, and the method for engineering surface can easy to be used for other metal oxide photoelectrodes.

Proton-Coupled Electron Transfer at the Surface of Polyoxovanadate-Alkoxide Clusters.

ConspectusProton-coupled electron transfer (PCET) is a fundamental process involved in all areas of chemistry, with relevance to biological transformations, catalysis, and emergent energy storage and conversion technologies. Early observations of PCET were reported by Meyer and co-workers in 1981 while investigating the proton dependence of reduction of a molecular ruthenium oxo complex. Since that time, this conceptual framework has grown to encompass an enormous scope of charge transfer and compensation reactions. In this Account, we will discuss ongoing efforts in the Matson Laboratory to understand the fundamental thermodynamics and kinetics of PCET processes at the surface of a series of Lindqvist-type polyoxovanadate clusters. This project aims to provide atomistic resolution of net H atom uptake and transfer at the surfaces of transition-metal oxide materials.First, we discuss our efforts aimed at understanding PCET at metal oxide surfaces using the Lindqvist-type polyoxovanadate-alkoxide (POV-alkoxide) cluster [nBu4N]2[V6O13(TRIOLNO2)2]. These clusters reversibly bind H atom equivalents at bridging oxide sites, mirroring the proposed uptake and release of e-/H+ pairs at transition-metal oxide surfaces. Summarized results include the measurement of bond dissociation free energies of surface hydroxide moieties (BDFE(O-H)) as well as mechanistic analyses that verify concerted proton electron transfer as the operative pathway for PCET at the surface of POV-alkoxide clusters.Next, we discuss net proton and H atom uptake at the surface of reduced variants of the Lindqvist-type POV-alkoxide cluster, [V6O7(OR)12]n (R = Me, Et; n = -2, -1, 0, + 1). In the case of these low-valent POV-alkoxide clusters, nucleophilic bridging sites are kinetically inhibited by functionalization of the cluster surface with organic ligands. This molecular modification enables site-selectivity in proton and H atom uptake to terminal oxide sites. The impact of reaction site and cluster electronics on reaction driving force of PCET is explored, with core electron density playing a critical role in dictating thermodynamics of H atom uptake and transfer. Additional work described here contrasts the kinetics of PCET at terminal oxide sites to the reactivity observed at bridging oxides in POV-alkoxide clusters.Overall, this Account summarizes our foundational knowledge regarding the assessment of PCET reactivity at the surfaces of molecular metal oxides. Drawing analogies between POV-alkoxide clusters and nanoscopic metal oxide materials provide design principles for the advancement of materials applications with atomic precision. These complexes are additionally highlighted as tunable redox mediators in their own right; our studies demonstrate how cluster surface reactivities can be optimized by modifying electronic structure and surface functionalities.

Boosting the activity and CO tolerance for methanol oxidation reaction in alkaline media by constructing the Pt-TMNs electrocatalysts

Developing the efficient and high CO tolerance electrocatalysts is important for methanol oxidation reaction. In this study, a sequence ofcatalysts were constructed by introducting various transition metal nitrides (TMNs) to modify the Pt/C catalyst. The corresponding electrochemical performance were evaluated to investigate the activity, kinetics, charge transfer rate, CO tolerance and stability for MOR in alkaline media. Based on the structural characterization analysis from ICP-MS, XRD, HRTEM and XPS, it could be indicated that the participation of TMNs mainly brought the electronic effect, but not for the geometric effect. The evident difference did not exist in the nanoparticle size, morphology and crystallinity of the related catalysts. After the evaluation on the catalytic performance for alkaline MOR, The TMNs-modified catalysts exhibited higher activity and lower onset potential potential compared with the commercial Pt/C. Among them, Pt-NbN/C showed the highest mass activity with 9.56-fold that of the commercial Pt/C. The faster charge transfer kinetics and reaction rate were confirmed by Tafel and EIS results. CA measurements indicated that they also exhibited higher stability and anti-CO poisoning ability for alkaline MOR, consistent with the CO stripping experiments. To quantitatively describe the realtionship of the electronic effect on the catalytic activity and CO tolerance, the d-band center was employed as a parameter to bulid the corresponding function. Interestingly, it was proposed that the rational d-band center could lead high MOR performance and anti-CO poisoning ability. The introduction of TMNs brought the evident shift of the Pt d-band center and boosted the catalytic activity and anti-CO poisoning ability for alkaline MOR.

Calculating of square-wave voltammograms—a practical on-line simulation platform

Square-wave voltammetry (SWV) is a widely used technique for getting insight into mechanistic and kinetic aspects of various electrochemical reactions. To date, this pulse-voltammetric technique has been utilized in numerous electrochemical studies and it remains one of the most sophisticated electrochemical methods available. As a result of its higher sensitivity and its potential to provide insights similar to cyclic voltammetry for electrode mechanisms characterization, the SWV is increasingly being included in undergraduate electrochemistry laboratory curriculums. The features of experimental SW voltammograms are affected by various factors, such as kinetics of charge transfer, diffusion, adsorption phenomena, and chemical reactions coupled to electron transfer step. To understand some of the physical and chemical phenomena hidden in a single experimental SW voltammogram, it is inevitable to get a help of computer simulations. The purpose of this article is to offer a basic introduction to SWV written in a simple language, intended to engage students and familiarize them with the fundamentals of this technique. The ultimate objective is to provide the aspiring young electrochemists with a simulation procedure using the MATHCAD software, which can be employed to compute SW voltammograms following a rather easy simulation approach. A detailed tutorial on simulating SW voltammograms with MATHCAD software is presented. The simple tutorial offers a step-by-step breakdown of the simulation process of a square-wave voltammogram. Additionally, a MATHCAD ready-to-use file for simulation of a common electrode mechanism is provided. The current work aims to assist undergraduate students in learning about electrochemical simulations that serve as a corner stone to more advanced studies in SWV.

Electrochemical Hydrogen Storage Kinetics and Microstructure of the Rapidly Quenched Alloy Mg2Ni0.75Zn0.25

The Mg2Ni0.75Zn0.25 alloys are prepared from Mg2Ni as master alloy and pure Zinc ingot by remelting process in this work. The microstructures, electrochemical properties and desorption kinetics of the as-cast and melt-spun alloys are investigated. The phase compositions and microstructures of the alloys are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD). The results show that the segregation atoms rich in Zn can inhibit the growth of Mg2Ni grains, especially the nanocrystalline grains formed in Mg2Ni0.75Zn0.25 alloy after melt-spinning process. The rapidly quenched Mg2Ni0.75Zn0.25 alloy exhibits the largest discharge performance (102.1 mAh g−1) and dehydrogenation activation energy (14.68 kJ mol−1). The improvement of the kinetic properties is related to the hydrogen diffusion rate (D) in the alloys and the charge transfer reaction on the surface. The rapidly quenched Mg2Ni0.75Zn0.25 alloy has the largest D, 6.187 × 10−11 cm2 s−1. The doping of Zn aggravates the corrosion of alloy electrodes, which destroys the oxide layer on the alloy surface, provides a channel for the diffusion of hydrogen atoms.

The effect of the SEI layer on the electrochemical impedance in the graphite/ Li[Ni0.5Mn0.3Co0.2]O2 lithium-ion full cells

In this work, we investigated the effect of the solid-electrolyte interface (SEI) on the charge transfer reaction on the negative electrode by the electrochemical impedance spectroscopy method. Also, the results were evaluated for the two types of full cells with lithium bis(trifluoromethanesulfonyl)imide and without additives to create different SEI layers on the graphite. Here we employed an equivalent circuit for full cells and evaluated high and low-frequency semicircles in four tests. The middle frequency was considered to the charge transfer and SEI layer resistance. Exposure to longer holding times at constant potential resulted in less change for the middle-frequency component than shorter holding times. The higher and lower resistance changes were attributed to the growth of the inner and outer SEI layers on the graphite surface. Also, the cell containing additive showed a lower rate of resistance change and lower activation energy for the middle-frequency semicircle. Improved SEI layer led to lower electrolyte reduction on the negative electrode surface. The XPS analysis confirmed the growth of the outer layer on the inner layer after a long hold time and the lower growth of the SEI layer in the presence of the additive.