Electrode Measurements Research Articles

Electrochemical Impedance Spectroscopy to Evaluate the Adsorption and Structural Changes of Liposome Dependent with Surface Charge

Liposome is well known as mimicking a cell, which is composed of lipid bilayer membrane. Liposome is spherical shape and formed by amphiphilic molecules, meaning that outer layer is composed of hydrophilic molecules and inner layer is composed of hydrophobic molecules. Evaluation of adsorption and rupture of liposome on a surface is very important to drug delivery system (DDS) or understand the capability of the cell.Many studies reported the adsorption and interaction of lipid bilayer using highly sensitive sensing methods without labeling such as quartz crystal microbalance (QCM), plasmonic devices such as SPR, LSPR and SERS, and electrochemical impedance spectroscopy (EIS). We focus on EIS as an evaluation tool for adsorption and rupture of liposome, since EIS is highly sensitive to the surface condition of the electrode and electrochemical measurement is simple.EIS is very sensitive to the surface condition of the electrode. We report here that surface charge is very important to evaluate the adsorption and interaction of liposome on the electrode surface, which are controlled by using self–assembled monolayer (SAM). So far as we know, there are little reports focusing on surface charge evaluate the adsorption and interaction of liposome on the electrode surface. Here, we report the effect of surface charge on electrochemical reactions due to SAMs which were coated on the Au electrode.Liposome preparation was described below. Thin organic film was formed with 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC). Then we obtained solution including DOPC which diameter was lower than 220 nm because the solution was filtered 20 times through the syringe filter (pore diameter was 220 nm). We used 1-Dodecanethiol (DDT), 11-Mercapto-1-undecanol (MUD or 11–HUT: 11–Hydroxy–1–undecanthiol) and 11-Amino-1-undecanthiol (11–AUT) for the SAM. These chemicals have same straight–chain alkane with thiol group to bind with Au surface, but head group is changed as CH3 for DDT meaning that the surface is neutral and hydrophobic, CH2OH for MUD meaning that the surface is charged negative and hydrophilic and CH2NH2 for 11–AUT meaning that the surface is charged positive and hydrophilic. Thus, we can discuss about the characteristics of Rct dependent with head group of SAM on the detection of liposome adsorption and rupture. As the results, most sensitive surface was obtained on use of 11–AUT in this study. In addition, we estimated the critical micelle concentration (CMC) of a surfactant, Triton–X 100, on the rupture process of liposome.As an example of results, we show two type of hydrophilic surface, type A and B. Type A was coated with 11-Mercapto-1-undecanol, which surface had hydroxy group and was negatively charged. Type B was coated with 11-Amino-1-undecanol, which surface had amino group and was positively charged.At first, we discussed about the results on type A. Fig. 1(Type A) shows Nyquist plots according to adsorption and rupture of liposome. After the adsorption of liposome, Rct decreased drastically. This characteristic was caused by surface charge after the liposome adsorption. As written above, the hydroxyl surface was charged negatively which repel the redox probe. After the liposome adsorption, surface charge changed to positive because the surface of DOPC was charged positively, which attracted the redox probes by charge polarity. After adding the surfactant, Rct increased and was almost same as that before the liposome adsorption. Next, we discussed about the results on type B. Fig. 1(Type B) shows Nyquist plots according to adsorption and rupture of liposome. After the adsorption of liposome, Rct increased drastically due to steric barrier of liposome. In this case, liposome adhered on the surface by hydrophilic interaction. Surface charge was not changed via liposome adsorption. After adding the surfactant, Rct decreased and was almost twice comparing with that before the liposome adsorption. This data show that ruptured liposome and/or surfactant adhered on the electrode surface. As discussed above, the amino surface was superior to detect adhesion and rupture of liposome comparing with other electrodes which coated with/without methyl and hydroxy SAM, when [Fe(CN)6]3-/4- was used as redox probes because of mixed surface conditions such as hydrophilicity and electric charge. Figure 1

Highly Active Fe-N/C Oxygen Electrocatalysts Based on Silicon Carbide Derived Carbon

Extensive research is currently being conducted in the field of non-platinum group metal oxygen reduction catalysts for low-temperature fuel cells1,2. Many of the synthesis methods used to produce these novel materials involve grinding the precursors in a planetary ball mill3,4. Consequently, more information is needed to understand how this procedure affects the physical properties of the resulting carbon-based materials. Additionally, it is crucially important to investigate the influence of the physical properties on the electrochemical performance of the electrocatalysts.In this work, several Fe-N/C type electrocatalysts were synthesized from silicon carbide derived carbon via ball milling. A number of parameters, such as grinding mode and ball diameter, were changed in order to study their effect on both the physical and electrochemical properties of the Fe-N/C catalysts. The main characterization methods used in this study were N2-sorption and laser diffraction, which provide insight into the pore and particle size distributions of the materials, respectively.From the rotating disc electrode measurements it is clear that highly active Fe-N/C catalysts can be successfully synthesized using a facile two-step process involving ball milling and pyrolyzing. Changing the ball milling parameters has a considerable effect on both the surface morphology as well as particle size distributions of the studied Fe-N/C catalysts. As a final step, the importance of these changes in the physical properties was studied in a single cell experimental setup. B.-Y. Song, M.-J. Li, Y.-W. Yang, and Y.-L. He, J. Clean. Prod., 249, 119314 (2020) http://www.sciencedirect.com/science/article/pii/S0959652619341848.D. Banham, J.-Y. Choi, T. Kishimoto, and S. Ye, Adv. Mater., 31, 1804846 (2019) https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201804846.S. Ratso et al., ACS Appl. Energy Mater., 2, 7952–7962 (2019) https://doi.org/10.1021/acsaem.9b01430.M. J. Workman et al., J. Power Sources, 348, 30–39 (2017) http://www.sciencedirect.com/science/article/pii/S0378775317302410. Figure 1

Use of in Situ Synchrotron Techniques to Probe the Oxidized Surface of Molybdenum Nitride Oxygen Reduction Electrocatalysis

The development of active and stable earth-abundant catalysts for the oxygen reduction reaction (ORR) is needed for widespread, economic development of fuel cell technologies. Designing and optimizing these non-platinum group metals is challenging, however, because they are susceptible to composition and structure changes, including dissolution, oxidation, and corrosion, both in air and under reaction conditions. To identify the active surface, and thus understand the properties that affect activity, the catalyst surface must be characterized in situ. Herein, we utilize a grazing incidence electrochemical cell to investigate in situ composition and morphology changes of a molybdenum nitride (Mo-N) thin film catalyst using grazing incidence x-ray absorption spectroscopy (GI-XAS) and x-ray reflectivity (XRR). In rotating ring disk electrode measurements, we find that the activity, selectivity, stability, and capacitance of the Mo-N catalyst is dependent on the maximum potential to which it has been exposed. Specifically, the overpotential required to reach -2 mA cm-2 geo decreases by over 90 mV when the maximum potential is increased from 0.3 to 0.8 V vs RHE (Figure 1). Because the Mo-N oxidizes rapidly in air, ex situ characterization methods including x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry can provide only limited insight into these in situ catalyst changes. Using in situ GI-XAS measurements at applied potentials between 0.3 and 0.9 V vs RHE, however, we are able to determine that the surface of the film oxidizes and becomes more amorphous when exposed to increasingly higher potentials (Figure 1). Furthermore, the surface remains oxidized on the order of several hours when returned to “ORR relevant potentials” (< 0.6 V vs RHE), indicating that this surface-oxidized nitride is the active surface for ORR. Using in situ XRR measurements, we find that there is no change in surface roughness at potentials below 0.7 V vs RHE, but the film roughens significantly at 0.8 V vs RHE, correlating with ex situ measurements of Mo dissolution at this potential (Figure 1). We therefore conclude that the intrinsic activity of the Mo-N catalyst increases when exposed to potentials up to 0.7 V vs RHE, while above that potential activity enhancements are due to the exposure of more active sites through dissolution. The in situ electrochemical surface-sensitive x-ray characterization as used here is a promising methodology for understanding and leveraging surface dynamics to improve the performance of non-traditional catalysts.Figure 1. RRDE measurements in O2-saturated 0.1M HClO4 at 1600 rpm and schematics illustrating how the catalyst composition and morphology change with applied potential. Figure 1

Oxygen Reduction Reaction Activity of Nanocolumnar Pt Thin Film Electrocatalyst Deposited on Carbon Support By High Pressure Sputtering

Proton-exchange membrane fuel cell (PEMFC) is one of the most important sources of clean energy especially for automotive applications, which currently utilizes platinum nanoparticles dispersed on carbon (Pt/C) as a catalyst. However, the catalyst activity and durability need to be improved and the cost of the fuel cell need to be reduced for successful commercialization. Extensive research has been done to improve the catalyst activity and durability, reduce the amount of platinum used and reduce its manufacturing cost. Continuous thin film layer approach is a promising candidate for non-conventional catalysts to address these challenges. For this purpose, nanocolumnar Pt thin film (Pt-TF) layers supported on carbon was fabricated by high pressure sputtering (HIPS) and investigated as oxygen reduction reaction (ORR) electrocatalysts for PEMFCs. HIPS is a simple physical vapor deposition method that is scalable and easily applicable to industrial sputter deposition systems, in which atoms come to the substrate surface with oblique angles and form columnar structures. Different Pt-TF/C weight ratios ranging from 5% to 20% and Pt:Ni (1:3) TF/C were studied. Weight loading was controlled by changing the sputter deposition time. X-ray diffraction analysis revealed the existence of Pt and formation of the Pt:Ni alloy on carbon support. Electrochemical characterization of the carbon-supported Pt-TF samples was conducted by cyclic voltammetry and rotating disk electrode measurements in an aqueous perchloric acid electrolyte. The electrochemically active surface area, mass activity and specific activity of the Pt-TF/C samples were found to be increasing as the Pt-TF/C ratio was increased.

Oxygen Reduction Reaction Activity of Nanocolumnar Pt:Ni Alloy Thin Films By High Pressure Sputtering

Self-supported nanocolumnar Pt-Ni alloy thin films (TFs) with different Pt:Ni compositions and Pt mass loadings were fabricated by high pressure sputtering (HIPS) on a microporous layer (MPL)-like surface composed of carbon particles in order to mimic the catalyst-coated gas diffusion layer (gas diffusion electrode) in a membrane electrode assembly and investigated as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte membrane fuel cells. HIPS is a simple physical vapor deposition method that is scalable and easily applicable to industrial sputter deposition systems. At high working gas pressures, columnar and less-dense structures are formed because of angular distribution of sputtered atoms that leads to a shadowing effect. Cauliflower-like microstructures were observed from scanning electron microscopy imaging. X-ray diffraction and quartz crystal microbalance analysis revealed that by simply changing the relative deposition power between Pt and Ni source, different Pt:Ni compositions can be achieved. Benchtop cyclic voltammetry and rotating disk electrode measurements were performed for electrochemical characterization of the Pt:Ni-TF/MPL-like-layer/glassy-carbon samples in an aqueous perchloric acid electrolyte. The electrochemically active surface area (ECSA) ranged between 22-42 m2/g for varying Pt:Ni compositions. Lower Pt mass loadings showed a higher ECSA likely due to smaller nanocauliflower diameters, while the ORR activity of all compositions increased as the Pt mass loading is increased. The catalytic performance of the Pt:Ni-TFs increased in the order of 3:1 < 1:1 < 1:3 with the 1:3 films exhibiting a specific activity of 1781 µA/cm2 and mass activity of 0.66 A/mg, indicating efficient catalyst utilization. The Pt:Ni-TFs were found to exhibit higher ORR activity than traditional high surface area carbon supported Pt nanoparticles, elemental Pt nanorods, and Pt-Ni nanorods.

The study on optogenetic tachyarrhythmia termination under pathological conditions from the single cell to the whole heart

Abstract Background Ventricular tachyarrhytmias (VTs) are common among patients suffering from cardiac remodeling and cause significant morbidity and mortality. Current research and treatment options for such VTs are suboptimal, hence new strategies are urgently needed. Optogenetics offers efficacious means to control cardiac rhythm, including shock-free VT termination. However, this has not been demonstrated in diseased hearts in vivo, while clinical translation would not only require such demonstration, but also an in-depth understanding of cellular responses. Purpose To assess the optogenetic response at the cardiac cell, tissue, and whole heart level in terms of rhtyhm control under pathological conditions by an integrative experimental platform including in vitro and in vivo models of cardiac disease. Methods Remodeling was induced in neonatal rat ventricular cardiomyocytes (NRVMs) by phenylephrine (PE) exposure. Pathological conditions leading to ventricular remodeling were mimicked by transverse aortic constriction (TAC) surgery in adult rats. The light-activated ion channel ReaChR was ectopically expressed in NRVMs and in hearts of TAC and sham animals by viral vector-based gene delivery. Results Electrical and structural remodeling was evidenced by elongated action potential durations (p&amp;lt;0.05) and increased cell capacitance (p&amp;lt;0.05) in PE-treated, but not in control cells (CTL). Light-induced ionic currents in ReaChR-expressing PE-treated and CTL NRVMs displayed comparable kinetic properties and current densities (p&amp;gt;0.05). Illumination (1 s) caused a sudden shift in membrane potential leading to a plateau at −7.3 mV for PE-treated and −18.9 mV for CTL cells (p&amp;gt;0.05). Hearts explanted from TAC animals showed increased average heart weight to body weight ratio, ventricular fibrosis and expression of hypertrophy markers (ANP, aSkMA, p&amp;lt;0.05), while tissue preparations showed significant APD increase compared to sham. In vivo gene delivery resulted in expression of the ReaChR-citrine transgene in ∼80% of isolated ventricular myocytes (VMs). Photocurrent densities were not different (p&amp;gt;0.05) in VMs from TAC and sham animals, which currents led to comparable shifts in membrane potential (65.3 mV for TAC and 63.9 mV for CTL). In line with this, illumination caused marked depolarization in tissue preparations (from −77.6 to −16.4 mV) in TAC animals as assessed by conventional sharp electrode measurements. Importantly, as anticipated, electrically-induced VT episodes could be terminated in open chest experiments in TAC animals (n=6; 76.3% of cases) by epicardial illumination in vivo. Conclusions Key operational parameters of the optogenetic response remained unaffected in models of cardiac disease, which allowed efficacious optogenetic VT termination in the diseased rat heart exhibiting structural and electrical remodeling. These findings corroborate the translational potential of shock-free therapy of cardiac arrhythmia by optogenetics. Funding Acknowledgement Type of funding source: Public grant(s) – EU funding. Main funding source(s): This work was supported by personal funding from the Netherlands Organization for Scientific Research (NWO, Vidi grant 1714336 to D.A.P.). D.A.P. is also a recipient of the European Research Council (ERC), Starting grant (716509). Additional support was provided by the Netherlands Heart Institute (ICIN grant 230.148-04 to A.A.F.d.V.).

Phantom Studies of Fused-Data TREIT Using Only Biopsy-Probe Electrodes

Transrectal electrical impedance tomography (TREIT) is a novel imaging modality being developed for prostate biopsy guidance and cancer characterization. We describe a novel fused-data TREIT (fd-TREIT) system and approach developed to improve imaging robustness and evaluate it on challenging clinically-representative phantoms. The new approach incorporates 8 electrodes (in 2 rows) on a biopsy probe (BP) and 12 electrodes on the face of a transrectal ultrasound (TRUS) probe and includes a biopsy gun, instrument tracking, 3D-printed needle guide, and EIT hardware and software. The approach was evaluated via simulation, a series of prostate-shaped gel phantoms, and an ex vivo bovine tissue sample using only absolute reconstructions. The simulations surprisingly found that using only biopsy-probe electrode measurements, i.e. omitting TRUS-probe electrode measurements, significantly improves robustness to noise thus leading to simpler modeling and significant decreases in computational times (~13x speed-up/reconstructions in ~27 minutes). The gel phantom experiments resulted in reconstructions with area under the curve (AUC) values extracted from receiver operator characteristic curves of >0.85 for 4 out of the 5 tests, and when incorporating inclusion boundaries resulted in absolute reconstructions yielding 1.9% and 12.2% average percent errors for 3 consistent tests and all 5 tests, respectively. Ex vivo bovine tests revealed qualitatively that the fd-TREIT approach can largely discriminate a complex adipose and muscle interface in a realistic setting using data from 9 biopsy probe states (biopsy core locations). The algorithms developed here on challenging phantoms suggest strong promise for this technology to aid in imaging during routine 12-core biopsies.

Influence of Ligand Denticity and Flexibility on the Molecular Copper Mediated Oxygen Reduction Reaction.

To date, the copper complex with the tris(2-pyridylmethyl)amine (tmpa) ligand (Cu-tmpa) catalyzes the ORR with the highest reported turnover frequency (TOF) for any molecular copper catalyst. To gain insight into the importance of the tetradentate nature and high flexibility of the tmpa ligand for efficient four-electron ORR catalysis, the redox and electrocatalytic ORR behavior of the copper complexes of 2,2′:6′,2″-terpyridine (terpy) and bis(2-pyridylmethyl)amine (bmpa) (Cu-terpy and Cu-bmpa, respectively) were investigated in the present study. With a combination of cyclic voltammetry and rotating ring disk electrode measurements, we demonstrate that the presence of the terpy and bmpa ligands results in a decrease in catalytic ORR activity and an increase in Faradaic efficiency for H2O2 production. The lower catalytic activity is shown to be the result of a stabilization of the CuI state of the complex compared to the earlier reported Cu-tmpa catalyst. This stabilization is most likely caused by the lower electron donating character of the tridentate terpy and bmpa ligands compared to the tetradentate tmpa ligand. The Laviron plots of the redox behavior of Cu-terpy and Cu-bmpa indicated that the formation of the ORR active catalyst involves relatively slow electron transfer kinetics which is caused by the inability of Cu-terpy and Cu-bmpa to form the preferred tetrahedral coordination geometry for a CuI complex easily. Our study illustrates that both the tetradentate nature of the tmpa ligand and the ability of Cu-tmpa to form the preferred tetrahedral coordination geometry for a CuI complex are of utmost importance for ORR catalysis with very high catalytic rates.

A facile mechanochemical preparation of Co3O4@g-C3N4 for application in supercapacitors and degradation of pollutants in water

Our study is aimed at synthesizing cobalt oxide (Co3O4) with graphite carbon nitride (g-C3N4) to form a Co3O4@g-C3N4 hybrid through a green mechanochemical one-pot synthetic approach for manufacturing efficient supercapacitor electrodes and photocatalysts. In the present study, the Co3O4@g-C3N4 hybrid revealed a significantly higher specific capacitance (Cs) (of ~ 457.2 Fg−1 at a current density of 1 Ag−1) than that of the pristine Co3O4, which proved its pseudocapacitive behavior, with a couple of redox peaks observed in three electrode measurements (obtained by using a 3.0-M KOH aqueous electrolyte). The optimized Co3O4@g-C3N4 hybrid was further embedded for a symmetric supercapacitor performance, delivering an excellent Cs of ~ 92 Fg−1 at a current density of 1 Ag−1; this was supplemented with a remarkable cycling stability (~ 92% over 5000 cycles). The Co3O4@g-C3N4 hybrid was further examined for photocatalysis activity using a rhodamine B (RhB) dye, and more than 95% RhB dye was degraded through the photocatalytic reduction process (after 60 min of UV irradiation). This Co3O4@g-C3N4 hybrid catalyst exhibited excellent reusability and stability and appears to be a highly efficient, cost-effective, eco-friendly, and reusable catalyst; the g-C3N4 present with the Co3O4 acted as a conductive nano-network, leading to a higher capacitive and photocatalytic performance.

Cobalt phosphide embedded N-doped carbon nanopolyhedral as an efficient cathode electrocatalyst in microbial fuel cells

Design and synthesis of effective and low-cost electrocatalysts for oxygen reduction reaction (ORR) is of great significance for the performance of microbial fuel cells (MFCs). Herein, we fabricated a cobalt phosphide embedded N-doped carbon nanopolyhedral (CoP@N-C) by simultaneous phosphidation and carbonization of ZIF-67 under N2 atmosphere. The physical and chemical properties of the electrocatalysts were analyzed in detail by scanning electron microscope, transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy and N2 adsorption–desorption isotherms. Results showed that the CoP@N-C had a dodecahedral shape with cobalt, nitrogen and phosphorus incorporating in porous graphical carbon. CoP compound which had a strong electron capture capability and ORR activity was embedded within the electrocatalysts. Introducing of P increased the contents of pyridinic-N, Co2+/Co3+ couples and oxygen vacancies, which provided sufficient catalytic active sites for ORR. The increased metallic Co content and mesoporous/macroporous surface area ensured efficient electron and mass transfer during ORR. Rotating disk electrode measurement revealed that the CoP@N-C exhibited a high ORR catalytic activity comparable to Pt/C, and an efficient four-electron pathway during ORR. When fabricated into activated carbon air cathode, the optimized CoP@N-C produced a maximum power density of 2236.8 mW m−2 in MFCs, which was about 2 times that of the bare activated carbon control. In addition to the superb ORR performance, the cost of the CoP@N-C was only ∼1/3 of commercial Pt/C. This study suggests that CoP@N-C could be an attractive non-precious metal ORR electrocatalyst for the application in high-performance MFCs.

Reprint of "Rotating ring-disc electrode measurements for the quantitative electrokinetic investigation of the V3+-reduction at modified carbon electrodes"

Thin film rotating-ring disc electrode (RRDE) technique is exploited to quantify the parasitic hydrogen evolution reaction (HER) competing with the desired V3+-reduction at surface modified carbon nanoparticles for application as electrocatalysts in the negative half-cell of vanadium redox-flow batteries (VRFB). Carbon based electrode materials are derived from standard Vulcan XC-72 carbon, treated by chemical surface etching techniques proposed for carbon felt-electrodes in the literature. Additional electrochemical characterization is performed using stationary cyclic voltammetry (CV) followed by fitting of CV data, Fourier-transform alternating-current cyclic voltammetry (FT-ACCV) and electrochemical impedance spectroscopy (EIS) followed by distribution of relaxation times (DRT) analysis. To our knowledge the present paper is the first study using the RRDE technique for separating HER and V3+-reduction reactions. It is demonstrated that the ratio of HER to V3+-reduction significantly depends on the chemical pretreatment of the carbon electrodes and that the V3+-reduction proceeds at an optimum rate at E − ERHE = −0.45 V. Separating the HER from the V3+-reduction also allows us to provide highly accurate values for the diffusion coefficient of the V3+-ion in sulfuric acid solutions.

Microstructural Evolution and ORR Activity of Nanocolumnar Platinum Thin Films with Different Mass Loadings Grown by High Pressure Sputtering

Nanocolumnar platinum thin films (Pt-TFs) with different Pt mass loadings were grown by high pressure sputtering (HIPS) and investigated as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte membrane fuel cell applications. Mass loading was controlled by changing the sputter deposition time. A cauliflower-like columnar microstructure was achieved by depositing the Pt-TFs onto a microporous layer (MPL)-like surface composed of carbon particles in order to mimic catalyst-coated gas diffusion electrodes. Microstructural evolution of HIPS Pt-TFs and their ORR activity were investigated. Electrochemical characterization of the nanocolumnar Pt-TFs was performed by cyclic voltammetry and rotating disk electrode measurements on Pt-TF/MPL-like-layer/glassy-carbon samples in an aqueous perchloric acid electrolyte. The electrochemically active surface area increased from 18 to 39 m2 g−1 as the Pt mass loading was decreased. Specific activity of the films was similar (∼600 μA cm−2) for all Pt mass loadings, due to the similar nanoparticle sizes of ∼5 nm as observed by transmission electron microscopy and X-ray diffraction. Mass activity of the films increased from 0.11 to 0.26 A mg−1 as the Pt mass loading was decreased, which is an indication of the effective Pt utilization and better access through the catalyst layer at lower Pt mass loadings.

Errors in the reference electrode measurements in real lithium-ion batteries

Reference electrodes (REs) implanted in lithium-ion batteries are essential indicators in the fields of health monitoring and safety management. The non-destructive charging profiles, for example, are usually determined by electrode potential measurements performed with the RE. However, errors in RE potential measurements, resulting in seriously flawed conclusions, are seldom discussed in real lithium-ion batteries. This study investigates the reliability of anode potentials measured with a Li/Cu RE implanted in commercial cells. Artefacts are advanced in RE measurements based on the inconsistency of measured anode potentials and lithium plating behaviors, and further validated by the excess anode overpotential while charging to high state of charge at high rates. Furthermore, artefact phenomenon is reflected in the electrochemical model highlighting the RE blocking of the Li-ion flow. Inhomogeneous lithium intercalation currents at the anode-separator interface are revealed to bring out the excess anode overpotential in RE measurements. Finally, the impact of critical parameters on potential artefacts is examined, and proper RE sizes and battery operating conditions are proposed to ensure the reliability of potential measurements. This work emphasizes the existence of artefacts in RE potential measurements, and provides a useful guide on eliminating errors and improving accuracy of RE in real lithium-ion batteries.

Single Alkali Metal Ion-Activated Porous Carbon With Heteroatom Doping for Supercapacitor Electrode.

A single alkali metal ion activation method was used to prepare sulfur-doped microporous carbons. A series of alkali metal ions such as Li+, Na+, K+, and Cs+ was used in the polymerization process of 3-hydroxythiophenol and formaldehyde to obtain metal ion anchored in the sulfur-containing resin, which was further treated to obtain xerogel and carbonized to obtain microporous carbon with sulfur doping. In this case, the monodispersed alkali metal ions could realize highly effective activation with low activating agent dosage. Intensive material characterizations show that the alkali metal ions determine the pore structure and surface properties of as-prepared carbons. C-Cs prepared by Cs+ ion possesses a high Brunauer–Emmett–Teller specific surface area of 1,037 m2 g−1 with interconnected microporosity and sulfur doping. The specific capacitance of C-Cs can reach up to 270.9 F g−1 in a two-cell electrode measurement system, whereas C-Cs-based supercapacitors can deliver an energy density of 7.6 Wh kg−1, which is much larger than that of other samples due to its surface functionalities and well-interconnected porosities.

Influence of Ammonia Contamination on HT-PEM Fuel Cell Platinum Catalyst

In this work the effect of NH3 contamination on platinum catalyst has been investigated in the frame of a high temperature polymer electrolyte membrane single fuel cell as well as rotating ring disk electrode measurements (RRDE) using phosphoric acid electrolyte. In the first part single cell operation in presence of 10 ppm NH3 in the cathode gas combined with electrochemical impedance spectroscopy was performed with a fuel cell test bench. In the second part of work RRDE experiments were accomplished in the presence of 10 and 100 ppm of NH4H2PO4 contamination in 0.5 mol L-1 H3PO4. It was revealed that platinum catalyst is strongly affected by ammonia contamination while the increasing ammonium concentrations reduce the electrochemical surface area (ECSA) of the Pt catalyst. These observed losses of ECSA were associated to adsorbed nitrogen compounds on the catalyst surface.

Effect of anion exchange ionomer content on electrode performance in AEM water electrolysis

Anion exchange membrane water electrolysis (AEMWE) has acquired substantial consideration as a cost-effective hydrogen production technology. The anion ionomer content in the catalyst layers during hydrogen and oxygen evolution reaction (HER and OER) is of ultimate significance. Herein, an in-situ half-cell analysis with reference electrodes was carried out for simultaneous potential measurements and identification of the influence of the anion exchange ionomer (AEI) content on anode and cathode performance. The measured half-cell potentials proved the influence of AEI content on the catalytic activity of HER and OER, which was supported by the rotating disk electrode (RDE) measurements. Cathode overpotential of Ni/C was not negligible and more affected by the AEI content than anode with the optimized AEI content of 10 wt% while NiO anode OER overpotential was independent of the AEI content. For the same AEI content, PGM catalysts showed higher electroactivity than Ni-based catalysts for HER and OER and the cathode catalyst's intrinsic activity is of high importance in the AEM electrolysis operation. Post-mortem analysis by SEM mapping of both AEI and catalyst distributions on the electrode surface showed the effect of AEI loading on the catalyst morphology, which could be related to the electrode performance.

Depletion Forces Induced by Mixed Micelles of Nonionic Block Copolymers and Anionic Surfactants.

Depletion forces were measured between a silica sphere and a silica plate in solutions containing nonionic Pluronic P123 poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymers and anionic sodium dodecyl sulfate (SDS) surfactants using colloidal probe atomic force microscopy. Prior research established synergistic depletion force enhancement in solutions containing SDS and unimeric Pluronic F108 block copolymers via formation of large pseudo-polyelectrolyte complexes. The current work addresses a more complex system where the polymer is above its critical micelle concentration, and surfactant binding alters not only the size and charge of the micelles but also the number of polymers per micelle. Force profiles were measured in 10 000 ppm P123 (1 wt %, corresponding to 1.72 mM based on average molar mass) solutions containing SDS at concentrations up to 64 mM and compared to micellar P123 solutions and to P123-free SDS solutions. Whereas force profiles in the SDS-free micellar P123 solutions were purely repulsive, P123/SDS complexation produced synergistic depletion force enhancement for SDS concentrations between 2 and 32 mM. The synergism that occurred within a finite SDS concentration range was explained by comparing the hydrodynamic size, molar mass, charge, and concentration of depletants in P123/SDS mixtures and their respective single-component solutions obtained with the aid of dynamic light scattering, static light scattering, and dodecyl sulfate ion-selective electrode measurements. These measurements showed that complexation produced effects that would be mutually counteracting with respect to depletion forces: decreasing the mixed micelle hydrodynamic diameter relative to SDS-free P123 micelles would tend to weaken depletion forces, while adding charge and decreasing the aggregation number of polymers per micelle (thereby increasing the number concentration of micellar depletants) would tend to strengthen depletion forces.

The mechanism of Li2O2-film formation and reoxidation – Influence of electrode roughness and single crystal surface structure

In this work, the role of the electrode surface structure on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in lithium ion containing dimethyl sulfoxide (DMSO) was elucidated for Pt single crystal electrodes and deliberately roughened polycrystalline gold and platinum electrodes. Both rotating ring disk electrode (RRDE) measurements and results obtained by differential electrochemical mass spectrometry (DEMS) show that the amount of insoluble Li 2 O 2 formed is proportional to the roughness factor and corresponds to one or two monolayers if referenced to the true surface area. The amount of soluble LiO 2 is independent of roughness, although the formation of the passivating Li 2 O 2 layer takes longer. On gold electrodes less side products are formed as compared to platinum electrodes. It was furthermore found that ORR on single crystalline Pt(100) leads to two monolayers of Li 2 O 2 , while in case of Pt(111)/Pt(pc) only one monolayer was reoxidized. The shape of the reoxidation peaks in the anodic potential scan is independent of roughness, but it depends not only on the electrode material (Au or Pt) but also on the atomic surface structure. Since Tafelslopes cannot be determined directly by usual methods for such surface confined reactions, we used ac voltammetry to determine the apparent transfer coefficient ( α′ ) and gain some insight into the reoxidation mechanism; the obtained α ′ of 0.3 hints to a rate determining first charge transfer. This agrees well with the detection of superoxide during oxidation of Li 2 O 2 on the surface. • Strong effect of electrode surface structure on electrochemistry in Li + -containing DMSO. • Superoxide as intermediate during lithium peroxide oxidation in DMSO. • Apparent transfer coefficient of lithium peroxide oxidation in Li + -containing DMSO. • Direct correlation of lithium peroxide formation and surface roughness.

Life-cycle analysis of zinc-cerium redox flow batteries

The life-cycle of a zinc-cerium redox flow battery (RFB) is investigated in detail by in situ monitoring of the half-cell electrode potentials and measurement of the Ce(IV) and H+ concentrations on the positive and negative side, respectively, by titrimetric analysis over its entire life. At a current density of 25 mA cm−2, the charge efficiency of the battery is initially limited by the zinc redox reaction, which leads to the incomplete reduction of Ce(IV) to Ce(III) during discharge and the accumulation of Ce(IV) on the positive side. Titration experiments confirm the accumulation of Ce(IV) on the positive side of the battery and reveal that the proton concentration on the negative half-cell of the battery increases over the cycles. This increases the rate of hydrogen evolution on the negative side and contributes to Ce(IV) precipitation on the positive side. These effects combine to cause capacity fade and ultimate failure of the battery. In order to mitigate these effects, the battery life-cycle is evaluated when the Nafion 117 cation exchange membrane is replaced with an anion exchange membrane (AEM). Among the AEMs tested, Fap-375-PP is found to be the most chemically stable in the presence of Ce(IV). Full life-cycle experiments show that Fap-375-PP can reduce the rate of enhancement in the proton concentration on the negative side and increases the life of the system relative to that possible using Nafion 117, although a very gradual proton enhancement on the negative side is still observed. A future focus should be to fabricate AEMs with extremely low proton leakage and high stability in presence of Ce(IV) in order to further enhance the life-cycle of zinc-cerium RFBs.

N8− Polynitrogen Stabilized on Nitrogen-Doped Carbon Nanotubes as an Efficient Electrocatalyst for Oxygen Reduction Reaction

In this work, non-traditional metal-free polynitrogen chain N8− deposited on a nitrogen-doped carbon nanotubes (PN-NCNT) catalyst was successfully synthesized by a facile cyclic voltammetry (CV) approach, which was further tested in an oxygen reduction reaction (ORR). The formation of PN on NCNT was confirmed by attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and Raman spectroscopy. Partial positive charge of carbon within NCNT facilitated electron transfer and accordingly induced the formation of more PN species compared to CNT substrate as determined by temperature-programmed decomposition (TPD). Rotating disk electrode (RDE) measurements suggested that a higher current density was achieved over PN-NCNT than that on PN-CNT catalyst, which can be attributed to formation of the larger amount of N8− on NCNT. Kinetic study suggested a four-electron pathway mechanism over PN-NCNT. Moreover, it showed long stability and good methanol tolerance, which indicates its great potential application. This work provides insights on designing and synthesizing non-traditional metal-free catalysts for ORR in fuel cells.