Higher Potential Range Research Articles

Investigating the Effects of Cascading Accelerated Stress Tests (ASTs) on the Localized Electrochemical Performance Degradation in Polymer Electrolyte Fuel Cells (PEFCs)

With a recent shift in focus from light-duty to heavy-duty vehicle applications, the durability and performance targets for polymer electrolyte fuel cells (PEFCs) have become even more stringent and challenging to achieve; for example, a net power output of 2.5 kW/g-PGM (1.07 A/cm2 current density) at 0.7 V is required after 25,000 hour-equivalent accelerated stress test (AST) [1]. Generally, different ASTs are designed to evaluate Pt electrocatalyst and support durability; for example, a square-wave (SW) AST with H2/N2 between 0.6 V to 0.95 V vs. reversible hydrogen electrode (RHE) targets Pt catalyst and a separate triangular-wave (TW) AST with a higher potential range (1 – 1.5 V vs. RHE) assesses the durability of carbon-based supports [2]. Recently, many studies [3]–[7] have revealed the heterogeneous nature of cathode catalyst layer degradation under different ASTs. Fuel cell electric vehicles are typically subjected to an enormous number of load/unload and start/stop cycles during regular operation. Though there is a considerable body of literature discussing the isolated effects of load/unload and start/stop cycles on durability and performance, there is a dearth of studies exploring the effects of cascading load/unload and start/stop cycles, a scenario more relevant to actual automotive conditions. In the present study, a segmented cell along with ex-situ Pt particle size mapping (through micro-X-ray diffraction) is used to understand the effects of cascading a DoE square-wave AST (0.6 V to 0.95 V vs. RHE) and a triangular-wave (1 – 1.5 V vs. RHE) on the durability and performance of a PEFC.The membrane electrode assemblies (MEAs) are subjected to two cascade ASTs. The first one involves 15k cycles of SW AST followed by 2.5k cycles of TW AST (referred to as Pt-followed-by-carbon, PtfCC, AST) and the other one involves 2.5k cycles of TW AST followed by 15k cycles of SW AST (referred to as Carbon-followed-by-Pt, CCfPt, AST). Multiple in-situ and post-mortem ex-situ techniques are used to obtain particle size distribution and spatial degradation profiles. Preliminary results indicate that the performance losses at the end-of-life (EOL) depend on the cascade order; PtfCC AST leads to higher losses compared to CCfPt AST in wet polarization conditions. The local current distributions are also strongly impacted by the cascade order during the aging process. Figure 1 shows the polarization performance of the samples at the beginning, middle (following the first AST), and the end-of-life of cascade ASTs.

Localized Electrochemical Performance Degradation in Polymer Electrolyte Fuel Cells (PEFCs)

Pt electrocatalyst durability in polymer electrolyte fuel cells (PEFCs) is generally evaluated through an accelerated stress test (AST); for example, one AST features repeated square-wave cycling with H2/N2 between 0.6 V to 0.95 V vs. reversible hydrogen electrode (RHE) [1]. A separate triangular-wave AST with a higher potential range (1 – 1.5 V vs. RHE) assesses the durability of carbon-based supports [2]. Recent studies [3]–[5] have revealed the heterogeneous nature of cathode catalyst layer degradation. In general, Pt particle size growth mimics the flow field geometry with greater particle size growth under lands compared to channels. Additionally, growth is typically shown to be greater near the air outlet than the inlet and is assumed to be correlated to local performance decay. The impact of such localized degradation on distributed cell performance is investigated in this work. In the present study, a segmented cell is used to quantify functional dependence of local current distributions in aged samples to heterogeneous catalyst layer degradation (Pt particle size growth and carbon support corrosion). The outcome of this enhanced understanding is to identify limiting factors in cell performance at end-of-life (EOL).Single cell studies with 25-cm2 active area are performed using catalyst-coated Nafion® XL membranes (Ion Power Inc.) and SGL-22 BB gas diffusion layers (GDLs) as membrane electrode assembly (MEA) materials and 7-channel serpentine flow field. An S++® current scan shunt (CSS) sensor plate (25-cm2) with 100 current and 25 temperature measurement segments is utilized for current and temperature mapping, respectively. The MEAs are subjected to DOE’s square-wave cycling (0.6 to 0.95 V vs. RHE), triangular-wave cycling (1 to 1.5 V vs. RHE), and a sequence of square-wave cycling followed by triangular-wave cycling. Complete in-situ electrochemical characterization and post-mortem ex-situ diagnostics such as micro-X-ray diffraction (micro-XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are used to obtain particle size distribution and spatial degradation profiles. Results indicate a strong dependence of current distributions on localized catalyst layer degradation. For example, MEA with relatively uniform current distributions at the beginning-of-life (BOL) in Figure 1 exhibits severe mass transport limitations (significantly higher current at the air inlet than the outlet) at EOL when subjected to triangular-wave carbon corrosion AST. Furthermore, an increase of ~1.5x in Tafel slope is observed for the aged sample at EOL, highlighting increased transport losses. These mass transport losses are believed to originate from loss of catalyst layer porosity and subsequent compaction due to carbon support corrosion [2].This work seeks to achieve a greater understanding of the functional dependence between catalyst growth and carbon corrosion and observed local performance.

Operando X-Ray Absorption Spectroscopic Study on Influence of Specific Adsorption of Sulfo Group in Perfluorosulfonic Acid Ionomer Towards ORR Activity of Pt/C Catalyst

Polymer electrolyte fuel cells (PEFCs) are clean energy devices with polymer electrolytes and are expected to play an important role in the development of a global renewable energy system and a pure hydrogen energy society in the future. PEFCs have already been applied for small-scale energy systems such as fuel cell vehicles (FCVs). Pt-based catalysts are basically used due to the relatively inefficient reaction kinetics and catalyst degradation under strong acidic conditions during the oxygen reduction reaction (ORR). However, there are still many difficulties in realizing acceptable cost-effective FCVs. It is known that the ORR activity of Pt-based catalysts is reduced by specific adsorption of anionic species. Perfluorosulfonic acid ionomers such as Nafion® are commonly included in the catalyst layers of PEFCs to provide protonic pathways for promoting the ORR1. However, direct observation of anion adsorption on practical Pt nanoparticle/C catalysts for perfluorosulfonic acid ionomers using X-ray absorption spectroscopy (XAS) still has less report. In this study, to achieve specific adsorption over a higher potential range that is at least equal to the ORR active potential (around 0.90 V vs. RHE), operando XAS measurements were performed; the electronic status and local structural change of Pt atoms induced by the specific adsorption of anions at any potential were observed2.Pt/C (29.1 wt.%; TEC10V30E) catalyst supported was purchased from TKK. Nafion® solution was employed to prepare Pt/C catalyst ink with I/C ranging from 0.0 to 1.0. And the amount of Pt/C was adjusted to form a 20 µgcarbon cm-2 catalyst layer after dropping 10 μL on a glassy carbon RDE. The electrochemical cell was constructed using a model electrode fabricated in the working electrode, a Pt mesh for the counter electrode, a reversible hydrogen electrode for the reference electrode, and 0.1 M HClO4 aq for the electrolyte. operando XAS measurement of Pt L-edge was carried out in SPring-8 (Japan).The specific activity decreased as the I/C ratio increased from 0.0 to 0.20. We utilized many methods to evaluate the adsorption species separately, including the measurements of ECSA and oxygen coverage, CO stripping voltammetry, operando X-ray absorption fine structure, and analysis of 5d orbital vacancy. The ECSA and oxygen coverage did not change with increasing ionomer content, indicating that the Pt/C catalyst activity was affected by other adsorption species. A comparison of the CO displacement charge and 5d orbital vacancies of the Pt/C catalysts with I/C = 0.0 and 1.0 suggests that the ionomer-specific adsorption increases when the I/C ratio of the Pt/C catalyst is 1.0; active sites on the surface of the Pt/C catalyst are occupied, resulting in lower catalyst activity. Acknowledgment This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Surface Engineering of Carbon Nanotubes with Inorganic-Organic Materials for Electrochemical Capacitors.

Composite electrodes comprised of inorganic-organic molecular materials are of great interest in applications such as electrochemical capacitors (ECs). ECs store and release charge via double layer capacitance (EDLC) or pseudocapacitance. The carbon materials used for EDLC has low capacitance, while pseudocapacitive materials such as redox active polymers or metal oxides have long term stability issues. Therefore, anchoring inorganic-organic materials on a carbon substrate can leverage the advantages of both EDLC and pseudocapacitance. Composite electrodes of kegging type polyoxometalates (POM) deposited on polydiallyldimethylammonium chloride (PDDA) via the layer-by-layer assembly has been well established and has shown great promise [1-3] . The issues are the limited operation window and the inert PDDA layer. Suitable alternatives that can complement the redox activity of POMs and enlarge the operating potential window are redox active polymers [4].The objectives of this work are to: 1) develop and optimize an electroactive inorganic-organic composite electrode based on a carbon nanotube (CNT) substrate modified with polyluminol (CpLum) and H5GeMo11VO40.24H2O (GeMo11V); 2) study the electrochemical behavior of the composite electrode with and without PDDA for electrochemical capacitors; and 3) investigate the interactions between each layer.GeMo11V was first deposited onto CNT using PDDA as an anchor. The vanadium atom in the kegging structure provided an additional electrochemical redox peak with improved capacitive behavior on the cyclic voltammogram (CV) as seen in figure 1. First, CpLum, and GeMo11V were applied on CNT (CNT-CpLum-GeMo11V), then co-deposited with PDDA (CNT-CpLum-PDDA-GeMo11V). For both composite electrodes, CpLum and GeMo11V contributed to the redox activity leading to a wider potential window. The CV of CNT-CpLum-GeMo11V showed more reversible redox peaks with a slightly reduced GeMo11V contribution compared to CNT-CpLum-PDDA-GeMo11V that had a smoother CV shape. The decrease in GeMo11V contribution was attributed to the smaller amount of positive charge within the CpLum chain needed to anchor the GeMo11V. Each layer had a distinct role in the inorganic-organic composite electrode. The CpLum polymer added additional redox activity in the higher potential range, while PDDA attracted and held the GeMo11V, which provided redox activity in the lower potential range. All three layers had a synergistic interaction and provided enhanced charge storage properties with good rate capability and cycling stability.REFERENCES 1. M. Genovese, Y. W. Foong and K. Lian, Electrochimica Acta, 199, 261 (2016).2. M. Genovese and K. Lian, Current Opinion in Solid State and Materials Science, 19, 126 (2015).3. M. Genovese, Y. W. Foong and K. Lian, Journal of The Electrochemical Society, 162, A5041 (2015).4. N. Casado, G. Hernández, H. Sardon and D. Mecerreyes, Progress in Polymer Science, 52, 107 (2016). Figure 1

Chrysalis-Like Graphene Oxide Decorated Vanadium-Based Nanoparticles: An Extremely High-Power Cathode for Magnesium Secondary Batteries

Rechargeable batteries based on magnesium virtually provide high volumetric capacity, safety, and cost savings thanks to the abundance, dendrite-free electrodeposition, and environmentally green properties of Mg metal anode. The lack of cathodes that can deliver high currents at high potential is one of the principal bottlenecks that limit the entrance of Mg batteries into the market. Here we report the synthesis and characterization of a novel cathode for magnesium secondary batteries based on graphene oxide (GO) and vanadium (V) active species. Thermogravimetric analysis, structural and vibrational analyses, and high-resolution electron microscopies elucidate the complex architecture that characterizes the proposed material and that bestows exceptional electrochemical properties to the cathode. The proposed synthesis is able to give rise to V-based nanoparticles with a very porous surface and wrapped inside a chrysalis-like GO ordered superstructure. Finally, a coin cell device is assembled using a Mg metal anode and the proposed material as cathode. This prototype is able to deliver good capacities when cycled at high current rates (1000 mA g−1) in a higher potential range with respect to classical cathodes for Mg batteries. Thus, a sufficient power (1.70 W g−1) is obtained, making this battery promising towards the substitution of lithium batteries.

Gradient Ti-doping in hematite photoanodes for enhanced photoelectrochemical performance

Hematite based photoanode is promising for solar water splitting while suffers from poor charge transport and separation efficiency that limit its practical application. Herein, we demonstrate two types gradient Ti-doped Fe2O3 photoanodes (Fe2O3–Ti (TiO2 deposited on the top of Fe2O3) and Ti–Fe2O3 (Fe2O3 on the top of TiO2)) to enhance charge transport and separation efficiency. Interestingly, Fe2O3–Ti and Ti–Fe2O3 photoanodes exhibit almost identical PEC performance with photocurrent of 1.50 mA cm−2 at 1.23 V vs. the reversible hydrogen electrode (RHE). However, the onset potential of Ti–Fe2O3 photoanode displays a cathodic shift of 80 mV comparing with that of Fe2O3–Ti photoanode. Moreover, the charge separation efficiencies on the surface (ηsurface) for Fe2O3–Ti and Ti–Fe2O3 can reach up to 96% at the higher potential range from 1.30 to 1.50 V vs. RHE, which are among the top values in the record of hematite-based photoanodes without co-cocatalyst. Further investigation demonstrates the forming of gradient Ti doping is not dependent on the location of the TiO2 layer, but mainly affected by the high annealing temperature. The enlarged contact area between hematite photoanode and the electrolyte, the improved charge separation efficiency, and increased charge carrier density are responsible for the enhanced PEC water splitting.

On-Line Monitoring of the Stability of Electrodes in Non-Aqueous Media

Stability of electrochemical systems is particularly important in applications. No matter if it is a fuel cell, a battery, a supercapacitor, a construction subject to corrosion or an electrode used for synthesis, economic considerations require a certain lifetime of these systems. Depending on the systems, instability can have several causes, like changes in the mechanical or crystal structure of electrodes, oxidation of materials, decomposition of electrolytes, loss of percolation and electrical conductivity, or material loss due dissolution. Many of these processes happen slowly, causing only minimal performance loss within laboratory timescales. Their studies involve therefore usually long-term measurements with ex situ analysis. In situ, real-time analysis requires very sophisticated and usually coupled analysis methods. In this work we show a powerful approach to study dissolution phenomena in non-aqueous electrochemical systems. A scanning electrochemical flow cell (SFC) combined with on-line inductively coupled plasma mass spectrometric (ICP-MS) analysis has proven to be a very valuable tool for the study of stability of electrocatalysts in aqueous solutions. This coupled technique is mainly connected to the works of Dr. Mayrhofer and Dr. Cherevko. It was very appealing to develop this method further and make it useable in organic systems too. This task might seem for the first glance to be almost trivial, however, the harsh conditions caused by the organic electrolytes limit the usability of materials to contrive these systems to a huge extent. Furthermore, the ICP-MS is standardized mainly for aqueous media and a lot of experimental work has to be devoted for the optimization of the device for each individual organic solvent. Most of the chemicals used are sensitive to atmospheric components, like O2, H2O, CO2 or even N2. Therefore, the experiments have to be carried out in a glovebox that ensures a controlled and very clean atmosphere. Platinum is often considered to be a model electrode and catalyst material. This metal is probably the most thoroughly studied one in electrochemistry, however, it still shows many interesting yet not well understood features. This is also true for the stability of the metal during potential cycling. The electrochemical stability window of organic electrolytes is usually much higher than that of water enabling the simultaneous cycling and downstream analysis of dissolution in a higher potential range. As a result, even the electrochemistry of platinum shows hitherto unveiled phenomena regarding its dissolution mechanism. In this work, we focus on the effect of water contamination, anions, cations and organic solvent molecules on the anodic and cathodic dissolution behavior of platinum. To demonstrate the benefits of this novel method on the field of non-aqueous electrochemistry the stability of other non-aqueous systems will be discussed shortly, too.

Surface‐Driven Energy Storage Behavior of Dual‐Heteroatoms Functionalized Carbon Material

AbstractHeteroatom modification represents one of the major areas of carbon materials' research in electrical energy storage. However, the influence of heteroatomic state evolution on electrochemical properties remains an elusive topic. Herein, thiophene‐2,5‐dicarboxylic acid is chemically activated to prepare O,S‐diatomic hybrid carbon material (OS–C). The heteroatoms and carbon matrix coexist in the form of CO/CO and CS/SS bonds, which introduce porous networks to the partially graphitized carbon skeleton and provide abundant active sites for better ion absorption. Moreover, the heteroatoms and carbon matrix are bridged to establish stable pseudocapacitive functional groups like quinoid unit and disulfide bonds, which can be electrochemically converted into benzenoid units and mercaptan anions through Faradaic reactions to further improve the reversible capacity. Combined with the detailed kinetic exploration and in situ investigation of the electrochemical impedance spectra, the energy storage mechanism for lithium/sodium is proposed in the following steps: Faradaic reactions at a higher potential range, energy storage at active sites, and ions intercalation on the graphitized parts in the low‐voltage states. Greatly, the electrode can store lithium up to the capacity of ≈700 mAh g−1, while also delivering ≈330 mAh g−1 of sodium storage, providing lifetimes in excess of thousands of cycles.

Ammonia Oxidation Reaction Mechanism on Pt-Ir Alloys: A Surface Enhanced Infrared Absorption Spectroscopy Study

Energy and environment are two of the most primary concerns of this century, thus leading to holistic research across numerous disciplines.1 Ammonia electro-oxidation reaction (AOR) is extremely crucial with regards to energy and environment as it holds spotlight in several fields such as wastewater remediation, analytical chemistry and as a source of renewable energy in direct ammonia fuel cells. In addition, AOR is also useful by being the producer of hydrogen via electrolysis.2 Ammonia has a greater promise compared to other compounds like ethanol and methanol due to its carbon-free nature, well-defined production, storage and transportation network and no net increase in carbon dioxide content of the environment.3 However, inadequate performance due to slow kinetics and expensive nature of electrocatalysts have impeded the utilization of ammonia oxidation technology on a large scale. Consequently, large amount of efforts have been put over the years to understand the mechanism properly which can assist in developing highly active and stable electrocatalysts. In this study, a powerful in-situ surface enhanced infrared absorption spectroscopy (SEIRAS) technique with the attenuated total reflection (ATR) was used to examine the mechanism and intermediates over Pt-Ir nanofilm deposited on a silicon hemispherical prism. Pt-Ir was chosen as it is the most promising alloy as electrocatalyst for AOR till date. Intermediates such as NO at 1478-1488 cm-1 previously found over Pt electrode6 and NO2 at 1331 cm-1 earlier found with CeO2-modified platinum catalyst7 were also observed in this study with Pt-Ir, thus establishing their presence at higher potential range. Most importantly, a weak band at 2140 cm-1 representing azide intermediate was also observed for the 1st time using FTIR, previously only seen using in-situ Raman spectroscopy.8 This work, confirming azide intermediate presence at higher potential and affirming the NO and NO2 for Pt-Ir too, provided much clearer understanding of the mechanism and intermediates within the most renowned Gerischer and Mauerer framework, henceforth opening pathway for further efficient AOR electrocatalyst design in future. Fig 1. Time-resolved IR spectra of the Pt-Ir nanofilm acquired simultaneously with the linear sweep voltammogram in 0.2 M NH3-10mM PBS buffer solution (pH 6.96). The reference spectrum was taken at 0.1V. References Liu, J., Liu, B., Ni, Z., Deng, Y., Zhong, C., & Hu, W., Electrochimica Acta 2014, 150, 146-150.Diaz, L. A., Valenzuela-Muñiz, A., Muthuvel, M., & Botte, G. G., Electrochimica Acta 2013, 89, 413-421.Zhong, C., Hu ,W. B., and Cheng Y. F., Journal of Materials Chemistry A 2013, 10, 3216-3238.Vitse, Frederic, Cooper, M., and Botte, G. G., Journal of Power Sources 2005, 1, 18-26.Satyapal, Sunita, et al. Catalysis Today 2007, 3, 246-256.Matsui, T., Suzuki, S., Katayama, Y., Yamauchi, K., Okanishi, T., Muroyama, H., and Eguchi, K.. Langmuir 2015, 31, 11717-11723.Katayama, Y., Okanishi, T., Muroyama, H., Matsui, T., and Eguchi, K., ACS Catalysis 2016, 3, 2026-2034.Vidal-Iglesias, F. J., Solla-Gullón, J., Pérez, J. M., and Aldaz, A.. Electrochemistry Communications 2006, 8, 102-106. Figure 1

Effect of Ferritic Phase Content on Pitting Corrosion Behavior of Cast Duplex Stainless Steel

1. Introduction Duplex stainless steel (DSS) has been increasingly used in seawater desalination plants, oil & gas-related facilities, and chemical plants. This is because it has high corrosion resistance and high strength compared to austenitic stainless steels. It has been known that the phase ratio between the ferritic (α) and the austenitic (γ) phases can greatly affect the corrosion resistance of DSS. However, the data for the corrosion behavior of the cast DSS with different α/γ phase ratio is limited. The objective of this study is to elucidate the effect of α phase content on pitting corrosion behavior of the cast DSS. 2. Experimental procedures 2-1. Material The chemical composition of the cast DSS is shown in Table 1. The DSS was annealed isothermally to control α phase content in the DSS. The specimen whose α phase content was 32 vol% (1100 °C for 48 hours, WQ), 43 vol% (1250 °C for 48 hours, WQ) and 50 vol% (1300°C for 48 hours, WQ) was prepared from 25%Cr-8.4%Ni-2%Mo DSS (TP No. "1B+Ni" in Table 1), and the the specimen whose α phase content was 50 vol% (1100 °C for 48 hours, WQ), 58 vol% (1150 °C for 48 hours, WQ), 70 vol% (1275 °C for 48 hours, WQ) and 77 vol% (1300°C for 48 hours, WQ) was prepared from 25%Cr-5.6%Ni-2%Mo DSS (TP No. 1B in Table 1). The α phase content of the prepared specimens were measured by an image analyser from the optical micrographs (magnification: x200). 2-2. Pitting potential measurement The surface of the specimens was finished with 1 μm diamond paste. The pitting potential measurement was carried out in a concentrated artificial seawater (TDS: ca. 4.7%) at 80±2 °C under deaerated atmosphere by purging argon. Potentiostatic polarization treatment was performed at -0.65 V vs. an Ag/AgCl (Saturated KCl) electrode (SSE) prior to the test, then the corrosion potential of the specimen was measured for 10 minutes. Potentiodynamic anodic polarization was performed at a sweep rate of 20 mV/min. The potential when the current density reached 1 A/m2 was defined to be the pitting potential (V'c,100). Throughout this paper, the potential values are expressed in V vs. SSE. 2-3. Potentiostatic polarization measurement The surface of the specimens was finished with 1 μm diamond paste. 25 wt% NaCl aqueous solution at pH= 0 was used as the test solution to simulate a severe environment in a pit. The solution temperature was 40±2 °C. The test was conducted under deaerated atmosphere by purging argon. Potentiostatic polarization treatment was performed at -0.65 V prior to the test, then the corrosion potential of the specimen was measured for 10 minutes. The potentiostatic polarization was conducted. The potentiostatic conditions were -0.30 V, -0.25 V, -0.20 V, and -0.15 V. After the corrosion test, surface observation by a scanning electron microscope (SEM) and the depth profile measurement in the corroded area by a contact probe profilometer were conducted. 3. Results The pitting potential with different α phase content are listed in Table 2. The pitting potentials of the specimen prepared from 25%Cr-5.6%Ni-2%Mo DSS were approximately 0.17 ~ 0.18V and the pitting potentials of the specimen prepared from 25%Cr-8.4%Ni-2%Mo DSS were approximately 0.22 ~ 0.25V. The pitting potential of the cast DSS in the concentrated artificial seawater (TDS: ca. 4.7%) does not depend on the α phase content. The dependence of the preferentially dissolved phase on the holding potential, which determined by the SEM observation after the potentiostatic test, are also listed in Table 2. γ phase was preferentially dissolved at the higher holding potential and α phase was preferentially dissolved at the lower holding potential. With decreasing α phase content, γ phase was tendency to preferential dissolution at the lower holding potential. After the potentiostatic polarization test, SEM observation and the depth profile measurement in the corroded area were conducted to estimate the corrosion rate of each phase. The corrosion rate of the α phase tended to increase with increasing α phase content. In particular, as for the specimen in the α phase content of 58 vol% or more, the corrosion rate of α phase at higher potential range was significantly increased. The results of the SEM/EDS analysis in corroded area suggest that increase in corrosion rate of the α phase with increasing α phase content was caused by the Cr nitride formation in the α phase. Figure 1

Oxygen Containing Carbon Materials for High Capacity and Fast Chargeable Anode Materials of Lithium Ion Batteries

The lithium-ion battery is the most promising energy storage devices for variety of applications from portable electronics to electric vehicles because of its high energy density, power density and cycle life. However, the upcoming boom for artificial intelligence (AI) assisted transportations, Internet of Things (IoT) or potential wireless financial technologies may require batteries with much higher energy density and fast chargeable capability. Silicon and silicon monoxide have been extensive investigated for high capacity anode for more than 10 years. However, they are still hard to be used in real practice because of large volumetric expansion, poor cycle life, and bad rate capability. On the other hand, graphite is the most popular commercialized anode material for Li-ion battery because of its excellent coulombic efficiency, long cycle life, low cost and ease of processing. However, the limited theoretical capacity (372 mAh/g) and small interlayer spaces (0.335 nm) made it difficult to be used in the application of Li-ion batteries with higher energy density and fast chargeable Li-ion batteries (Fig.1a). In this study, we have introduced a novel Graphene-Like-Graphite (GLG) anode material to be used in Li-ion batteries with higher capacity and good rate capability. According to the Li-NMR study, lithium ions can intercalate into graphene layers with oxygen at 0-1.2V (vs Li) with non-stage phenomenon and delivered a capacity more than 372mAh/g. Meanwhile, at a higher potential range from 1.2 to 2V (vs Li), lithium ions continuous react with oxygen containing functional groups reversibly on the basal plane of each graphene layer. As a result, the GLG could have an initial discharge capacity up to 608mAh/g which is much larger than conventional graphite (372mAh/g). It was investigated that the higher oxygen content offers a higher reversible capacity over 1.2V (vs Li) discharge. Atom resolution STEM is also carried out for the characterization of single layer graphene of the GLG. It was learned that the GLG graphene layer has pore structure with the size less than 2nm, moreover the oxygen containing functional groups were attached on both basal plane and pores` s edge. The GLG was also characterized with NCM111 cathode for full-cell rate capability and cyclability. The cell charged to 60% of the capacity up to 6C (10min) charge with 103wh/kg cell design, while have good cycle ability. XPS, HAXPES, C-NMR were also used for the characterization of the GLG materials. Finally, a structure model was proposed for the next generation high rate, high capacity carbon based anode materials. Figure 1

Catalytic Activity and Stability of Ta Compounds for Oxygen Reduction Reaction

Durability is essential to electrocatalyst for fuel cell application. In this study, electrochemical stability of partially oxidized tantalum carbonitride (Ta-CNO), which is one of non-precious metal electrocatalyst for oxygen reduction reaction, has been investigated. The activity was the most stable around the rest potential in oxygen atmosphere, where was ca. 1.0 V vs. RHE, in chronoamperometry. It significantly decreased in higher potential range than the rest potential, and slightly decreased in lower potential range than the rest potential. Activity decrease ratio of the Ta-CNO was almost the same to a conventional Pt/C with rectangular potential wave between 0.6 to 1.0 V vs. RHE. The activity decrease of the Ta-CNO of the mixture with carbon black was larger than that of the Ta-CNO itself for both in constant potential and potential cycling.

Potential Dependent Adsorption Geometry of 2,5-Dihydroxybenzoic Acid on a Au(111) Surface: An in Situ Electrochemical Scanning Tunneling Microscopy Study

Adsorption and electrochemical behaviors of 2,5-dihydroxybenzoic acid (DHB) at the electrochemical interface of Au(111) electrode and 0.1 M aqueous perchloric acid solution have been studied by cyclic voltammetry and in situ electrochemical scanning tunneling microscopy. Under modulation of the substrate potential, three distinct phases labeled as I, II, and III are observed. DHB molecules take the flat-lying configuration and form the herringbone structure in phase I, which exists at lower potential range. DHB molecules take upstanding configuration and form short-range ordered phase II at higher potential range. A transitional phase consisted of alternately arranged flat-lying and upstanding DHB molecules is disclosed at intermediate potential. The potential induced structural transition can be ascribed to the deprotonation process of carboxylic group and redox reaction of hydroquinone moiety. The present study provides important experiment evidence for understanding the adsorption, redox, and structural transition of hydroquinone molecules on solid electrodes.

Electrochemical Aspects of the Reverse Micelle Extraction of Proteins

The mechanism of the solvent extraction of cytochrome c (Cyt c) via reverse micelle formation was studied from an electrochemical point of view. Potentiometric measurements showed that the Galvani potential difference of the oil/water (O/W) interface played a crucial role in the spontaneous extraction of Cyt c with bis(2-ethylhexyl)sulfosuccinate (AOT). However, the dependence of the extraction efficiency on the concentration of an aqueous electrolyte (KCl) could be explained not by the effect of the interfacial potential, but by the change in the interfacial tension (gamma). Electrocapillary measurements showed that the adsorption of AOT anions to the O/W interface resulted in a significant decrease of gamma in a higher potential range, where reverse micelles were formed. The bottom level of gamma in the higher potential range was increased with [KCl]. The lower extraction efficiency for higher [KCl]'s was elucidated by a "size exclusion effect". This was also supported by water-content measurements by the Karl Fisher method.

Electrochemical AFM study of LiMn 2O 4 thin film electrodes exposed to elevated temperatures

Surface morphology changes of LiMn 2O 4 thin film positive electrodes in lithium-ion batteries after repeated potential cycling or storage at elevated temperatures were observed by in situ atomic force microscopy (AFM) to elucidate the origin of capacity fading of LiMn 2O 4. After repeated potential cycling in the overall potential range from 3.50 to 4.30 V at elevated temperatures, the entire thin film surface was covered with small round-shaped particles accompanied by capacity fading of the electrode, while no significant changes were observed at 25 °C. The discharge capacity decreased more significantly when cycled in the lower potential range (3.81–4.07 V) than when cycled in the higher potential range (4.04–4.30 V). After storage at elevated temperatures at a depth of discharge (DOD) of 75%, which is located in the lower potential range, similar surface morphology changes were observed. In addition, discharge capacity markedly decreased, and the crystallinity of the LiMn 2O 4 thin film was lowered after storage. Hence, the observed changes in morphology at elevated temperatures are closely related to capacity fading of the LiMn 2O 4 thin film. The loss of crystallinity was caused by the formation of small particles on the LiMn 2O 4 surface, which would be accelerated on the LiMn 2O 4 surface in contact with an electrolyte solution through some kind of dissolution/precipitation reaction.

Study on the electric double layer of a cylindrical reverse micelle with functional theoretical approach

The iterative method in functional analysis is applied to looking for a solution of the Poisson-Boltzmann equation in order to describe the problems of the distribution of the potentials in the electric double layer (EDL) inside the water pool for a cylindrical inverse micelle. Potentials as a function of the position of a particular point in EDL are computed, which display a quantitative agreement with those from earlier calculation of Debye and Huckel in the case of low potentials. But it is also shown that in the higher-potential range the iterative calculations can give more accurate results. These results indicate the utility of this functional analysis technique in the description of the properties of EDL for a cylindrical inverse micelle.

Nucleation and growth mechanism for the electropolymerization of aniline in trifluoroacetic acid/lithium perchlorate/propylene carbonate medium

In the present work, the nucleation and growth mechanism for the electropolymerization of aniline in propylene carbonate medium containing 0.06 M trifluoroacetic acid and 0.05 M lithium perchlorate was investigated at different potentials on highly oriented pyrolytic graphite (HOPG) by potentiostatic current-time transients (i-t) and atomic force microscopic (AFM) measurements. The electrochemical data fitted with the theoretical curves for nucleation and growth suggest that the electropolymerization of aniline consists of progressive nucleation followed by 3D growth at an early stage and layer-by-layer growth in subsequent periods. The results obtained from transient analysis were in good agreement with the results of the AFM analysis. In our previous studies with aqueous solutions, we observed only progressive nucleation followed by a 3D growth mechanism for the electropolymerization of aniline in a higher potential range, 1.5–2.0 V vs. Ag/AgCl. Hence, the results obtained from the present work indicate that the nucleation and growth mechanism depends on the medium.

Study of Self Oscillatory Belousov-Zhabotinsky Systems Under the Perturbation of External EMF

An examination of the current and potential oscillations in the self oscillatory Belousov-Zhabotinsky system under the application of external EMF is presented for the first time. The system involves Mn(II) as the metal ion catalyst and malic acid/citric acid/malonic acid as the substrate. External EMF shifts the oscillatory profile to the higher potential range by the magnitude of applied EMF. The amplitude of current oscillations increases with the magnitude of external EMF. The behaviour of the system with and without a complexing agent (tetrasodium pyrophosphate) is rationalised in terms of individual steps involved in the overall reaction.

A high-resolution probe for space potential measurements

Abstract An instrument for measuring space potential is described. The instrument features a high-spatial resolution sensing probe which consists of one or two strands of carbon fibre on the end of a wire support. A technique of automatically controlling the corona current generated by the carbon fibre in an electric field is used to determine local space potentials in the range 0 to –30 kV. The overall accuracy of the system is about 4% when the probe is positioned optimally. The instrument could be modified to cover a higher potential range and could be adapted for monitoring positive as well as negative potentials.

Breakdown of Passivity of Nickel by Fluoride: II . Surface Analytical Studies

Passive layers on nickel and their change by the action of fluoride have been studied by surface analyses such as x‐ray photoelectron spectroscopy (XPS) and low energy ion scattering (ISS). The thickness of the layers is deduced from the height of the XPS signals , O1s, and F1s and their attenuation by covering layers. Argon sputtering gives information on the in‐depth structure of the passivating films in combination with XPS and the higher depth resolution of ISS. Their thickness and chemical composition change with the electrode potential and the time of exposure to . A multilayer structure is found with an inner oxide and outer hydroxide film and, in a higher potential range, a fluoride layer in between. The layer structure shows a close correspondence to the results of the electrochemical examination.