Platinum Surface Area Research Articles

A Semi-Empirical Catalyst Degradation Model Based on Voltage Cycling under Automotive Operating Conditions in PEM Fuel Cells

Catalyst degradation in membrane electrode assemblies was studied by voltage cycling in hydrogen/air atmosphere. The sensitivity of loss of electrochemically active surface area (ECSA) of the platinum catalyst during voltage cycling to various operating parameters relevant for automotive applications was measured. The investigated stressors were humidity, temperature, upper and lower potential limit and cycle duration. ECSA loss increased at high humidity, temperature and upper potential limit. The impact of the lower potential limit was less pronounced. ECSA loss per cycle increased for longer cycle durations suggesting that the number of cycles and the time spent at high potential in each cycle are of equal importance. A semi-empirical ECSA loss model based on the accelerated stress tests was derived and validated in order to predict platinum surface area loss after voltage cycling and the resulting current-voltage characteristics after degradation.

Analysis of Oxygen Transport Resistances in the Catalyst Layers with Different Carbon Supports in PEFC

In polymer electrolyte fuel cells (PEFCs), the catalyst layer (CL) of the cathode needs a large amount of Pt because of the slow oxygen reduction reaction. Since electron, proton, and oxygen are necessary for the cathode reaction, achieving the optimum structure of electrode CL and the efficient transport of the reactants is significantly effective to reduce the usage of Pt catalyst. In this study, the effects of carbon structure on oxygen transport were evaluated using CLs fabricated under several conditions. We compared the performances using fabricated CLs with Ketjen black and Vulcan. Furthermore, the oxygen transport resistance in the CLs was evaluated. Pore size distribution (PSD) of the CL was measured by nitrogen physisorption method, and the CL structural parameters were estimated using the estimation model (1). Using the limiting current density method, we evaluate various oxygen transport resistances in the CL and discuss the contributions of these resistances to the cell performance. Figure 1 shows the estimated schematics of Pt-supported Ketjen black and Vulcan with ionomer. To investigate the structure of the fabricated CLs, we measured the PSDs by nitrogen physisorption method, and the results are shown in Figure 2. In the case of using Ketjen black, there is a small peak around 3-4 nm pore diameter, whereas in the case of Vulcan this peak does not exist. The small peak is considered to correspond to the pores in the carbon particles with a diameter of ~ 10 nm, and the difference in the PSDs for the self-produced CL is caused by the characteristics of the Vulcan with few pores in the particle. From these results, it is expected that most of the platinum particles are located on the outer surface of the Vulcan, and oxygen can easily diffuse to the platinum particles through the ionomer. Figure 3 shows the characteristics of the oxygen transport resistance of different thick CLs. By multiplying the measured oxygen transport resistance in the CL by the thickness of the CL, it is possible to evaluate only the change in the diffusion resistance in the CL pores, eliminating the influence of the oxygen transport resistance on the platinum surface and the dissolution resistance into the ionomer (1). From the gradients of the lines in Fig. 3, the effective diffusion coefficients can be estimated: DCL,eff O2=7.2×10-7 [m2/s] for the CL with Ketjen black and DO2 CL,eff =4.3×10-7 [m2/s] for that with Vulcan. The smaller effective diffusion coefficient with Vulcan is caused by the lower porosity. Figure 4 shows the characteristics of the oxygen transport resistance of the CLs having different platinum surface areas. The vertical axis represents the oxygen transport resistance in the CL, and the horizontal axis represents the inverse of the platinum surface area. Here, Pt-supported carbons with three different Pt densities were used, and the carbon amounts were set similar. Based on the gradients of the lines, the value of the oxygen transfer rate constant kPt at the platinum surface are estimated to be kPt=3.7×10-3 [m/s] for the CL with Ketjen black and kPt=9.3×10-3 [m/s] for that with Vulcan. Figures 5 and 6 show the results calculating the oxygen transport resistance of the fabricated CLs using the parameters estimated from the experiment. The oxygen dissolution rate kdiss=7.0×10-3 [m/s], estimated in the previous study (1), was applied here. With the CL with Ketjen black, the resistance at the platinum surface, R Pt , is a dominant factor, whereas the contribution of the resistance at the platinum surface with Vulcan reduces. This is considered to be because platinum particles are arranged outside the carbon particles. However, the diffusion resistance in the pores with Vulcan increases due to the lower porosity. This suggest that it is effectiveto increase the porosity for further reduction in the oxygen transport resistance in the thick CL with Vulcan. Reference Tabe, et al., ECS Trans., 80(8), 205 (2017). Figure 1

Development of a Hydrogen Contaminant Detector

As fuel cell vehicles (FCV) are introduced and commercialized, durability remains a critical characteristic towards competing with the lifecycle of conventional vehicle engines1. Reforming and electrolysis still remain as the dominant production processes for the foreseeable future for the hydrogen fuel. Coupled with transportation, storage, and delivery into FCVs, numerous sources of contamination are possible to introduce impurities into hydrogen fuel, which can enter into and poison the fuel cell, leading to rapid degradation of performance. In this work, we detail the development of an electrochemical hydrogen contaminant detector (HCD) designed to measure the quality of hydrogen fuel dispensed at the filling station against the specifications outlined by the SAE J27192. Specifically, the role that mass transport plays in the sensor response is discussed. The sensor consists of a two-electrode system, for hydrogen oxidation and evolution in the fueling system environment, which consist of a low surface area platinum and platinum-rhodium alloy couple. A Nafion electrolyte coats the tip of the HCD to conduct protons between the electrodes. Baseline performance is measured on clean hydrogen, which rapidly degrades when the impurities are presented. Experimental response of the HCD to carbon monoxide is presented3. A thin Nafion film, provides rapid response within 30 seconds, but quickly degraded and delaminated off the electrode surfaces. Development of more durable Nafion electrolyte film is discussed which shows much slower response time due to increased thickness. The effect of relative humidity, alternate electrolytes and high-pressure on the HCD response are also presented. References 1) U.S. Drive Fuel Cell Tech Team Roadmap, https://www.energy.gov/eere/vehicles/downloads/us-drive-fuel-cell-technical-team-roadmap (2017). 2) SAE International Surface Vehicle Standard J2719TM, http://standards.sae.org/j2719_201511/ (2015). 3) C.J. Banas, L.J. Bonville, U. Pasaogullari and T.M. Molter, ECS Trans., 80(8), 497-507 (2017).

Correlation of Changes in Electrochemical and Structural Parameters due to Voltage Cycling Induced Degradation in PEM Fuel Cells

Membrane electrode assemblies were degraded by voltage cycling in hydrogen/air atmosphere. The impact of degradation on fuel cell performance was measured by various electrochemical characterization techniques. Loss of electrochemically active surface area was correlated to kinetic voltage losses at low current density as well as losses at high current density due to oxygen transport limitations. It was found that the oxygen transport resistance scales proportionally to the inverse of normalized platinum surface area. The change in the catalyst layer structural properties due to voltage cycling was visualized by electron microscopy. A new method of calculating changes in platinum loading of degraded samples by transmission electron microscopy is presented and shows redistribution of platinum in the catalyst layer due to platinum dissolution.

In situ determination of the electrochemically active platinum surface area: key to improvement of solid acid fuel cells

Surface oxide reduction is demonstrated for measuring the active Pt surface area in a solid electrolyte system at 240 °C.

Investigation of Oxygen Transport Resistance in M-ACLS Electrodes for PEFC Cathodes

1.Introduction Significant reduced use of platinum catalyst is essential for full-scale implementation of polymer electrolyte fuel cells (PEFCs). Toshiba has developed an alternating catalyst layer structure (ACLS) catalytic electrode fabricated by a sputtering process and is studying its application in PEFCs.1 The ACLS cathode has been modified and previous studies have reported good power generation characteristics and high durability at a platinum loading of 0.15 mg cm-2 using a modified ACLS (M-ACLS).2 The power generation characteristics of PEFCs strongly depends on oxygen transport in the catalyst layer in addition to the catalytic activity. Because the catalyst layer structure of the M-ACLS electrode is characterized by nanosheet platinum, which differs from commonly used nanoparticulate Pt/C, it is necessary to understand the oxygen transport capability in order to reduce the platinum loading. In recent years, measurement of oxygen transport resistance by the limiting current method using a PEFC single cell is almost established.3,4 In this presentation, we report the result of investigating the oxygen transport resistance of the M-ACLS electrode using the limiting current method ２． Experimental A catalytic electrode precursor containing platinum and pore-forming material was deposited on a commercially available gas diffusion layer substrate by using a sputtering device, and then the pore-forming material was removed to prepare the M-ACLS anode and the M-ACLS cathode. The electrode structure was observed by SEM. Various properties such as the specific surface area of the platinum catalyst, the roughness factor (the ratio of the platinum surface area to the electrode area), and power generation characteristics were evaluated with reference to the Fuel Cell Commercialization Conference of Japan protocol. Furthermore, the limiting current was obtained in temperature range of 50 °C to 80 °C using two different kinds of diluted oxygen gas (oxygen dry mole fraction 0.01, dilution gas N2 or He). Transport resistance was separated by utilizing the difference in oxygen diffusibility between the two kinds of dilution gasses or pressure dependency.3,4 ３．Results and discussion Figure 1 shows an example of a cross-sectional SEM photograph of a M-ACLS catalytic electrode laminated with a porous platinum sheet, which is found to have a high porosity without carrier. Figure 2 shows a typical I-V curve using the limiting current method. It can be seen that the value of the limiting current density changes, reflecting the difference in oxygen diffusibility in the two kinds of dilution gases. In this presentation, we report the oxygen transport resistance analysis results of M-ACLS cathode, oxygen transport resistance per unit platinum surface area, and superiority of M-ACLS catalytic electrode to over nanoparticulate Pt/C. (1) W. Mei, T. Fukazawa, Y. Nakano, Y. Akasaka, K. Naito, ECS Trans., 50(2), 1377 (2012) (2) W. Mei, T. Fukazawa, T. Yang, N. Yoshinaga, Y. Kanai, ECS Trans., 69(17), 755 (2015) (3) T. Mashio, A. Ohma, S. Yamamoto and K. Shinohara, ECS Trans., 11(1), 529 (2007) (4) N. Nonoyama, S. Okazaki, A. Z. Weber, Y. Ikogi, T. Yoshida, J. Electrochem. Soc., 158 (4), B416 (2011) Figure 1

Temperature and Relative Humidity Effect of Start-up / Shut-Down Damage in PEMFCs

For proton exchange membrane fuel cells (PEMFCs), meeting automotive lifetime requirements during transient operating conditions such as start-up/shut-down (SUSD) remains one of the main challenges to date. During SUSD, a hydrogen/air front moves through the anode, causing oxidation of the cathode carbon support.1 While changing the support material from conventional to graphitized carbon blacks has a mitigating effect on degradation,2 the dependence of SUSD degradation on temperature and relative humidity (RH) has not yet been thoroughly quantified. In the first part of this work, we study the effect of temperature on SUSD degradation in 50 cm2 single cell experiments and compare the results with model predictions based on the carbon oxidation reaction (COR) kinetics for conventional and graphitized carbon supports. Polarization curves on commercially available membrane electrode assemblies (MEAs) with conventional carbon supports exhibit a clear trend of performance degradation, which is more severe at higher temperatures (Figure 1). While SUSD cycles performed at 5 °C hardly cause any activity loss, SUSD cycles at 40 and 80 °C result in a severe performance degradation, illustrated by comparing polarization curves after 100 SUSD cycles. Further, a one-dimensional steady-state SUSD model, as proposed by Gu et.al,3 is adapted to predict the COR current induced by SUSD cycles. On MEAs with conventional carbon supports, the predicted COR currents vs. SUSD temperature coincide well with measured degradation rates (≈ 10-fold lower degradation rates at 5 °C vs. 80 °C in comparison to ≈ 8-fold lower COR currents predicted by our model). However, for MEAs with graphitized carbon support, the measured performance degradation decreases by a factor of ≈ 10 when lowering the SUSD temperature from 80 °C to 5 °C, which is in strong contrast to predicted ≈ 39-fold decrease of the COR currents. As we will show, this discrepancy can be explained by a change of the prevalent degradation mechanism from COR to platinum surface area loss, which is not considered in the model.4 In the second part of this work, we focus on the impact of RH on SUSD degradation. The model used in the first part of this study is therefore extended by the water activity dependence of the COR kinetics, which is determined experimentally via exhaust gas analysis in half-cell experiments. A predicted factor of ≈ 4 between the COR during SUSD events carried out at low RH (25 %) and full humidification (100 %) at 80 °C on conventional carbon supported electrodes can be calculated, when a COR reaction order of one with respect to RH is applied. Within the accuracy of the model, this agrees well with the experimentally determined factor of ≈ 3 for the decrease in performance. In summary, in this work we will compare experimental SUSD degradation rates vs. temperature, RH, and carbon-support type with predictions from a simple kinetic model. Acknowledgments The authors gratefully acknowledge financial support by Volkswagen AG and supply of graphitized carbon electrode decals by Greenerity GmbH.

Electrochemical oxidation of ethylene glycol in a channel flow reactor

Electrochemical oxidation of ethylene glycol has been studied in a channel flow reactor (CFR) on high surface area platinum at three different flow rates and varying potentials. Sampled current potential obtained from chronoamperometry experiments agrees well with the voltammetry data reported in the literature. The current at any potential was observed to be a weak function of the flow rate. The products of the oxidation reaction have been identified using high performance liquid chromatography (HPLC). In addition to all the usual C2 fractions (glycolaldehyde, glycolic acid, glyoxylic acid, glyoxal and oxalic acid) already reported, an important C1 fraction (formic acid) has been observed in significant quantities at low flow rates. The results of this study suggest cleavage of CC bond, though the exact pathway remains unclear. Further, distinct changes in the product profile (amount of different C1 and C2 fractions) were observed with flow rate. Glycolic acid was the only product that was observed in significant quantities at all flow rates. The results suggest interplay of contact time of the reactants with the thin film catalyst, kinetics and reaction pathway and demonstrate the usefulness of a channel flow reactor.

Investigation of Oxygen Transport Resistance in M-ACLS Electrodes for PEFC Cathodes

Modified alternating catalyst layer structure (M-ACLS) is a promising low-platinum technology for application in polymer electrolyte fuel cells (PEFCs). Because the catalyst layer structure of an M-ACLS electrode is characterized by nanosheet platinum, which differs from the commonly used Pt/C, it is necessary to understand the oxygen transport capability. In this study, the oxygen transport resistance was investigated using limiting current measurement. It is found that, compared with Pt/C, M-ACLS cathodes exhibited far lower oxygen transport resistance per unit platinum surface area.

Ultra-fine Pt nanoparticles on graphene aerogel as a porous electrode with high stability for microfluidic methanol fuel cell

Abstract Platinum-decorated graphene aerogel as a porous electrode for flow-through direct methanol microfluidic fuel cell is introduced. Ultra-fine platinum nanoparticles with size ranged from diameter 1.5 nm–3 nm are evenly anchored on the graphene nanosheets without agglomeration. The electrode is characterized by scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. Catalytic activity is confirmed by cyclic voltammetry. The electroactive surface area and catalytic activity of platinum on graphene oxide (Pt/GO) are much larger than commercial platinum on carbon black (Pt/C). A counterflow microfluidic fuel cell is designed for contrasting the cell performance between flow-over type and flow-through type electrodes using Pt/C on carbon paper and Pt/GO, respectively. The Pt/GO electrode shows 358% increment in specific power compared with Pt/C anode. Apart from catalytic activity, the effect of porous electrode conductivity to cell performance is also studied. The conductivity of the porous electrode should be further enhanced to achieve higher cell performance.

PEM Fuel Cell Start-up/Shut-down Losses vs Temperature for Non-Graphitized and Graphitized Cathode Carbon Supports

One of the key figures for the success of proton exchange membrane fuel cells (PEMFCs) in automotive applications is lifetime. Damage of the cathode carbon support, induced by hydrogen/air fronts moving through the anode during start-up/shut-down (SUSD), is one of the lifetime limiting factors. In this study, we examine the impact of varying the temperature at which SUSD events take place, both experimentally and by a kinetic model. For MEAs with conventional carbon supports, the model prediction of carbon oxidation reaction (COR) currents as a function of temperature matches well with the temperature dependence of experimentally determined SUSD degradation rates (predicting ≈8-fold lower COR currents compared to ≈10-fold lower measured degradation rates at 5°C compared to 80°C). This, however, is not the case for MEAs with graphitized carbon supports, where a factor of ≈39 lower COR currents are predicted when decreasing SUSD temperature from 80 to 5°C, in contrast to the measured decrease by a factor of ≈10. As we will show, this is explained by a change of the governing degradation mechanism from predominantly carbon corrosion induced losses at higher temperature to predominantly voltage cycling induced platinum surface area losses near/below room temperature.

Statistical Analysis for the Electrochemical Performance of a 3D Reconstructed Catalytic Layer

The structure of a catalyst layer (CL) in a proton exchange membrane fuel cell (PEMFC) varies according with the deposition technique and the chemical composition that build it up. Then, the electrical, ionic and catalytic properties depend on the final structure. These characteristics have also an impact on the overall response of the PEMFC. In this work, stochastic reconstruction of the microstructure of a PEMFC CL and a scaling method are used to determine the effective transport coefficients and a statistical electrochemical surface area of platinum associated with the active sites. The case study contains three stages: 1) the charge transport continuity equation is used to determine conduction efficiency. 2) The platinum surface is determined by a statistical algorithm that considers the percolation and the three phase union condition. 3) Finally, an analytical model for electrochemical behavior is applied. These numerical and analytical models are applied to hypothetical microstructures of the carbon support, ionomer electrode load and platinum to carbon weight ratio.

Preliminary Study of a Hydrogen-Vanadium Flow Battery

Hydrogen-vanadium flow batteries offer a feasible solution for storing electrical energy from the grid or directly from renewable energy sources such as wind and solar. While charging, a hydrogen-vanadium flow battery stores energy in the form of hydrogen and vanadium (V). During discharge, hydrogen is consumed at the negative electrode and vanadium (V) is reduced to vanadium (IV) at the positive electrode. Vanadium systems demonstrate no issues with membrane fouling or metal dendrite formation.1 Additionally, vanadium solutions have low volatility, low corrosivity, and do not produce toxic vapors.1 Due to the relatively high cost of vanadium, the hydrogen-vanadium flow battery is attractive over the all-vanadium system due to the 50% reduction in the amount of vanadium solution required. Past research by Yufit et. al. has shown the feasibility of the hydrogen-vanadium flow battery and the importance of vanadium electrode wettability on fuel cell performance.1 Additionally, studies by Menictas et. al. also revealed crossover of vanadium species during operation of the vanadium-oxygen flow battery, sparking our interest in vanadium’s effect on the hydrogen electrode catalyst.2 In this study, we examine the performance of a hydrogen-vanadium flow battery when using interdigitated flow fields at both electrodes and a high surface area carbon nanotube electrode as the vanadium electrode. With a reference electrode placed in the vanadium side, we separate the cell performance into individual electrode performance. Using the half-cell results and electrochemical impedance measurements we identify the components and processes that have the greatest influence on the performance of the flow cell during discharge and charge. Additionally, we explore if crossover of vanadium through the polymer electrolyte membrane results in any negative effect on the platinum catalyst at the hydrogen electrode. This will be determined by employing electrochemical measurement techniques using a platinum rotating disc electrode and a 3-electrode arrangement. In turn, the effect of vanadium crossover to the hydrogen electrode will be investigated by measuring effective exchange current density and electrochemical active surface area (ECSA) of platinum when vanadium (IV) and vanadium (V) are present in the electrolyte.

Voltage Cycling Induced Losses in Electrochemically Active Surface Area and in H2/Air-Performance of PEM Fuel Cells

The influence of voltage cycling profiles on the degradation of MEAs (membrane electrode assemblies) for PEM (proton exchange membrane) fuel cells was investigated using MEAs with carbon supported catalysts. The loss of electrochemically active surface area (ECSA) of the cathode electrodes significantly increased with the upper potential limit. The ECSA loss was correlated with the performance decrease for hydrogen/air polarization curves, revealing purely kinetic losses at low and additional mass-transport related voltage losses at high platinum surface area normalized current densities (≡specific current densities). The absolute voltage losses only depended on the specific current density, independent of the extent of ECSA loss and the geometric current density.

Performance of the hydrogen–air fuel cell with a Russian analogue of the Aquivion solid polymer electrolyte

The results of testing of membrane electrode assemblies (MEA) of a hydrogen–air fuel cell (FC) based on the domestic analog of the Aquivion polymer electrolyte with a shortened polymer chain synthesized by a new procedure of aqueous emulsion copolymerization of fluorinated monomers are presented. The obtained data are compared with the performance of MEA based on the commercial Nafion electrolyte. The stress testing of MEA in FC functioning without a load at reduced relative moisture content of the gas and at 90°C showed for each MEA a decrease in the cathode catalyst (platinum) surface area and an increase in the resistance caused by partial destruction of the electrolyte. The current–voltage characteristics and stability of the Aquivion-based MEA exceed the performance attained using the commercial Nafion electrolyte.

Platinum-Tin Nano-Catalysts Supported on Alumina for Direct Dehydrogenation of n-Butane.

Al2O3 supports were prepared by a precipitation method using various basic solutions (NaOH, KOH, NH4OH, and Na2CO3) as precipitation agents, and Pt/Sn/Al2O3 nano-catalysts were then prepared by a sequential impregnation method. The prepared catalysts were applied to the direct dehydrogenation of n-butane to n-butenes and 1,3-butadiene. The effect of precipitation agents on the physicochemical properties and catalytic activities of Pt/Sn/Al2O3 nano-catalysts in the direct dehydrogenation of n-butane was investigated. Catalytic performance of Pt/Sn/Al2O3 nano-catalysts decreased in order of Pt/Sn/Al2O3 (NaOH) > Pt/Sn/Al2O3 (KOH) > Pt/Sn/Al2O3 (NH4OH) > Pt/Sn/Al2O3 (Na2CO3). Among the catalysts tested, Pt/Sn/Al2O3 (NaOH) nano-catalyst showed the best catalytic performance in terms of yield for total dehydrogenation products (TDP, n-butenes and 1,3-butadiene). Hydrogen chemisorption experiments revealed that platinum surface area of the catalyst was closely related to the catalytic performance. Yield for TDP increased with increasing platinum surface area of the catalyst.

A voltammetric method of measuring the specific surface area and amount of platinum in microsamples of electrode material and membrane-electrode assembly of hydrogen fuel cells

A method based on cyclic voltammetry is proposed for determining platinum content, measuring the specific area of the active surface of platinum nanoparticles, and studying the dynamics of these values in a small amount (micrograms) of sample material.

Development of carbon supports with increased corrosion resistance for Pt/C catalysts for oxygen electroreduction

The influence of different surface modifications of carbon supports on the corrosion resistance of 50 wt % Pt/C catalysts on their basis was studied. The corrosion resistance was measured from changes in the electroactive surface area of platinum in the course of potential cycling from 1.0 to 1.5 V versus the reversible hydrogen electrode (potential sweep rate, 0.5 V/s) during 60000 cycles. A 40% Pt/Vulcan XC-72 commercial catalyst was used as the reference sample. The supports were modified by the carbonization of the high surface area carbon black Ketjenblack DJ-600 and by the additional activation of the carbon-carbon composite Sibunit-1562. It was found that the preliminary carbonization of the Ketjenblack DJ-600 support with a propane-butane mixture at 770°C and the activation of Sibunit-1562 with subsequent thermal treatment at 500°C increased and decreased, respectively, the corrosion resistance of the 50 wt % Pt/C catalysts on their basis.

Electrochemical and structure characteristics of PtCoCr/C-Catalyst with platinum content 50 wt % and cathode on its basis for fuel cell with proton-conducting polymer electrolyte

Electrochemical and structure characteristics of PtCoCr/C-catalyst with platinum content 50 wt % under model conditions and in cathode of membrane-electrode assembly (MEA) of hydrogen-oxygen fuel cell are studied. The metal-phase nanoparticles are shown to represent a Pt3Co alloy with partial inclusion of chromium, the nanoparticles surface being enriched with platinum. The platinum mass activity and the PtCoCr/C-catalyst high corrosion resistance do not depend on the amount of platinum deposited onto XC72 carbon black (20 or 50 wt %). Herewith the platinum surface area decreases in the same way as the carbon black specific surface area (measured with the BET method); the latter is 227, 169, and 105 m2/g for pure carbon black and that containing 20 and 50 wt % Pt, respectively. Testing of the 50PtCoCr/C-catalyst in the MEA cathode active layer in hydrogen-oxygen fuel cell showed performance not inferior to MEAs with pure-platinum systems, the catalyst being more stable.

Synthesis and characterization of a new family of aryl-trifluoromethanesulfonylimide Li-Salts for Li-ion batteries and beyond

The battery energy-storage industry is evolving rapidly so new battery components are needed with high stability and improved energy density, as well as enhanced safety. In this paper, results on new salts, safer degradation and good electrochemical performances are reported. Four organic anions for Li-salts were synthesized and their conductivity, viscosity and electrochemical potential window in EC/DEC (3/7) solutions were examined. These salts have high thermal stability and safer degradation products (compared to LiPF6 and Li-TFSI), which were identified by TGA-MS. Cyclic voltammetry measurements showed their electrochemical window and oxidation limits were at least 4.3 and 4.5 V vs Li/Li+ using a platinum and high surface area carbon material working electrode, respectively. The salts passivated the common aluminum current collector at 4.4 V vs Li/Li+ and without corrosion. The properties of one Li salts were evaluated in half cell configuration as a model system using lithium iron phosphate (LFP), lithium titanate oxide (LTO) and graphite as electrodes. The performance of the salt showed promising behavior in the model system, compared to benchmark salts such as LiPF6 and Li-TFSI.