bluuebunny/crossref_metadata_2025_split huggingface dataset:
Symmetric Redox Flow Batteries with Bifunctional Molecules
Authors: Cording Faye , Friedl Jochen , Stimming Ulrich 
Published: February 2020

The continued integration of renewable energy sources into the power grid, as well as the development of decentralised energy systems, requires energy storage in order to capture and store the energy produced intermittently from renewable sources. One energy storage option is the Redox Flow Battery (RFB) which has several advantages over other secondary batteries. As the active species of an RFB remain in solution during charge and discharge, degradation of the electrodes is minimised. Further, due to external storage of the electrolytes, the energy and power of an RFB can be adjusted independently by varying the volume of stored electrolyte or size of the cell stack. The most mature RFB is the all-vanadium RFB but this also has drawbacks, such as slow electron transfer kinetics of the vanadium ions1 and a requirement for the use of acidic electrolytes.
Polyoxometalates (POMs) are anionic metal-oxygen clusters of early transition metals, commonly vanadium, molybdenum and tungsten, which can undergo redox reactions in which multiple electrons are transferred. The electrochemical properties of POMs prompted their investigation by our group and the development of a POM RFB which was based on the reactions of [PV14O42]9- at the cathode and [SiW12O40]4- at the anode.2 This work demonstrated that an RFB cell with multi-electron redox reactions occurring in each half-cell could be created by using POMs and that the charge transfer reactions of POMs are relatively fast.2 The [PV14O42]9-/[SiW12O40]4- RFB was classified as an asymmetric RFB due to the use of different POM active species in each half-cell. Alternatively, symmetric RFBs can be designed which utilise the same active material in both half-cells.
Our group has also investigated the approach of using bifunctional molecules, which can undergo redox reactions at positive and negative potentials, as the active species in symmetric RFBs. This includes the use of fullerene species functionalised with ferrocene units.3 POMs can also be bifunctional species when composed of two different redox-active metals. In this poster, we outline the results of work in our group on the use of bifunctional species in symmetric RFBs, including the study of a POM for a symmetric RFB which has shown good stability in charge-discharge testing so far in conditions that are only mildly acidic.

References

J. Friedl and U. Stimming, Electrochimica Acta, 2017, 227, 235–245.

J. Friedl, M. V. Holland-Cunz, F. Cording, F. L. Pfanschilling, C. Wills, W. McFarlane, B. Schricker, R. Fleck, H. Wolfschmidt and U. Stimming, Energy Environ. Sci., 2018, 11, 3010–3018.

J. Friedl, M. A. Lebedeva, K. Porfyrakis, U. Stimming and T. W. Chamberlain, J. Am. Chem. Soc., 2018, 140, 401–405.
Studying Aging of Lithium Ion Batteries – Observing Gas Evolution with in-Operando Mass Spectrometry
Authors: Mattinen Ulriika , Lindbergh Göran , Lindström Rakel Wreland , Klett Matilda 
Published: February 2020

Increasing our understanding on different aging processes and mechanisms linked to the lifetime and safety of lithium ion batteries is crucial for extending their usability in e.g. hybrid and electric vehicles followed by potential 2nd life applications. Coupling a mass spectrometer (MS) to a special on-line electrochemical cell hosting battery components enables time resolved detection of gases that are evolving during cycling and other aging. Gas evolving processes are for example decomposition of the electrolyte, formation of the SEI (solid electrolyte interphase) and other side reactions [1-3].
In this work, an in-house made adjustable electrochemical in-operando cell with a connection to the MS is used to study aging-related gas evolution at two types of cells: laboratory-scale lithium ion batteries and larger commercial cylindrical batteries. The design of the in-operando cell is flexible for different battery chemistries and to some extent different sizes.
The commercial cylindrical cells used in this study are NMC-based Li-ion batteries. The battery can is pierced to allow gas diffusion inside the leak-tight housing connected to the MS. Aging of the large batteries can be inhomogeneous [4] and therefore it is highly interesting to measure the gas evaluation also from large cells and compare these to small laboratory-scale cells aged at more defined conditions. For the commercial batteries, the possibility to perform long term aging experiments is desirable. The cell construction used in this work allows replacing the gas sampled from the cell head-space, ensuring constant pressure in the measurement chamber and enabling prolonged measurements. A safety valve is installed to release overpressure in case of an extensive gas evolution.
The goal of the presented work is to quantify gaseous products evolving upon battery aging with different operating parameters such as rate of charging [5], temperature, state of charge and voltage window to gain more insight to the aging phenomena.
[1] S. Meini, M. Piana, N. Tsiouvaras, A. Garsuch, H.A. Gasteiger, Electrochemical and Solid-State Letters 15(4) (2012) A45-A48.
[2] B.B. Berkes, A. Jozwiuk, M. Vracar, H. Sommer, T. Brezesinski, J. Janek, Analytical Chemistry 87(12) (2015) 5878-5883.
[3] D. Streich, A. Gueguen, M. Mendez, F. Chesneau, P. Novak, E.J. Berg, Journal of the Electrochemical Society 163(6) (2016) A964-A970.
[4] M. Klett, P. Svens, C. Tengstedt, A. Seyeux, J. Swiatowska, G. Lindbergh, R. Wreland Lindstroem, J. Phys. Chem. C 119(1) (2015) 90-100.
[5] A.S. Mussa, M. Klett, M. Behm, G. Lindbergh, R.W. Lindström, Journal of Energy Storage 13 (2017) 325-333.
Utilization of Carbon Nanotube Based Catalyst for the Performance Enhancement of Aqueous Organic Redox Flow Battery
Authors: Lee Wonmi , Ji Jungyeon , Kwon Yongchai 
Published: February 2020

Alloxazine and ferrocyanide were introduced as redox couple for aqueous organic redox flow battery (AORFB). Alloxazine was further modified by carboxylic acid (COOH) (COOH-alloxazine) to increase the aqueous solubility. For improving the performance of AORFB, the redox reactivity of the rate determining reaction (RDR) should be enhanced. Carboxylic acid group doped carbon nanotube (CA-CNT) catalyst was used for increasing the redox reactivity of RDR. The CA-CNT induced a better redox reactivity of COOH-alloxazine that was RDR because of the function of COOH as a proton donor. The strengthened hydrophilic property of COOH-alloxazine and the increased number of active sites were another reasons for causing the better redox reactivity. Regarding AORFB full cell testing, when the CA-CNT was adopted as the catalyst for the negative electrode, the performance of AORFB increased. According to the detailed results, charge/discharge overpotential and IR drop potential were enhanced, coulombic and energy efficiencies also increased, and discharging capacity reached to the similar level to that of vanadium redox flow battery.
Reference
[1] "Effect of carboxylic acid doped carbon nanotube catalyst on the performance of aqueous organic redox flow battery using the modified alloxazine and ferrocyanide redox couple", W. Lee, B.W. Kwon and Y. Kwon, ACS Applied Materials & Interfaces, 10, 36882-36891, 2018
Heterogeneous Electron Transport at PEDOT-PSS Electrode-Electrolyte Interfaces
Authors: Wijeratne Kosala , Ail Ujwala , Brooke Robert , Vagin Mikhail , Liu Xianjie , Fahlman Mats , Crispin Xavier 
Published: February 2020

Heterogeneous electron transport (HET) is important in many technologies, including batteries, fuel cells, medical sensors, organic electrochemical synthesis, food analysis, corrosion protection, and thermogalvanic cell. HET takes place at the interface between a solid electrode and a reactant in a liquid electrolyte, and it depends on the type of reactants, electrodes, solvents, and electrolyte. HET has been well studied for metal, semiconductor, metal oxide, carbon electrode. The current passing at the electrode/electrolyte interface is related to the density of electronic states of the electrode, the concentration of reactant and the rate of electron transfer and the electronic level of the reactant in the solution
Here, we study the HET between a conducting polymer electrode and a redox electrolyte, and we found that a new phenomenon is observed. Conducting polymers possess a unique combination of properties compared with most of the inorganic electrodes: acid resistance, the absence of surface-insulating oxide, low temperature and solution processability, a high natural abundance of their elements, molecular porosity. Conducting polymers are in-homogeneous conductors composed of ordered and disordered regions through which electronic transport takes place via percolation paths.
We studied the heterogeneous electron transport between the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and redox electrolyte ferro/ferricyanide in an aqueous electrolyte. We discovered that the density of percolation paths in the bulk of the material dictates the rate of electron transfer at the electrolyte–polymer electrode interface. This reveals one of the key parameters of designs to achieve efficient electrochemical technologies based on polymer electrodes.
We use this finding to optimize the electrical power generated by a thermogalvanic cell (TGC), which is an electrochemical device that converts heat energy into electricity. The power produced by the TGC increased by four orders of magnitude upon changing the morphology and electrical conductivity of the PEDOT electrode.
References:

Wijeratne K, Vagin M, Brooke R, & Crispin X (2017) Poly(3,4-ethylenedioxythiophene)-tosylate (PEDOT-Tos) electrodes in thermogalvanic J. Mater. Chem. A 5:19619 –19625.

Wijeratne K, Ail U, Brooke R, Vagin M, Liu X, Fahlman M, & Crispin X (2018) Bulk electronic transport impacts on electron transfer at conducting polymer electrode-electrolyte interfaces. PNAS, 115:11899 - 11904.
Novel Perceptions of Lithium Ion Batteries: Isotopic Labeling for Insights into Lithium Losses and Solid Electrolyte Interphase Formation By Means of Plasma-Based Techniques
Authors: Nowak Sascha , Evertz Marco , Diehl Marcel , Kenkel Alexander , Winter Martin 
Published: February 2020

Since their introduction in the early 90’s, the lithium ion battery (LIB) has to face challenging demands for mobile and stationary applications, respectively. In state-of-the-art LIBs, carbonaceous negative electrodes and lithium transition metal oxide (e.g. LiNi1/3Co1/3Mn1/3O2 (NCM111)) positive electrodes are used delivering outstanding energy densities. However, the cell suffers from performance losses - especially at elevated charging cut-off voltages exceeding 4.4 V - which cause is still a matter of discussion in literature.1,2

One postulated degradation mechanism is assigned to the passivation layer on the carbonaceous negative electrode, which is called the solid electrolyte interphase (SEI). It is formed during the first cycle due to the high reductive potential affecting the electrolyte and consuming active lithium. Nonetheless, it is still unknown which lithium source, either electrolytic or cathodic lithium, is electrochemically lost during this SEI formation. In order to quantify the lithium loss in both positive and negative electrodes, plasma-based analytical techniques are well suited for these investigations.
In this work, inductively coupled plasma-optical emission spectroscopy (ICP-OES) is used to investigate the lithium loss in charge/discharge aged layered NCM-based cathode materials as well as the lithium loss in carbonaceous anodes using glow discharge-sector field-mass spectrometry (GD-SF-MS). Additionally, investigations of 6Li-enriched cathode material or electrolyte solutions (6LiPF6) were conducted using inductively coupled plasma-mass spectrometry (ICP-MS) and GD-SF-MS for bulk and depth-resolved quantification of lithium losses in charge/discharge aged LIBs. Therefore, a NCM111 material is synthesized using 6Li-enriched components as source material as well as an isotope labelled conducting salt and cycled in a full-cell set-up to elucidate the origin of lithium losses. With this approach, it is possible to distinguish between lithium losses either from the conducting salt or the cathode material.
Furthermore, the origin of the lithium, which forms the SEI, can be traced via this approach. The electrode-near SEI consists of lithium originating from the electrolyte, while a mixed interlayer of lithium from both electrolyte and electrode is formed afterwards. Eventually, lithium in the electrolyte-near SEI originates from the cathode material (see Figure).

1 J. Vetter, P. Novák, M.R. Wagner, C. Veit, K.-C. Möller, J.O. Besenhard, M. Winter, M. Wohlfahrt-Mehrens, C. Vogler, A. Hammouche, J. Power Sources, 2005
, 147, 269-281.

2 J. Kasnatscheew, M. Evertz, B. Streipert, R. Wagner, R. Klöpsch, B. Vortmann, H. Hahn, S. Nowak, M. Amereller, A. C. Gentschev, P. Lamp and M. Winter, Phys. Chem. Chem. Phys., 2016, 18 , 3956-3965.

Figure 1
Online Characterization of Porous Separators for Disproportionation Redox Flow Batteries
Authors: Smith Kirk P , Ascencio Pedro , Howey David Alastair , Monroe Charles W 
Published: February 2020

Disproportionation redox flow batteries (DRFBs) employ active species whose oxidation states in both electrolytes are identical in the fully discharged condition, as seen in Figure 1. This feature allows for the use of simple porous materials for separators instead of more expensive, less robust ion-exchange membranes. DRFBs with porous separators tolerate crossover, because recombination of reduced and oxidized active species through the separator only affects round-trip efficiency, and does not permanently degrade the battery’s capacity. This advantage presents challenges when attempting to characterize DRFB performance, however, because crossover is always present, and substantial voltage relaxation occurs when performing open-circuit holds. A new characterization method is used to estimate the relationship between system state-of-charge and open-circuit potential (Nernst-equation parameterization, Figure 2) simultaneously with the instantaneous rate of crossover inside the reactor. This method, based on a simplified reactor model for DRFBs, consists of an adaptive observer which uses transient current and voltage data from the battery to quantify these interrelated phenomena.
The online characterization method was used to perform a parameter study probing the effects of liquid flowrates, active-species concentration, separator thickness/porosity, and solvent choice on the performance of porous separators in DRFBs by evaluating crossover rates, Nernst curves, and efficiencies. The DRFB used in this study consisted of vanadium acetylacetonate in various organic solvents, with tetraethylammonium tetrafluoroborate as a supporting salt. Various polypropylene separators (originally designed for lithium ion batteries) were used in the DRFBs.
This adaptive observer method is shown to be straightforward to implement and useful for characterizing the performance of different porous separators in DRFBs. Additionally, the overall parameter study allows for a greater understanding of the tradeoffs involved in operating DRFBs, independent of separator.

Figure 1
Spray-Drying As a Versatile Synthesis Method for Fluorophosphate-Based Compounds As Cathodes Material for Na-Ion Batteries
Authors: Bodart Jérôme , Eshraghi Nicolas , Mahmoud Abdelfattah , Vertruyen Bénédicte , Cloots Rudi , Boschini Frederic 
Published: February 2020

Fluorophosphate compounds attract much attention as cathode materials for Na-ion batteries. Indeed, thanks to the inductive effect of the fluoride and phosphate groups, such compounds exhibit a relatively high working potential and good theoretical capacity [1]. In this work, we focus on the iron (Na2FePO4F (NFPF)) and vanadium (Na3V2(PO4)3F3(NVPF)) based fluorophosphate materials which are characterized by a high theoretical capacity of 124 mAh/g and 128 mAh/g, respectively. In addition, the iron-based phase is also more environmental friendly due to the low toxicity of the iron.
The preparation of such complex phases using conventional solid-state route requires at least two steps with long heat treatment durations. Here, we report a facile aqueous synthesis using the spray-drying method that can be used for both NFPF and NVPF materials and that can be tuned in order to optimize the composition and the morphology of the desired materials.
The major limitation of phosphate-based electrodes is their low intrinsic electronic conductivity. The synthesis of composites with carbon is an effective strategy for the enhancement of the electronic conductivity of these compounds. Spray-drying is a suitable method to incorporate carbon in composite compounds due to the high homogeneity of the obtained particle [2]. It is also a cost effective and up-scalable technique which can produce large quantities of the desired material.
Here, we report the influence of the carbon addition of the structural, morphological and electrochemical properties of NFPF and NVPF compounds. The prepared composite materials were investigated by combining several characterisation techniques such as XRD, SEM and TEM. The electrochemical properties were evaluated by galvanostatic cycling and electrochemical impedance spectroscopy in Na-ion batteries.
[1] Eshraghi, N., Caes, S., Mahmoud, A., Cloots, R., Vertruyen, B., & Boschini, F. (2017). Sodium vanadium (III) fluorophosphate/carbon nanotubes composite (NVPF/CNT) prepared by spray-drying: good electrochemical performance thanks to well-dispersed CNT network within NVPF particles. Electrochimica Acta, 228, 319-324.
[2]Vertruyen, B., Eshraghi, N., Piffet, C., Bodart, J., Mahmoud, A., & Boschini, F. (2018). Spray-Drying of Electrode Materials for Lithium-and Sodium-Ion Batteries. Materials, 11(7), 1076.
Studies on Full Na-Ion Batteries with a Hard Carbon Anode and Oxide Cathode Materials
Authors: Mikhailova Daria , Maletti Sebastian , Leones Rita , Pampel Jonas , Dörfler Susanne , Giebeler Lars 
Published: February 2020

The limited abundance of lithium on the Earth forces the search of alternative battery systems for mobile and stationary applications. Sodium-ion batteries could be a reasonable replacement for lithium-ion ones if a compromise between electrochemical performance and cost can be found.
Since the ionic radius of Na+ is larger than of Li+, the choice for electrode materials is more restricted compared to Li-ion batteries, despite the similar chemistry of Na- and Li-compounds in many cases. The reason for that is a lower stability of crystalline phases with Na in fully charged or discharged states because of a larger volume change upon sodiation/desodiation.
Anode materials like metallic alloys on the basis of Sn, Sb or Ge represent the most crucial point in Na-ion batteries because of a huge volume difference between sodiated and desodiated states, resulting in fast capacity fading due to reducing the particle size and contact loss. Hence, nowadays solely hard carbons (HC) can exhibit electrochemical performance suitable for a potential application. The structure of hard carbon consists of amorphous areas (sp
3-hybridization of carbon) embedding and partially crosslinking layered graphitic segments of low dimensional graphene layers (sp
2-hybridization of carbon). Electrochemical insertion of sodium into hard carbon involves two steps: a slope potential region resulting from very stable intercalation of Na-ions between graphitic layers, and a plateau in potentials from adsorption of ions in micropores. Upon desodiation, a large irreversible capacity up to 70 % of the total first discharging capacity is usually observed, which includes the solid-electrolyte interface (SEI) formation, and Na-ions being stably trapped between graphitic layers [1].
In our present work, we studied electrochemical performance of full Na-ion batteries with olivine-like NaFePO4 or layered-type NaNi0.5Ti0.5O2 cathodes, and HC anode materials. In order to overcome the problem with irreversible capacity loss, hard carbon materials were partially or fully sodiated (discharged) prior to electrochemical tests. A NaPF6-containing electrolyte modified with 1-butyl-1-methylpyrrolidinium hexafluorophosphate was used. The observed specific capacities of about 150 mAh g-1 for NaFePO4/HC batteries after 20 cycles are comparable with half NaFePO4/Na cells [2], while NaNi0.5Ti0.5O2/HC batteries show about 75 mAh g-1 (Fig. 1). The reason for a lower capacity retention of NaNi0.5Ti0.5O2 upon cycling is discussed.
Figure 1. Specific capacity of full Na-ion batteries with NaFePO4 (NFPO) and NaNi0.5Ti0.5O2 (NNTO) cathodes and hard carbon (HC) anodes, normalized on the cathode weight, at C/10 rate meaning 1Na intercalated during 10 h.
References
[1] E. Irisarri et al., J. Electrochem. Soc., 162 (2015) A2476-A2482.
[2] G. Ali et al., ACS Appl. Mater. Interfaces, 8 (2016) 15422−15429.

Figure 1
Carbon Hybrids As Versatile Electrocatalysts for Energy Related Reactions
Authors: Fernandes Diana Mesquita , Freire Cristina 
Published: February 2020

Since their discovery, carbon nanomaterials (CMs) have been attracting considerable experimental and theoretical interest because of their exceptional structures and properties. Due to their unique structural diversity and the ease of tuning their chemical, electronic and crystalline properties, CMs are attractive for a wide range of electrochemical applications, such as electrocatalysis, fuel cells, batteries and supercapacitors. Also, their properties, such as fast electron transportation, excellent mechanical strength and high surface area, suggest their ability to detect analytes and to promote a fast electron transfer between the electrode and the analyte, which make them promising ECs. CMs have also been presented as effective electrocatalysts that fulfill the requirements for several electrochemical reactions of massive importance in energy conversion systems. Additionally, the possibility of chemical modification and/or functionalization broadens their utility and gives rise to favourable electrocatalytic properties with regard to several electrochemical processes.
Platinum nanoparticles supported on carbon materials (Pt/C) are the most effective known ORR/HER catalysts, leading to low ORR/HER overpotential, large current densities, and selectivity toward a direct 4-electron pathway in the case of ORR. Nevertheless, the required high Pt loading associated with its high cost, scarcity, declining activity and possible Pt-deactivation by methanol crossover for ORR, have limited the large-scale application of Pt-based ECs. Therefore, research efforts have been devoted to developing alternative ECs, with a competitive activity with the Pt/C but more stable and cost-effective. In this context, we have developed several ECs (POM@CMs, metal oxides@CMs and biomass-derived CMs) with good electrocatalytic activity towards ORR and/or HER.

Figure 1. ORR by Co4(PW9)2@Carbon material in alkaline medium

Figure 1