TY - JOUR
AB - The substitution of heavier, more metallic atoms into classical organic ligand frameworks provides an important strategy for tuning ligand properties, such as ligand bite and donor character, and is the basis for the emerging area of main-group supramolecular chemistry. In this paper, we explore two new ligands [E(2-Me-8-qy)3] [E = Sb (1), Bi (2); qy = quinolyl], allowing a fundamental comparison of their coordination behavior with classical tris(2-pyridyl) ligands of the type [E′(2-py)3] (E = a range of bridgehead atoms and groups, py = pyridyl). A range of new coordination modes to Cu+, Ag+, and Au+ is seen for 1 and 2, in the absence of steric constraints at the bridgehead and with their more remote N-donor atoms. A particular feature is the adaptive nature of these new ligands, with the ability to adjust coordination mode in response to the hard–soft character of coordinated metal ions, influenced also by the character of the bridgehead atom (Sb or Bi). These features can be seen in a comparison between [Cu2{Sb(2-Me-8-qy)3}2](PF6)2 (1·CuPF6) and [Cu{Bi(2-Me-8-qy)3}](PF6) (2·CuPF6), the first containing a dimeric cation in which 1 adopts an unprecedented intramolecular N,N,Sb-coordination mode while in the second, 2 adopts an unusual N,N,(π-)C coordination mode. In contrast, the previously reported analogous ligands [E(6-Me-2-py)3] (E = Sb, Bi; 2-py = 2-pyridyl) show a tris-chelating mode in their complexes with CuPF6, which is typical for the extensive tris(2-pyridyl) family with a range of metals. The greater polarity of the Bi–C bond in 2 results in ligand transfer reactions with Au(I). Although this reactivity is not in itself unusual, the characterization of several products by single-crystal X-ray diffraction provides snapshots of the ligand transfer reaction involved, with one of the products (the bimetallic complex [(BiCl){ClAu2(2-Me-8-qy)3}] (8)) containing a Au2Bi core in which the shortest Au → Bi donor–acceptor bond to date is observed.
AU - García-Romero, Álvaro
AU - Waters, Jessica E.
AU - Jethwa, Rajesh B
AU - Bond, Andrew D.
AU - Colebatch, Annie L.
AU - García-Rodríguez, Raúl
AU - Wright, Dominic S.
ID - 12737
IS - 11
JF - Inorganic Chemistry
SN - 0020-1669
TI - Highly adaptive nature of group 15 tris(quinolyl) ligands─studies with coinage metals
VL - 62
ER -
TY - JOUR
AB - A series of triarylamines was synthesised and screened for their suitability as catholytes in redox flow batteries using cyclic voltammetry (CV). Tris(4-aminophenyl)amine was found to be the strongest candidate. Solubility and initial electrochemical performance were promising; however, polymerisation was observed during electrochemical cycling leading to rapid capacity fade prescribed to a loss of accessible active material and the limitation of ion transport processes within the cell. A mixed electrolyte system of H3PO4 and HCl was found to inhibit polymerisation producing oligomers that consumed less active material reducing rates of degradation in the redox flow battery. Under these conditions Coulombic efficiency improved by over 4 %, the maximum number of cycles more than quadrupled and an additional theoretical capacity of 20 % was accessed. This paper is, to our knowledge, the first example of triarylamines as catholytes in all-aqueous redox flow batteries and emphasises the impact supporting electrolytes can have on electrochemical performance.
AU - Farag, Nadia L.
AU - Jethwa, Rajesh B
AU - Beardmore, Alice E.
AU - Insinna, Teresa
AU - O'Keefe, Christopher A.
AU - Klusener, Peter A.A.
AU - Grey, Clare P.
AU - Wright, Dominic S.
ID - 13041
IS - 13
JF - ChemSusChem
SN - 1864-5631
TI - Triarylamines as catholytes in aqueous organic redox flow batteries
VL - 16
ER -
TY - JOUR
AU - Archer, Lynden A.
AU - Bruce, Peter G.
AU - Calvo, Ernesto J.
AU - Dewar, Daniel
AU - Ellison, James H. J.
AU - Freunberger, Stefan Alexander
AU - Gao, Xiangwen
AU - Hardwick, Laurence J.
AU - Horwitz, Gabriela
AU - Janek, Jürgen
AU - Johnson, Lee R.
AU - Jordan, Jack W.
AU - Matsuda, Shoichi
AU - Menkin, Svetlana
AU - Mondal, Soumyadip
AU - Qiu, Qianyuan
AU - Samarakoon, Thukshan
AU - Temprano, Israel
AU - Uosaki, Kohei
AU - Vailaya, Ganesh
AU - Wachsman, Eric D.
AU - Wu, Yiying
AU - Ye, Shen
ID - 14701
JF - Faraday Discussions
KW - Physical and Theoretical Chemistry
SN - 1359-6640
TI - Towards practical metal–oxygen batteries: General discussion
ER -
TY - JOUR
AU - Attard, Gary A.
AU - Calvo, Ernesto J.
AU - Curtiss, Larry A.
AU - Dewar, Daniel
AU - Ellison, James H. J.
AU - Gao, Xiangwen
AU - Grey, Clare P.
AU - Hardwick, Laurence J.
AU - Horwitz, Gabriela
AU - Janek, Juergen
AU - Johnson, Lee R.
AU - Jordan, Jack W.
AU - Matsuda, Shoichi
AU - Mondal, Soumyadip
AU - Neale, Alex R.
AU - Ortiz-Vitoriano, Nagore
AU - Temprano, Israel
AU - Vailaya, Ganesh
AU - Wachsman, Eric D.
AU - Wang, Hsien-Hau
AU - Wu, Yiying
AU - Ye, Shen
ID - 14702
JF - Faraday Discussions
KW - Physical and Theoretical Chemistry
SN - 1359-6640
TI - Materials for stable metal–oxygen battery cathodes: general discussion
ER -
TY - JOUR
AB - Redox flow batteries (RFBs) rely on the development of cheap, highly soluble, and high-energy-density electrolytes. Several candidate quinones have already been investigated in the literature as two-electron anolytes or catholytes, benefiting from fast kinetics, high tunability, and low cost. Here, an investigation of nitrogen-rich fused heteroaromatic quinones was carried out to explore avenues for electrolyte development. These quinones were synthesized and screened by using electrochemical techniques. The most promising candidate, 4,8-dioxo-4,8-dihydrobenzo[1,2-d:4,5-d′]bis([1,2,3]triazole)-1,5-diide (−0.68 V(SHE)), was tested in both an asymmetric and symmetric full-cell setup resulting in capacity fade rates of 0.35% per cycle and 0.0124% per cycle, respectively. In situ ultraviolet-visible spectroscopy (UV–Vis), nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) spectroscopies were used to investigate the electrochemical stability of the charged species during operation. UV–Vis spectroscopy, supported by density functional theory (DFT) modeling, reaffirmed that the two-step charging mechanism observed during battery operation consisted of two, single-electron transfers. The radical concentration during battery operation and the degree of delocalization of the unpaired electron were quantified with NMR and EPR spectroscopy.
AU - Jethwa, Rajesh B
AU - Hey, Dominic
AU - Kerber, Rachel N.
AU - Bond, Andrew D.
AU - Wright, Dominic S.
AU - Grey, Clare P.
ID - 14733
JF - ACS Applied Energy Materials
KW - Electrical and Electronic Engineering
KW - Materials Chemistry
KW - Electrochemistry
KW - Energy Engineering and Power Technology
KW - Chemical Engineering (miscellaneous)
TI - Exploring the landscape of heterocyclic quinones for redox flow batteries
ER -
TY - JOUR
AB - The short history of research on Li-O2 batteries has seen a remarkable number of mechanistic U-turns over the years. From the initial use of carbonate electrolytes, that were then found to be entirely unsuitable, to the belief that (su)peroxide was solely responsible for degradation, before the more reactive singlet oxygen was found to form, to the hypothesis that capacity depends on a competing surface/solution mechanism before a practically exclusive solution mechanism was identified. Herein, we argue for an ever-fresh look at the reported data without bias towards supposedly established explanations. We explain how the latest findings on rate and capacity limits, as well as the origin of side reactions, are connected via the disproportionation (DISP) step in the (dis)charge mechanism. Therefrom, directions emerge for the design of electrolytes and mediators on how to suppress side reactions and to enable high rate and high reversible capacity.
AU - Jethwa, Rajesh B
AU - Mondal, Soumyadip
AU - Pant, Bhargavi
AU - Freunberger, Stefan Alexander
ID - 14687
JF - Angewandte Chemie International Edition
KW - General Chemistry
KW - Catalysis
SN - 1433-7851
TI - To DISP or not? The far‐reaching reaction mechanisms underpinning Lithium‐air batteries
ER -
TY - JOUR
AB - Singlet oxygen (1O2) formation is now recognised as a key aspect of non-aqueous oxygen redox chemistry. For identifying 1O2, chemical trapping via 9,10-dimethylanthracene (DMA) to form the endoperoxide (DMA-O2) has become the mainstay method due to its sensitivity, selectivity, and ease of use. While DMA has been shown to be selective for 1O2, rather than forming DMA-O2 with a wide variety of potentially reactive O-containing species, false positives might hypothetically be obtained in the presence of previously overlooked species. Here, we first give unequivocal direct spectroscopic proof by the 1O2-specific near infrared (NIR) emission at 1270 nm for the previously proposed 1O2 formation pathways, which centre around superoxide disproportionation. We then show that peroxocarbonates, common intermediates in metal-O2 and metal carbonate electrochemistry, do not produce false-positive DMA-O2. Moreover, we identify a previously unreported 1O2-forming pathway through the reaction of CO2 with superoxide. Overall, we give unequivocal proof for 1O2 formation in non-aqueous oxygen redox and show that chemical trapping with DMA is a reliable method to assess 1O2 formation.
AU - Mondal, Soumyadip
AU - Jethwa, Rajesh B
AU - Pant, Bhargavi
AU - Hauschild, Robert
AU - Freunberger, Stefan Alexander
ID - 13044
JF - Faraday Discussions
KW - Physical and Theoretical Chemistry
SN - 1359-6640
TI - Singlet oxygen in non-aqueous oxygen redox: Direct spectroscopic evidence for formation pathways and reliability of chemical probes
ER -
TY - JOUR
AB - Capacity, rate performance, and cycle life of aprotic Li–O2 batteries critically depend on reversible electrodeposition of Li2O2. Current understanding states surface-adsorbed versus solvated LiO2 controls Li2O2 growth as surface film or as large particles. Herein, we show that Li2O2 forms across a wide range of electrolytes, carbons, and current densities as particles via solution-mediated LiO2 disproportionation, bringing into question the prevalence of any surface growth under practical conditions. We describe a unified O2 reduction mechanism, which can explain all found capacity relations and Li2O2 morphologies with exclusive solution discharge. Determining particle morphology and achievable capacities are species mobilities, true areal rate, and the degree of LiO2 association in solution. Capacity is conclusively limited by mass transport through the tortuous Li2O2 rather than electron transport through a passivating Li2O2 film. Provided that species mobilities and surface growth are high, high capacities are also achieved with weakly solvating electrolytes, which were previously considered prototypical for low capacity via surface growth.
AU - Prehal, Christian
AU - Mondal, Soumyadip
AU - Lovicar, Ludek
AU - Freunberger, Stefan Alexander
ID - 12065
IS - 9
JF - ACS Energy Letters
TI - Exclusive solution discharge in Li-O₂ batteries?
VL - 7
ER -
TY - JOUR
AB - The inadequate understanding of the mechanisms that reversibly convert molecular sulfur (S) into lithium sulfide (Li2S) via soluble polysulfides (PSs) formation impedes the development of high-performance lithium-sulfur (Li-S) batteries with non-aqueous electrolyte solutions. Here, we use operando small and wide angle X-ray scattering and operando small angle neutron scattering (SANS) measurements to track the nucleation, growth and dissolution of solid deposits from atomic to sub-micron scales during real-time Li-S cell operation. In particular, stochastic modelling based on the SANS data allows quantifying the nanoscale phase evolution during battery cycling. We show that next to nano-crystalline Li2S the deposit comprises solid short-chain PSs particles. The analysis of the experimental data suggests that initially, Li2S2 precipitates from the solution and then is partially converted via solid-state electroreduction to Li2S. We further demonstrate that mass transport, rather than electron transport through a thin passivating film, limits the discharge capacity and rate performance in Li-S cells.
AU - Prehal, Christian
AU - von Mentlen, Jean-Marc
AU - Drvarič Talian, Sara
AU - Vizintin, Alen
AU - Dominko, Robert
AU - Amenitsch, Heinz
AU - Porcar, Lionel
AU - Freunberger, Stefan Alexander
AU - Wood, Vanessa
ID - 12208
JF - Nature Communications
KW - General Physics and Astronomy
KW - General Biochemistry
KW - Genetics and Molecular Biology
KW - General Chemistry
KW - Multidisciplinary
SN - 2041-1723
TI - On the nanoscale structural evolution of solid discharge products in lithium-sulfur batteries using operando scattering
VL - 13
ER -
TY - JOUR
AB - Polydicyclopentadiene (pDCPD), a thermoset with excellent mechanical properties, has enormous potential as a lightweight, tough, and stable matrix material owing to its highly cross-linked macromolecular network. This work describes generating pDCPD-based foams and hierarchically porous carbons derived therefrom by combining ring-opening metathesis polymerization (ROMP) of DCPD, high internal phase emulsions (HIPEs) as structural templates, and subsequent carbonization. The structure and function of the carbon foams were characterized and discussed in detail using scanning electron, transmission electron, or atomic force microscopy (SEM, TEM, AFM), electron energy-loss spectroscopy (TEM-EELS), N2 sorption, and analyses of electrical conductivity as well as mechanical properties. The resulting materials exhibited uniform, shape-retaining shrinkage of only ∼1/3 after carbonization. No structural failure was observed even when the pDCPD precursor foams were heated to 1400 °C. Instead, the high porosity, void size, and 3D interconnectivity were fully preserved, and the void diameters could be adjusted between 87 and 2.5 μm. Moreover, foams have a carbon content >97%, an electronic conductivity of up to 2800 S·m–1, a Young’s modulus of up to 2.1 GPa, and a specific surface area of up to 1200 m2·g–1. Surprisingly, the pDCPD foams were carbonized into shapes other than monoliths, such as 10’s of micron thick membranes or foamy coatings adhered to a metal foil or grid substrate. The latter coatings even adhere upon bending. Finally, as a use case, carbonized foams were applied as porous cathodes for Li–O2 batteries where the foams show a favorable combination of porosity, active surface area, and pore size for outstanding capacity.
AU - Kovačič, Sebastijan
AU - Schafzahl, Bettina
AU - Matsko, Nadejda B.
AU - Gruber, Katharina
AU - Schmuck, Martin
AU - Koller, Stefan
AU - Freunberger, Stefan Alexander
AU - Slugovc, Christian
ID - 12227
IS - 11
JF - ACS Applied Energy Materials
KW - Electrical and Electronic Engineering
KW - Materials Chemistry
KW - Electrochemistry
KW - Energy Engineering and Power Technology
KW - Chemical Engineering (miscellaneous)
SN - 2574-0962
TI - Carbon foams via ring-opening metathesis polymerization of emulsion templates: A facile method to make carbon current collectors for battery applications
VL - 5
ER -
TY - JOUR
AB - Redox mediators could catalyse otherwise slow and energy-inefficient cycling of Li–S and Li–O2 batteries by shuttling electrons or holes between the electrode and the solid insulating storage materials. For mediators to work efficiently they need to oxidize the solid with fast kinetics but with the lowest possible overpotential. However, the dependence of kinetics and overpotential is unclear, which hinders informed improvement. Here, we find that when the redox potentials of mediators are tuned via, for example, Li+ concentration in the electrolyte, they exhibit distinct threshold potentials, where the kinetics accelerate several-fold within a range as small as 10 mV. This phenomenon is independent of types of mediator and electrolyte. The acceleration originates from the overpotentials required to activate fast Li+/e− extraction and the following chemical step at specific abundant surface facets. Efficient redox catalysis at insulating solids therefore requires careful consideration of the surface conditions of the storage materials and electrolyte-dependent redox potentials, which may be tuned by salt concentrations or solvents.
AU - Cao, Deqing
AU - Shen, Xiaoxiao
AU - Wang, Aiping
AU - Yu, Fengjiao
AU - Wu, Yuping
AU - Shi, Siqi
AU - Freunberger, Stefan Alexander
AU - Chen, Yuhui
ID - 10813
JF - Nature Catalysis
KW - Process Chemistry and Technology
KW - Biochemistry
KW - Bioengineering
KW - Catalysis
SN - 2520-1158
TI - Threshold potentials for fast kinetics during mediated redox catalysis of insulators in Li–O2 and Li–S batteries
VL - 5
ER -
TY - GEN
AB - Insufficient understanding of the mechanism that reversibly converts sulphur into lithium sulphide (Li2S) via soluble polysulphides (PS) hampers the realization of high performance lithium-sulphur cells. Typically Li2S formation is explained by direct electroreduction of a PS to Li2S; however, this is not consistent with the size of the insulating Li2S deposits. Here, we use in situ small and wide angle X-ray scattering (SAXS/WAXS) to track the growth and dissolution of crystalline and amorphous deposits from atomic to sub-micron scales during charge and discharge. Stochastic modelling based on the SAXS data allows quantification of the chemical phase evolution during discharge and charge. We show that Li2S deposits predominantly via disproportionation of transient, solid Li2S2 to form primary Li2S crystallites and solid Li2S4 particles. We further demonstrate that this process happens in reverse during charge. These findings show that the discharge capacity and rate capability in Li-S battery cathodes are therefore limited by mass transport through the increasingly tortuous network of Li2S / Li2S4 / carbon pores rather than electron transport through a passivating surface film.
AU - Prehal, Christian
AU - Talian, Sara Drvarič
AU - Vizintin, Alen
AU - Amenitsch, Heinz
AU - Dominko, Robert
AU - Freunberger, Stefan Alexander
AU - Wood, Vanessa
ID - 9980
KW - Li2S
KW - Lithium Sulphur Batteries
KW - SAXS
KW - WAXS
T2 - Research Square
TI - Mechanism of Li2S formation and dissolution in Lithium-Sulphur batteries
ER -
TY - JOUR
AB - “Hydrogen economy” could enable a carbon-neutral sustainable energy chain. However, issues with safety, storage, and transport of molecular hydrogen impede its realization. Alcohols as liquid H2 carriers could be enablers, but state-of-the-art reforming is difficult, requiring high temperatures >200 °C and pressures >25 bar, and the resulting H2 is carbonized beyond tolerance levels for direct use in fuel cells. Here, we demonstrate ambient temperature and pressure alcohol reforming in a fuel cell (ARFC) with a simultaneous electrical power output. The alcohol is oxidized at the alkaline anode, where the resulting CO2 is sequestrated as carbonate. Carbon-free H2 is liberated at the acidic cathode. The neutralization energy between the alkaline anode and the acidic cathode drives the process, particularly the unusually high entropy gain (1.27-fold ΔH). The significantly positive temperature coefficient of the resulting electromotive force allows us to harvest a large fraction of the output energy from the surrounding, achieving a thermodynamic efficiency as high as 2.27. MoS2 as the cathode catalyst allows alcohol reforming even under open-air conditions, a challenge that state-of-the-art alcohol reforming failed to overcome. We further show reforming of a wide range of alcohols. The ARFC offers an unprecedented route toward hydrogen economy as CO2 is simultaneously captured and pure H2 produced at mild conditions.
AU - Manzoor Bhat, Zahid Manzoor
AU - Thimmappa, Ravikumar
AU - Dargily, Neethu Christudas
AU - Raafik, Abdul
AU - Kottaichamy, Alagar Raja
AU - Devendrachari, Mruthyunjayachari Chattanahalli
AU - Itagi, Mahesh
AU - Makri Nimbegondi Kotresh, Harish
AU - Freunberger, Stefan Alexander
AU - Ottakam Thotiyl, Musthafa
ID - 9113
IS - 8
JF - ACS Sustainable Chemistry and Engineering
TI - Ambient condition alcohol reforming to hydrogen with electricity output
VL - 9
ER -
TY - JOUR
AB - Electrodepositing insulating lithium peroxide (Li2O2) is the key process during discharge of aprotic Li–O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and dissolved lithium superoxide governs whether Li2O2 grows as a conformal surface film or larger particles, leading to low or high capacities, respectively. However, better understanding governing factors for Li2O2 packing density and capacity requires structural sensitive in situ metrologies. Here, we establish in situ small- and wide-angle X-ray scattering (SAXS/WAXS) as a suitable method to record the Li2O2 phase evolution with atomic to submicrometer resolution during cycling a custom-built in situ Li–O2 cell. Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative structural information from complex multiphase systems. Surprisingly, we find that features are absent that would point at a Li2O2 surface film formed via two consecutive electron transfers, even in poorly solvating electrolytes thought to be prototypical for surface growth. All scattering data can be modeled by stacks of thin Li2O2 platelets potentially forming large toroidal particles. Li2O2 solution growth is further justified by rotating ring-disk electrode measurements and electron microscopy. Higher discharge overpotentials lead to smaller Li2O2 particles, but there is no transition to an electronically passivating, conformal Li2O2 coating. Hence, mass transport of reactive species rather than electronic transport through a Li2O2 film limits the discharge capacity. Provided that species mobilities and carbon surface areas are high, this allows for high discharge capacities even in weakly solvating electrolytes. The currently accepted Li–O2 reaction mechanism ought to be reconsidered.
AU - Prehal, Christian
AU - Samojlov, Aleksej
AU - Nachtnebel, Manfred
AU - Lovicar, Ludek
AU - Kriechbaum, Manfred
AU - Amenitsch, Heinz
AU - Freunberger, Stefan Alexander
ID - 9301
IS - 14
JF - Proceedings of the National Academy of Sciences
KW - small-angle X-ray scattering
KW - oxygen reduction
KW - disproportionation
KW - Li-air battery
SN - 0027-8424
TI - In situ small-angle X-ray scattering reveals solution phase discharge of Li–O2 batteries with weakly solvating electrolytes
VL - 118
ER -
TY - JOUR
AB - Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) based water-in-salt electrolytes (WiSEs) has recently emerged as a new promising class of electrolytes, primarily owing to their wide electrochemical stability windows (~3–4 V), that by far exceed the thermodynamic stability window of water (1.23 V). Upon increasing the salt concentration towards superconcentration the onset of the oxygen evolution reaction (OER) shifts more significantly than the hydrogen evolution reaction (HER) does. The OER shift has been explained by the accumulation of hydrophobic anions blocking water access to the electrode surface, hence by double layer theory. Here we demonstrate that the processes during oxidation are much more complex, involving OER, carbon and salt decomposition by OER intermediates, and salt precipitation upon local oversaturation. The positive shift in the onset potential of oxidation currents was elucidated by combining several advanced analysis techniques: rotating ring-disk electrode voltammetry, online electrochemical mass spectrometry, and X-ray photoelectron spectroscopy, using both dilute and superconcentrated electrolytes. The results demonstrate the importance of reactive OER intermediates and surface films for electrolyte and electrode stability and motivate further studies of the nature of the electrode.
AU - Maffre, Marion
AU - Bouchal, Roza
AU - Freunberger, Stefan Alexander
AU - Lindahl, Niklas
AU - Johansson, Patrik
AU - Favier, Frédéric
AU - Fontaine, Olivier
AU - Bélanger, Daniel
ID - 9447
IS - 5
JF - Journal of The Electrochemical Society
KW - Renewable Energy
KW - Sustainability and the Environment
KW - Electrochemistry
KW - Materials Chemistry
KW - Electronic
KW - Optical and Magnetic Materials
KW - Surfaces
KW - Coatings and Films
KW - Condensed Matter Physics
SN - 0013-4651
TI - Investigation of electrochemical and chemical processes occurring at positive potentials in “Water-in-Salt” electrolytes
VL - 168
ER -
TY - GEN
AB - Redox mediators could catalyse otherwise slow and energy-inefficient cycling of Li-S and Li-O 2 batteries by shuttling electrons/holes between the electrode and the solid insulating storage materials. For mediators to work efficiently they need to oxidize the solid with fast kinetics yet the lowest possible overpotential. Here, we found that when the redox potentials of mediators are tuned via, e.g., Li + concentration in the electrolyte, they exhibit distinct threshold potentials, where the kinetics accelerate several-fold within a range as small as 10 mV. This phenomenon is independent of types of mediators and electrolyte. The acceleration originates from the overpotentials required to activate fast Li + /e – extraction and the following chemical step at specific abundant surface facets. Efficient redox catalysis at insulating solids requires therefore carefully considering the surface conditions of the storage materials and electrolyte-dependent redox potentials, which may be tuned by salt concentrations or solvents.
AU - Cao, Deqing
AU - Shen, Xiaoxiao
AU - Wang, Aiping
AU - Yu, Fengjiao
AU - Wu, Yuping
AU - Shi, Siqi
AU - Freunberger, Stefan Alexander
AU - Chen, Yuhui
ID - 9978
KW - Catalysis
KW - Energy engineering
KW - Materials theory and modeling
T2 - Research Square
TI - Sharp kinetic acceleration potentials during mediated redox catalysis of insulators
ER -
TY - JOUR
AB - Aprotic alkali metal–O2 batteries face two major obstacles to their chemistry occurring efficiently, the insulating nature of the formed alkali superoxides/peroxides and parasitic reactions that are caused by the highly reactive singlet oxygen (1O2). Redox mediators are recognized to be key for improving rechargeability. However, it is unclear how they affect 1O2 formation, which hinders strategies for their improvement. Here we clarify the mechanism of mediated peroxide and superoxide oxidation and thus explain how redox mediators either enhance or suppress 1O2 formation. We show that charging commences with peroxide oxidation to a superoxide intermediate and that redox potentials above ~3.5 V versus Li/Li+ drive 1O2 evolution from superoxide oxidation, while disproportionation always generates some 1O2. We find that 1O2 suppression requires oxidation to be faster than the generation of 1O2 from disproportionation. Oxidation rates decrease with growing driving force following Marcus inverted-region behaviour, establishing a region of maximum rate.
AU - Petit, Yann K.
AU - Mourad, Eléonore
AU - Prehal, Christian
AU - Leypold, Christian
AU - Windischbacher, Andreas
AU - Mijailovic, Daniel
AU - Slugovc, Christian
AU - Borisov, Sergey M.
AU - Zojer, Egbert
AU - Brutti, Sergio
AU - Fontaine, Olivier
AU - Freunberger, Stefan Alexander
ID - 9250
IS - 5
JF - Nature Chemistry
KW - General Chemistry
KW - General Chemical Engineering
SN - 1755-4330
TI - Mechanism of mediated alkali peroxide oxidation and triplet versus singlet oxygen formation
VL - 13
ER -
TY - GEN
AB - Here, we employ micro- and nanosized cellulose particles, namely paper fines and cellulose
nanocrystals, to induce hierarchical organization over a wide length scale. After processing
them into carbonaceous materials, we demonstrate that these hierarchically organized materials
outperform the best materials for supercapacitors operating with organic electrolytes reported
in literature in terms of specific energy/power (Ragone plot) while showing hardly any capacity
fade over 4,000 cycles. The highly porous materials feature a specific surface area as high as
2500 m2ˑg-1 and exhibit pore sizes in the range of 0.5 to 200 nm as proven by scanning electron
microscopy and N2 physisorption. The carbonaceous materials have been further investigated
by X-ray photoelectron spectroscopy and RAMAN spectroscopy. Since paper fines are an
underutilized side stream in any paper production process, they are a cheap and highly available
feedstock to prepare carbonaceous materials with outstanding performance in electrochemical
applications.
AU - Hobisch, Mathias A.
AU - Mourad, Eléonore
AU - Fischer, Wolfgang J.
AU - Prehal, Christian
AU - Eyley, Samuel
AU - Childress, Anthony
AU - Zankel, Armin
AU - Mautner, Andreas
AU - Breitenbach, Stefan
AU - Rao, Apparao M.
AU - Thielemans, Wim
AU - Freunberger, Stefan Alexander
AU - Eckhart, Rene
AU - Bauer, Wolfgang
AU - Spirk, Stefan
ID - 8081
TI - High specific capacitance supercapacitors from hierarchically organized all-cellulose composites
ER -
TY - JOUR
AB - Large overpotentials upon discharge and charge of Li-O2 cells have motivated extensive research into heterogeneous solid electrocatalysts or non-carbon electrodes with the aim to improve rate capability, round-trip efficiency and cycle life. These features are equally governed by parasitic reactions, which are now recognized to be caused by the highly reactive singlet oxygen (1O2). However, the link between the presence of electrocatalysts and 1O2 formation in metal-O2 cells is unknown. Here, we show that, compared to pristine carbon black electrodes, a representative selection of electrocatalysts or non-carbon electrodes (noble metal, transition metal compounds) may both slightly reduce or severely increase the 1O2 formation. The individual reaction steps, where the surfaces impact the 1O2 yield are deciphered, showing that 1O2 yield from superoxide disproportionation as well as the decomposition of trace H2O2 are sensitive to catalysts. Transition metal compounds in general are prone to increase 1O2.
AU - Samojlov, Aleksej
AU - Schuster, David
AU - Kahr, Jürgen
AU - Freunberger, Stefan Alexander
ID - 7672
IS - 12
JF - Electrochimica Acta
TI - Surface and catalyst driven singlet oxygen formation in Li-O2 cells
VL - 362
ER -
TY - GEN
AB - With the lithium-ion technology approaching its intrinsic limit with graphite-based anodes, lithium metal is recently receiving renewed interest from the battery community as potential high capacity anode for next-generation rechargeable batteries. In this focus paper, we review the main advances in this field since the first attempts in the
mid-1970s. Strategies for enabling reversible cycling and avoiding dendrite growth are thoroughly discussed, including specific applications in all-solid-state (polymeric and inorganic), Lithium-sulphur and Li-O2 (air) batteries. A particular attention is paid to review recent developments in regard of prototype manufacturing and current state-ofthe-art of these battery technologies with respect to the 2030 targets of the EU Integrated Strategic Energy Technology Plan (SET-Plan) Action 7.
AU - Varzi, Alberto
AU - Thanner, Katharina
AU - Scipioni, Roberto
AU - Di Lecce, Daniele
AU - Hassoun, Jusef
AU - Dörfler, Susanne
AU - Altheus, Holger
AU - Kaskel, Stefan
AU - Prehal, Christian
AU - Freunberger, Stefan Alexander
ID - 8067
KW - Battery
KW - Lithium metal
KW - Lithium-sulphur
KW - Lithium-air
KW - All-solid-state
SN - 2664-1690
TI - Current status and future perspectives of Lithium metal batteries
ER -