Chem Commun Research Articles

Evaluating the Stability and Performance of Nasicon in Low-Cost High Charge Density Redox Flow Battery Electrolytes

Solid superionic conductor membranes are being considered as alternatives to polymer-based membranes for use in redox flow batteries (RFBs) due to their superior abilities to mitigate reactant crossover,1 and enable the deployment of aqueous electrolytes comprising small, inorganic earth-abundant reactants.2,3 Much however remains to be understood about the evolution of the electrochemical performance and microstructural stability of these membranes while they are immersed in aqueous electrolytes.In this work, we evaluate the suitability of von Alpen sodium superionic conductor (NaSICON) as a prospective RFB membrane material by examining its resistance, permeability and interfacial morphology over time as a function of electrolyte pH and composition, as well as temperature. NaSICON is found to have a stable resistance profile for several weeks while immersed in neutral to strongly alkaline ([OH-] = 3 M) aqueous electrolytes. Its permeability to polysulfide-based and permanganate-based small-molecule RFB reactants is negligible compared to that of Nafion. Its area-specific resistance falls dramatically with increasing temperature and decreasing membrane thickness; we project that a membrane with a thickness of 100 μm or lower, if operated slightly above ambient temperature (~ 40 °C), can enable power densities comparable to or better than those of conventional polymer membrane-containing RFBs. Nevertheless, the glassy phase of the NaSICON microstructure at the membrane-electrolyte interface was found to undergo small amounts of etching while in contact with aqueous electrolytes containing sodium ions; this etching became significantly more extensive when potassium ions were present in the electrolyte, leading in certain instances to complete disintegration of the membrane.The extraordinary high stability of NaSICON in strongly alkaline electrolyte permits the construction of flow cells containing a positive electrolyte based on permanganate, a high-potential, inexpensive reactant with high volumetric capacity (> 100 Ah/L). The flow cells had open-circuit voltages 1.2 V and greater, along with negligible reactant crossover and very low capacity fade (< 0.02 %/day). This work highlights the promise of ceramic membranes as effective separators in RFBs operating under neutral pH to strongly alkaline pH conditions. It also points to the need for further research on the long-term stability of the membrane and its interface with the electrolyte in solid-state membranes under investigation as separators in aqueous RFBs. (1) Yu, X.; Gross, M. M.; Wang, S.; Manthiram, A. Aqueous Electrochemical Energy Storage with a Mediator-Ion Solid Electrolyte. Advanced Energy Materials 2017, 7 (11), 1602454, https://doi.org/10.1002/aenm.201602454. DOI: https://doi.org/10.1002/aenm.201602454 (acccessed 2021/03/12).(2) Wei, X.; Xia, G.-G.; Kirby, B.; Thomsen, E.; Li, B.; Nie, Z.; Graff, G. G.; Liu, J.; Sprenkle, V.; Wang, W. An aqueous redox flow battery based on neutral alkali metal ferri/ferrocyanide and polysulfide electrolytes. J. Electrochem. Soc. 2016, 163 (1), A5150-A5153. DOI: 10.1149/2.0221601jes].(3) Colli, A. N.; Peljo, P.; Girault, H. H. High energy density MnO4-/MnO42- redox couple for alkaline redox flow batteries. Chem Commun (Camb) 2016. DOI: 10.1039/c6cc08070g.

(Digital Presentation) Evaluating Stability and Performance of Nasicon Membranes for Crossover Mitigation in Aqueous Redox-Flow Batteries

Most polymer-based membranes that are used in prototypical aqueous redox-flow batteries (RFBs) do not adequately prevent crossover of small-molecule reactants, causing high rates of capacity fade. Ceramic superionic conductor membranes are an attractive alternative due to their superior abilities to mitigate crossover;1 they can thus enable the deployment of electrolytes containing earth-abundant, small-molecule reactants.2 3 We test the performance and stability of a von Alpen sodium superionic conductor Na3.1Zr1.55Si2.3P0.7O11 (NaSICON) as an RFB membrane by examining its resistance, permeability and interfacial morphology as a function of electrolyte composition and temperature. The resistance of NaSICON is stable for several weeks while immersed in neutral to strongly alkaline ([OH-] = 3 M) aqueous electrolytes, and its permeability to polysulfide-based and permanganate-based small-molecule RFB reactants is negligible compared to that of Nafion. The glassy phase of the NaSICON microstructure at the membrane-electrolyte interface undergoes small amounts of etching while in contact with aqueous electrolytes containing sodium ions, which becomes more extensive when potassium ions are present in the electrolyte, leading in certain instances to complete disintegration of the membrane. We report a ferrocyanide-permanganate flow cell at a pH of 14.5 with a ~ 700 μm-thin NaSICON membrane supporting weeks of cycling with apparently negligible reactant crossover and very low capacity fade (< 0.04 %/day). Area-specific resistance of NaSICON falls dramatically with increasing temperature and decreasing membrane thickness, and a membrane that is 100 µm thick or thinner can enable power densities at above-ambient temperatures that are comparable to power densities of polymer membrane-containing flow cells.(1) Yu, X.; Gross, M. M.; Wang, S.; Manthiram, A. Aqueous Electrochemical Energy Storage with a Mediator-Ion Solid Electrolyte. Advanced Energy Materials 2017, 7 (11), 1602454, https://doi.org/10.1002/aenm.201602454. DOI: https://doi.org/10.1002/aenm.201602454 (acccessed 2021/03/12).(2) Wei, X.; Xia, G.-G.; Kirby, B.; Thomsen, E.; Li, B.; Nie, Z.; Graff, G. G.; Liu, J.; Sprenkle, V.; Wang, W. An aqueous redox flow battery based on neutral alkali metal ferri/ferrocyanide and polysulfide electrolytes. J. Electrochem. Soc. 2016, 163 (1), A5150-A5153. DOI: 10.1149/2.0221601jes].(3) Colli, A. N.; Peljo, P.; Girault, H. H. High energy density MnO4-/MnO42- redox couple for alkaline redox flow batteries. Chem Commun (Camb) 2016. DOI: 10.1039/c6cc08070g.

(Invited) Diagnostic Tools to Evaluate Materials for High-Performance PBI Systems

Even so, high-temperature PEM fuel cells (HT-PEMFC) based on phosphoric acid doped PBI-type membranes share many similarities with their low-temperature PEM fuel cells counterpart, as they use the same cell chemistry. Additionally, their structure and material selection for the membrane electrode assemblies (MEA) are very similar (1).An essential difference between these two systems is the liquid and, therefore, a mobile electrolyte partially flooding the gas diffusion electrode. The acid distribution within the MEA depends not only on its components but also on the operating conditions. Therefore, it is challenging to manage the acid household effectively for this type of fuel cell. Our collaborators and group members developed novel diagnostic tools to observe the acid distribution within membranes (2), catalyst layers (3, 4), gas diffusion layers (5, 6), and MEAs (7-9) over the past years. These processes occur on various length and time scales. For this reason, different characterization techniques are required to investigate them.For example, the NMR spectroscopy can elucidate phosphoric acid's preferred distribution sites inside the catalyst layer's pore structure. The micropores are filled first, followed by the larger mesopores (3). X-ray computed tomography showed that catalyst and microporous layer cracks are the phosphoric acid's main pathway to exit the cell and contribute mainly to its acid loss (4, 5). Impedance spectroscopy combined with the distribution of relaxation time analyses is one of the few full cell characterization techniques. It is a powerful tool for investigating the acid household to evaluate different catalyst materials (7).References R. Zeis, Beilstein J. Nanotechnol., 6, 68 (2015).F. Mack, S. Heissler, R. Laukenmann and R. Zeis, Journal of Power Sources, 270, 627 (2014).E. Zhang, N. Fulik, H. Zhang, N. Bevilacqua, R. Zeis, F. Xu, E. Brunner and S. Kaskel, Chem Commun (Camb), 57, 2547 (2021).J. Halter, N. Bevilacqua, R. Zeis, T. J. Schmidt and F. N. Büchi, Journal of Electroanalytical Chemistry, 859, 113832 (2020).N. Bevilacqua, M. G. George, S. Galbiati, A. Bazylak and R. Zeis, Electrochimica Acta, 257, 89 (2017).S. Chevalier, M. Fazeli, F. Mack, S. Galbiati, I. Manke, A. Bazylak and R. Zeis, Electrochimica acta, 212, 187 (2016).N. Bevilacqua, T. Asset, M. A. Schmid, H. Markötter, I. Manke, P. Atanassov and R. Zeis, Journal of Power Sources Advances, 7, 100042 (2021).A. Weiß, S. Schindler, S. Galbiati, M. A. Danzer and R. Zeis, Electrochimica Acta, 230, 391 (2017).N. Bevilacqua, M. Schmid and R. Zeis, Journal of Power Sources, 471, 228469 (2020). Figure 1

Is Cathode a Bottleneck for Enabling Extreme Fast Charging?

Extreme fast charging (XFC) of lithium-ion batteries (LiB) in the timespan of 10 to 15 minutes has been identified as one of the key enablers of widespread battery electric vehicle (BEV) adoption because it would offer a recharge experience comparable to refueling.1,2 For this reason, the support and research community have invested significant resources and efforts to enable XFC. While lithium plating has been identified as a key bottleneck for XFC on the anode side, and significant research is underway to eliminate that during XFC, 3–8 a comprehensive understanding of the implications of XFC to the LiB cathode is absent.A few cathode-focused coin-cell studies, with limited (up to 100) XFC cycling, have been published recently. These have started to fill the knowledge gap on the cathode side. 9–12 However, very few cathode-focused XFC studies in extended cycle settings with appropriate pouch cells are available.13,14 Coin cells, by design, have higher impedance; therefore, they produce distinctly different polarization and utilization behavior at XFC conditions. Consequently, they could provide distinctly different degradation behavior. For XFC conditions, choosing appropriate cell designs relevant to commercial cells is paramount for the comprehensive understanding of cathode degradation issues in extended cycling conditions because many of the cathode issues manifest in later cycling. In this regard, a single-layer pouch cell (SLPC) that has comparable impedance and utilization behavior to commercial pouch cells serves an alternative to coin cells—thereby, eliminating issues with cell designs and extended cycling and providing a much-needed comprehensive understanding.This presentation will provide a comprehensive understating of the implications of XFC to NMC532 and NMC811 cathodes tested in gr/NMC SLPCs. The gr/NMC SLPCs are well-defined and fast-charge capable. The comprehensive test matrix includes charging conditions between 1C and 9C and state-of-charge between 35 and ~98%. Cycling was carried out up to 1000 times, with targeted post-testing at specific intervals to capture degradation issues in cathodes and evolution with cycling. We highlight the key cycling degradation modes and the underlying mechanism through electrochemical analyses and supporting post-testing insights that answer the key question as to how much one should be concerned about cathode issues under XFC conditions and, finally, provide pathways to further minimize them. References S. Ahmed et al., J. Power Sources, 367, 250–262 (2017).Y. Liu, Y. Zhu, and Y. Cui, Nat. Energy, 4, 540–550 (2019).T. R. Tanim, M. G. Shirk, R. L. Bewley, E. J. Dufek, and B. Y. Liaw, J. Power Sources, 381, 56–65 (2018).T. R. Tanim et al., Cell Rep. Phys. Sci., 1, 100114 (2020).A. M. Colclasure et al., Electrochimica Acta, 337, 135854 (2020).P. Chinnam, Sensitivity and Reliability of Key Electrochemical Markers for Detecting Lithium Plating with Extreme Fast Charging, Prep. (2020). B. R. Chen, M. R. Kunz, T. R. Tanim, and E. J. Dufek, Cell Rep. Phys. Sci.2, 2, 100352 (2021) M. T. F. Rodrigues et al., ACS Appl. Energy Mater., 4, 1063–1068 (2021).Y. Yang et al., Adv. Energy Mater., 9, 1900674 (2019).A. Raj, M.-T. Rodrigues, and D. P. Abraham, J Electrochem Soc, 167, 120517.S. Xia et al., Nano Energy, 53, 753–762 (2018).S.-B. Son et al., J. Electrochem. Soc., 167, 140506 (2020).T. R. Tanim et al., J. Electrochem. Soc., 166, A1926–A1938 (2019).T. Liu et al., Chem Commun, 56, 6973–6976 (2020).

Role of pH in the stability of cytosine-cytosine mismatch and canonical AT and GC base pairs mediated with silver ion: a DFT study

Metallo-nucleic acids have been investigated for their applications in the field of nanodevices and genetic expansion. The cytosine-Ag+-cytosine mismatch base pair interactions and their stability in nucleic acids have attracted the attention of chemists. We report a systematic study of canonical, mismatch, Ag+ mediated system with CC, AT, and GC base pairs computationally. The stability of such mismatch base pairs is dependent on the pH range ~ 5 to 9 and the duplexes beyond this range are unstable. The DFT calculations performed with the model DNA duplexes comprising of such mismatch pairs reveal the stability trend while varying the pH conditions. The stability of canonical Watson–Crick ATGC base pairs was compared with the CCAT and CCGC mismatch base pairs and the calculated results at B3LYP-D3/6-31G(d) level of theory in the aqueous phase suggest that the base stacking and hydrogen bonding are well maintained in the former case, however, the larger perturbations in the geometry are observed with the mispair and relatively unstable. The calculated binding energy B3LYP-D3/6-31G(d) level of theory of ATGC is energetically more stable (~ 20 kcal/mol) than the mismatch base pairs. The Ag+ mediated mismatch base pairs i.e., C_CAT and C_CGC examined at the same level of theory suggest that the CC mismatch base pairs complexed with proper alignment to the Ag+ ion and the AT and GC bases maintained the hydrogen bonding interactions. The relative binding energies have been calculated with 6–311 + G(d,p) basis set using B3LYP-D3 and wb97xd DFT functionals in the study. The mismatched base pair duplex systems i.e., C_CAT and C_CGC are structurally similar to the canonical Watson–Crick base pairs and energetically stable by ~ 40 and ~ 50 kcal/mol compared to the canonical ATGC base pairs. The experimental report on the thermal transition profile in 5’-(A)10C(A)10–3’ and 5’ (T)10C(T)10–3’ duplexes showed remarkable stability and corroborate the calculated results (Ono et al. in Chem Commun 4825−4827, 2008). The stability of Ag+ mediated mismatch bases at the higher pH 9 was also examined and the nucleobases such as guanine and thymine would be deprotonated under this condition. The calculated results suggest that the CCA_T and CCG_C duplexes are largely distorted with the complexation of Ag+ with the AT and GC base pairs and would in turn denature the duplex. The AIM analysis performed at B3LYP-D3/6-31G(d) level of theory for all the studied Ag+ mediated complexes reveals that the Ag+ interaction with the corresponding nucleobases was electrostatic in nature. The role of pH in governing the stability of C–Ag+-C complex formation in mismatch base nucleic acids is crucial for their application of genetic expansion and nucleic acid-based nanodevices.Graphical abstract

Study and optimization of Diels-Alder reaction of piperine in aqueous ionic solutions using Gn.HCl as a catalyst

Study and optimization of Diels-Alder reaction of piperine in aqueous ionic solutions using Gn.HCl as a catalyst

Isolation, characterization and semi-synthesis of natural products dimeric amide alkaloids

Isolation, characterization and semi-synthesis of natural products dimeric amide alkaloids

Binding Expedient of 2-carbamido-1,3-indandione to Nucleic Acids: Potential Fluorescent Probe.

Fluorescent and computational methods were used to elucidate the binding expedient of 2-carbamido-1,3-indandione (CAID) tautomers to nucleotides. The dependence of the fluorescence emission of CAID loaded nucleic acids sequences to compound concentration, temperature and time variation was investigated. It was found that the subject compound binds to nucleic acids but does not intercalate. According to our quantum-chemical calculations on the conjugation between CAID and nucleotides, the binding in the formed complexes may be through hydrogen bonds. Two possible types of complexes were considered-CAID to the phosphate group and CAID to the nucleobase. To estimate the binding affinity, the interaction energies of the formed complexes were calculated. Tautomer 2-carboamide-1-hydroxy-3-oxo-indane is preferred in the formation of complexes, and the phosphate group complexes were more stable. Generally, the guanosine and deoxyguanosine monophosphate complexes were the most preferred regardless of the complex type. Because of the lack of cytotoxic effect on untransformed cell lines of mouse embryo fibroblasts Balb/c 3T3 according to our previous report (Markova et al, (2017) Bulg Chem Commun, 49D, 221-226) and the affinity to nucleic acids, we can suggest that the subject compound could be suitable to be used as a novel type of fluorescent biomarker.

(Keynote) Electromagnetic Field Stimulated MOFs

Electromagnetic, external stimuli can be used to switch Metal-Organic Framework (MOF) materials and to achieve control over the pores of these materials on different ways. We designed MOFs with switchable moieties in their side-chains, such as azobenzene, to be switchable under irradiation of UV/Vis light. Additionally, we developed devices to be able to measure the impact of electromagnetic fields in-situ. We focused on surface anchored MOF (SURMOF) thin films, deposited on asymmetric, porous α-Al2O3 supports as gas separation membrane layers. It is possible to control the gas transport properties of the materials using, but also using electric fields, and measure changes gas separation (permeability and selectivity) of binary mixtures in-situ, using the Wicke-Kallenbach technique. The light switchable systems were investigated on their CO2 separation performance: By switching the azobenzene between cis and trans isomers inside the pore windows, it was possible to switch dipolar moments, thus changing the adsorption properties towards the quadrupolar moment of CO2. Using electric fields of 500 V/mm we could show on the prominent example of ZIF-8, a zeolitic imidazolate framework, that it has a strong impact on the gas transport properties, especially looking at the molecular sieving. The mechanistic of the electric field influence on the ZIF is as follows: The electric field distorts the lattice of the MOF, shifting the Zn2+ ions, lowering the symmetry of the unit cell. This effect leads to polarized polymophs of the structure, sharpening the molecular sieving through a stiffening effect. The purification of Propylene/Propane, a highly desired separation for the plastics industry, could be increased through the electric field stimuli by 33%.References Knebel, A. et al. Defibrillation of soft porous metal-organic frameworks with electric fields. Science 358, 347–351; 10.1126/science.aal2456 (2017).Wang, Z. et al. Tunable molecular separation by nanoporous membranes. Nat. Commun. 7, 13872; 10.1038/ncomms13872 (2016).Müller, K. et al. Switching Thin Films of Azobenzene-Containing Metal-Organic Frameworks with Visible Light. Chem. Eur. J. 23, 5434–5438; 10.1002/chem.201700989 (2017).Knebel, A. et al. Azobenzene Guest Molecules as Light-Switchable CO 2 Valves in an Ultrathin UiO-67 Membrane. Chem. Mater. 29, 3111–3117; 10.1021/acs.chemmater.7b00147 (2017).Tan, N. Y. et al. Investigation of the terahertz vibrational modes of ZIF-8 and ZIF-90 with terahertz time-domain spectroscopy. Chem Commun 51, 16037–16040; 10.1039/c5cc06455d (2015). Figure 1

Monomerization of far-red fluorescent proteins

Anthozoa-class red fluorescent proteins (RFPs) are frequently used as biological markers, with far-red (λem ∼ 600-700 nm) emitting variants sought for whole-animal imaging because biological tissues are more permeable to light in this range. A barrier to the use of naturally occurring RFP variants as molecular markers is that all are tetrameric, which is not ideal for cell biological applications. Efforts to engineer monomeric RFPs have typically produced dimmer and blue-shifted variants because the chromophore is sensitive to small structural perturbations. In fact, despite much effort, only four native RFPs have been successfully monomerized, leaving the majority of RFP biodiversity untapped in biomarker development. Here we report the generation of monomeric variants of HcRed and mCardinal, both far-red dimers, and describe a comprehensive methodology for the monomerization of red-shifted oligomeric RFPs. Among the resultant variants is mKelly1 (emission maximum, λem = 656 nm), which, along with the recently reported mGarnet2 [Matela G, et al. (2017) Chem Commun (Camb) 53:979-982], forms a class of bright, monomeric, far-red FPs.

235 - Influence of pH on the reactions of heme peroxidase-derived oxidants with R19S

Oxidant production by heme peroxidases (such as myeloperoxidase [MPO], lactoperoxidase, eosinophil peroxidase and peroxidasin) impacts host defense and macromolecular structure and has the potential to cause tissue damage. Marked increases in phagocyte MPO, capable of producing highly reactive hypochlorous acid (HOCl), have been noted in multiple chronic inflammatory diseases. However, measuring MPO-derived oxidants at the site of production in vivo is technically challenging. The rhodamine-based probe R19S, first described by X. Chen et al (Chem Commun 2011; 47:4373-4375), becomes fluorescent R19 after reaction with HOCl but does not react with superoxide, hydrogen peroxide or several other reactive species. Thus, R19S may be useful to study MPO activity in situ. We sought to characterize the potential responses of R19S to other heme peroxidase-derived oxidants to establish whether a fluorescent response is solely indicative of HOCl or may include others. We analyzed responses of R19S to HOCl (positive control), hydrogen peroxide (negative control), hypobromous acid (HOBr), hypothiocyanous acid (HOSCN), hypoiodous acid (HOI) and taurine chloramine (TauCl) at pH 5.5 and 7.5. A similar study was recently published by A.M. Albrett et al (J Biol Chem 2018; ahead of print). Our results show strong agreement with their study at neutral pH (with a response hierarchy of HOI > HOCl > HOBr > HOSCN), although the overall responses of HOBr and HOSCN relative to HOCl were greater. At pH 5.5, we observed an altered hierarchy, with HOBr and HOI responses diminished (mean of 14.0±0.5% and 65.1±1.0% of HOCl, respectively, vs. 83.2±2.3% and 165.8±6.4% at pH 7.5), while HOSCN response was increased (93.3±5.1% of HOCl, vs. 37.6±0.2% at pH 7.5). Although TauCl did not cause fluorescence at neutral pH, modest response was detectible at acidic pH (9.8±0.2% of HOCl). These data illustrate that the environment of R19S determines its responsiveness to peroxidase-derived oxidants and should be considered when interpreting results.

Simultaneous oxygen and boron trifluoride functionalization of hexagonal boron nitride: a designer cathode material for energy storage

Covalent functionalization is a way to tune the electrochemical properties of hexagonal boron nitride (h-BN) monolayers. The wide bandgap insulator h-BN may become metallic conductor upon functionalization with strong oxidants, such as (fluorosulfonyl)oxy radicals (·OSO $$_{2}$$ F), as known since 1978 ( Bartlett et al in J Chem Soc Chem Commun 5:200, 1978), with electrical conductivity of 1.5 S/cm (Shen et al in J Solid State Chem 147:74, 1999) that greatly surpasses commercial cathode material Li $$_{x}$$ CoO $$_{2}$$ while retaining excellent ionic conductivity. Functionalized boron nitrides (FBN-s) have great potential for cathode applications in energy storage devices, for example, in solid-state batteries. While (fluorosulfonyl)oxy functionalization is unlikely to result in rechargeable cathodes, similarly to graphene fluoride (CF $$_{x}$$ ), some other FBN-s discussed here may do. In the present work, fluorene, oxygen and combined oxygen and boron trifluoride functionalizations are studied, on the basis of band structure calculations. Due to the open surfaces of FBN-s, fast ionic diffusion with Li, Na and Mg ions is possible, enabling batteries with voltages of 2.1–5.6 V, theoretical energy densities of 800–1200 Wh/kg and fast charge and discharge.

Influence of Li+ on the Compact and Porous Anodizing of Ti: Achieving Porous Anodizing Conditions Just By the Addition of Li+ Ion

The incorporation of foreign atoms in trace amounts modifies electronic properties and spectral response by the so-called band gap engineering 1. Among different dopants, the incorporation of Li+ cations into TiO2 is important for expanding the oxide’s technological applications. Li+ and H+ doping of TiO2 was carried out using electrochemical processes or salt impregnation, which improved solar to electricity efficiency of Dye Sensitized Solar cells and Perovskite solar cells (where a TiO2 layer is used as electronic transporting layer), as well as photocatalytic performance 2-3. Thermochemical treatments, N and V doping by standard ion implantation or Ag doping by metal plasma ion implantation was also reported 4-6. We recently reported 7 that Li+ is incorporated in the bulk of compact TiO2 layers during the anodization of Ti in lithium perchlorate (LiClO4), moving in the opposite direction expected for a cation under the applied electric field. Using Elastic Recoil Detection Analysis (ERDA) we observed that Li+ is accumulated in the form of more or less flat concentration profile along the thickness of compact layer (Fig. 1). Moreover, cell voltage profiles are strongly affected when Li+ is added to the electrolyte independent of anion of the salt. When the Li+ concentration is increased from 0.1 M to 0.5 M by addition of perchlorate or nitrate, the cell voltage transient changes from a curve typical for a compact anodizing with sparking to that of porous anodizing (Fig. 2). This transient change and the fact that the potential plateau during anodizing decreases as [Li+] is increased indicates that Li+ incorporation into the oxide greatly increases ionic conductivity and Ti oxide dissolution. Preliminary results show that a thick irregular tubular oxide structure is formed. The direct incorporation of Li+ into tubular TiO2 during its formation opens new possibilities for techniques of tubular oxide preparation. A mechanism for Li incorporation against the electric field is presented, as well as for the enhanced oxide dissolution. 1. Y.-C. Nah, I. Paramasivam and P. Schmuki, ChemPhysChem, 2010, 11, 2698–2713. 2. B. H. Meekins and P. V. Kamat, ACS Nano, 2009, 3, 3437–3446. 3. L. Tsui, M. Saito, T. Homma and G. Zangari, J Mater Chem A, 2015, 3, 360–367. 4. F. Giordano, A. Abate, J. P. Correa Baena, M. Saliba, T. Matsui, S. H. Im, S. M. Zakeeruddin, M. K. Nazeeruddin, A. Hagfeldt and M. Graetzel, Nat. Commun., 2016, 7, 10379. 5. N. A. Kyeremateng, N. Plylahan, A. C. S. dos Santos, L. V. Taveira, L. F. P. Dick and T. Djenizian, Chem Commun, 2013, 49, 4205–4207. 6. Y.-Y. Chang, Y.-N. Shieh and H.-Y. Kao, Thin Solid Films, 2011, 519, 6935–6939. 7. J. A. Penafiel-Castro, B. Hahn, R. L. Maltez, G. Knornschild, P. Allongue, and L. F. P. Dick, Chemical Communications , 2018, 54, 3251-3254. Figure 1

Rational Design of 2D Sn/MXene Hybrid As Anode Battery with Long Cycling and High Rate Performance

Current lithium ion batteries (LIBs) can’t provide sufficient energy density due to a limiting capacity of 372 mAh/g from graphite anode and a low capacity from cathode. Therefore, searching novel electrode materials for large energy storage that can deliver much higher energy density becomes critical. Li-M (M = Si, Al, Sn) alloy batteries are in particular attracting more attention due to the conspicuous advantages on industrial availability, specific capacity and rate capability. Sn has a 3 times greater capacity of ~1000 mAh/g that allows it as one of primary candidates for the next-generation LIBs. Scientists have made numerous attempts to stabilize the Sn alloy geometry by constructing various structures. However, most of these nano-structured particles can’t long survive because of the severe agglomeration and pulverization, nevertheless some types of carbon may limit the particle growth. Here we report a rational design of 2D Sn/MXene hybrid as anode battery with long cycling (over 1000 cycles) and high rate performance (over 5C), which is based on our previous work on Sn (Kang et al Nano Letter 2018; Liu et al Nano Letter 2016; Liu et al Chem Commun 2017) and MXene (Nagui et al Adv Mater 2011). The excellent Li+/e- conductivity and strong chemical/physical bonding of the interface between MXene and Sn lead to the improved half-cell (VS Li) and full-cell (VS NMC) battery performance at both coin and pouch cell scales. The structure evolution of the hybrid composite, the SEI forming and disappearing, and the interface between electrode and electrolyte upon cycling will be investigated via electrochemical measurements and in-situ TEM technique. Our strategy based on the benefits of MXene and the major capacity contribution of loaded metal active material can elevate the development and utilization of this new type of 2D hybrid materials with a high rate capability, high storage capacity, and low voltage, making it a promising candidate for next-generation batteries.

Engineering Pore Architecture into 2D Morphology: Synthesis of Multifunctional Nitrogen-Doped Porous Carbon Nanosheets Towards Long Calendar Life Lithium-Sulfur Battery

Owing to its high theoretical capacity, lithium-sulfur battery (Li-S) is considered as one of the leading alternatives to conventional lithium-ion batteries (LIBs) for electrical vehicles and grid-scale energy storage systems. The sulfur cathode has a theoretical capacity of 1675 mAh/g, accounting for an energy density as high as 2600 Wh/kg when coupled with lithium metal anode.1 Nevertheless, Li-S still need to overcome several challenges before being implemented in practical applications. The major issues include the low conductivity of sulfur, large volume change and severe polysulfide shuttling.2 In the recent reports, carbon material have been considered as an efficient sulfur host material to promote Li-S’s performance. However, it is difficult to solve all the problems simultaneously by a simple carbon material design. For instance, carbon nanotube has the advantages of its excellent conductivity, large surface area to volume ratio and prominent mechanical strength. However, it lacks porous sulfur reservoir to store the active sulfur, which makes their dissolution into electrolyte inevitable.3 Therefore, it is of great importance to develop multi-functional carbon materials for high-performance Li-S. Porous carbon materials have been intensively studied as the sulfur host due to its tunable porosity, large pore volume and controllable morphologies.4 The micro/meso pores can not only provide enough void space for sulfur volume expansion but also squeeze the cyclic sulfur molecules into short chain sulfur species and hence physically immobilize them from detrimentally shuttling to the anode side. To these aspects, we applied a dual-template strategy to synthesize nitrogen-doped two-dimensional porous carbon nanosheets (N-PCS). During the synthesis, we successfully integrating carbon pores into rational-designed secondary structure. The 2D carbon skeleton can effectively form conductive pathway for rapid electron/ion transfer. Moreover, when further doped with nitrogen, the carbon matrix enables a significantly improved conductivity and stronger interaction with polysulfides species due to the chemical bonding. With the advantages, when using N-PCS and sulfur composite as active material, an initial discharge capacity of 1360 mAh/g can be achieved at 0.1 C, showing a sulfur utilization as high as 81%. After 1000 cycles at 0.5 C, the cell can still retain ~50% of its initial capacity. At 1 C rate, N-PCS/S cathode is capable of delivering a high discharge capacity of 996 mAh/g, indicating its excellent electron conductivity and rate capability. Reference M. K. Song, E. J. Cairns and Y. Zhang, Nanoscale, 2013, 5, 2186-2204.Y. Yang, G. Zheng and Y. Cui, Chem. Soc. Rev., 2013, 42, 3018-3032.X. Liang, Z. Wen, Y. Liu, H. Zhang, J. Jin, M. Wu and X. Wu, J. Power Sources, 2012, 206, 409-413.S. Niu, W. Lv, G. Zhou, Y. He, B. Li, Q. H. Yang and F. Kang, Chem Commun (Camb), 2015, 51, 17720-17723. Figure 1

Synthesis of Pt-M (M=Ir, Pd) Bimetallic Nanocrystals with Controlled Shape and Composition As a High-Performance Electrocatalyst for Ammonia Electrolysis

Ammonia is a promising hydrogen storage carrier owing to its higher hydrogen capacity relative to liquid hydrogen (108 vs 71 g/L), non-flammability, well-developed technologies for synthesis and distribution.1-2 To utilize ammonia as the hydrogen storage carrier, it is essential to develop a highly efficient and durable catalyst that decomposes ammonia into hydrogen and nitrogen. Platinum (Pt) is the most effective catalyst for the electrolysis of ammonia, but it is rapidly deactivated during the reaction due to the strong adsorption of nitrogen on the surface. Thus, it is critical to develop a highly efficient and robust catalyst that surpasses Pt catalyst, enabling the utilization of ammonia as a safe and efficient hydrogen storage carrier. In this work, we synthesized nano-sized Pt-Ir (and Pt-Pd) alloy cubes as a high-performance electrocatalyst for ammonia electrolysis. During the synthesis, both elemental composition and shape of nanocrystals were systemically controlled for improving their electrocatalytic performance (Fig. 1a). Among the as-synthesized catalysts, the Pt-Ir nanocubes exhibited ~7.2 and ~4.6 times higher specific (mA/cm2) and mass (A/mg) activities, respectively, relative to a state-of-the-art commercial Pt/C catalyst (Tanaka) at 0.6 V (vs RHE, Fig. 1b). The significantly enhanced activity can be attributed to reduced adsorption strength of nitrogen, thus mitigating the deactivation of active sites of the catalyst. Hanada, N.; Hino, S.; Ichikawa, T.; Suzuki, H.; Takai, K.; Kojima, Y., Hydrogen generation by electrolysis of liquid ammonia. Chem Commun 2010, 46 (41), 7775-7777.Vitse, F.; Cooper, M.; Botte, G. G., On the use of ammonia electrolysis for hydrogen production. Journal of Power Sources 2005, 142 (1), 18-26. Figure 1

Understanding Evolution of Silicon Electrode SEI through Model Lithium Silicate Thin Film Layers

Silicon is being considered for next generation energy storage anode material due to its very high specific capacity (3579 mAh/g), low overpotential, fast reaction kinetics and minimal environmental impact1. However, there are several problems to be addressed before silicon is realized in actual battery applications. These problems include a large change in volume during lithium insertion causing mechanical degradation as well as electrochemical degradation caused by a solid-electrolyte interphase (SEI) layer that is reported to not be electrochemically passivating2. The non-passivating SEI formed on silicon is potentially a major cause of a relatively stunted cycle life for silicon anode Li ion batteries because it consumes Li ions and solvents from the electrolyte3. There is not a good understanding of what complicated and diverse reactions are at work as the SEI layer is formed on the untreated surface of silicon during initial charging and discharging of the battery and how it develops during continued cycling. To better understand the nature and evolution of the silicon SEI films, model systems of SEI structures were formed using sol-gel precursors deposited over clean sputtered 50nm thick silicon films. Chemistries from Li2Si2O5 to Li4SiO4 were synthesized from starting materials of lithium hydroxide and TEOS in a solution of methanol solvent with a controlled moisture environment. These films were then studied for Li transport and stability of silicon anode cycling against a Li reference and counterelectrode using standard 2032 coin cell configurations. Cycled anodes were then recovered and studied using NR, ICP-OES, Raman, ATR IR and TOF-SIMS. The first observations of these model films was the dependence on stoichiometry for electrochemical behavior. While electrodes with only a native oxide layer behaved normally, with expected lithiation plateaus in the silicon, when electrodes with films of different lithium silicate compositions (Li2Si2O5 or Li2SiO3) were used, these plateaus were not present or shifted. Additionally, these films showed morphological and chemical changes on lithiation. While the reason for these electrochemical behavioral changes has not been fully understood, these model systems start to tease apart the complexity of crystal structure and compositional changes that manifest in the silicon SEI, and may give some indication as to why the instability and low cycle capability of the silicon anodes is observed in practice. Su, X. et al. Silicon-Based Nanomaterials for Lithium-Ion Batteries: A Review. Adv Energy Mater 4, doi:ARTN 130088210.1002/aenm.201300882 (2014).Veith, G. M. et al. Direct measurement of the chemical reactivity of silicon electrodes with LiPF6-based battery electrolytes. Chem Commun 50, 3081-3084, doi:10.1039/c3cc49269a (2014).Delpuech, N. et al. Correlation between irreversible capacity and electrolyte solvents degradation probed by NMR in Si-based negative electrode of Li-ion cell. Electrochem Commun 33, 72-75, doi:10.1016/j.elecom.2013.05.001 (2013). Figure 1

Impedance Spectroscopy and Differential Electrochemical Mass Spectrometry As Tools for Characterization of Mediated Oxidation of Organic Pollutants

Persistent Organic Pollutants (POP) are hazardous environmental contaminants of mainly synthetic origin, highly toxic and chemically inert. They accumulate in the environment and in living organisms. Most POPs do not ignite themselves and they cannot be combusted. Therefore it is very important to find an alternative processes of POP neutralization. Mediated Electrochemical Oxidation has been proven to be an efficient approach, in which those dangerous substances are electrochemically combusted under ambient conditions. Mediated electrochemical oxidation is an indirect electrolysis, where pollutants are oxidized through the mediation of some electrochemically generated redox reagents, which act as an intermediary for electrons shuttling between the electrode and the target molecule. This technique enables the possibility to oxidize an (electro)inactive compounds.1 Recently, we have derived the exact analytical solution for impedance of catalytic processes involving redox mediators. The results obtained for general case in the rigorous treatment provide a powerful research tool that can be used in studies of many important catalytic processes.2 Unusual impedance characteristics have been found for systems having unequal diffusivities of the oxidized and reduced forms of the redox mediator. Depending on the ratio of diffusion coefficients the spectra are either markedly deformed at low frequency range or an inductive loop appears at the complex plane. It is impossible to fit these spectra in the whole frequency range, neither with the Gerischer impedance nor with any other known transfer function.2 We show that the key parameters of the studied systems, such as both heterogeneous and homogeneous rate constants, which are limiting factors for the electrochemical combustion efficiency, can be readily obtained even from a single impedance spectrum.2 In this research, silver(II) compounds were used as redox mediators for electrochemical combustion of organic molecules.3 As reported by us previously, the redox potential of the system Ag(II)/Ag(I) can reach up to 2.9V in sulfuric acid media.4 Moreover the average lifetime of the produced radical oxidant was estimated to be in order of seconds.5 Initially, investigations were carried out for a model organic molecule - acetic acid, which is known to be difficult to oxidize, and next for 1,2-dichlorobenzene an organic compound from POP group. The catalytic activity of Ag(II) was characterized mainly by using electrochemical methods with a particular emphasis placed on Electrochemical Impedance Spectroscopy (EIS). We have also performed analysis of volatile products by using mass spectrometry coupled with electrochemical measurements DEMS (Differential Electrochemical Mass Spectroscopy). This technique allows to detect in situ volatile electrooxidation products and/or intermediates. The latter were monitored for catalytic electrooxidation of acetic acid and 1,2-dichlorobenzene in function of electrode potential, for both compounds a large amount of CO2 was detected. 1. M. Panizza and G. Cerisola, Chemical Reviews, 2009, 109, 6541-6569. 2. R. Jurczakowski and P. Polczynski, J Phys Chem C, 2014, 118, 7980-7988. 3. M. Fleischmann and D. Pletcher, Tetrahedron Letters, 1968, 9, 6255-6258. 4. P. Polczynski, R. Jurczakowski and W. Grochala, Chem Commun, 2013, 49, 7480-7482. 5. P. Polczynski, R. Jurczakowski and W. Grochala, J Phys Chem C, 2013, 117, 20689-20696.

A New Architecture Design for Observing Lithium Oxide Growth-Evolution Employing Geometric Catalyst Positioning

A common route to overcoming the large overpotentials and poor reversibility in current Li-O2 batteries has been to develop various solid-state catalysts (i.e. noble metals, metal oxides) decorated on the oxygen electrodes.[1-2] Although these approaches have yielded incremental improvements, catalytic sites are easily deactivated by the continuous precipitation of solid products.[3] Understanding the mechanisms of discharge product formation and evolution and optimizing the catalyst systems are necessary to guide future Li-O2 cell design.[4] In our previous report,[5] we demonstrated that dispersing catalyst particles in an insulating membrane over the oxygen electrode helps to maintain their function by reducing passivation of the active surfaces during lithium peroxide formation. The major benefit of this approach is that the oxygen evolution reaction (lithium peroxide dissolution) is facilitated by these isolated catalytic sites. While the catalytic membrane architecture is quite effective in practical cells, it is important to investigate the exact chemistry and morphology of products far from the electrode surface and thereby elucidate the remarkable function of these electrically isolated sites. In this work we demonstrate a new architecture using anodic aluminum oxide (AAO) membranes as a porous scaffold with Pd nanoparticles dispersed throughout as the catalytic sites. This approach allows us to directly observe lithium-oxide product formation and evolution both in the presence of catalysts and without to better understand the mechanistic influence of catalyst positioning. We show that AAO membranes can be readily cross-sectioned (without destroying the well-defined pore structure), and can incorporate the formation of integrated lithium-oxide products. As a result, we clearly observe a planar-to-particulate morphological transition in Li-O2 products during cell discharge and the reverse during charge. The Pd-AAO interlayer facilitates the uniform growth of discharge products as well as the evolution reaction, minimizing the buildup of residues seen in the absence of Pd. In this talk, we will provide evidence for improved charge transfer and reduced overpotentials as a result of catalyst positioning inside the AAO membrane pores. The novelties of this work demonstrate how the catalyst positioning is important and how insolated catalyst sites can function separately from electrical contact to the electrode for improved columbic round trip efficiency for next generation Li-O2 cell designs. [1] Ryu, W. H.; Yoon, T. H.; Song, S. H.; Jeon, S.; Park, Y. J.; Kim, I. D. Nano Lett 2013,13, 4190-7. [2] Gittleson, F. S.; Ryu, W. H.; Schwab, M.; Xiao Tong, Andre D. Taylor, Chem Commun 2016, In press. DOI: 10.1039/C6CC01778A [3] Gittleson, F. S.; Ryu, W. H.; Taylor, A. D. ACS Appl Mater Interfaces 2014,6, 19017-19025. [4] Gittleson, F. S.; Yao, K. P. C.; Kwabi, D. G.; Sayed; Ryu, W.-H.; Shao-Horn, Y.; Taylor, A. D., ChemElectroChem 2015, 2, 1446-1457. [5] Ryu, W. H.; Gittleson, F. S.; Schwab, M.; Goh, T.; Taylor, A. D., Nano Lett 2015, 15, 434-441

Molecular Scale Coating and Nanoscale Carbon Cage Confined Sulfur Cathodes Applied in Lithium Sulfur Batteries

Lithium sulfur (Li-S) batteries have been intensively concerned in recent years as next generation Li batteries1. Compared with state-of-the-art Li-ion batteries, Li-S batteries own ultrahigh theoretical capacity and energy density, which are considered as most promising candidates applied to electric vehicles and hybrid electric vehicles. However, insulation of sulfur and dissolution of polysulfides are two main issues in sulfur cathodes which hinder the cycle life and application safety of Li-S batteries. To overcome these issues, developing conductive hosts and coating materials are prevailing approaches to improve the performance of Li-S batteries. Herein, we report molecular layer deposited (MLD) alucone coating and nanoscale metal organic framework derived carbon (MOF-C) confined sulfur cathodes in Li-S batteries. Surface coating with carbon or metal oxides has been proven to be a promising approach towards mitigating the shuttle effect in Li-S batteries. An ideal coating material should both cover on based material completely to prevent sulfur migration and also allow Li-ions and electrons transferring through smoothly. Based on these requirements, atomic and molecular layer deposition (ALD and MLD) are ideal technique to synthesize ultrathin and conformal coatings due to the self-limiting nature2 , 3. For the first time, we demonstrate that an MLD alucone coating directly on sulfur electrodes can dramatically improve the cycling stability and capability of Li-S cells. Furthermore, the alucone coated sulfur cathode delivers a discharge capacity of 710 mAh g-1, which is over two times higher than the bare sulfur cathode after 100 cycles4. The alucone coating demonstrated long durability during cell cycling, which explores a new direction in the protection of sulfur cathodes. Porous structured materials are prevailing in sulfur cathode to confine sulfur molecule in host materials. Herein, we developed a new carbon family, metal organic framework derived carbon materials (MOF-Cs) with tunable porous structure via in-situ ammonia treatment5. The ammonia treated MOF-C as carbon host shows an impressive improvement on sulfur cathodes, which performed twice higher discharge capacity retention than that of the pristine MOF-C. This research sheds light to design MOF-C materials with controlled nanostructure not only for Li–S batteries, but also for expanded applications in different energy storage systems. References 1 Bruce, P. G., Freunberger, S. A., Hardwick, L. J. & Tarascon, J. M. Li-O2 and Li-S batteries with high energy storage. Nature materials11, 19-29, (2012). 2 Meng, X., Yang, X. Q. & Sun, X. Emerging applications of atomic layer deposition for lithium-ion battery studies. Adv Mater24, 3589-3615, (2012). 3 Li, X. et al. Atomic layer deposition of solid-state electrolyte coated cathode materials with superior high-voltage cycling behavior for lithium ion battery application. Energy & Environmental Science7, 768, (2014). 4 Li, X., Lushington, A., Liu, J., Li, R. & Sun, X. Superior stable sulfur cathodes of Li-S batteries enabled by molecular layer deposition. Chem Commun (Camb)50, 9757-9760, (2014). 5 Li, X. et al. Tunable porous structure of metal organic framework derived carbon and the application in lithium–sulfur batteries. J Power Sources 302, 174-179, (2016). Figure 1