Abstract: Charge storage behavior in nitride nanomaterials depends on a number of particle properties and also on the nature of the electrode (1-9). Vanadium nitride is a promising supercapacitor material on account of pseudocapacitance arising from the surface oxide/oxynitride phase interactions. We have previously reported excellent charge storage behavior of nanoparticulate vanadium nitride on account of the surface reactions occurring on the surface of the oxide exo-shell. Vanadium oxide is a superior pseudocapacitor material but suffers from poor electronic conductivity(10). Forming a thin surface oxide layer on nanoparticle nitrides yields the benefits of the charge storage along with charge storage occurring in the nitride core itself. However, there is evidence showing that the surface oxide suffers from instability in highly alkaline solutions on account of side-reactions. In addition, the core nitride itself becomes a poor conductor when prepared as fine nanoparticles ( 〈 10 nm)(3). In this study, we tailor nitride nanoparticles to engineer architectures similar to that shown in Figure 1 by the use of suitable dopants. By using wet chemical procedures, we generate a number of doped nitrides with doped surface oxide structure. We use ab-initio first principle studies to guide our dopant selection with improved electronic conductivity of surface oxide/core nitride and stability of surface oxide being parameters driving our dopant selection. We demonstrate in this study doped VN with superior electronic conductivity, high capacity and long cycle life. In-depth surface characterization using XPS and electrochemical impedance spectroscopy (EIS) to probe change in charge-storage mechanisms are conducted herein to obtain fundamental understanding into the nature of the various doped nitride materials. Change in nanoparticle morphology and surface composition are also examined and related to charge storage behavior. Results of these studies will be presented and discussed. References 1. D. Choi, G. E. Blomgren and P. N. Kumta, Advanced Materials , 18 , 1178 (2006). 2. P. Jampani, A. Manivannan and P. N. Kumta, The Electrochemical Society Interface , 19 , 57 (2010). 3. P. J. Hanumantha, M. K. Datta, K. S. Kadakia, D. H. Hong, S. J. Chung, M. C. Tam, J. A. Poston, A. Manivannan and P. N. Kumta, Journal of The Electrochemical Society , 160 , A2195 (2013). 4. D. Choi, Synthesis, Structure and Electrochemical Characterization of Transition Metal Nitride Supercapacitors Derived by a Two-Step Metal Halide Approach, in Materials Science and Engineering , Carnegie Mellon University, Pittsburgh (2005). 5. D. Choi, G. E. Blomgren and P. N. Kumta, Advanced Materials , 18 , 1178 (2006). 6. D. Choi and P. N. Kumta, Journal of the Electrochemical Society , 153 , A2298 (2006). 7. D. Choi and P. N. Kumta, Journal of the American Ceramic Society , 90 , 3113 (2007). 8. D. Choi and P. N. Kumta, Journal of the American Ceramic Society , 94 , 2371 (2011). 9. D. W. Choi and P. N. Kumta, Electrochemical and Solid State Letters , 8 , A418 (2005). 10. P. H. Jampani, K. Kadakia, D. H. Hong, R. Epur, J. A. Poston, A. Manivannan and P. N. Kumta, Journal of The Electrochemical Society , 160 , A1118 (2013).

Abstract: Introduction Lithium sulfur and lithium-air batteries hold much promise for the future of batteries on account of their theoretical capacities of 2567 and 3505 Wh/kg respectively(1). The dissolution of sulfur through the formation of soluble polysulfides and the poor electronic conductivity of sulfur are however, major problems hindering Li-S battery progress (1-3). In addition, particle fracture and delamination as a result of repeated volumetric expansion and contraction have also been identified as factors responsible for poor long term performance(4, 5). In our previous work on lithium-sulfur batteries, we have shown the effectiveness of using a thin Li-ion conducting barrier layer in improving the cycling characteristics(6). In this work, we develop a unique strategy to directly prepare sulfur wire mattes ( Figure 1 ) capable of being spun as yarn and thereupon being used directly in the form of ‘textile fabric batteries’. Using these wires, we generate two other morphologies to specifically tackle fade and conductivity issues existing in sulfur cathodes. This results in sulfur cathodes with high electronic conductivity, minimal volumetric expansion and improved rate capabilities and cyclability. In addition, the electrodes that we use in this study allow us to obtain high areal capacities.  Figure 1 shows SEM and EDAX map of the same. Results of these studies will be presented and discussed. Captions Figure 1: (a) Scanning electron microscopy image of the sulfur wires (b) EDAX map indicating the Sulfur distribution. References 1.         P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nature Materials , 11 , 19 (2012). 2.         J. Cabana, L. Monconduit, D. Larcher and M. Rosa Palacin, Advanced Materials , 22 , E170 (2010). 3.         B. Scrosati and J. Garche, Journal of Power Sources , 195 , 2419 (2010). 4.         L. Ji, M. Rao, S. Aloni, L. Wang, E. J. Cairns and Y. Zhang, Energy & Environmental Science , 4 , 5053 (2011). 5.         Z. Wei Seh, W. Li, J. J. Cha, G. Zheng, Y. Yang, M. T. McDowell, P.-C. Hsu and Y. Cui, Nat Commun , 4 , 1331 (2013). 6.         P. J. Hanumantha, B. Gattu, O. Velikokhatnyi, M. K. Datta, S. S. Damle and P. N. Kumta, Journal of The Electrochemical Society , 161 , A1173 (2014). Figure 1

Abstract: The need to transition from the ubiquitous lithium-ion chemistry to more abundant raw-material based systems is precipitated by the additional advantages of such chemistries including lower cost and improved safety. Sodium (SIB) and magnesium (MIB) ion based systems are of greatest relevance on account of the theoretical energy density of both systems and the relative abundance of both elements in the earth’s crust. In order for Na-ion and Mg-ion batteries to compete with the much researched Li-ion systems, considerable improvements in energy density, cyclability and rate capability is required prior to their consideration for practical use as electrical energy storage (EES) devices. Identification of suitable cathodes and anodes which can exhibit high specific capacity, low irreversible loss, high coulombic efficiency and long cycle/calendar life will be a paradigm shift in the development of high energy density SIBs. Layered cathodes of sodium Na x MnO 2 (0 〈 x ≤ 1; M = Mn, Ni, Co) have received considerable interest due to their structural similarity with well-known Li-ion battery electrodes LiMO 2 (M = Mn, Ni, Co). Ternary molybdenum compounds of M x Mo 6 T 8 (M = metal, transition element, rare-earths; T = chalcogen) are known as ‘Chevrel phase (CP)’ since 1971 (1). The crystal structure of Chevrel phase consists of Mo 6 - octahedron clusters surrounded by eight chalcogens (S, Se) atoms at the corners of a distorted cube (2). The Mo 6 S 8 units are linked with each other and form a three-dimensional framework with open cavities/channels that can be filled with a wide-variety of guest atoms giving rise to ternary Chevrel phase compounds M x Mo 6 S 8 (0 〈 x 〈 4). Among the three different Chevrel phase families (Mo 6 T 8 , T = S, Se, Te), sulfide CPs have received significant attention due to their high ionic mobility at room temperature allowing the transport of monovalent (Li + , Na + ), and bivalent (Mg 2+ ) cations serving as cathodes for rechargeable batteries (3-5). Out interest in the present work stems from the rapid synthesis of Cu 2 Mo 6 S 8 and Cu 2 Mo 6 Se 8 Chevrel phases in a time-efficient manner and correspondingly use of de-cuprated Mo 6 S 8 and Mo 6 Se 8 as promising cathodes for rechargeable magnesium batteries (6). High energy mechanical milling (HEMM) of stoichiometric mixtures of molybdenum and copper chalcogenide (CuT and CuT 2 ) followed by short thermal treatments at elevated temperature resulted in Chevrel phases (Cu 2 Mo 6 T 8 ; T = S, Se), serving as cathodes for Na and Mg ion batteries. Electrochemical performances of the Mo 6 S 8 and Mo 6 Se 8 phases were evaluated by cyclic voltammetry (CV), galvanostatic cycling, electrochemical impedance spectroscopy (EIS). Using EIS (Fig. 1), a comparison is made between the nature of the ion trapping mechanisms occurring during the respective sodium/magnesium intercalation and deintercalation processes. References 1.         R. Chevrel, M. Sergent and J. Prigent, Journal of Solid State Chemistry , 3 , 515 (1971). 2.         Ø. Fischer, Appl. Phys. , 16 , 1 (1978). 3.         D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich and E. Levi, Nature , 407 , 724 (2000). 4.         W. R. McKinnon and J. R. Dahn, Physical Review B , 31 , 3084 (1985). 5.         E. Gocke, W. Schramm, P. Dolscheid and R. Scho¨llhorn, Journal of Solid State Chemistry , 70 , 71 (1987). 6.         P. Saha, M. K. Datta, O. I. Velikokhatnyi, A. Manivannan, D. Alman and P. N. Kumta, Progress in Materials Science , Figure 1

Abstract: With the growing interest in alternative energy sources and the cognitive recognition of the benefits of green energy, there is clearly a pressing need for the development of sustainable and clean energy storage systems (1-3). The scope of electrochemical charge storage devices extends beyond mobile devices into large scale grid level charge storage(4). Load leveling and power quality management applications would be perfectly served by storage of excess charge generated from renewable energy sources in supercapacitors. Supercapacitors are unique electrochemical energy storage devices with high power density and long cyclability. State of the art materials such as high surface area carbons, hydrated ruthenium oxide (5-7) and MnO 2 (3, 8-10) suffer from either poor capacity or rate capability. We have previously demonstrated excellent charge storage behavior of nanoparticulate vanadium nitride on account of the surface reactions occurring on the surface of the oxide exo-shell. However, there is limited understanding into the exact nature of the charge storage behavior and its dependence on the synthesis and processing route. In the present work, we explore the effect of materials processing and electrode properties on the capacitive charge storage in VN based supercapacitors. Dependence of capacitance on particle and electrode properties are evaluated and reported here-in. Tailoring the particle size, crystallinity and porosity are of paramount importance to achieve high capacitances at high scan rates. To gain a fundamental understanding into the charge storage mechanism of nitride materials shown in Figure 1, slurries of the nitride were cast on nickel current collectors and characterized used various materials and electrochemical characterization techniques including X-ray photo-electron spectroscopy (XPS), cyclic voltammetry and electrochemical impedance spectroscopy. Results of these studies will be presented and discussed. References 1. P. Simon and Y. Gogotsi, Nature Materials , 7 , 845 (2008). 2. J. R. Miller, Science , 335 , 1312 (2012). 3. R. Kötz and M. Carlen, Electrochimica Acta , 45 , 2483 (2000). 4. M. Conte, Fuel Cells , 10 , 806 (2010). 5. J. W. Long, K. E. Swider, C. I. Merzbacher and D. R. Rolison, Langmuir , 15 , 780 (1999). 6. B. E. Conway, Journal of the Electrochemical Society , 138 , 1539 (1991). 7. B. E. Conway, Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications , Kluwer Academic/Plenum Publishers, New York (1999). 8. C. C. Hu and T. W. Tsou, Electrochemistry Communications , 4 , 105 (2002). 9. J. M. Miller, B. Dunn, T. D. Tran and R. W. Pekala, J. Electrochem. Soc. , 144 , L309 (1997). 10. M. Toupin, T. Brousse and D. Belanger, Chemistry of Materials , 14 , 3946 (2002). Figure 1 caption: TEM image of nanoparticulate VN evaluated extensively using various electrochemical methods

Abstract: The formation of the solid electrolyte interphase (SEI) is critical to stabilization of lithium metal electrodes. 1,2 When the electrodes contact electrolyte, a thin solid layer is immediately deposited on the surface. Ideally, this layer should be electronically insulating, while conducting Li-ions, and only a few nanometers thick to ensure that lithium can diffuse to the electrode surface without the reduction of any electrolyte components. 2 Unfortunately, much research has shown that even after initial formation, the SEI layer continues to grow, and eventually leads to cell failure by limiting the ability of lithium to diffuse to the electrode surface. 3,4 In order make electrodes practical for use in lithium metal batteries, the growth of the SEI needs to be well controlled and limited in thickness. Previous work has shown that the use of high surface area porous metal anodes can prevent dendrite formation, another key barrier to commercialization of lithium metal batteries. 5 However, as the number of cycles increases and the SEI layer on the electrode grows too thick, the pore network fills and lithium diffusion is limited, and plating subsequently reverts to unwanted dendritic growth. In this work, a method for improving the cycling stability of these porous foam electrodes by controlling the SEI is examined. Accordingly, the work focuses on the utilization of novel surface additives to achieve this goal. The approach has shown to greatly increase the number of achievable cycles. The engineered systems already show ~99% efficiency over 100 cycles, far better than the 70 cycles at ~95% efficiency previously obtained using unmodified foams. By controlling the initial SEI formation and limiting its thickness, saturation of the pore network can be inhibited, thus extending the stable cycling window. Acknowledgements: The authors acknowledge the financial support of DOE grant DE-EE 0007797, Edward R. Weidlein Chair Professorship funds, and the Center for Complex Engineered Multifunctional Materials (CCEMM). References Aurbach, E. Zinigrad, Y. Cohen, H. Teller, Solid State Ionics , 148 , 405-416 (2002). Peled, S. Menkin, J. Electrochem. Soc. , 164 (7), A1703-1719 (2017). Zheng, S. W. Lee, Z. Liang, H. Lee, K. Yan, H. Yao, H. Wang, W. Li, S. Chu, and Y. Cui, Nature Nanotech. 9 , 618-623 (2014) Vetter et al., Journal of Power Sources 147 , 269–281 (2005) A. Day, P. Jampani, P. M. Shanthi, B. Gattu, P. N. Kumta. ECS 232, National Harbor Maryland (2017).

Abstract: INTRODUCTION Lithium has the potential of being the pre-eminent negative electrode in energy storage systems given its small ionic radius, high charge/mass ratio [reflected in a very negative reduction potential (-3.04 V wrt SHE)] and high theoretical capacity (~3862 mAh/g). The shuttling attribute of Li+ is also rivalled by hydronium ions though limited by aqueous potential window. The transition to lithium anode based systems however, has primarily been stymied by safety concerns owing to the fact that lithium forms dendrites in the process of plating/de-plating. Dendrite formation is a well-known metallurgical phenomenon occurring as a result of several energy minimization processes including preferential growth during crystallization Dendrite formation and growth in lithium are however not well-understood owing to the additional factor of solid-electrolyte interphase (SEI) formation(1). The control of lithium dendrite formation is a veritable challenge that could very well make universal adoption of battery systems possible for both stationary and mobile applications. A number of approaches have previously been proposed for the same with varying degrees of success at addressing the issue (2-7). A common strategy involves the use of polymeric/carbon coatings as a method to address fracture. The coating either aids in preventing dendrite growth by allowing for directed growth or acts as a mechanical barrier to rupture and thus cell-failure. Such an approach however lacks scalability given that there is the associated problem of volumetric change especially in thicker lithium electrodes. In this work, a multi-pronged approach has been taken to solve the issue of dendrite formation in thick lithium electrode involving the use of composite lithium anodes (CLAs) suitable for bearing the significant volumetric change associated with lithium plating-deplating while ensuring prevention of dendrite formation. The nature of the composite lithium anodes will be discussed along with electrochemical stability and voltage hysteresis behavior. Figure 1 shows the dendrite-free SEM images of CLA electrodes as evidence of the improved cycling characteristic obtained for composite current collector based lithium electrodes in a half-cell configuration. References 1. J. Steiger, Mechanisms of Dendrite Growth in Lithium Metal Batteries, in, Karlsruhe, Karlsruher Institut für Technologie (KIT), Diss., 2015 (2015). 2. K. Yan, H.-W. Lee, T. Gao, G. Zheng, H. Yao, H. Wang, Z. Lu, Y. Zhou, Z. Liang, Z. Liu, S. Chu and Y. Cui, Nano Letters, 14, 6016 (2014). 3. G. Zheng, S. W. Lee, Z. Liang, H.-W. Lee, K. Yan, H. Yao, H. Wang, W. Li, S. Chu and Y. Cui, Nature Nanotechnology, 9, 618 (2014). 4. J.-H. Han, E. Khoo, P. Bai and M. Z. Bazant, Scientific Reports, 4, 7056 (2014). 5. Z. Liang, G. Zheng, C. Liu, N. Liu, W. Li, K. Yan, H. Yao, P.-C. Hsu, S. Chu and Y. Cui, Nano Letters, 15, 2910 (2015). 6. A. Aryanfar, Dendrites Inhibition in Rechargeable Lithium Metal Batteries, in, http://caltech. edu/CaltechTHESIS: 05012015-161434189 (2015). 7. F. Ding, W. Xu, G. L. Graff, J. Zhang, M. L. Sushko, X. Chen, Y. Shao, M. H. Engelhard, Z. Nie, J. Xiao, X. Liu, P. V. Sushko, J. Liu and J.-G. Zhang, Journal of the American Chemical Society, 135, 4450 (2013). Figure caption: SEM images of the morphology of (a) lithium electrode and (b) Li-CLA electrode cycled at high current density~1A/g (30 cycles). A clear absence of dendritic structures is observed in the Li-CLA electrode. Figure 1

Abstract: Introduction Lithium-ion batteries with their unique high voltage, high energy density chemistries have come to fruition decades of fundamental research conducted in electrochemical systems and materials. The development of a number of plug-in hybrid and fully electric vehicles (EV) using lithium-ion technology and their favorable market response is the harbinger of a long-awaited transition in automotive technology. Despite these advances, there is still a genuine need for increasing energy densities for the successful transition to EVs (1, 2). Advances in lithium-ion anode technology have made it possible to obtain ~1500 mAh/g anodes with superior cycle life (3-5). However, cathode research has been rather stymied in contrast on account of the challenges faced in designing stable, conductive materials with high capacities. Cathode capacities thus far have been limited to ~ 300 mAh/g in high voltage (1, 6) lithium manganese-nickel-cobalt oxide chemistries. Lithium sulfur and lithium-air batteries though well-known but challenging to execute, hold much more promise of matching anode capacities on account of their theoretical capacities of 2567 and 3505 Wh/kg respectively(2). The dissolution of sulfur through the formation of soluble polysulfides and the poor electronic conductivity of sulfur are however, major problems hindering Li-S batteries. It has previously been demonstrated that the use of highly conductive porous carbon matrix and carbon nanotubes can help circumvent these issues (7-10). In addition, the use of a carbon matte as a barrier layer to polysulfide transport has been demonstrated to be effective in retaining high capacity(11). There is however a need to translate this design into thick electrodes capable of delivering high overall electrode capacity. In this study, we coat pristine sulfur particles with carbon and an ionically conducting matrix using a simple chemical method. The thick electrodes were prepared using this procedure and were tested in 2025 coin cells with lithium counter/reference electrodes. We demonstrate excellent charge storage behavior of these composite electrodes at various charge-discharge rates. Extended cycling of these composite electrodes reveals much improved capacity retention. Figure 1 shows the electrochemical results of these different configurations. Results of these studies will be presented and discussed. References 1. M. M. Thackeray, C. Wolverton and E. D. Isaacs, Energy & Environmental Science , 5 , 7854 (2012). 2. P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nature Materials , 11 , 19 (2012). 3. M. K. Datta, J. Maranchi, S. J. Chung, R. Epur, K. Kadakia, P. Jampani and P. N. Kumta, Electrochimica Acta , 56 , 4717 (2011). 4. R. Epur, M. K. Datta and P. N. Kumta, Electrochimica Acta , 85 , 680 (2012). 5. W. Wang, R. Epur and P. N. Kumta, Electrochemistry Communications , 13 , 429 (2011). 6. C. S. Johnson, N. Li, C. Lefief and M. M. Thackeray, Electrochemistry Communications , 9 , 787 (2007). 7. X. Ji, K. T. Lee and L. F. Nazar, Nature Materials , 8 , 500 (2009). 8. J. Schuster, G. He, B. Mandlmeier, T. Yim, K. T. Lee, T. Bein and L. F. Nazar, Angewandte Chemie International Edition , 51 , 3591 (2012). 9. X. Liang, Z. Wen, Y. Liu, H. Zhang, J. Jin, M. Wu and X. Wu, Journal of Power Sources , 206 , 409 (2012). 10. J. Wang, L. Lu, D. Shi, R. Tandiono, Z. Wang, K. Konstantinov and H. Liu, ChemPlusChem , 78 , 318 (2013). 11. Y.-S. Su and A. Manthiram, Nat Commun , 3 , 1166 (2012). Figure 1 caption: Improvement in sulfur capacity retention by use of a lithium-ion conducting matrix

Abstract: There is an ever increasing demand for renewable and non-carbonaceous clean energy sources to fulfill massive global energy demand 1 . Hydrogen (H 2 ) as a fuel is clearly the frontrunner due to its non-carbonaceous nature and superior energy density than the carbonaceous energy sources 1 . Acid assisted proton exchange membrane (PEM) based water electrolysis is promisingly at the forefront among all other conventional hydrogen production methods. Commercial development of PEM water electrolyzer has been stymied due to requirement of highly expensive and scarce noble metal based electro-catalysts such as Pt, RuO 2 , IrO 2 ; which exhibit excellent oxygen evolution reaction (OER) activity in PEM water electrolysis 2 . Therefore, identification and development of ultra-low noble metal containing electro-catalyst system which can exhibit superior electrochemical performance than state of the art-noble metals based electro-catalysts in highly aggressive acidic media for OER, will indeed lead to significant reduction in capital costs of the water splitting process 2 . In the pursuit of this objective, based on theoretical first principles calculations of the total energies and electronic structures, the present authors have identified fluorine (F) doped transition metal oxide (TMO) based solid solution electro-catalyst with ultra-low noble metal for OER in PEM water electrolysis. The F-doped synthesized TMO in two dimensional (2D) thin film morphology exhibits electro-catalytic performance (i.e. overpotential and electro-catalytic activity) similar to that of IrO 2  thin film electro-catalyst. Therefore, aiming to further improve the reaction kinetics and also achieve superior electro-catalytic activity, tailoring of the 2D material length scale to 1D vertically aligned nanotubular (VANT) architecture has been executed. Over the past few years, electro-catalysts with 1D nanostructured morphologies such as nanowires (NWs) as well as nanotubes (NTs) have garnered significant attention as a potentially effective materials for water splitting due their inherent benefits such as high electro-catalytic surface area, high aspect ratios (length-to-width ratio) and facile electron transport though 1D nanotubular arrays 3 . Therefore, in order to enhance the electrochemical performance of as prepared 2D thin film electro-catalyst i.e. F-doped TMO for OER, we have explored 1D nanotube (NT) structured-morphology; retaining similar electro-catalyst composition. In this study, a sacrificial template-assisted approach has been utilized to grow VANTs on titanium (Ti) substrate.  Fig. 1  displays the SEM micrograph showing top view, cross-sectional view of F-doped TMO NTs. The electrochemical characterization of synthesized electro-catalysts has been carried out in three-electrode configuration using 1N sulfuric acid (H 2 SO 4 ) solution as a proton source as well as the electrolyte, Pt wire as counter electrode and Hg/Hg 2 SO 4  as the reference electrode (+0.65 V with respect to normal hydrogen electrode, NHE), with a scan rate of 10 mV/sec and at temperature of 40 o C. 1D VANTs of F-doped TMO grown on Ti substrate showed onset potential of ~1.43  vs  NHE, similar to that of IrO 2  (total loading=0.3 mg/cm 2 ) and lower charge transfer resistance (R ct ) than 2D thin films of F-doped TMO. The 1D F-doped TMO VANTs also exhibit remarkable ~2.3 and ~ 2.6 fold higher electro-catalytic OER activity (current density) than that of 2D thin film architectures of F-doped TMO and IrO 2  respectively. In addition, the chronoamperometry test conducted in 1N H 2 SO 4  solution at ~1.5 V ( vs  NHE) for 24 hours shows minimal loss in current density demonstrating good electrochemical stability of the F-doped TMO VANTs, comparable to that of IrO 2 2D thin films. In summary, we have synthesized high performance 1D vertically aligned nanotubes of F-doped TMO OER electro-catalyst. The superior electrocatalytic activity of the F-doped TMO VANTs is attributed to the presence of vertical channels in 1D morphology, exhibiting higher electrochemical surface area (ECSA) than 2D thin film architectures. These encouraging results of 1D-F-doped TMO VANTs with ultra-low noble metal content and superior OER kinetics show potential of these systems for water electrolysis. The results of this study will be presented and discussed. References: 1. Ball, M.; Wietschel, M. International Journal of Hydrogen Energy 2009, 34, (2), 615-627. 2. Patel, P. P.; Datta, M. K.; Velikokhatnyi, O. I.; Kuruba, R.; Damodaran, K.; Jampani, P.; Gattu, B.; Shanthi, P. M.; Damle, S. S.; Kumta, P. N. Scientific reports 2016, 6. 3. Liu, G.; Xu, J.; Wang, Y.; Wang, X. Journal of Materials Chemistry A 2015, 3, (41), 20791-20800. Acknowledgements: Financial support of NSF-CBET grant# 1511390, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM) is acknowledged. Figure 1

Abstract: There is a critical need to develop clean, environmental friendly and sustainable energy sources to substitute the rapidly depleting conventional fossil fuels - causing serious global environmental concerns. In the pursuit of this need, hydrogen is attracting immense attention due to its clean, non- carbonaceous nature and also, high energy density as compared to petroleum based energy sources [ 1 ] . Over the past few decades, catalytic methane conversion, steam reforming and coal gasification etc. have been widely used for hydrogen production. However, the toxic greenhouse gases (CO/CO 2 ) produced render these techniques environmentally less attractive. Therefore, hydrogen production from water splitting (H 2 O® H 2 + 0.5 O 2 ) is considered a far cleaner and more efficient technique among all other conventional hydrogen production methods. However, the efficiency of water electrolysis has been severely constrained by the energy intensive anodic oxygen evolution reaction (OER) (4OH − → O 2 + 2H 2 O + 4e − ) which is the other important half reaction in addition to hydrogen evolution reaction (HER). To date, platinum group metal (PGM) based materials such as Pt, RuO 2 , IrO 2 are well known for their superior electrochemical performance towards OER. Commercial implementation of these electrocatalsts for water splitting has been largely limited due to their high cost and scarcity [ 2 ] . Thus, identification and development of earth abundant, cheap and PGM-free electro-catalysts, demonstrating excellent electro-catalytic activity and robust stability (for OER); comparable/superior to state-of-the art PGM/noble metals based electro-catalysts is critically desired [ 3 ] . Therefore, in the present study, exploiting theoretical first principles approaches, we have engineered anionic fluorine (F) doped transition metal non-oxide pnictide (TMN) based electro-catalyst for OER in alkaline mediated water electrolysis. We have observed remarkable enhancement in the electro-catalytic activity by incorporation of F into the as-synthesized TMN based electro-catalyst. The electro-catalyst powder with F content of 5 wt. % ( Fig. 1 ) has been synthesized using solid state approaches. The as-synthesized electro-catalyst powder was coated on porous titanium (Ti) substrate (total catalyst loading=1 mg/cm 2 ) and used as an anode. The electro-catalyst with F content of 5 wt. % exhibited excellent electro-catalytic performance, outperforming the benchmark IrO 2 for OER in alkaline water splitting. The electrochemical response of the electro-catalysts has been evaluated in a three-electrode configuration system, using 1N KOH solution. Correspondingly, Pt wire and Hg/Hg 2 SO 4 are used as a counter electrode and reference electrode (+0.65 V with respect to normal hydrogen electrode, NHE) respectively. Electrochemical characterization of the electrocatalyst has been performed with a scan rate of 10 mV/sec at 40 o C. The generated PGM-free electro-catalyst exhibited significantly lower charge transfer resistance (R ct ) than benchmark IrO 2. In addition, this PGM-free electro-catalyst displayed remarkable ~7.6 fold higher electro-catalytic OER activity (i.e. current density, at 1. 55V) than that of IrO 2 and reached a current density of ~ 10 mA/cm 2 at an overpotential of ~ 300 mV. The chronoamperometry test conducted in 1N KOH solution at ~1.55 V ( vs NHE) for 24 hours shows the minimal loss in current density, signifying a robust electrochemical stability of the as-prepared electro-catalyst. In summary, we have synthesized high performance PGM-free F doped TMN pnictide based electro-catalyst for alkaline mediated water splitting. The observed enhanced electrocatalytic activity of this electro-catalyst is mainly attributed to the modified electronic structure (as supported by the theoretical study) and lower charge transfer resistance (i.e. lower activation polarization). Based on these results we believe that this PGM-free electro-catalyst is indeed a promising and reliable system for sustainable and economic hydrogen production. Results of this work will be presented and discussed. References: [1] M. Momirlan, T. N. Veziroglu, Renewable and Sustainable Energy Reviews 2002 , 6 , 141-179. [2] S. D. Ghadge, P. P. Patel, M. K. Datta, O. I. Velikokhatnyi, R. Kuruba, P. M. Shanthi, P. N. Kumta, RSC Advances 2017 , 7 , 17311-17324. [3] M. K. Datta, K. Kadakia, O. I. Velikokhatnyi, P. H. Jampani, S. J. Chung, J. A. Poston, A. Manivannan, P. N. Kumta, Journal of Materials Chemistry A 2013 , 1 , 4026-4037. Figure 1

Abstract: Recently, energy storage systems based on bivalent Mg 2+ ions spurred considerable interest as a promising high energy density alternative battery system among others [1, 2]. Magnesium (Mg) has several positive attributes which set it apart from Li-ion battery system. It is environmental friendly, cost effective (~$ 2700/ton for Mg compared to $64,000/ton for Li) and is relatively more abundant in the earth’s crust (~13.9% Mg compared to ~0.0007% of Li) compared to hitherto used popular systems. Additionally, magnesium is more stable in air compared to lithium, and is theoretically capable of rendering higher volumetric capacity (3832 mAh/cc for Mg vs. 2062 mAh/cc for Li). In the year 2000, Aurbach and coworkers successfully demonstrated a prototype Mg cell using the Mo 6 S 8 Chevrel Phase a new class of cathodes, Mg anode, and the 0.25 molar Mg(AlCl 2 EtBu) 2 /tetrahydrofuran electrolyte where Mg 2+ can be (de)intercalated reversibly ~ 1-1.2V offering an energy density ~ 60 Whkg -1 up to 2000 cycles with little fade in capacity [3]. Relatively fast and easy intercalation of Mg 2+ ions at room temperature makes Mo 6 S 8 a model cathode for magnesium battery. However, Mo 6 S 8 is a metastable phase at room temperature, and is therefore indirectly stabilized when generated via leaching of the metal from the thermodynamically stable ternary Chevrel phase compounds, M x Mo 6 T 8 (M = metal, T = S, Se, Te) [4]. Typical synthesis approach of Cu x Mo 6 S 8 (Cu x CP) requires high temperature reactions of elemental blends in an evacuated quartz ampoules (EQA) at ~1150 ○ C for 7 days [3] or by a molten salt (MS) route using Mo-MoS 2 -CuS reactants in a KCl salt, and heat treating the reaction mixtures at ~850 ○ C for 60h in an Ar atmosphere [5]. Both approaches are extremely tedious and require chemical leaching either in 6 molar HCl/H 2 O or 0.2 molar I 2 /acetonitrile solutions for several days at room temperature for complete removal of copper [5]. Herein, we report a rapid solution chemistry route (total manufacturing time required for the synthesis of CP is only ~12h) for the synthesis of Mo 6 S 8 following modification of a previous report [6] which only reported the synthesis of the Cu analog of the Mo 6 S 8 phase. The structural analysis (XRD and SEM) shows the formation of phase-pure micrometer (~1-1.5 mm) size cuboidal shaped Cu 2 Mo 6 S 8 and Mo 6 S 8 crystals [See Fig. 1(a-d )]. Electrochemical performance of the resultant Mo 6 S 8 cathode exhibits a discharge capacity ~ 76 mAhg -1 with excellent capacity retention up to ~100 cycles, when cycled at a current rate of 20mA/g (~C/6). The excellent cyclability, rate capability and high Coulombic efficiency (~99.3% at ~1.C rate) of the Mo 6 S 8 cathode, renders the solution chemistry route a convenient approach for synthesizing the electrochemically active model Chevrel phase Mo 6 S 8 . Results of these studies will be presented and discussed. References [1] Aurbach D, Suresh G, Levi E, Mitelman A, Mizrahi O, Chusid O, et al. Progress in Rechargeable Magnesium Battery Technology. Advanced Materials. 2007;19:4260-7. [2] Kim HS, Arthur TS, Allred GD, Zajicek J, Newman JG, Rodnyansky AE, et al. Structure and compatibility of a magnesium electrolyte with a sulphur cathode. Nat Commun. 2011;2:427. [3] Aurbach D, Lu Z, Schechter A, Gofer Y, Gizbar H, Turgeman R, et al. Prototype systems for rechargeable magnesium batteries. Nature. 2000;407:724-7. [4] Rabiller P, Rabiller-Baudry M, Even-Boudjada S, Burel L, Chevrel R, Sergent M, et al. Recent progress in chevrel phase syntheses: A new low temperature synthesis of the superconducting lead compound. Materials Research Bulletin. 1994;29:567-74. [5] Lancry E, Levi E, Mitelman A, Malovany S, Aurbach D. Molten salt synthesis (MSS) Of Cu 2 Mo 6 S 8 - New way for large-scale production of Chevrel phases. Journal of Solid State Chemistry. 2006;179:1879-82. [6] Nanjundaswamy KS, Vasanthacharya NY, Gopalakrishnan J, Rao CNR. Convenient synthesis of the Chevrel phases metal molybdenum sulfide, M x Mo 6 S 8 (M = copper, lead, lanthanum or gadolinium). Inorganic Chemistry. 1987;26:4286-8. Acknowledgements: The authors gratefully acknowledge the financial support as part of the Department of Energy’s National Energy Technology Laboratory’s program DOE-NETL) (contract number DE-FE0004000). PNK also acknowledge the Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM) for partial support of this research.