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Platinum (Pt) is a critical element in making electrocatalysts for oxygen reduction reaction (ORR) occurring at the cathode of polymer electrolyte membrane fuel cells (PEMFCs). To address the Pt abundance issue and to enhance Pt catalysis, Pt is often alloyed with another transition metal M (i.e. M = Fe, Co, and Ni). Ordered intermetallic PtM alloys are considered as one of the most promising candidates to achieve both high activity and stability in practical fuel cell applications. The transition metals in ordered intermetallic PtM alloys occupy specific sites, and are stabilized by both metallic and ionic bonding. Ordered intermetallic structures are formed via high temperature (>600 °C) annealing of disordered PtM alloys, as the atomic ordering is a thermodynamically driven process. However, the high temperature annealing inevitably leads to the migration and agglomeration of the nanoparticles forming randomly alloyed particles with poor dispersion and broad size distributions, due to weak adhesions to the carbon support under typical processing conditions. To prevent this coalescence during annealing, protective coating of the nanoparticles with inorganic shells or physical barriers has been suggested. However, these studies were limited to the synthesis of intermetallic nanoparticles on carbon supports at low metal loadings, or require an additional step of removing the coating layer from the surface of the nanoparticles to expose the active sites. Thus, it is essential to develop a general approach that can produce highly dispersed, structurally ordered nanoparticles while achieving controls over the size and size distribution. We propose to use the functionalized carbon supports to control PtM alloy nanoparticle size and prevent nanoparticles from aggregating during the high temperature annealing through improving the metal-support interactions. A strong electrostatic attraction between the negative charge from Pt precursor (PtCl6 2 -) and positive charge from the amino groups (C-NH2+) on the surface of the functionalized carbon will be established during the wet impregnation synthesis. Such bonds will help to make the PtM nanoparticle size smaller and more uniformly distributed over the surface of support. The ordered intermetallic 30 wt.% PtCo/KB-NH2 catalyst demonstrated an average size of 2.7 nm and uniform size distribution. In addition, 30 wt.% PtCo/KB-NH2 catalyst exhibited a mass activity of 535 A/gPt (H2/O2) and a rated power density of 1.05 W/cm2 at 0.67 V (H2/air), meeting the DOE targets.

The promising performance from the platinum group metal (PGM) catalysts make them the most practical catalysts for the commercialization of the polymer membrane fuel cells (PEMFCs). However, the excellent initial performance is not good enough for massive applications, particular for the fuel cell vehicles, which requires the long-term durability. Both the performance and the durability of catalysts strongly impact the applications in a wide range of operations of fuel cells, from stationary power generation to the transportation power propulsion. Catalyst stability plays a very important role on reducing the operation cost and increasing the lifetime of PEMFCs. Herein, a concept is proposed, which enhances the lifetime of PEMFCs through engineering the surface of catalyst supports. By covalently grafting NH2 groups on carbon (NGCB) surface, followed by polymerizing polyaniline (PANI) onsite on NFCB surface (using introduced NH2 groups as precursor), Pt L-edge goes to higher energy level, suggested by XAS measurement. Such modification can increase the barrier for Pt’s oxidation. In this study, carbon supports with different PANI loadings were synthesized and the Pt nanoparticles were loaded onto these supports. The synthesized catalysts were characterized for their morphology and structure using TEM, XRD, BET and Hg porosimetry. Both RDE and MEA tests were carried out for these catalysts for their fuel cell performance. The results show that the energy levels of Pt L-edge were increased with PANI loading. Besides, the membrane electrode assembly (MEA) testing results prove that the catalyst stability was improved with PANI loading in certain range. Three different PANI loadings were analyzed: 0.2, 0.25 and 0.33 in mass fraction of NFCB. MEAs results show that the beginning of life (BOL) performances of three catalysts were almost same. But when it comes to the catalyst stability test, the performance losses between BOL and EOL at 0.8 A·cm-2 in air are 120 mV, 90 mV and 45 mV for the three catalysts, respectively, after 30k square wave cycling using the standard testing protocol from the Department of Energy (DOE).

Lithium-ion batteries (LIBs) are the major power sources for electronic and transportation applications due to their high specific energy, good cyclability and environmental friendliness1, 2 Intercalation compounds were commercially employed as the positive (cathode) electrode material. However, they have a limited capacity due to the mono-valence change of host materials and the accompanied 1-e- transfer process, which accommodates 1-Li ion intercalation. These materials can’t meet the growing demand on higher specific energy and energy/power density. To achieve high specific energy cathode materials, efforts are being made to find alternative cathode materials for LIBs: (1) materials with transition metal ions capable of multi valence changes, and (2) materials with high potentials (vs. Li/Li+). Compared with intercalation cathode materials, conversion cathode materials can store multiple electrons instead of 1 electron of the intercalation materials. However, the conversion materials have not been used as practical LIB cathode materials due to the low electric conductivity, and structural stability. Iron oxyfluoride (FeOF) was proposed3, 4 as a promising candidate because its high theoretical specific capacity of 885 mAh/g, leading to an exceptionally high theoretical specific energy of 2938 Wh/kg for 3- electron reactions. Graphene was employed to solve the low conductivity and structural stability. As the results from the improved FeOF structure, the nanostructured FeOF with the incorporated graphene sheets shows the superior performance to its blank. The FeOF/G initial specific capacity reached 621 mAh/g (Fig. 1) with an initial Coulombic efficiency of 94.7%, while the blank FeOF initial specific capacity can reach 586 mAh/g but has a drastically low Coulombic efficiency of 38.7%. SEM and TEM (Fig. 2) were employed to observe the morphology. The structure evolution during charge/discharge process were also characterized by in situ XAS and high resolution XRD. The results showed that the graphene nano-sheets serve as substrates to stabilize the structure of FeOF and form a framework to stabilize the discharged species through bonding them to their original sites without migration, in which the graphene sheets serve as a “cage” to trap the discharged species. Thus, the FeOF/Graphene composite can keep the (de)lithiation reaction reversible during discharge and charge process and could be a promising cathode material for Li-ion batteries. Fig. 1 Charge/discharge curves of FeOF (BLK) and FeOF/graphene (GRP). Fig. 2 SEM image (a) and TEM image (b) of FeOF/Graphene hybrid material. J. B. Goodenough and K.-S. Park, Journal of the American Chemical Society, 2013, 135, 1167-1176. J.-M. Tarascon and M. Armand, Nature, 2001, 414, 359-367. A. Kitajou, H. Komatsu, R. Nagano and S. Okada, Journal of Power Sources, 2013, 243, 494-498. K. M. Wiaderek, O. J. Borkiewicz, E. Castillo-Martínez, R. Robert, N. Pereira, G. G. Amatucci, C. P. Grey, P. J. Chupas and K. W. Chapman, Journal of the American Chemical Society, 2013, 135, 4070-4078. Figure 1

The participation of anion redox in lithium transition metal oxides such as Li2RuO3 and Li2MnO3 for positive electrodes have opened a new avenue to boost up the energy density of current lithium-ion batteries. There are many schools of thoughts for the physical origin proposed to be responsible for anion redox and more direct and clear experimental evidence of anion redox is needed to further understand and utilize this phenomena. In the first part of this work, we demonstrated the electronic signature of oxygen-oxygen coupling, direct evidence central to lattice oxygen redox (O2-/(O2)n-) in charged Li2-xRuO3 after Ru oxidation (Ru4+/Ru5+) upon first-electron removal with lithium de-intercalation. Experimental and simulated Ru L3-edge X-ray absorption spectra (XAS) revealed that the increase in the high-energy shoulder intensity upon lithium de-intercalation resulted from increased O-O coupling, inducing (O-O) σ* with π overlap with Ru d-manifolds, in agreement with the similar changes in the O K-edge XAS spectra. Further support came from experimental and simulated O K-edge X-ray emission spectra (XES), where the broadening of the oxygen nonbonding feature upon charging also originated from creation of (O-O) σ* states. By combining differential electrochemistry mass spectrometry (DEMS) with core-level spectroscopies, we are able to quantify the percentage of this lattice oxygen redox across different Li2RuxM(1-x)O3 (M=Ti, Cr, Mn, Fe, Ir, Sn) chemistries, through which we proposed a preliminary electronic descriptor for reversible bulk oxygen redox activity. This study constructed a transferrable framework to rationally interpret the spectroscopic features by combining experiments and theory, and pinpointed the key spectra footprints related to lattice oxygen redox from a molecular level. We also proposed a simple descriptor to rationalize and facilitate novel positive electrode materials design for reversible anion redox activities in high-energy Li-ion batteries.

Lithium ion batteries as the major power source play a critical role in our life today due to their high specific energy, good cyclability and environmental friendliness. Intercalation compounds were commercially employed as the positive (cathode) electrode material. However, they have a limited capacity due to the mono-valence change of host materials and the accompanied 1-e- transfer process, which accommodates 1-Li ion intercalation. These materials can’t meet the growing demand on higher specific energy and energy/power density. Transition-metal oxides, fluorides and oxyfluorides have attracted a lot of interest due to their ability to deliver high electrochemical specific energy arising from 2-3 electrons transferred. FeOF was proposed as a promising candidate1 because it has a high theoretical specific capacity, 885 mAh/g (3-electron process) and 590 mAh/g (2-electron process), leading to an exceptionally high specific energy of 1328 Wh/kg. However, the electrochemical performance of FeOF is limited in practice due to its low electronic conductivity and poor structure stability during charge/ discharge cycling. Graphene, a single−layer of sp2 carbon, has been considered as one of the most attractive carbon materials for its excellent charge carrier mobility, mechanical robustness and thermal and chemical stability2. Our approach for solving the low conductivity and structural stability is to incorporate the graphene sheets into the nanostructure FeOF so that the conductivity, stability and relocation can be comprehensively addressed. As the results from the improved FeOF structure, the nanostructured FeOF with the incorporated graphene sheets shows the superior performance to its blank. The FeOF/G initial specific capacity reached 621 mAh/g (Fig. 1) with an initial Coulombic efficiency of 94.7%, while the blank FeOF initial specific capacity can reach 586 mAh/g but has a drastically low Coulombic efficiency of 38.7%. It has been demonstrated that the performance improvement can be attributed to the introduction of the graphene sheets which improved the electric conductivity and provide a substrate to stabilize the FeOF particles evidenced by the morphology observation and structure characterization. TEM (Fig. 2) were employed to observe the morphology change after introducing graphene. The structure evolution during charge/discharge process were also characterized by in situ XAS and high resolution XRD. The results showed that the graphene sheets provide substrates for FeOF nanoparticle to anchor on so that the formed metallic Fe particles don’t relocate, the intra- and inter-particle conductivity can be effectively improved by forming FeOF/graphene sandwiched structure, and finally these graphene sheets can hold the FeOF nanoparticles together to maintain the structural integrity. The incorporation of graphene sheets into the nanostructured metal oxides and metal oxyfluorides provide an effective and robust tool for tailoring the structure of nanomaterials. (1) Kitajou, A.; Komatsu, H.; Nagano, R.; Okada, S. Journal of Power Sources 2013, 243, 494. (2) Kucinskis, G.; Bajars, G.; Kleperis, J. Journal of Power Sources 2013, 240, 66. Figure 1

In the past few years, concerns over lithium reservoir depletion have driven researchers to go beyond lithium ion battery[1]. Sodium ion battery (SIB) has been considered as a promising candidate as sodium is highly abundant and widely distributed around the world. One of the challenges in state of the arts sodium ion battery is searching for cathode materials that can provide electrochemical performance comparable to lithium ion battery and electrolytes compatible with the related cathode materials. Among the reported cathode materials for SIB, O3 or O'3 type layered transition metal oxides are of great interest due to their high specific capacities[2]. In order to get a better understanding on these transition metal oxides, it is important to decouple the mixing transition metals and carry out a thorough investigation on the end member of the series. One of the end members, NaMnO2, has been reported with high specific capacity but shown low coulombic efficiency[3], which may be associated with electrolytes decomposition. Therefore, it is critical to search for a suitable electrolyte as well as additives. The influence of FEC (Fluoroethylene Carbonate) additive and some commonly used electrolytes in sodium ion battery were examined in NaMnO2/Na coin cells. For the cell using 1M NaClO4/PC as electrolyte, coulombic efficiency is relatively low at first but increases to 94% within ten cycles. While the coulombic efficiency of NaPF6/EC+DMC stays as low as 80% till 40 cycles. Apparently, the coulombic efficiency can be improved by adding FEC as additive in both electrolytes. The study regarding function mechanism for the FEC additive will be comprehensively understood by in-situ high energy X-ray diffraction and high precision electrochemical test, which could serves a good guide for the exploration of suitable electrolytes for high performance cathode materials of SIB. Figure 1

Lithium-ion batteries (LIBs) are the major power sources for electronic and transportation applications due to their high specific energy, good cyclability and environmental friendliness. Intercalation compounds were commercially employed as the positive (cathode) electrode material. However, they have a limited capacity, which are not likely to meet the growing demand on specific energy and energy/power density. Transition-metal oxides, fluorides and oxyfluorides have attracted a lot of interest due to their ability to deliver high electrochemical specific energy arising from 2-3 electrons transferred. FeOF was proposed as a promising candidate1 because it has a high theoretical specific capacity, 885 mAh/g (3-electron process) and 590 mAh/g (2-electron process), leading to an exceptionally high specific energy of 1328 Wh/kg. However, the electrochemical performance of FeOF is drastically different in practice due to its low electronic conductivity and poor structure stability during charge/discharge cycling process. To overcome these obstacles, conducting carbon matrices have been introduced to absorb the volume changes and to improve the structural stability of the electrodes. Graphene, a single−layer of sp2 carbon lattices, has been considered as one of the most attractive carbon materials for its excellent charge carrier mobility, mechanical robustness and thermal and chemical stability2. Our approach is to prepare a mixture of precursor of FeOF and graphene oxide in solution and to ensure a better bonding between FeOF and GO through a hydrothermal procedure. The resulted hybrid material showed much improved initial columbic efficiency and cyclability compared with the blank FeOF material. The initial specific capacity reached 621 mAh/g (Fig. 1) and the capacity retention was 78.9% (specific capacity 493 mAh/g) after 100 cycles at 0.1 C rate. It has been demonstrated that the performance improvement could be attributed to introduction of graphene which improved the electric conductivity and provide a substrate to stablize the FeOF particles by morphology observation and structure characterization. SEM (Fig. 2) and TEM were employed to observe the morphology change after introducing graphene. The structure evolution during charge/discharge process were also characterized by in situ XAS and high resolution XRD. The results showed that the graphene nano-sheets serve as substrates to stabilize the structure of FeOF and form a framework to stabilize the Fe clusters through bonding them to their original sites without migration. Thus, the FeOF/Graphene composite can keep the (de)lithiation reaction reversible during discharge and charge process. Figure 1

High energy density batteries are becoming essential to satisfy the demands of fast growing portable electronic and electric vehicle markets. There are great efforts in the battery community to explore new materials with a high energy density. However, the challenge is formidable and even if potential materials can be identified, it still takes years, if not a decade, to commercialize. Therefore, it is reasonable to investigate modifications of existing materials to improve battery energy density. LiCoO2, the first commercialized material, is still the most used cathode material to-date due to its simple synthesis process, high energy density, and good cycle life. Conventionally, only a limited amount of its capacity was utilized due to the concern of its structural instability. However, with better understanding of this electrode material, more and more energy has been achieved by pushing its cutoff voltage to higher values without sacrificing electrochemical performance. Currently, LiCoO2 is operated as high as 4.4V in full cells, which is equivalent to 4.45V vs. Li, and yields a specific capacity of 180mAh/g. This is close to a 20% capacity increase compared to the early 140 mAh/g capacity. In this study, we investigated the possibility of increasing the LiCoO2 upper cutoff voltage to even higher voltages, such as 4.5V or even 4.6V, with capacities greater than 190 mAh/g. It has been well understood that LiCoO2 will go through a phase transition when half the lithium is removed from the structure. This phase transition will affect the stability of its structure and lead to poor cycling performance. Doping is a common method to suppress the phase transition. In order to study the doping effect, aluminum doped LiCoO2 (LCO-A) cathode materials were prepared by ShanShan, China. The electrochemical characterization clearly indicates that the phase transition is suppressed for the doped LiCoO2, which demonstrated excellent cycling performance. Following their electrochemical characterization, the LiCoO2 cathode materials were further studied to examine their chemical composition, morphologies, structure, and surface properties. The results shed further light on the development of high energy LiCoO2. Acknowledgement Support from David Howell and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies Program is gratefully acknowledged. This work was performed, in part, at the Electron Microscopy Center for Materials Research, Center for Nanoscale Materials and Advanced Photon Source, Offices of Science, Offices of Basic Energy, and Offices of Sciences User Facility operated for U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Lithium/sulfur (Li/S) battery has been under scrutiny in the past decades owing to its low cost, abundance, nontoxic as well as much higher energy density than conventional lithium ion battery.1 Lithium/selenium (Li/Se) battery has also attracted an increasing attention in recent years owing to its comparable volumetric capacity with sulfur and much higher electronic conductivity (~ 20X) than sulfur.2 It has been intensively reported that the electrolytes play a great role on the electrochemical performance of selenium and sulfur based cathodes.3 Among them, carbonate-based and ether-based electrolytes are two kinds of popular electrolytes for selenium-sulfur based cathodes. Selenium has been found to be well adaptive to carbonate-based electrolytes; the space-confined selenium displays excellent electrochemical performance in Li-Se battery with carbonate-based electrolytes.4 While the ether-based electrolytes could facilitate the redox reaction of sulfur-based cathodes and therefore could offer higher reversible capacity than that of carbonate-based electrolytes. It was found that Se is reduced to the polyselenides, Li2Sen (n≥4), Li2Se2, and Li2Se sequentially during the lithiation process, and Li2Se is oxidized to Se through Li2Sen (n≥4) during the de-lithiation process in the 1st cycle, which undergoes similar reaction process to the sulfur system.5 Therefore, it is very important to design rational Se cathodes with conductive host to constrain the polyselenides and avoid the shuttle effect. However, even with a very good encapsulation of selenium or selenium-sulfur in the various carbon host materials, most of the previous reported Se/C or Se-S/C cathodes still show a gradual capacity fading in ether-based electrolytes.6-8 It has been widely reported that sulfur/carbon composites with sulfur loading ranging from 30 wt. %-75wt. % can maintain a stable reversible capacity above 600 mAh g-1 within 100 cycles in ether-based electrolytes by optimizing the structure of carbon host materials.9 Therefore, the confinement of carbon host materials for polysulfides and polyselenides may be different although they both suffer from dissolution of reaction intermediates in ether-based electrolytes. To the best of our knowledge, such a ubiquitous phenomenon has been paid less attention and not yet well addressed. Moreover, the detailed capacity fading mechanism of Se-based cathodes in ether-based electrolytes is still unknown. Herein, we are motivated to disclose the lithiation/de-lithiation process and capacity fading mechanism of Se-based cathodes in ether-based electrolytes upon continuous cycling by using in-situ X-ray absorption near edge spectroscopy. Microporous carbon (MPC) was selected as carbon host to enhance the confinement for polysulfides and polyselenides. Se2S5/MPC composite was then prepared by a modified vaporization-condensation method to ensure a good encapsulation of Se2S5 into the MPC host. The in-situ XANES results clearly illustrate that the reaction reversibility of Se was gradually decreased upon continuous cycling which should be responsible for the common capacity fading of Se-based cathodes in ether-based electrolytes. We expect our current study could enable a better understanding on the lithiation/de-lithiation process of Se-based cathodes and facilitate the development of high performance Li/Se and Li/Se-S battery in the future. Acknowledgements: Research at the Argonne National Laboratory was funded by U.S. Department of Energy, Vehicle Technologies Office. Argonne National Laboratory is operated for the U.S. Department of Energy by UChicago Argonne, LLC, under contract DE-AC02-06CH11357. References 1. Evers, S.; Nazar, L. F. Acc. Chem. Res. 2013, 46, (5), 1135-1143. 2. Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M. Nat. Mater. 2012, 11, (1), 19-29. 3. Yang, C.-P.; Yin, Y.-X.; Guo, Y.-G. J. Phys. Chem. Lett. 2015, 6, (2), 256-266. 4. Luo, C.; Xu, Y.; Zhu, Y.; Liu, Y.; Zheng, S.; Liu, Y.; Langrock, A.; Wang, C. Acs Nano 2013, 7, (9), 8003-8010. 5. Cui, Y.; Abouimrane, A.; Lu, J.; Bolin, T.; Ren, Y.; Weng, W.; Sun, C.; Maroni, V. A.; Heald, S. M.; Amine, K. J. Am. Chem. Soc. 2013, 135, (21), 8047-8056. 6. Shaofeng, J.; Zhian, Z.; Yanqing, L.; Yaohui, Q.; XiWen, W.; Jie, L. J. Power Sources 2014, 267, 394-404. 7. Yaohui, Q.; Zhian, Z.; Shaofeng, J.; Xiwen, W.; Yanqing, L.; Yexiang, L.; Jie, L. J. Mater. Chem. A 2014, 2, (31), 12255-61. 8. Xiang, P.; Lei, W.; Xuming, Z.; Biao, G.; Jijiang, F.; Shu, X.; Kaifu, H.; Chu, P. K. J. Power Sources 2015, 288, 214-20. 9 Xu, G. L.; Wang, Q.; Fang, J. C.; Xu, Y. F.; Huang, L.; Sun, S. G. J. Mater. Chem. A 2014, 2, 19941-19962. Figure 1

Iron oxyfluoride (FeOF) was recently found to be a conversion type cathode material for lithium ion batteries because of its high theoretical capacity[1] (885mAh). Rutile structure FeOF was both environmental friendly and economic which is promising to be put into market. During the charge and discharge process, the valence of iron changes from 3+ to 0 which means that it can deliver 3 electrons. Although there were a lot of work done by researchers on FeOF cathode, the cyclability of this cathode was still too poor[2]. In-situ pair distribution function (PDF) was performed on FeOF batteries by Wiadereck et.al[3]. However, more valance and local structure evolution was yet to be revealed. In order to increase the cycle life of FeOF, it is very important to clearly elucidate the failure mechanism by clearly understand the atom environment in real-time during the cycling. Synchrotron X-ray near-edge structure (XANES) could be very helpful to illustrate the local structure and state of charge of the element we are interested in[4]. With the help of XANES, we can apply in-situ characterization of FeOF cathode to better elucidate real-time local structure and valence change at different state of charge (SOC) and depth of discharge (DOD) in order to better illustrate the mechanism of the iron ion evolution and FeOF failure mechanism. In this study, FeOF was prepared in our lab and mixed with carbon black, PVDF and NMP to form a uniform slurry. The cathode was prepared by coating the slurry on aluminum foil. The in-situ test coin cell was assembled by FeOF cathode, Celgard separator and lithium foil anode and was sealed in our home-made coin cell shell. K-edge of Fe was measured during the in-situ characterization to observe the valence change and local structure evolution during the discharge and charge process between the voltage range of 4V and 1V. The in-situ XANES spectrum was plotted in Fig.1. From 0% DOD to around 50% DOD, the K-edge shifted to low energy direction and then shifted back to high energy direction. This phenomenon indicated that there were two different mechanism during discharge process. To better analyze the in-situ XANES data, the contour plot and the charge/discharge profile were shown in Fig.2. The XANES and charge/discharge profile correlated with each other very well. At the beginning of discharge process, the K-edge shifted towards low energy direction and the intensity increased gradually, which means this is a Li+intercalation process. At the end of the discharge process, the K-edge shifted back to the high energy direction and there was a sharp intensity change which corresponding to the conversion process. Similar conversion and deintercalation process could be observed at the beginning and end of the charge process respectively. In conclusion, by applying in-situ XANES technic, we clearly visualize the valence and local structure evolution mechanism during real working condition and got our preliminary conclusion that the charge/discharge process of FeOF battery contains two typical process. Li+ intercalation occurs at high voltage range and conversion process occurs at lower voltage range. Reference [1] A. Kitajou, H. Komatsu, R. Nagano, S. Okada, Synthesis of FeOF using roll-quenching method and the cathode properties for lithium-ion battery, Journal of Power Sources, 243 (2013) 494-498. [2] N. Pereira, F. Badway, M. Wartelsky, S. Gunn, G.G. Amatucci, Iron Oxyfluorides as High Capacity Cathode Materials for Lithium Batteries, Journal of The Electrochemical Society, 156 (2009) A407-A416. [3] K.M. Wiaderek, O.J. Borkiewicz, E. Castillo-Martínez, R. Robert, N. Pereira, G.G. Amatucci, C.P. Grey, P.J. Chupas, K.W. Chapman, Comprehensive Insights into the Structural and Chemical Changes in Mixed-Anion FeOF Electrodes by Using Operando PDF and NMR Spectroscopy, Journal of the American Chemical Society, 135 (2013) 4070-4078. [4] A.N. Mansour, P.H. Smith, W.M. Baker, M. Balasubramanian, J. McBreen, In situ XAS investigation of the oxidation state and local structure of vanadium in discharged and charged V2O5 aerogel cathodes, Electrochimica Acta, 47 (2002) 3151-3161. Figure 1

Proton exchange membrane fuel cells (PEMFCs) that use hydrogen and oxygen in air as fuels to produce electricity have attracted extensive interests over the past decades.1 The high efficiency and zero emission make PEMFCs promising candidates for viable propulsive systems in electric automobiles.2 One of the major challenges that hinder the commercialization of PEMFCs vehicles is the poor stability of Pt nanoparticles on carbon supports, which mainly due to the dissolution and re-deposition of Pt and migration of Pt over carbon supports.3 4Both of them will cause the agglomeration of Pt nanoparticles, resulting in loss of Pt electrochemical surface area (ECSA) and the increasing of activation overpotentials. Aiming to minimize the growth of Pt nanoparticles due to the Pt migration on carbon supports, fundamental understanding of their interaction is required, so as to modify the carbon supports to enhance the binding energy between Pt and carbons. In our recent work, Pt of 3% to 5% loading was deposited on XC-72 carbon black, graphene, functionalized XC-72 carbon black and functionalized graphene, where the Pt clusters or islands of about 3-6 atoms thickness on different supports can be achieved by a general two step method. The dispersion and morphology of Pt on pristine graphene, SO3H-graphene and NH2-graphene were then characterized by high resolution transmission electron microscopy (HRTEM). It is clearly shown that spherical Pt nanoparticles of very small size were uniformed dispersed on functionalized graphene, whereas on pristine graphene, some rod-like Pt crystals were observed. It indicates that the presence of functional groups prevents the migration of Pt nuclei on the two-dimentional graphene sheet during the synthetic process. X-ray absorption near edge structure (XANES) of Pt L-edge and C K-edge were performed to further characterize the interaction between Pt and different supports. The increasing of the intensity of the Pt L-edge adsorption peak compared with unsupported Pt suggests electron withdrawn from Pt to carbon supports might exists between Pt and carbon supports and the interaction strength follows the order of Pt/SO3H-Graphene > Pt/SO3H-XC72 carbon black > Pt/Graphene > Pt/XC72 carbon black. On the other hand, the shift of Pt L-edge adsorption peak to higher photon energy also indicates the possible increase of oxidation state of Pt due to the Pt-C interaction. This study will shed light on the strategy to improve not only the durability but also activity of Pt based catalysts in fuel cells. (1) Gasteiger, H. A.; Markovic, N. M. Science 2009, 324, 48. (2) Debe, M. K. Nature 2012, 486, 43. (3) Xie, J.; Wood, D. L.; More, K. L.; Atanassov, P.; Borup, R. L. Journal of The Electrochemical Society 2005, 152, A1011. (4) Shao-Horn, Y.; Sheng, W. C.; Chen, S.; Ferreira, P. J.; Holby, E. F.; Morgan, D. Topics in Catalysis 2007, 46, 285.

Lithium-ion batteries (LIBs) based on intercalation, such as C/LiCoO2, are dominant in consumer electronics, mainly ascribed to their superiority over their competitors in energy density. To meet our expectations for use in electrical vehicles (EVs), however, LIBs need to further improve their capability in energy density. In this context, intensive investigation has been undertaking for new battery materials of high capacities. A new reactivity concept named “conversion reaction” was first reported with transition metal oxides 1 at the very beginning of the 21st century. Since then, more and more binary compounds were discovered having the similar electrochemical reactions in LIBs, such as metal sulfides, metal fluorides, and metal nitrides 2. In comparison to the intercalation-based materials, the conversion-based materials can generally provide much higher capacities and this makes these new classes of materials important candidates for new battery technologies. CuS has been regarded as one promising cathode material via conversion reactions, featuring a theoretical capacity of 560 mAh/g, flat discharge plateaus, and good electrical conductivity. In spite of these advantages, CuS was reported with severe capacity fading 3. To circumvent this technical hurdle, Chung and Sohn 4 discovered that narrowing voltage window could help improve cycleability of CuS in LIBs, but CuS still could not sustain long-term high-efficient discharge-charge cycling. In comparison to CuS, there were even fewer studies reported on Cu2S. In this talk, we are going to present our recent progress on both CuS and Cu2S cathodes. We confirmed that a suitable selection on voltage windows is essential for securing reliable cycleability of the CuS and Cu2S cathodes. On the other hand, we found current collectors also have some effects on the LIB cathodes. To explore the underlying mechanism, we applied advanced synchrotron-based techniques of in situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) to track time-resolved structural changes of CuS and Cu2S during discharge-charge cycles. Based on all these efforts, we developed a set of conditions for achieving long-term high-efficient CuS (see figure 1) and Cu2S cathodes in LIBs. In addition, the electrochemical characteristics of CuS and Cu2S also will be comparatively discussed. This work is potentially significant for developing next-generation high-energy batteries for EVs. References: (1) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J. M. Nature 2000, 407, 496. (2) Cabana, J.; Monconduit, L.; Larcher, D.; Palacin, M. R. Adv Energy Mater 2010, 22, E170. (3) Debart, A.; Dupont, L.; Patrice, R.; Tarascon, J. M. Solid State Sciences 2006, 8, 640. (4) Chung, J. S.; Sohn, H. J. Journal of Power Sources 2002, 108, 226. Figure 1

Vanadium redox flow battery (VRB) is one of the most suitable energy storage systems for large-scale intermittently renewable energy storage systems1-2. In the VRB, positive and negative electrolytes play important roles to store the energy3-4. Consequently, in order to develop new electrolyte solutions for the VRBs with higher energy and power density, as well as longer cycling life and better safety characteristics, the in-depth understanding of the relationship between the oxidation state /local structure changes of the electrolytes and electrochemical performance is critically important. Synchrotron radiation based X-ray adsorption fine structure (XAFS) could be very informative when applied to probe the environment around atoms of all states of matter5. Also the X-ray near-edge structure (XANES) could be especially powerful to determine the average oxidation state and local symmetry of the elements in all phases. With these considerations in mind, we carried out in situ XANES measurements during cycling of an all vanadium redox flow battery (VRB). In this study, the home-made VRB single cell was charged at a constant current density up to a 1.65 V, then the cell was discharged at the constant current density until the voltage reach 0.85 V3. In situXANES characterization was performed at the K-edge of the vanadium to monitor the change of the valence state of V in both positive and negative electrolyte solutions. To better illustrate the XANES spectra evolution, 2D contour plots of XANES spectra for both positive and negative electrolytes have been presented in Fig 1(a) and (b). In addition, the VRB voltage profile in the first charge/discharge process is displayed on the side of the XANES spectra. Obviously, the electrochemical process for both sides is well correlated with the evolution of the XANES data. For example, the inflection point at 1.65 V in the voltage profile coincides well the critical point at contour plot of XANES spectra. The spectra of vanadium XANES during the first charge process is shown in Fig 1.(c) and (d). During the first charge process, the electrolytes were charged at a constant current density until the V4+ was converted to V2+ (negative electrode electrolyte) and V5+(positive electrode electrolyte). Hence, in the positive half-cell, the K-edge of the vanadium continuously shifts toward the higher binding energy. This shift indicates an increase in the average valence state of vanadium in the electrolyte (Fig.1c), while the K-edge of vanadium will shifts back to the lower binding energy, which indicate an decrease in the average valence state of vanadium in the electrolyte (not shown in this abstract). Meanwhile, in the negative half-cell, the K-edge of the vanadium continuously shifts toward to the lower binding energy during the charge process (Fig. 1d), while it will shift back during the discharge process (not shown in this abstract). In summary, a new synchrotron based in situ XANES technique has been applied to study the average oxidation state of the electrolytes in the all vanadium redox flow battery (VRB) under realistic cycling conditions. [1] Zhenguo Yang, et al. Chemical reviews., 2011,111, 3577-3613. [2] M. Skyllas-Kazacos, et al. J. Electrochem.Soc., 2011, 158, R55-R79. [3] C. K. Jia, et al. J. Power Sources., 2010,195, 4380-4383. [4] Y Qin, et al. J. Chem. Eng. Data., 2010, 55, 1276-1279. [5] Mansour, et al. Electrochimica Acta., 2002, 47, 3151-3161.

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