How Do We Design and Perfect Atom- and Energy-efficient Synthesis of Revolutionary New Forms of Matter with Tailored Properties? Progress on Grand Challenge New Horizons for Grand Challenge Remaining ChallengeRefreshed Grand Challenge? A new class of two-dimensional transition metal carbides, MXenes (M 2 C, M 2 C 3 and M 4 C 3 ), are being synthesized with guidance from first- principles modeling, to exhibit conductivity rivaling graphene and very high capacitive energy storage. M. Naguib and Y. Gogotsi, Acc. Chem. Res., 2014 [ /ar500346b]. Y. Xie, et al., 2014, ACS Nano, 8:9606. Ab initio computations will be used to predict, and then synthesize specific MXenes from among the ~70 binary and hundreds of possible ternary MXenes, with functional properties tailored for enhanced electrical energy storage in batteries and capacitors. Integrated computational modeling, model-guided materials synthesis and characterization, and final testing/validation is clearly a more efficient route to the discovery of novel functional materials than current Edisonian approaches. This Grand Challenge should continue to be a focusing goal for unleashing the ever-growing power of in silico predictions to guide the development of transformative functional materials. Submitted by: David Wesolowski Affiliation: Oak Ridge National Laboratory

Scientific Achievement A new family of 2D materials (MXenes) with electrical conductivity exceeding that of graphene and hydrophilic surfaces similar to transition metal oxides have been synthesized using tailorable selective extraction routes. Significance and Impact MXene synthesis opens the path to improved electrochemical energy storage materials. MXenes also serve as a model system for understanding ion dynamics in slit pores and at O- or OH-terminated surfaces, as well as surface redox processes that lead to increased power and energy density Research Details o First-principles calculations were carried out using DFT to predict the effect of transition metal (Ti, Nb, V, etc.), structure (Ti 2 C vs Ti 3 C 2 ) and surface termination (O, OH) on electrochemical properties of MXenes. o Synthesis of Ti 2 C, Ti 3 C 2, Nb 2 C and V 2 C was performed by selective etching of Al from the respective MAX phases. Electrochemical characterization guided by modeling was conducted in electrolytes containing H +, Li +, Na +, K + and Mg 2+ ions. Computationally-Designed 2D Transitional Metal Carbides Show Great Promise for Electrical Energy Storage Work was performed at Drexel University and ORNL M. Naguib, Y. Gogotsi, Accounts of Chemical Research, (2014) doi: /ar500346b Y. Xie, et al. J. Am. Chem. Soc. 136, (2014) Y. Xie, et al. ACS Nano, 8 (9), 9606–9615 (2014) Schematics of the M 2 AX crystal structure, M 3 X 2 and M 4 X 3 layers. Electron localization functions of (110) section of Ti 2 CO 2 with two Li (a), Na (b), and Mg (c) metal layers adsorbed

How Do We Design and Perfect Atom- and Energy-efficient Synthesis of Revolutionary New Forms of Matter with Tailored Properties? Progress on Grand Challenge New Horizons for Grand Challenge Remaining ChallengeRefreshed Grand Challenge? Integrated synthesis, characterization and computational modeling reveals how surface and pore morphology, and electronic structure, control the unprecedented performance of supercapacitors incorporating onion- like carbon (OLC) nanoparticles. D. Pech, et al. 2010, Nature Nanotech., 5:651; J.K, McDonough, et al. 2012, Carbon, 50:3298; G. Feng, et al., J. Phys. Chem. Lett. 2013, 4:3367; Develop coarse-grained models, validated through experiments and molecular dynamics simulations, to design and synthesize new hierarchical carbon nanostructures for electrical energy storage. Efficient algorithms and modeling approaches must be developed that can directly incorporate validated atomic-molecular model input in the design of electrical energy storage systems that accurately treat electrolyte transport limitations. This Grand Challenge is central to the Mesoscale Science and Materials Genome Initiatives. Advances in computer software and hardware will open new horizons for validated predictive modeling of novel functional interfacial systems. Submitted by: David Wesolowski Affiliation: Oak Ridge National Laboratory

Research Details o Molecular modeling provides fundamental insights into OLC synthesis (P. Ganesh, et al. 2011, J. Appl. Phys., 110:073506) and electrode-electrolyte interactions (G. Feng, et al. 2013, J. Phys. Chem. Lett., 4:3367). o Electrodeposited OLC microelectrode-on-a-chip architectures exhibit extremely high power density and cycle life, with energy densities approaching thin film Li-ion batteries (D. Pech, et al. 2010, Nature Nanotech., 5:651; J.K. McDonough, et al. 2012, Carbon, 50:3298; M. Beidaghi and Y. Gogotsi 2014, Energy Environ. Sci., 7:867). o OLC is an ideal substrate for sorption of highly-reversible, redox-active quinones in pseudocapacitors that exhibit extremely rapid charging/discharging (D. Anjos, et al. 2013, Nano Energy, 2:702). o OLC adds enhanced conductivity and high surface curvature to composite mesoporous carbons that exhibit hierarchical nanopore architectures (P. Fulvio, et al. 2011, Adv. Func. Mater., 21:2208). o Open pore structure and high capacitance at large surface potentials enable eutectic ionic liquid electrolyte supercapacitor function at -50 to 100  C (S. Li, et al. 2012, J. Phys. Chem. Lett., 3:2465). Scientific Achievement Graphenic onion-like carbon (OLC) nanoparticle electrodes are shown to exhibit unprecedented capacitive energy storage properties due to their high conductivity and sub-spherical surface morphology. Significance and Impact 2-10 nm OLC particles have been fabricated into microsupercapacitors and pseudocapacitors with high power and energy density and long-cycle-life, ionic- liquid supercapacitors with operating ranges of -50 to 100  C, and novel composite electrode materials. Onion-Like Carbon: A Transformative Material for Electrical Energy Storage FIRST EFRC research performed at Drexel and Vanderbilt Universities and Oak Ridge National Laboratory