A symmetric all-organic non-aqueous redox flow-type battery was investigated employing the neutral small molecule radical 3-phenyl-1,5-di-p-tolylverdazyl,which can be reversibly oxidized and reduced in one-electron pr...A symmetric all-organic non-aqueous redox flow-type battery was investigated employing the neutral small molecule radical 3-phenyl-1,5-di-p-tolylverdazyl,which can be reversibly oxidized and reduced in one-electron processes,as the sole charge storage material.Cyclic voltammetry of the verdazyl radical in 0.5 M tetrabutylammonium hexa fluoro phosphate(TBAPF6)in acetonitrile revealed redox couples at-0.17 V and-1.15 V vs.Ag+/Ag,leading to a theoretical cell voltage of 0.98 V.From the dependence of peak currents on the square root of the scan rate,diffusion coefficients on the order of 4 x 10 6 cm2 s-1 were demonstrated.Cycling performance was assessed in a static cell employing a Tokoyuma AHA anion exchange membrane,with 0.04 M verdazyl as catholyte and anolyte in 0.5 M TBAPF6 in acetonitrile at a current density of 0.12 mA cm-2.Although coulombic efficiencies were good(94%-97%)throughout the experiment,the capacity faded gradually from high initial values of 93%of the theoretical discharge capacity to 35%by the 50th cycle.Voltage and energy efficiencies were 68%and 65%,respectively.Postcycling analysis by cyclic voltammetry revealed that decomposition of the active material with cycling is a leading cause of cell degradation.展开更多
Pure organic radical molecules on metal surfaces are of great significance in exploration of the electron spin behavior.However,only a few of them are investigated in surface studies due to their poor thermal stabilit...Pure organic radical molecules on metal surfaces are of great significance in exploration of the electron spin behavior.However,only a few of them are investigated in surface studies due to their poor thermal stability.The adsorption and conformational switching of two verdazyl radical molecules,namely,1,5-biisopropyl-3-(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)-6-oxoverdazyl(B2 P)and 1,5-biisopropyl-3-(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-4-yl)-6-oxoverdazyl(B4 P),are studied by scanning tunneling microscopy(STM)and density functional theory(DFT).The adsorbed B2 P molecules on Au(111)form dimers,trimers and tetramers without any ordered assembly structure in which two distinct appearances of B2 P in STM images are observed and assigned to be its"P"and"T"conformations.The"P"conformation molecules appear in the STM image with a large elliptical protrusion and two small ones of equal size,while the"T"ones appear with a large protrusion and two small ones of different size.Likewise,the B4 P molecules on Au(111)form dimers at low coverage,strip structure at medium coverage and assembled structure at high coverage which also consists of above-mentioned two conformations.Both B2 P molecules and B4 P molecules are held together by weak intermolecular interaction rather than chemical bond.STM tip induced conformational switching of both verdayzl radicals is observed at the bias voltage of+2.0 V.The"T"conformation of B2 P can be switched to the"P"while the"P"conformation of B4 P can be switched to the"T"one.For both molecules,such a conformational switching is irreversible.The DFT calculations with Perdew-BurkeErnzerhof version exchange-correlation functional are used to optimize the model structure and simulate the STM images.STM images of several possible molecular conformations with different isopropyl orientation and different tilt angle between verdazyl radical and Au(111)surface are simulated.For conformations with different isopropyl orientation,the STM simulated images are similar,while different tilt angles of verdazyl radical lead to significantly different STM simulated images.Combined STM experiments and DFT simulations reveal that the conformational switching originates from the change of tilting angle between the verdazyl radical and Au(111)surface.The tilt angles in"P"and"T"conformations are 0°and 50°,respectively.In this study,two different adsorption conformations of verdazyl radicals on the Au(111)surface are presented and their exact adsorption structures are identified.This study provides a possible way to study the relationship between the electron spin and configuration conversion of pure organic radical molecules and a reference for designing more conformational switchable radical molecules that can be employed as interesting molecular switches.展开更多
基金supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada (C. A. D.: DG, 04279 J. B. G.: DG, 435675 and S. M. B.: CGS D scholarship)+1 种基金support form the Canada Foundation for Innovation (CFI) the New Brunswick Innovation Foundation (NBIF)the University of New Brunswick. J. B. G. would like to thank the University of Western Ontario for support
文摘A symmetric all-organic non-aqueous redox flow-type battery was investigated employing the neutral small molecule radical 3-phenyl-1,5-di-p-tolylverdazyl,which can be reversibly oxidized and reduced in one-electron processes,as the sole charge storage material.Cyclic voltammetry of the verdazyl radical in 0.5 M tetrabutylammonium hexa fluoro phosphate(TBAPF6)in acetonitrile revealed redox couples at-0.17 V and-1.15 V vs.Ag+/Ag,leading to a theoretical cell voltage of 0.98 V.From the dependence of peak currents on the square root of the scan rate,diffusion coefficients on the order of 4 x 10 6 cm2 s-1 were demonstrated.Cycling performance was assessed in a static cell employing a Tokoyuma AHA anion exchange membrane,with 0.04 M verdazyl as catholyte and anolyte in 0.5 M TBAPF6 in acetonitrile at a current density of 0.12 mA cm-2.Although coulombic efficiencies were good(94%-97%)throughout the experiment,the capacity faded gradually from high initial values of 93%of the theoretical discharge capacity to 35%by the 50th cycle.Voltage and energy efficiencies were 68%and 65%,respectively.Postcycling analysis by cyclic voltammetry revealed that decomposition of the active material with cycling is a leading cause of cell degradation.
文摘Pure organic radical molecules on metal surfaces are of great significance in exploration of the electron spin behavior.However,only a few of them are investigated in surface studies due to their poor thermal stability.The adsorption and conformational switching of two verdazyl radical molecules,namely,1,5-biisopropyl-3-(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)-6-oxoverdazyl(B2 P)and 1,5-biisopropyl-3-(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-4-yl)-6-oxoverdazyl(B4 P),are studied by scanning tunneling microscopy(STM)and density functional theory(DFT).The adsorbed B2 P molecules on Au(111)form dimers,trimers and tetramers without any ordered assembly structure in which two distinct appearances of B2 P in STM images are observed and assigned to be its"P"and"T"conformations.The"P"conformation molecules appear in the STM image with a large elliptical protrusion and two small ones of equal size,while the"T"ones appear with a large protrusion and two small ones of different size.Likewise,the B4 P molecules on Au(111)form dimers at low coverage,strip structure at medium coverage and assembled structure at high coverage which also consists of above-mentioned two conformations.Both B2 P molecules and B4 P molecules are held together by weak intermolecular interaction rather than chemical bond.STM tip induced conformational switching of both verdayzl radicals is observed at the bias voltage of+2.0 V.The"T"conformation of B2 P can be switched to the"P"while the"P"conformation of B4 P can be switched to the"T"one.For both molecules,such a conformational switching is irreversible.The DFT calculations with Perdew-BurkeErnzerhof version exchange-correlation functional are used to optimize the model structure and simulate the STM images.STM images of several possible molecular conformations with different isopropyl orientation and different tilt angle between verdazyl radical and Au(111)surface are simulated.For conformations with different isopropyl orientation,the STM simulated images are similar,while different tilt angles of verdazyl radical lead to significantly different STM simulated images.Combined STM experiments and DFT simulations reveal that the conformational switching originates from the change of tilting angle between the verdazyl radical and Au(111)surface.The tilt angles in"P"and"T"conformations are 0°and 50°,respectively.In this study,two different adsorption conformations of verdazyl radicals on the Au(111)surface are presented and their exact adsorption structures are identified.This study provides a possible way to study the relationship between the electron spin and configuration conversion of pure organic radical molecules and a reference for designing more conformational switchable radical molecules that can be employed as interesting molecular switches.
