A commercial product of carbon nano-particles, Cabot MONACH 1300 pigment black （CMPB）, was studied for basic structural information and electrochemical performance in neutral aqueous electrolytes, aiming at applicat...A commercial product of carbon nano-particles, Cabot MONACH 1300 pigment black （CMPB）, was studied for basic structural information and electrochemical performance in neutral aqueous electrolytes, aiming at applications in supercapacitors. As confirmed by SEM and HRTEM, the CMPB had a hierarchical struc- ture, containing basic 10 nm nano-spheres which combined into ca. 50 nm agglomerates which further aggregated into larger particles of micrometres. The capacitance of this commercial material was found to increase with decreasing the size of hydrous cation （Li＋→Na＋ → K＋）, instead of the cation crystal radius （K＋→ Na＋→Li＋） when coupled with the same anion （cl-）. In electrolytes with the same cation concentration （K＋）, changing the anion from the larger dianion （SO42 ） to the smaller monoanion （cl-） also increased the capacitance at high potential scan rates （〉50 mV/s）. Increasing electrolyte concentration produced expected effect, including raising the electrode capacitance, but lowering the equivalent series resistance （ESR）, charge transfer resistance （CTR）, and the diffusion resistance. At higher temperatures, the CMPB exhibited slightly higher capacitance, which does not agree with the Gouy-Chapman theory on electric double layer （EDL）. A hypothesis is proposed to account for the capacitance increase with temperature as a result of the CMPB opening up some micro-pores for more ions to access in response to the temperature increase.展开更多
The lattice Boltzmann method was employed to simulate electroosmotic driven flow and Debye layer screening in con- ducting electrolyte around a porous structure with average size of 40 nm. The charge screening around ...The lattice Boltzmann method was employed to simulate electroosmotic driven flow and Debye layer screening in con- ducting electrolyte around a porous structure with average size of 40 nm. The charge screening around the nanopores was investigated by solving the vector-superpositioned potential equilibrium distribution function and adding electro-kinetic force term to the evolution equation. In this intermediate case of moderate Debye length, the electrophoresis problem becomes complicated. The motion of the particles distorts the screening cloud, which becomes asymmetric, resulting in very complex interactions between the electrolyte, the screening cloud and the particle; but the Electroosmotic Flow （EOF） behaviour was still considered based on the Helmoholtz-Smoluchowski model with adaptation to fit nanoporous flow in the porous structure. In the present approach, the flow in the nanopores is directly modelled; the detailed flow information can be obtained by simplifying the repeated macrostructure. Due to the symmetry of the domain, the size of computational domain can be largely reduced by less repeated spherical nanoparticles. Each pore of the medium contains several lattice nodes on the simplified curved edges and potential gradients are produced by adjusting the zeta potential value. The velocity results for pressure-driven and EOF flows agree well with the analytical solutions and recent experimental results. In particular, the interface between solid particles and fluids, the influences of porosity, solid particle diameter, yield stress and electric parameters in EOF were investigated. The anti-adhesion effect of electroosmotic pumping effect was evaluated, and the pulsed DC was applied in order to enhance the performance of the electroosmotic pumping. The results demonstrate that the present lattice Boltzmann model is capable of modelling flow through nanoporous media at certain restrictions while some results deviate from the predictions based on the macroscopic theories.展开更多
基金E.ON AG for funding through the E.ON International Research Initiative-Energy Storage 2007
文摘A commercial product of carbon nano-particles, Cabot MONACH 1300 pigment black （CMPB）, was studied for basic structural information and electrochemical performance in neutral aqueous electrolytes, aiming at applications in supercapacitors. As confirmed by SEM and HRTEM, the CMPB had a hierarchical struc- ture, containing basic 10 nm nano-spheres which combined into ca. 50 nm agglomerates which further aggregated into larger particles of micrometres. The capacitance of this commercial material was found to increase with decreasing the size of hydrous cation （Li＋→Na＋ → K＋）, instead of the cation crystal radius （K＋→ Na＋→Li＋） when coupled with the same anion （cl-）. In electrolytes with the same cation concentration （K＋）, changing the anion from the larger dianion （SO42 ） to the smaller monoanion （cl-） also increased the capacitance at high potential scan rates （〉50 mV/s）. Increasing electrolyte concentration produced expected effect, including raising the electrode capacitance, but lowering the equivalent series resistance （ESR）, charge transfer resistance （CTR）, and the diffusion resistance. At higher temperatures, the CMPB exhibited slightly higher capacitance, which does not agree with the Gouy-Chapman theory on electric double layer （EDL）. A hypothesis is proposed to account for the capacitance increase with temperature as a result of the CMPB opening up some micro-pores for more ions to access in response to the temperature increase.
文摘The lattice Boltzmann method was employed to simulate electroosmotic driven flow and Debye layer screening in con- ducting electrolyte around a porous structure with average size of 40 nm. The charge screening around the nanopores was investigated by solving the vector-superpositioned potential equilibrium distribution function and adding electro-kinetic force term to the evolution equation. In this intermediate case of moderate Debye length, the electrophoresis problem becomes complicated. The motion of the particles distorts the screening cloud, which becomes asymmetric, resulting in very complex interactions between the electrolyte, the screening cloud and the particle; but the Electroosmotic Flow （EOF） behaviour was still considered based on the Helmoholtz-Smoluchowski model with adaptation to fit nanoporous flow in the porous structure. In the present approach, the flow in the nanopores is directly modelled; the detailed flow information can be obtained by simplifying the repeated macrostructure. Due to the symmetry of the domain, the size of computational domain can be largely reduced by less repeated spherical nanoparticles. Each pore of the medium contains several lattice nodes on the simplified curved edges and potential gradients are produced by adjusting the zeta potential value. The velocity results for pressure-driven and EOF flows agree well with the analytical solutions and recent experimental results. In particular, the interface between solid particles and fluids, the influences of porosity, solid particle diameter, yield stress and electric parameters in EOF were investigated. The anti-adhesion effect of electroosmotic pumping effect was evaluated, and the pulsed DC was applied in order to enhance the performance of the electroosmotic pumping. The results demonstrate that the present lattice Boltzmann model is capable of modelling flow through nanoporous media at certain restrictions while some results deviate from the predictions based on the macroscopic theories.
