(457e) Thermodynamics in Nano-Porous Electrodes

Thermodynamics of fluids in porous media is qualitatively different from that in the bulk due to the finite-size effects, varying dimensionality, and the surface forces that are introduced by the porosity.  Thermodynamics of gas molecules in porous media has been extensively studied [1].  On the other hand, it is relatively recently that thermodynamics of electrolytes in porous electrodes has been drawing particular attention [2]. 

For the thermodynamics in porous electrodes, voltage plays an important role as a thermodynamic field, in addition to chemical potential and temperature which are the thermodynamic fields also necessary for describing adsorption of gas molecules.  Having this in mind, we have developed a Monte Carlo simulation method for studying thermodynamics of porous electrodes in the constant-voltage grand-canonical ensemble [3]. With this method, the anomalous pore size dependence of capacitance [4] and phase transition in porous electrodes [5] have been studied.

We extended the method for two-component electrolytes and applied it to a two component primitive model, for which the diameters of the ions are different for the two components.  We found some thermodynamic behaviors that are similar to those of one component electrolytes such as the pore size dependence on the capacitance.  Moreover, we also found other behaviors that are specific to multi-component systems.  For example, it was found that the ratio of the content of the two components forming the electrical double layers changes as a function of thermodynamic parameters such as voltage.  Those findings are discussed in relation to practical problems such as development of electrochemical capacitors or ion-selective adsorbents. 

This work was supported by JSPS KAKENHI Grant Number 24550169.  Part of the computation in this work was performed using the supercomputers of Research Institute for Information Technology of Kyushu University and those of Cybermedia Center of Osaka University.

[1] L. D .Gelb, K. E. Gubbins, R. Radhakrishnan, and M. Sliwinska-Bartkowiak, Rep. Prog. Phys., 62, 1573 (1999).

[2] J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, and P. L. Taberna, Science, 313, 1760 (2006).

[3] K. Kiyohara and K. Asaka, J. Chem. Phys., 126, 214704 (2007); 2007 AIChE Annual Meeting.

[4] K. Kiyohara T. Sugino, and K. Asaka, J. Chem. Phys., 132, 144705 (2010).

[5] K. Kiyohara, T. Sugino, and K. Asaka, 2010 AIChE Annual Meeting; J. Chem. Phys., 134, 154710 (2011); J. Chem. Phys., 136, 094701 (2012).