Evidence from Monte Carlo simulations for a second contact value theorem for a double layer formed by 2:1/1:2 salts at low electrode charges

A generalization of a recently advanced second contact theorem [Henderson and Boda, J. Electroanal. Chem. 582, 16 (2005)], a local contact condition for the charge profile of a symmetric valency restricted primitive model planar double layer at low electrode charge, is proposed to cater to asymmetric 2:1/1:2 electrolytes. Monte Carlo simulations performed for such asymmetric electrolytes at a set of physical states with different concentrations and temperatures present convincing evidence that the generalization of the Henderson-Boda expression is valid at low electrode charge. Theoretical support is provided by the corresponding modified Poisson-Boltzmann results, which are seen to follow the simulation data closely.