The electrocapillarity and zero-frequency differential capacitance, C-d, have been studied using pendant drop method, at the Hg interface of an ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C(2)mim(+)][TFSA(-)], and have been compared with those of [C(2)mim(+)]BF4-, an IL with the common cation and a different anion, to focus on the anion dependence of zero-frequency C-d. The Hg interface of [C(2)mim(+)][TFSA(-)], the IL of the larger anion in the present study, exhibits greater zero-frequency C-d than that of [C(2)mim(+)]BF4-, the IL of the smaller anion. This behavior contradicts a simple expectation in which larger ion leads to smaller C-d. This apparent contradiction is explained by proximity of the charged moiety of TFSA(-) to the electrode surface compared with that of BF4-. The potential dependence of zero-frequency C-d for the two ILs both exhibits one-hump camel shape around the potential of zero charge (E-pzc), which has been predicted to be specific behavior of the electrical double layer of ILs by theory and simulation. The humps are located at potentials more negative than E-pzc. From a mean-field lattice-gas theory for the EDL in ILs, this negative shift can be interpreted that the charged moiety for C(2)mim(+) is more easily condensed in the EDL than those for BF4- and TFSA(-). (C) 2017 Elsevier B.V. All rights reserved.