In this work we perform molecular dynamics simulations of mixtures of a prototypical protic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), with lithium tetrafluoroborate (LiBF4), confined between two borophene walls of three different surface charges, −1, 0 and +1 e/nm2, where e is the elementary charge. The properties of the system are analyzed by means of ionic density profiles, angular orientations of [BMIM]+ cations close to the wall and vibrational densities of states for the salt cations close to the walls. The lateral structure of the first layer close to the surface is also studied on one hand, calculating Minkowski parameters and the Shannon entropy of the patterns of the 2D density maps of the anions placed there and, on the other hand, computing the 2D-Fourier transform of the positions of these anions. Our results are compared with those obtained previously for the same mixtures confined between two graphene walls. Although similarities exist between both cases, interesting differences are observed in the lateral structure that the ionic liquid adopts near borophene interfaces due to their strong anisotropy. In particular, we have observed that borophene induces more markedly ordered 2D patterns in the innermost layer of the ionic liquid electric double layer, specially when they are charged. It is this feature that makes borophene a potential candidate for battery electrode applications with possibilities beyond those of graphene.

The financial support of the Spanish Ministry of Economy and Competitiveness (Projects MAT2017-89239-C2-1-P, MAT2017-89239-C2-2-P, CTQ2015-65816-R and PGC2018-093745-B-I00) is gratefully acknowledged. Moreover, this work was funded by the Xunta de Galicia (ED431D 2017/06, ED431E 2018/08 and GRC ED431C 2016/001) and the Junta de Castilla y León (Project VA124G18). All these research projects were partially supported by FEDER. H. M-C. and J. M. O-M. thank the Spanish Ministry of Education for their FPU grant. Facilities provided by the Galician Supercomputing Centre (CESGA) are also acknowledged, as well as funding from the European Union (COST Actions CM1206 and MP1303).

Peer reviewed