Improved Charge Storage Capacity of Supercapacitor Electrodes by Engineering Surfaces: The Case of Janus MXenes

Abstract

Surface engineering in two-dimensional (2D) materials has turned out to be a useful technique to improve their functional properties. By designing Janus compounds MM′C in the MXene family of compounds M 2 C, where the two surfaces are constituted by two different transition metals M and M′, we have explored their potentials as electrodes in a supercapacitor with an acidic electrolyte. Using density functional theory (DFT) in conjunction with the classical solvation model, we have made an indepth analysis of the electrochemical parameters of three Janus MXenes, passivated by oxygen: NbVC, MnVC, and CrMnC. Comparisons with the corresponding end-point MXenes Nb 2 C, V 2 C, Mn 2 C, and Cr 2 C are also made. We find that the surface redox activity enhances due to the formation of Janus, improving the charge storage capacities of MXene electrodes significantly. Our analysis reveals that the improved functionality has its root in the variations in the charge state of one of the constituents in the Janus compound, which, in turn, has its origin in the electronic structure changes due to surface manipulation. Our work, which is the first on the electrochemical properties of Janus MXenes for supercapacitor applications, suggests surface engineering by forming appropriate Janus compounds as a possible route to extract high energy density in MXene electrode−acidic electrolyte-based energy storage devices.

Exploring the large chemical space in search of thermodynamically stable and mechanically robust MXenes via machine learning

“…, stoichiometries) of MXenes considered, it was observed that: (i) Janus MXenes and MXenes with distinct surface terminations and transition metals have not yet been successful synthesized due to the difficulty of composing the bottom and top surfaces of MXenes with different elements or groups. 11,58,59 (ii) For hybrid transition metal MXenes, although there are several cases of successful synthesis, 60–62 most utilized mixed surface terminations, not considering the single element type of surface termination ( i.e. , uniform surface termination) used in the aNANt database.…”

Computational study based prediction of new photocatalysts for water splitting by systematic manipulation of MXene surfaces

“…2(a) and (b)). 43,44 Accordingly, there can be four possible structural models of surface functionalised Janus MXenes: Model 1, where the functional groups occupy sites A and B; Model 2, where they occupy sites C and A; Model 3 where they occupy sites B and D and Model 4 where the sites of occupancy are C and D (Fig. 2(c) and (d)).…”