Computational Screening of MXene Electrodes for Pseudocapacitive Energy Storage

Abstract

MXenes (two-dimensional transition-metal carbides and nitrides) are promising materials for capacitive energy storage due to the large chemical space of existing and potential compositions, but only a few of them have been experimentally explored. In this work, we computationally screen a series of MXene electrodes (M n+1X n T x : M = Sc, Ti, V, Zr, Nb, Mo; X = C, N; T = O, OH; n = 1–3) to simulate their pseudocapacitive performance in the aqueous H2SO4 electrolyte. We find that nitride MXenes exhibit better pseudocapacitive performance than carbide MXenes. Especially, Ti2NT x is predicted to have a high gravimetric capacitance over a wide voltage window, whereas Zr n+1N n T x MXenes are predicted to possess the best areal capacitive performance. Evaluating the descriptors for the capacitance trends, we find that more positive hydrogen adsorption free energy (weak binding to H) and smaller change of the potential at the point of zero charge after H binding lead to higher capacitance. Our work provides helpful guidance to selectively develop high-performance MXene pseudocapacitors and to further screen MXene electrodes.

Atomic Sulfur Covalently Engineered Interlayers of Ti3C2 MXene for Ultra‐Fast Sodium‐Ion Storage by Enhanced Pseudocapacitance

“…The adsorption of Na atoms with high concentration on one side of the above MXenes was used to explore the high storage capacity for Na atoms. The DFT calculation information is provided in the Supporting Information . The initial structures of bare, O‐, F‐, S‐functionalized Ti 3 C 2 (the same symmetry group P ‐3 M 1) were fully relaxed, and the optimized structure data were listed in Table S2 in the Supporting Information.…”

“…The DFT calculation information is provided in the Supporting Information. [67,68] The initial structures of bare, O-, F-, S-functionalized Ti 3 C 2 (the same symmetry group P-3 M1) were fully relaxed, and the optimized structure data were listed in Table S2 in the Supporting Information. Figure 4a-h shows the optimized geometric structures of the most stable Na on Ti 3 C 2 , Ti 3 C 2 O 2 (O-functionalized Ti 3 C 2 ), Ti 3 C 2 F 2 (F-functionalized Ti 3 C 2 ), and Ti 3 C 2 S 2 (S-functionalized Ti 3 C 2 ).…”

The Recent Advances in the Mechanical Properties of Self-Standing Two-Dimensional MXene-Based Nanostructures: Deep Insights into the Supercapacitor

“…The pseudocapacitance characteristics and internal mechanism of various MXenes as supercapacitors deeply studied in H 2 SO 4 electrolyte, in addition to the factors determine the capacitance effect via DFT calculations [ 81 ]. This is included various MXenes (M n+1 X n T x ), where M = Sc, Ti, V, Zr, Nb, Mo; X = C, N; T = O, OH; n = 1–3) in H 2 SO 4 electrolyte [ 82 ]. The predicted capacitance performance of Ti 3 C 2 T x , Mo 2 CT x , and V 2 CT x [ 82 , 83 ] were similar to the experimentally measured capacitances 235, 245, 90, and 380 F g −1 , respectively [ 77 , 79 , 82 ].…”

“…Mainly, Ti 2 NT x is expected to possess a high gravimetric capacitance under any applied voltage in H 2 SO 4 , owing to the low atomic weight and favorable redox chemistry of Ti. Meanwhile, Zr n+1 N n T x is anticipated to possess the best areal capacitive performance [ 82 ]. The higher capacitance performance is attributed to the higher adsorption free energy and lower change of the potential at the point of zero charge after H binding [ 82 ].…”

“…Meanwhile, Zr n+1 N n T x is anticipated to possess the best areal capacitive performance [ 82 ]. The higher capacitance performance is attributed to the higher adsorption free energy and lower change of the potential at the point of zero charge after H binding [ 82 ]. The relationship between the charge storage of nitride and carbide MXenes against the shift in the point-of-zero-charge (V PZC ) and H 2 adsorption free energy (ΔG H ) displayed that the large ΔG H and the low Δpzc lead to higher charge storage per unit of formula ( Figure 9 ) [ 82 ].…”