(544j) Development of Heteroatomic Constant Potential Method for Mxene-Based Supercapacitors

Molecular dynamics (MD) simulations using the constant potential method (CPM) have been proven to be an essential technique for studying the charge storage and charging dynamics of homogeneous electrodes.^1–3 However, the CPM cannot capture the distinct atomic nature of heteroatomic electrodes, such as MXenes.³ To overcome this limitation, we developed the heteroatomic constant potential method (HCPM) for MXene supercapacitors. The proposed HCPM model takes into account the electronegativities of various atoms in heteroatomic electrodes. To predict the charge responses of MXene atoms, this model is adjusted to align with the density functional theory (DFT) results by using derivative-free optimization. We also performed molecular dynamics simulations using both HCPM and CPM for MXene electrodes with solvent-in-salt electrolytes. Although the two methods show similar accumulated charge storage on the electrodes, the results showed that HCPM provides a more reliable depiction of electrode atom charge distribution and charge response compared with CPM. Furthermore, the simulations showed that the two methods exhibit similar anion structures near the MXene surface, while cations are drawn closer to the MXene surface in HCPM. These results highlight the crucial influence of electrode electronegativity and charge response on the atom charge distribution on electrodes and electrolyte structure. In the future, the tunable parameters of our HCPM model can be easily adapted to other heteroatomic electrodes, including different types of MXenes, metal-organic frameworks (MOFs), and carbonaceous electrodes with structural defects, providing new avenues for exploring heteroatomic supercapacitors.

Reference

(1) Reed, S. K.; Lanning, O. J.; Madden, P. A. Electrochemical Interface between an Ionic Liquid and a Model Metallic Electrode. Journal of Chemical Physics 2007, 126 (8).

(2) Merlet, C.; Rotenberg, B.; Madden, P. A.; Taberna, P. L.; Simon, P.; Gogotsi, Y.; Salanne, M. On the Molecular Origin of Supercapacitance in Nanoporous Carbon Electrodes. Nat Mater 2012, 11 (4), 306–310.

(3) Xu, K.; Shao, H.; Lin, Z.; Merlet, C.; Feng, G.; Zhu, J.; Simon, P. Computational Insights into Charge Storage Mechanisms of Supercapacitors. ENERGY & ENVIRONMENTAL MATERIALS 2020, 3 (3), 235–246.