Electronic Reconstruction and Carrier Dynamics Governing Quantum Capacitance in Transition-Metal-Modified Borophene

Abstract

Quantum capacitance (CQ), traditionally interpreted using the density of states (DOS) framework, is a key parameter governing the electronic compressibility of low-dimensional materials. Using spin-polarized first-principles calculations, we show that this approximation is incomplete for metallic two-dimensional systems. Transition-metal modified honeycomb borophene is used as an example to show that CQ is fundamentally determined by DOS, while carrier dynamics govern the effective utilization of these states in practical charge storage. Adsorption of transition-metal induces strong d–p orbital hybridization and spin-dependent electronic reconstruction near the Fermi level (EF), resulting in a nonmonotonic variation of CQ across the Mn–Cr–V series. Particularly, Mn shows a reduced capacitance (102 μF cm–2), while Cr maintains a moderate performance (492 μF cm–2). In contrast, V adsorption significantly improves CQ (548 μF cm–2), nearly doubling that of pristine borophene (∼347 μF cm–2). The role of carrier mobility is highlighted by extracting the effective mass, ∼0.62 me (V) and ∼1.14 me (Cr), through band structure analysis. This study establishes a unified framework in which CQ is determined by DOS, while transport properties provide insight into how effectively these states are accessed under operating conditions. These findings provide a generalized electronic-structure-based design rule for optimizing CQ in low-dimensional systems.