Boron and oxygen co-regulating p-d hybridization in confined MXene for improved intercalation pesudocapacitance

Abstract

Intercalation pseudocapacitance is the key point to achieving the balance between the volumetric capacitance and the rate performance of energy storage. However, the low pseudocapacitive reactivity of the active center still limits the energy density of the pseudocapacitance devices. Herein, we propose a strategy that regulates the p-d hybridization of confined MXene via the co-doping of B and O atoms (BO-MXene) for outstanding electrochemical performance. Both experiments and density functional theory (DFT) reveal that the inner doped O atoms in low 2p orbital energy strengthen the hybridization of Ti and electron-deficient B in MXene for high retention of B atoms, weaken the Ti-O covalency in MXene. As a result, the weakened p-d hybridization of Ti and O for the outer surface and strengthened p-d hybridization of Ti and B for the inner, promote the adsorption of protons and electron transfer, respectively. Further, the BO-MXene-based hybrid supercapacitors achieve a significant volumetric energy density of 56.86 Wh L^-1 at 25.6 kW L^-1. This electronic structure via tuning the p-d hybridization in MXene proposes a new path for designing proton-confined intercalation pseudocapacitance.