Tuning the Electronic And Transport Properties of CaMoO₄ Nanofibers with High-Spin Ni for Efficient and Stable Supercapacitors

Calcium molybdate (CaMoO₄) has recently garnered considerable attention for supercapacitors due to its stable crystal structure and cost-effective preparation. However, CaMoO₄ prepared by traditional processes still suffered from insufficient electrochemical active sites and poor electrical conductivity so far, thus leading to the performance of CaMoO₄-based supercapacitors being inferior to the state-of-the-art ones. CaMoO₄ nanofibers with a high specific surface area exhibit great potential for supercapacitors due to their ability to offer increased charge storage. Herein, mesoporous CaMoO₄ nanofibers anchored with Ni nanoparticles were fabricated via electrospinning combined with subsequent thermal treatment. Density functional theory calculation and UV-vis spectrophotometer results show that high-spin state Ni nanoparticles can tune the electronic structure of CaMoO₄ nanofibers, decreasing the band gap by about 0.67 eV. Electron paramagnetic resonance (EPR) studies imply that Ni doping influences the electronic structure by reducing the oxygen vacancy concentration and introducing hyperfine structures associated with Ni spins. These can result in higher power and energy density in supercapacitors. As a result, a specific capacitance of 1253.7 F·g^-1 at a current density of 0.5 A·g^-1 and an 86% retention rate after 2000 cycles at a higher current density of 5 A·g^-1 have been achieved for Ni_0.25Ca_0.75MoO₄-based supercapacitor. Furthermore, an asymmetric supercapacitor (ASC) device with the optimized CaMoO₄/Ni//AC structure has been demonstrated with the energy density of 49.43 Wh·kg^-1 and power density of 2700 W·kg^-1, thus enabling lightening a red light-emitting diode. The current strategy might pave the way for CaMoO₄ for practical applications for high-power supercapacitors.