Targeted synthesis and reaction mechanism discussion of Mo2C based insertion-type electrodes for advanced pseudocapacitors

Abstract

Mo₂C is one of the few compounds that possess good electronic conductivity. Meanwhile, it possesses a natural 1D zigzag tunnel structure that is ideally suited for fast ion diffusion. Here, an effective approach is demonstrated for fabrication of structurally stable N-doped Mo₂C/C nanobelts. They demonstrate high and fast energy storage ability with initial capacitances of 1139 C g⁻¹ at 1 mV s⁻¹, 151 C g⁻¹ at an extremely high scan rate of 2000 mV s⁻¹ and 208 C g⁻¹ at a discharge current density of 200 A g⁻¹. After electrochemical activation of cycling, the capacity is continuously enhanced and much higher capacitances of 2523 C g⁻¹ at 1 mV s⁻¹ and 1403 C g⁻¹ at 50 A g⁻¹ are achieved after 15 000 cycles at 50 mV s⁻¹. Using the power law, it is evaluated that a surface-controlled capacitive process makes the main contribution to the capacity, which is over 90% when the scan rates are higher than 10 mV s⁻¹ and still high as 73% at 1 mV s⁻¹. From in situ synchrotron XRD, it is found that there is a negligible change in the crystal structure and volume during charging/discharging, reflecting an insertion-type charge storage mechanism.