MXene coupled with molybdenum dioxide nanoparticles as 2D-0D pseudocapacitive electrode for high performance flexible asymmetric micro-supercapacitors

Recently, two-dimensional (2D) transition metal carbides and carbonitrides (MXenes), have shown great potential in micro-supercapacitors (MSCs). However, the maximum voltage output of symmetric MXene MSCs is limited to 0.6 V due to the oxidation effects at high anodic potentials. Herein, we developed asymmetric micro-supercapacitors (AMSCs) based on titanium carbide MXene (Ti3C2Tx) and MXene-MoO2 electrodes with an enlarged voltage window of 1.2 V, which is twice wider than that of symmetric MXene MSCs. The 2D-0D MXene-MoO2 microelectrode is fabricated by homogenous dispersing zero-dimensional (0D) MoO2 nanoparticles into MXene layers to impede layers stacking and MoO2 nanoparticles aggregation. Notably, the AMSCs delivered good electrochemical performances of areal capacitance of ∼19 mF cm−2 and volumetric capacitance of 63 F cm−3 at a scan rate of 2 mV s−1, and high energy density of 9.7 mW h cm−3 at a power density of 0.198 W cm−3. The AMSCs also presented exceptionally mechanical flexibility under different bending states and excellent cyclic stability, with 88% capacitance retention after 10000 cycles at a discharge current density of 0.5 mA cm−2. For practical application, the serially connected AMSCs are fully affordable to power electronics, which is beneficial for soft and wearable power devices. Keywords: 2D-0D structure, Flexible material, MXene, Molybdenum dioxide, Asymmetric micro-supercapacitors, Energy storage