Interfacial charge storage synergy in erbium-oxide/MXene hybrids for advanced energy storage

MXenes offer possibilities to simultaneously realize fast electron and ion transport, but need increased capacitance and cycling stability for use in supercapacitor electrodes. However, restacking of Ti 3 C 2 MXene layers limits ion accessibility, capacitance, and cycling stability. Here, we demonstrate superior electrochemical response in nanocomposites with hydrothermally synthesized Er 2 O 3 nanoparticles on nanofacets of selectively-etched Ti 3 C 2 MXenes. These nanocomposites exhibit five-fold higher capacitance of 2758 F g −1 at 1 A g −1 and a 7% greater stability than pristine Ti 3 C 2 MXenes. Asymmetric supercapacitors exhibit nearly tripled energy density of 113.13 Wh kg −1 at a two-fold power density of 659.03 W kg −1 when benchmarked against pristine MXenes. Quantum capacitance from literature reported density of states, trasatti’s and power-law analyses indicate that the enhanced properties arise from synergistic coupling of double-layer capacitances in MXene and Er 2 O 3 , and pseudocapacitance from an interplay of redox-activities. These insights from our findings should inform and pave way for the rational design of MXene/rare-earth-oxide nanocomposites for efficient and durable supercapacitor electrodes.