MXene-conducting polymer electrochromic microsupercapacitors

Solution processable two-dimensional transition metal carbides, commonly known as MXenes, have drawn much interest due to their diverse optoelectronic, electrochemical and other useful properties. These properties have been exploited to develop thin and optically transparent microsupercapacitors. However, color changing MXene-based microsupercapacitors have not been explored. In this study, we developed titanium carbide--poly(3,4-ethylenedioxythiophene) (PEDOT) heterostructures by electrochemical deposition using a non-aqueous monomeric electrolytic bath. Planar electrodes of such hybrid films were carved directly using an automated scalpel technique. Hybrid microsupercapacitors showed five-fold areal capacitance and higher rate capabilities (2.4 mF cm−2 at 10 mV s−1, retaining 1.4 mF cm−2 at 1000 mV s−1) over the pristine MXene microsupercapacitors (455 μF cm−2 at 10 mV s−1, 120 μF cm−2 at 1000 mV s−1). Furthermore, the electrochromic behavior of PEDOT/Ti3C2Tx microsupercapacitors was investigated using in-situ UV–vis and resonant Raman spectroscopies. A high-rate color switch between a deep blue and colorless state is achieved on both electrodes in the voltage range of −0.6 to 0.6 V, with switching times of 6.4 and 5.5 s for bleaching and coloration, respectively. This study opens new avenues for developing electrochromic energy storage devices based on MXene heterostructures.