Organic-inorganic all-pseudocapacitive asymmetric energy storage devices

Two-dimensional transition metal carbides (MXenes) have shown extraordinary promise for pseudocapacitive energy storage under negative potential in aqueous electrolytes, yet they lack matching positive electrodes. Here, we report an organic compound namely 2,5-dihydroxy-1,4-benzoquinone (DBQ), adsorbed on reduced graphene oxide (rGO) sheets as a positive electrode, which can deliver high capacitance (similar to 500 F/g, similar to 800 F/cm(3) at 2 mV/s), rate performance (83 F/g or 133 F/cm(3) at 10 V/s), and remarkable cycle life (83% after 100,000 cycles), which is the highest for any reported discrete organic molecule. First-principle calculations were used to further understand the charge storage mechanism, find the preferred orientation of the adsorbed molecules, and to pinpoint the origin of the high pseudocapacitance and long cycle life. Optimized compositions of DBQ@rGO were paired with pseudocapacitive Ti3C2Tx MXene to manufacture devices composed of two entirely different classes of materials, where they electrochemically complement each other to expand the voltage window (and thus energy density) in aqueous electrolytes. As manufactured devices delivered energy density of 40 W h/kg at a power density of 2.9 kW/kg and capacitance retention of over 90% after 10,000 cycles.