Solid-solution Ru Cu1-O2 nanocrystals: A promising negative electrode for high-energy-density aqueous hybrid supercapacitors

The low specific capacitances (SCs) of traditional carbonaceous negative electrodes significantly limit the enhancement in energy density of aqueous hybrid supercapacitors (AHCs). It is still hugely challengeable to explore a candidate with large SCs, which can stably operate in the negative potential region meanwhile. For this propose, we design and fabricate solid-solution RuxCu1-xO2 nanocrystals (NCs), which exhibit competitive SCs and electrochemical stability within the potential range from -0.9 V to 0.0 V in the aqueous KOH electrolyte. The incorporation of Cu enhances the electrochemical utilization of RuO2, reaction kinetics, electronic conductivity, and hydrogen evolution overpotentials, which are all highly dependent upon the added contents of Cu species. The optimized Ru0.8Cu0.2O2 (RuCu82) electrode of a high mass loading of 5 mg cm–2 reveals the best electrochemical capacitances in terms of reversible SCs and capacitance degradation at room temperature and -20°C. Furthermore, the reversible K+-(de)intercalation induced pseudocapacitance is proposed for electrochemical charge storage process of RuCu82. In particular, remarkable specific energy of 59.1 Wh kg–1 at 400 W kg−1 and excellent cycling stability are achieved in the assembled NiCoO2//RuCu82 AHCs. Our contribution here presents a new promising negative electrode platform with high SCs and electrochemical stability for next-generation AHCs.