Nickel Alloying Significantly Enhances the Power Density of Ruthenium‐Based Supercapacitors

Abstract Supercapacitors operating at high frequencies while exhibiting high capacitance have been challenging to fabricate due to high resistance and constrained ion diffusion in the active layers. To overcome these limitations, thin layers of pseudocapacitive materials with high theoretical capacitance can be used. Still, construction of such electrodes exhibiting effective ion diffusion, sufficient electrochemically‐active surface area, and high conductivity has encountered significant difficulties. Here, we integrated nickel atoms into a ruthenium layer through a simple electrochemical deposition method, producing a thin electrode comprising hexagonal nickel ruthenium (NiRu) nanodendrites. Further oxidation of the NiRu alloy generated a thin surface layer of pseudocapacitive RuO 2 exhibiting significant areal capacitance. A symmetric device from two NiRu/RuO 2 electrodes displayed an energy density of 0.714 μWh cm −2 with a remarkable power density of 1500 mW cm −2 , ∼250 W cm −3 for a full device. The NiRu/RuO 2 supercapacitor outperforms commercial capacitors in both energy and power densities and may replace bulky capacitors in microelectronic devices.