Water-soluble inorganic salt with ultrahigh specific capacitance: Ce(NO3)3 can be designed as excellent pseudocapacitor electrode

•The ultrahigh specific capacitance of 2060 F/g of Ce(NO3)3 salt was obtained.•Water-soluble Ce(NO3)3 salt can be directly used as electrode in KOH electrolyte.•In situ chemical and electrochemical activations of Ce(NO3)3-Ni foil function well.•Electronegativity can identify the active metal cations with high pseudocapacitance.

The improvement of the performance of pseudocapacitors has previously been limited to the synthesis of electrode materials with different structures and sizes. The water-soluble inorganic salts have not been explored their pseudocapacitance in aqueous electrolyte. Here, for the first time, we demonstrated that the ultrahigh specific capacitance of 2060 F/g can be obtained by the direct use of commercial Ce(NO3)3 as electrode materials in KOH electrolyte without any additional processing. As main capacitive charge-storage ions, Ce3+/Ce4+, which undergo chemical reactions and electrochemical reactions, can deliver high practical specific capacitance that is close to its theoretical value. The results challenge the view that the synthesis of advanced electrode materials with specific structures is the important step to increase the specific capacitance of inorganic pseudocapacitors.

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