Ammonium ion pre-intercalation stabilized tunnel h-WO3 for fast NH4+ storage

We report a pre-intercalated NH 4 + stabilized tunnel h -WO 3 anode for an ammonium-ion hybrid supercapacitor (A-HSC). The A-HSC delivers an ultra-high areal capacitance (2239.7 mF cm −2 ), areal energy density (1010.1 μWh cm −2 ), and decent durability.