Cubic Prussian blue crystals from a facile one-step synthesis as positive electrode material for superior potassium-ion capacitors

- The PB electrode delivers excellent rate and cycling capability in 0.5 mol l−1 K2SO4 electrolyte solution.
- The hybrid K-ion capacitor (KIC) is assembled based on activated carbon and high quality cubic Prussian blue in K2SO4 electrolyte solution.
- The KIC exhibits excellent cycling stability without apparent capacity fading over 1200 cycles.
- The KIC given an energy density as high as 28 Wh kg−1.

Cubic Prussian blue (PB) crystals are prepared by a facile one-step synsthesis. The structure and morphology of the as-prepared samples are characterized by X-ray power diffraction, inductively coupled plasma, scanning electron microscopy and electrochemical measurement. The PB electrode exhibits superior electrochemical behavior in K2SO4 aqueous solution including high reversible capacity (80 mAh g−1 at the current density of 0.5 A g−1), outstanding rate capability and good cycling stability. The K-ion capacitor (KIC) is also fabricated by using PB as a positive electrode and commercial activated carbon as an negative electrode, and it presents a maximum energy density of 28 Wh kg−1 at the current density of 1 A g−1 (corresponding to 7.5 mA cm−2). Furthermore, the KIC also exhibits excellent cycling stability at the current density of 2 A g−1 with capacity retention of nearly 98% over 1200 cycles. Our synthesized electrode material provides a new way for fabricating high performance electrode materials for superior KIC.

A KIC was fabricated by employing a Prussian blue positive electrode and an activated carbon negative electrode in K2SO4 aqueous electrolyte.104