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.

Graphical abstractA KIC was fabricated by employing a Prussian blue positive electrode and an activated carbon negative electrode in K2SO4 aqueous electrolyte.Download high-res image (104KB)Download full-size image