Enhancing activated carbon supercapacitor electrodes using sputtered Cu-doped BiFeO3 thin films

This work describes the fabrication of a composite supercapacitor electrode made of Cu-doped BiFeO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>3</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> (Cu-BFO) films on an activated carbon (AC) electrode using radio-frequency (RF) magnetron sputtering. To prevent exfoliation of Cu-BFO and AC upon immersion in an electrolyte, the nickel foam sandwiching electrode technique was introduced. The Cu-BFO films significantly enhanced electrochemical properties, increasing specific capacitance by up to 151% compared to that of an AC electrode. This was attributed to Faradaic reactions and specific surface area in the Cu-BFO/AC electrode. The highest specific capacitance achieved was 169 F <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>g</mml:mtext> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:math> at 0.5 A <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>g</mml:mtext> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:math> , and cycling stability retention was 93.12% after 500 cycles. However, the remaining percentage of the specific capacitance decreased differently with increasing thickness, which is also discussed. Furthermore, an asymmetric supercapacitor using Cu-BFO/AC and AC electrodes demonstrated a high energy density of 4.71 Wh <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>kg</mml:mtext> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:math> , power density of 2.66 kW <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>kg</mml:mtext> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:math> , and over 90% retention after 1000 cycles, highlighting its durability. The uniform RF magnetron sputtering deposition is vital for mass production. Combined with impressive retention in asymmetric supercapacitors, this scalability suggests a promising pathway for large-scale manufacturing. Consequently, this work could pave the way for the large-scale production of supercapacitors.