Cr-doped (Co, Ni)3S4/Co9S8/Ni3S2 nanowires/nanoparticles grown on Ni foam for hybrid supercapacitor

Abstract Utilizing a 4: 1 of Co/Cr molar ratio in the starting material, Cr-doped (Co, Ni)3S4/Co9S8/Ni3S2 nanowires/nanoparticles can grow on Ni foam (NF) hydrothermally. The sample shows excellent supercapacitive performance with a specific capacity of 310.3 mAh g−1 at 1 A g−1 (320.27 mAh cm−2 at 1 mA cm−2), which is superior to Ni3S2/NF, (Co, Ni)3S4/Ni3S2/NF and less Cr-doped (Co, Ni)3S4/Co9S8/Ni3S2/NF. Density functional theory (DFT) calculations disclose that the incorporation of Cr into Ni3S2 or spinel-type Ni3S4 can improve the electron conductivity, promote the electron transfer from Ni/S to Cr, and boost the adsorption of –OH, which is evidenced from XPS spectra. It promotes the electrochemical reaction between active sites and OH− in solution, resulting in enhanced supercapacitive property. Furthermore, it is expected that the doped Cr substitutes the B position of spinel-type AB2S4 (such as NiIINiIII2S4). The Cr-doped (Co, Ni)3S4/Co9S8/Ni3S2/NF//activated carbon asymmetrical supercapacitor (ASC) shows a maximum energy density of 53.24 Wh kg−1 at power density of 543.26 W kg−1, which is superior to previously reported ASC devices.