Blossoming of Multivalent Iron Phosphate Microplatelets Grown on Multiwall Carbon Nanotube Frameworks: Investigation of Supercapacitive Performance through Symmetric and Asymmetric Configurations

Abstract

The present study explores the impact of non-toxic and higher oxidation state iron phosphate-blossomed microplatelets [Fe7(PO4)6] anchored on multiwall carbon nanotubes (MWCNTs) toward supercapacitor applications, which is not only the first report for the synthesis of Fe7(PO4)6 by chemical bath deposition but also for the design of symmetric and asymmetric supercapacitive devices. “Dip and dry” coated MWCNTs on the copper have been employed as the substrate to fabricate the Cu/MWCNTs/Fe7(PO4)6 electrode. Interestingly, the designed Cu/MWCNTs/Fe7(PO4)6 electrode exhibited superior capacitance (727 F/g) compared to bare MWCNTs (49.8 F/g) and Fe7(PO4)6 (147.8 F/g) at 100 mV/s scan rate. The standalone electrode has been well optimized through diverse characterizations followed by the fabrication of a symmetric device in an aqueous KOH electrolyte yielding 227 F/g specific capacitance, whereas an asymmetric solid-state device assembled using Cu/MWCNTs/Fe7(PO4)6 and SS/MWCNT electrodes with a conducting KOH electrolyte embedded in a non-conducting PVA polymer matrix yielding 163 F/g. Complete studies of symmetric and asymmetric devices have been incorporated herein.

Unlocking the synergetic potential of cobalt iron phosphate and multiwalled carbon nanotube composites towards supercapacitor application

“…33 Furthermore, the spectrum reveals a 1662 cm −1 peak associated with O–H bond bending and a series of peaks between 3100 and 3400 cm −1 indicating O–H stretching. 27,31,33 These FTIR findings provide valuable insights into the molecular structure and bonding interactions within Co 3 Fe 4 (PO 4 ) 6 . Also, no residue for the used H 2 O 2 was observed inside the CNT network.…”

“…Notably, the peak at wavenumber 541 cm −1 is attributed to P–O bond stretching, 31 and another at 661 cm −1 signifies Co–O bond stretching and the presence of the Co 2+ oxidation state. 32 At 1036 cm −1 , the spectrum displays an assigned peak related to asymmetric P–O stretching, 27 whereas 2385 cm −1 corresponds to P–H bond stretching. 33 Furthermore, the spectrum reveals a 1662 cm −1 peak associated with O–H bond bending and a series of peaks between 3100 and 3400 cm −1 indicating O–H stretching.…”

“…Deposition of MWCNTs was performed by following a previous report. 27,28 In order to functionalize the MWCNTs, a reflux technique was employed for 48 h at 80 °C using H 2 O 2 to introduce –COOH functional groups. The final product was thoroughly cleaned several times with double distilled water (DDW), and air dried at 60 °C for a period of 12 h. For achieving stable and effective dispersion, sonication was performed on desired MWCNTs using the TritonX-100 surfactant and 50 ml of double-distilled water at a ratio of 1 : 100 (Tx-100 : water) for 2 h in which mirror polished stainless steel was immersed for 10 s to allow the MWCNTs to adsorb (Fig.…”

“…This dual charge storage mechanism significantly enhances the electrode's performance when compared to the previous report on MWCNTs/Fe 7 (PO 4 ) 6 . 27 The improvement is attributed to the substitution of Fe 3+ with Co 2+ , resulting in two redox centres with different oxidation states.…”