Synergistic Effects and Characterization of CoMn2O4/Graphene in DSSC Counter Electrodes

This work is focused on fabricating a counter electrode (CE) for application in a dye-sensitized solar cell (DSSC). Cobalt manganese oxide (CoMn 2 O 4 ) nanoparticles (NPs) and its nanocomposite with graphene were prepared by a hydrothermal method. The nanocomposites of cobalt manganese oxide with graphene as CoMn 2 O 4 /(graphene) x (where x = 0.2, 0.4, and 0.6) were synthesized as an electrode material, and a cell was fabricated for the x = 0.6 nanocomposite to investigate the activity for use in DSSCs. These nanocomposites were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) spectroscopy. SEM analysis revealed the nature of the particles, and the average grain size was in good agreement with XRD results. EDX showed the ratio of the respective samples. The XRD pattern showed the hexagonal structure of CoMn 2 O 4 NPs with an average size of 39.45 nm. The FTIR spectrum indicated O–H stretching bonds and the vibrational bending of MnO at the interstitial sites. For electrochemical analysis, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed. Through CV analysis, an anodic peak current ( I pa ) was observed at 41.42 µA, while the cathodic peak current ( I pc ) was observed at −37.13 µA, and peak-to-peak separation (Δ E pp ) = 0.31 V for CoMn 2 O 4 NPs. For graphene, I pa = 180.45 µA, I pc = −230 µA, and Δ E pp = 0.25 V, while I pa = 100.23 µA, I pc = 80.65 µA, and Δ E pp = 0.16 V for the CoMn 2 O 4 /graphene ( x = 0.6) nanocomposite, which also showed excellent electrocatalytic properties. The charge transfer mechanism on the surface of the electrode was found to have rapid oxidation–reduction behavior and can be used as an alternative to platinum as the CE in the DSSC. The CV analysis of the CoMn 2 O 4 /graphene ( x = 0.6) nanocomposite-based DSSC showed that the I pa current was observed at 26.85 mA, while the I pc current was observed at −27.25 mA in the two-electrode system. The R s values for CoMn 2 O 4 /graphene with x = 0.2, 0.4, and 0.6 were 142.80 Ω, 141.33 Ω, 135.18 Ω, and 131.18 Ω, respectively, as an electrode material. The exchange current density J = 2.13 × 10 −3 A/cm 2 was found using the charge transfer resistance value ( R ct = 6.03 Ω cm 2 ) and was verified by the Tafel curve. Graphical Abstract