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 (CoMn₂O₄) nanoparticles (NPs) and its nanocomposite with graphene were prepared by a hydrothermal method. The nanocomposites of cobalt manganese oxide with graphene as CoMn₂O₄/(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 CoMn₂O₄ 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 (ΔE_pp) = 0.31 V for CoMn₂O₄ NPs. For graphene, I_pa = 180.45 µA, I_pc = −230 µA, and ΔE_pp = 0.25 V, while I_pa = 100.23 µA, I_pc = 80.65 µA, and ΔE_pp = 0.16 V for the CoMn₂O₄/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 CoMn₂O₄/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 CoMn₂O₄/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/cm² was found using the charge transfer resistance value (R_ct = 6.03 Ω cm²) and was verified by the Tafel curve. Graphical Abstract: (Figure presented.)