Electrochemical investigations of 2,6-pyridinedicarboxylic acid metal complexes and their composites with polypyrrole using electrochemical deposition technique

Four metal complexes of 2,6-pyridinedicarboxylic acid (PDC): AgPDC, CdPDC, CuPDC and ZnPDC were integrated with polypyrrole (PPY) to create four new composites: PPY-AgPDC, PPY-CdPDC, PPY-CuPDC and PPY-ZnPDC for studying their electrochemical performance as potential hybrid electrodes. XRD studies reveal AgPDC, CuPDC and ZnPDC were similar to previously reported structures; whereas, CdPDC was identified as a new crystal. FESEM analysis of the composites revealed that the metal complexes were embedded irregularly within the microspheres of PPY. PPY and its composites were synthesized by electrochemical polymerization using sodium para-toluenesulfonate as dopant on ITO glass in a three-electrode cell where their cyclic voltammetry performance was recorded at room temperature in the potential range of − 0.5 to + 0.9 V at 50 mV.s⁻¹ scan rate. Based on the shape of the voltammograms, the composite films exhibited enhanced capacitive behavior in 0.1 M KCl solution and enhanced pseudocapacitive behavior in 0.1 M KCl + 0.01 M K₃[Fe(CN)₆]. This electrochemical pseudocapacitive trait is also reflected by improved conductivity values as determined by the impedance study of the extracted composite films in the form of solid electrolytes that was conducted at frequency range of 40 Hz–5 MHz. The prepared PPY has a conductivity of 1.04 × 10⁻⁵ S.cm⁻¹. PPY-CdPDC exhibited the highest conductivity, σ = 4.78 × 10⁻⁵ S.cm⁻¹ with least bulk resistance, \({R}_{{\text{b}}}\) $R_{\text{b}}$ = 19.05 Ω followed by PPY-CuPDC (σ = 3.25 × 10⁻⁵ S.cm⁻¹; \({R}_{{\text{b}}}\) $R_{\text{b}}$ = 20.92 Ω), PPY-ZnPDC (σ = 3.01 × 10⁻⁵ S.cm⁻¹; \({R}_{{\text{b}}}\) $R_{\text{b}}$ = 20.98 Ω) and PPY-AgPDC (σ = 2.16 × 10⁻⁵ S.cm⁻¹; \({R}_{{\text{b}}}\) $R_{\text{b}}$ = 31.55 Ω). All fabricated composites achieved higher conductivities, reduced resistance, than pure PPY film. These electrochemical traits are positively promising for their future application as hybrid electrode materials.