## Result and Discussion
### EIS and Tafel Plot Studies
\begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \(\mathbf{R_{\rm dl}}\) & \(\mathbf{R_{\rm ad}}\) & \(\mathbf{C_{\rm dl}}\) & \(\mathbf{R_{\rm CT}}\) & \(\mathbf{Q_{\rm CFE}}\) & \multirow{2}{*}{**nC\({}_{\rm CFE}\)**} & \(\mathbf{C_{\rm CFE}}\) & \(\mathbf{A}\) & \(\mathbf{i_{0}}\) \\  & \(\mathbf{\Omega\ cm^{2}}\) & \(\mathbf{\Omega\ cm^{2}}\) & \(\mathbf{\mu\)Fcm\({}^{-2}}\) & \(\mathbf{\Omega\ cm^{2}}\) & \(\mathbf{\mu\Omega^{-1}cm^{-2}s^{n}}\) & & & \\ \hline PPy (dark) & 17.91 & 3.93 & 2.30 & 26.52 & 1.0687 & 0.74 & 0.013 & 41.308 & 4.53 \\ PPy (light) & 17.89 & 3.91 & 2.48 & 24.87 & 1.2032 & 0.74 & 0.015 & 39.667 & 3.47 \\ Irregular-shaped & 17.88 & 3.69 & 2.78 & 22.85 & 1.527 & 0.74 & 0.020 & 39.224 & 1.92 \\ Irregular-shaped & & & & & & & & & \\ particles/PPy (light) & & & & & & & & & \\ nanowires/PPy & & 17.84 & 2.42 & 5.86 & 19.81 & 2.757 & 0.74 & 0.040 & 37.099 & 1.16 \\ nanowires/PPy & & & & & & & & & \\ (light) & & 17.83 & 2.37 & 6.02 & 19.19 & 3.276 & 0.74 & 0.051 & 36.747 & 1.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Data from electrochemical impedance spectroscopy (ohmic resistance (R\({}_{\rm el}\))), adsorption resistance (R\({}_{\rm ad}\)), diffuse layer capacitance (C\({}_{\rm dl}\)), catalytic charge transfer resistance (R\({}_{\rm CT}\)), and capacitance expressed in terms of a constant phase element (Q\({}_{\rm CFE}\), R\({}_{\rm CFE}\), and C\({}_{\rm CFE}\)). Data from Tafel plot studies (slope (A), exchange current density (\(\mathrm{i_{0}}\))). ‘dark’ = without light illumination; ‘light’ = with light illumination. Figure 6: (a) Nyquist and (b) Bode plots showing measured data (individual data points) and modelled data (solid lines) using the equivalent circuit depicted in (c): (i) CaMn\({}_{2}\)O\({}_{4}\) nanowires/PPy (with light illumination),(ii) CaMn\({}_{2}\)O\({}_{4}\) nanowires/PPy (without light illumination), (iii) irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) particles/PPy (with light illumination), (iv) irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) particles/PPy (without light illumination) (dark), (v) PPy only (with light illumination) and (vi) PPy only (without light illumination). (Figure 6 (c) is reprinted with permission from ref. [17]. Copyright (2018) American Chemical Society). have made adsorption much less of an impediment than the catalytic turnover process, with the R\({}_{\rm CT}\) being, in all cases greater than the R\({}_{\rm ad}\). Both the R\({}_{\rm CT}\) and the R\({}_{\rm ad}\) were low in comparison with previous conducting polymer films prepared by us [17]; this is to be expected from the higher applied bias. Comparing the nanowires/PPy with the irregular-shaped particle/PPy, the resistances were marginally lower for the former than the latter, under both dark and light conditions, but of the same order as the control PPy film. The CaMn\({}_{2}\)O\({}_{4}\) nanowires/PPy was, therefore, a slightly better catalyst than the irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) particles/PPy, particularly under light illumination. The ohmic resistance, R\({}_{\rm el}\), was of the same order for all samples (17.83-17.91 \(\Omega\) cm\({}^{2}\)) (Table 2). Higher C\({}_{\rm dl}\) values were observed for both samples under light illumination. Hence the major effect of the light illumination appears to be the increase in the electrochemically active area of the films. Figure 7 shows Tafel plots of the catalysts at much higher overpotentials than previously examined [17], with resulting data tabulated in the last two columns of Table 2. The exchange current density, i\({}_{\rm o}\), provides a measure of the rate of catalysis at the reversible potential when the overpotential is zero. The catalytic performance as a function of increasing bias is given by the Tafel slope. As shown in Table 2, the higher applied potential also appears to have had a beneficial effect on the Tafel data, which were improved relative to previous studies [17].