## Result and Discussion
### Studies on Current Density  
Figure 5 shows the electrocatalytic performance of the samples, tested in 0.2 M Na\({}_{2}\)SO\({}_{4}\) aqueous solution, with the pH adjusted to 12, at 1.00 V (vs Ag/AgCl) bias, with and without light illumination.  
Figure 4: Transmittance spectra of (**a**) irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) particles and (**b**) CaMn\({}_{2}\)O\({}_{4}\) nanowires; Tauc plots of (**c**) irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) particles and (**d**) CaMn\({}_{2}\)O\({}_{4}\) nanowires.  
Figure 5: Chrono-amperograms at 1.00 V (vs Ag/AgCl) in 0.2 M Na\({}_{2}\)SO\({}_{4}\) (pH 12) over 1 h of operation, with and without light illumination (0.25 sun), of Fluorine doped tin oxide (FTO) glass slides coated with thin films of: (**a**) polypyrrole only (control), (**b**) polypyrrole containing irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) particles, and (**c**) polypyrrole containing CaMn\({}_{2}\)O\({}_{4}\) nanowires. (* = “light on’, # = “light off”).  
As shown in Figure 5, a significant increase in both dark- and photo-current was observed for the PPy/CaMn\({}_{2}\)O\({}_{4}\) films in comparison to the control PPy film alone. A significant increase in photocurrent was also observed when a small amount of CaMn\({}_{2}\)O\({}_{4}\) powder was added to the PPy polymer. The control PPy film exhibited light and dark current densities of 447 \(\mu\)A cm\({}^{-2}\) and 230 \(\mu\)A cm\({}^{-2}\), respectively, whereas the films prepared from the mixture of CaMn\({}_{2}\)O\({}_{4}\) and PPy produced 701 \(\mu\)A cm\({}^{-2}\) and 326 \(\mu\)A cm\({}^{-2}\) for irregular-shaped particles, and 769 \(\mu\)A cm\({}^{-2}\) and 380 \(\mu\)A cm\({}^{-2}\) for nanowires in light and dark, respectively. It is also clear that the CaMn\({}_{2}\)O\({}_{4}\) nanowires/PPy film produced higher dark and photocurrents than the irregular-shaped CaMn\({}_{2}\)O\({}_{4}\)/PPy film. Evolved gas was traced using a customised apparatus, as shown in Figure S1. The analysis confirmed the production of oxygen at the anode as shown in Figure S2.  
Catalytic and photocatalytic activities occur on the surface of catalysts. Hence, in order to examine the intrinsic catalytic properties of materials, it is often convenient to normalise the indicators of photocatalytic activity with the specific surface area of materials. Table 1 compares the BET specific surface areas and increases in dark- and photo-current with regard to the control electrode, between irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) powder and CaMn\({}_{2}\)O\({}_{4}\) nanowires. Since the optical bandgap energies of irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) powder and CaMn\({}_{2}\)O\({}_{4}\) nanowires are nearly the same, the differences in the surface-area-normalised increase in photo-current, \(\Delta\)I\({}_{\text{L}}\)/S, is expected to arise from the difference in particle shapes. Table 1 shows that \(\Delta\)I\({}_{\text{L}}\)/S values of irregular-shaped CaMn\({}_{2}\)O\({}_{4}\) powder and CaMn\({}_{2}\)O\({}_{4}\) nanowires are similar to each other. The results suggest that the influence of particle shapes on the light-driven catalysis of CaMn\({}_{2}\)O\({}_{4}\) is relatively weak. It is speculated that the exposed facets along the growth-direction of nanowires do not have significantly different catalytic activities compared to the other crystal faces. On the other hand, the surface-area-normalised increase in photo-current, \(\Delta\)I\({}_{\text{D}}\)/S, was higher for the electrode with nanowires than the electrode with irregular-shaped particles. The reason may be attributed to the difference in electric conductivity within the CaMn\({}_{2}\)O\({}_{4}\)/PPy composite electrode. Rod- or wire- shaped particles have a lower percolation threshold [16] and, given the semiconducting nature of CaMn\({}_{2}\)O\({}_{4}\), wire-shaped particles will result in higher electrical conductivity than irregular-shaped particles in polymer composites.