## 3 Results
### Catalyst Characterization
#### 3.1.4 Electrochemical Proprieties  
As a preamble to the conversion of photo-energy, photocatalysis requires deep electrochemical characterization. It allows us, in particular, to better understand the semiconducting properties. ZBO Cyclic Voltammetry is intended to describe the stability of the semiconductor and determine the redox couple's specific potential. Figure 6 shows the density potential traced in the dark, the decrease current below (\(\sim\)\(-\)0.4 V), indicating a water reduction into hydrogen while the current rises over (\(\sim\)0.67 V) is due to oxygen evolution (O\({}_{2}\) + 2 H\({}_{2}\)O + 2 e\({}^{-}\)\(\rightarrow\) H\({}_{2}\)O\({}_{2}\)). The significant difference between the peaks anodic and cathodic indicates a slow charge transfer which corresponds to a sluggish elec  
Figure 5: (**a**) the dissipation factor \(\tan\)\(\delta\) (**b**) the dielectric relaxation time \(\tau\) as a function of the energy (h\(\
u\)). trochemical system and can be related to the irreversible electrochemical mechanism [56]. The semi-logarithmic characteristic (Tafel) in Figure S8 in the Supplementary Data gives a current exchange density of 3.14 \(\times\) 10\({}^{-7}\) mA cm\({}^{-2}\) and a potential of \(-\)0.7 V, confirming good electrochemical stability in the basic medium. Photo-electrochemistry offers knowledge about the properties of the semiconductor. The location of electronic bands has great importance for the prediction of interfacial reactions in photocatalysis, and it is located using the flat band potential. The flat band potential is determined from the capacitance-potential plot using the Mott-Schottky relation [57]:  
\[\mathrm{C}^{-2}=\frac{2}{\mathrm{e}\varepsilon\epsilon_{0}\mathrm{A}^{2} \mathrm{N}_{\mathrm{D}}}\bigg{(}\mathrm{E}-\mathrm{E}_{\mathrm{fb}}-\frac{ \mathrm{kT}}{\mathrm{e}}\bigg{)} \tag{12}\]  
where k is the Boltzmann constant, T the absolute temperature, kT the thermal energy (\(\sim\)26 meV), \(\epsilon_{0}=8.85\times 10^{-12}\) F/m the permittivity of free space [58], e the charge of an electron, and A is the surface area of the electrode. The permittivity \(\varepsilon\) (\(\sim\)76) is determined from the dielectric measurement on sintered pellet, while the hole density \(\mathrm{N}_{\mathrm{D}}=3.53\times 10^{20}\) cm\({}^{-3}\) is determined from the slope. The curve \(\mathrm{C}^{-2}(\mathrm{E})\) exhibits good linearity and it is represented in Figure 7. The potential \(\mathrm{E}_{\mathrm{fb}}=(0.54\,\mathrm{V})\) is easily obtained by extrapolating the plot to infinite capacity (\(\mathrm{C}^{-2}=0\)). The positive slope confirms the n-type conduction. The space charge width (W\(\sim\)3.45 nm) was calculated under optimal band bending at the interface (\(\mathrm{E}-\mathrm{E}_{\mathrm{fb}}\)) using the following equation [59; 60]:  
\[\mathrm{W}=\bigg{(}\frac{2\varepsilon\epsilon_{0}(\mathrm{E}-\mathrm{E}_{ \mathrm{fb}})}{\mathrm{e}\mathrm{N}_{\mathrm{D}}}\bigg{)}^{0.5} \tag{13}\]  
The space charge width W is less than the diameter size D calculated from DRX, so the recombination of the pairs \(\big{(}\mathrm{e}^{-}/\mathrm{h}^{+}\big{)}\) is kept at a low level. The width of depletion extends over several crystallographic units, which is advantageous in photocatalysis. Usually, the conduction band position of n-type semiconductors is 0.1 V above the flat band levels [37]. So, the conduction band (\(\mathrm{E}_{\mathrm{CB}}=-5.19\) eV /0.44 V) indicates that the CB is composed mainly of oxides derived from Orbital 3D. Hence, the energy of the valance band (\(\mathrm{E}_{\mathrm{VB}}=\mathrm{E}_{\mathrm{CB}}-\mathrm{E}_{\mathrm{g}}=-7. 99\) eV /3.24 V). Figure 6: The cyclic J (E) voltammetry of ZnBi\({}_{2}\)O\({}_{4}\) plotted in NaOH (0.1 M) with a scan rate of 10 mV s\({}^{-1}\).