N2 Intercalation Enhances the Band Structure of WO3 Electrodes: Insights from Mott-Schottky Analysis

Mott-Schottky (Mott-Schottky) plots derived from alternating-current impedance measurements were used to elucidate the band structure of N2 intercalated WO3 electrodes. As illustrated in Figure 8, the characteristic behavior of n-type semiconductors was confirmed for all WO3 samples, as the reciprocal of the square of capacitance (C^-2 [F^-2 cm^4]) exhibited a linear increase with applied potentials exceeding the flat-band (E_FB) potentials. The E_FB values and donor carrier densities (N_D [cm^-3]) were determined from the x-intercept and slopes of the linear plots, respectively (Table 2). The E_FB value of the WO3-0 electrode was measured to be 0.38 V, closely aligning with previously reported values for WO3 electrodes (0.36-0.41 V vs. Ag/AgCl) [32, 33]. However, the E_FB values for the N2 intercalated WO3 electrodes (0.23-0.36 V) were lower than that of the WO3-0 electrode. Notably, the N_D values for the N2 intercalated WO3 electrodes were higher than that for the WO3-0 electrode. Specifically, the highest N_D value was observed for WO3-2.5 (4.15 ￗ 10^19 cm^-3), exceeding those of the WO3-0, WO3-0.62, WO3-1.2, WO3-5, and WO3-7.5 electrodes by factors of 1.12, 1.09, 1.08, 1.03, and 1.06, respectively. The negative shift in the E_FB potential and the enhancement in N_D are typically advantageous for improving the photoelectrochemical (PEC) performance of water oxidation.