Fig. 6. Gas chromatograms showing the evolved gases in (a) the anode and (b) the cathode compartments of the Ru–ZnP/TiO₂/FTO (black) electrode and background (red) after 1 hour of PEC operation. Peaks with retention times of 0.8 min, 1.3–1.4 min, and 1.9 min are attributed to hydrogen, oxygen, and nitrogen, respectively. Inset in (a) shows the time course of oxygen evolution monitored using an oxygen sensor for the Ru–ZnP/TiO₂/FTO (black) and ZnP-ref/TiO₂/FTO (red) electrodes and background (blue). Conditions: TiO₂ thickness = 6 μm; external bias: 0 V vs. NHE; and electrolyte: PB (0.1 M, initial pH 7.0).