Scheme 1 Preparation process of TO/TOB/NC photoelectrodes

Fig. 1 SEM image of TO a, SEM images and cross-section of TO/TOB b and TO/TOB/NC c, EDS d and mapping e of TO/TOB/NC, XRD patterns of TO, TO/TOB and TO/TOB/NC f, HRTEM image g of TO/TOB/NC photoelectrodes

Fig. 2 XPS spectra of survey a, Ti b, O c, Br d, Ni e, Co f of TO, TO/TOB and TO/TOB/NC

Fig. 3 Open-circuit potential variations a and photoinduced current densities b of TO, TOB, TO/TOB, TO/NC and TO/TOB/NC coupled with 316L SS under intermittent illumination. Long-term photoinduced OCP-time curves c of TO/TOB/NC coupled with 316L SS under intermittent illumination d; A and C present original optical morphologies of 316L SS, B shows the morphology of A after 24 h immersion in 3.5 wt% NaCl in the absence of TO/TOB/NC photoelectrode being coupled with, D presents the morphology of C after 24 h immersion in 3.5 wt% NaCl coupling with TO/TOB/NC under AM 1.5G

Fig. 4 CV curves of TO a, TO/TOB b and TO/TOB/NC c at different scanning rates; the ECSA results d of the TO, TO/TOB and TO/TOB/NC photoelectrodes. Photoluminescence spectra e and electrochemical impedance spectra f of the TO, TO/TOB and TO/TOB/NC photoelectrodes

Fig. 5 LSV curves a and Tafel plots b of TO, TO/TOB and TO/TOB/NC. The ultraviolet-visible diffuse reflectance spectra c of TO, TO/TOB, TO/TOB/NC and TOB; plots of (αhν)2 versus Eg d of TO and TOB. Mott-Schottky plots of TO e and TOB f. XPS VB result of TO g, TOB h

Fig. 6 Possible mechanism of improving photocathodic protection performance of TO/TOB/NC photoelectrode