Study On The Photogenerated Cathodic Protection For 304 Stainless Steel By Ti-based Nanocomposites

Metal corrosion has not only brought huge economic losses,but caused serious environmental pollution and other problems.Therefore,it's urgent to develop effective metal protection technology.Photogenerated cathodic protection is a new kind of cathodic protection technology which uses the photoelectric conversion of semiconductor to protect metal materials,it has attracted the attention of many scholars due to its advantages in energy saving and environmental protection.Among many semiconductor materials,Ti-based nanocomposites have been widely used in the field of photoelectric catalysis given the excellent photoelectric properties.Among them,semiconductor TiO₂is a research hotspot in the field of photocathodic protection owe to its special photocatalytic performance,high stability and low toxicity.However,thanks to the wide bandgap of TiO₂,the low utilization of visible light,and the high recombination rate of electron-hole(e^--h⁺)pairs generated by photoexcitation,the application of TiO₂ in photocathodic protection field was severely limited.At present,the decoration means of TiO₂ consist of element doping,construction of heterostructure,noble metal deposition,quantum dots(QDs)sensitization and so on.This paper aimed to improve the photoelectrochemical(PEC)properties of Ti-based nanocomposites and conducted research and discussion with the goal of photogenerated cathodic effective protection of304 stainless steel(304SS).The work of this paper is as follows:Part one:Study on the photocathodic protection properties of Ti doped Fe₂O₃nanorods for 304 stainless steelTi doped Fe₂O₃ composite photoanodes(Ti-Fe₂O₃)were synthesized via hydrothermal method and two-step annealing method.The photocathodic protection performances of photoanodes were studied by measuring the transient photocurrent densities,open circuit potential(OCP),Tafel curves and impedance(EIS)under visible light.The experimental results showed that the Fe₂O₃ photoanode with hydrothermal treatment for 8 h had the highest photocurrent densities and the best PEC performance,the photogenerated cathodic protection for 304SS was the most effective under visible light.The transient photocurrent densities increased from 0.5 m A·cm^-2 to 0.9 m A·cm^-2after Ti doping.Under visible light,the results of Tafel curves displayed that the corrosion potential of 304SS coupled with composite photoanodes decreased from-375 m V to-501m V,the performance of photocathodic protection was improved.The EIS results showed that the charge transfer resistance(R_ct)of the Ti-Fe₂O₃ composite photoanode was decreased,which enhanced the conductivity of Fe₂O₃ photoanode.Moreover,the 304SS could be continuously protected for up to 10 h in the dark condition.Part two:Study on the photocathodic protection for 304 stainless steel by PbS quantum dots modified TiO₂ nanotubesQDS modified TiO₂ nanotubes(TiO₂NTs)photoelectrodes were successfully synthesized via electrochemical anodization combined with successive ion layer adsorption and reaction(SILAR)method.PbS(x)/TiO₂ NTs(x=2,4,6,8)samples were prepared by changing the deposition amounts of PbS.The results indicated that the PbS(6)/TiO₂ NTs displayed a stronger photocurrent density of 3.2 m A·cm^-2 and the optical absorption red-shifted to the visible light region compared with pure TiO₂.Moreover,a more negative OCP(-720 m V)was obtained when the PbS(6)/TiO₂ NTs photoanode coupled with 304SS under visible light irradiation.The results showed that the composite films as a stable photoanode displayed highly effective photocathodic protection performance for 304SS.Part three:Study on the photocathodic protection of 304 stainless steel by CdS/N/TiO₂ composites filmsThe N-doped CdS/TiO₂ composite photoelectrode(NCT)was fabricated by anodic oxidation,SILAR and impregnation-annealing methods.The results implied that when the SILAR cycles was 12,the transient photocurrent densities of CdS/TiO₂ was the highest and the photogenerated cathodic protection was the most effective.After doping with N element,the absorption range of the NCT composite films to sunlight was further expanded to the visible region,and the transient photocurrent densities was enhanced from 0.1 m A·cm^-2 to 0.5 m A·cm^-2,which effectively improved the PEC performance of the composite photoanode.Compared with pure TiO₂,the OCP decreased from-410 m V to about-1033 m V when the NCT film was coupled with 304SS under simulated solar light,which improved the photogenerated cathodic protection performance for 304SS.