Research On Energy-storing Photocathodic Protection Coatings Based On BiVO₄/WO₃

Metal corrosion is a widespread natural phenomenon.Metal corrosion can lead to material failure,structural breakage,and system failure,resulting in various types of economic losses.At present,cathodic protection and coating are still the most significant and wide technology in the field of metal corrosion prevention.However,traditional cathodic protection technology also has certain limitations.External current cathodic protection has a heavy dependence on energy supply.Sacrificial anode cathodic protection continuously releases various metal ions into the environment during the application process.Therefore,it is very urgent to improve the traditional cathodic protection method or to promote technological innovation.Photocathodic protection is a new strategy that combines photocatalytic technology with traditional cathodic protection technology,which is applied to the field of metal corrosion protection.The basic principle is that photocatalytic materials generate photoelectrons under illumination and conduct them to the protected metal,causing the metal to be cathodically polarized and protected.Due to the energy-saving and environment-friendly characteristics of photocathodic protection technology,its related research has received extensive attention from scholars at home and abroad in recent years.Photocathodic protection technology has gradually become a research hotspot.However,the technology still faces many technical challenges in the process of moving toward engineering applications.Among them,the continuation of the cathodic protection effect in the dark is the primary technical problem that needs to be solved.In this paper,for the continuation of the cathodic protection in the dark,based on the energy storage strategy,spherical BiVO₄/WO₃ and flaky BiVO₄/WO₃ photocatalytic composites were prepared using the technical idea of the composite of photocatalytic material bismuth vanadate（BiVO₄）and energy storage material tungsten trioxide（WO₃）.On this basis,the two prepared photocatalytic composites with different morphologies were used as functional fillers and compounded with epoxy resin to prepare energy-storing photocathodic protection coatings.The coatings were brushed onto the surface of 304 stainless steel（304SS）to obtain in-situ protection.The following research results were obtained through comprehensive testing and characterization of the composition,structure,and performance of the two photocatalytic composites and their modified coatings:1.Spherical BiVO₄（sBiVO₄）and WO₃ powder materials were prepared separately,and then spherical BiVO₄/WO₃ photocatalytic composites(sB₁W₁,sB₇W₁ and sB₁₂W₁)with different Bi/W ratios were prepared by in-situ synthesis.The basic properties of the materials were characterized by using SEM,XRD,and XPS.The photoelectrochemical performance of the above materials was tested by using UV-DRS,FL,and electrochemical testing.The test results showed that sB₇W₁ had a wider light absorption range,higher electron-hole separation rate,and better photocathode protection performance.The maximum photocurrent density that could be generated by the sB₇W₁photoanode under illumination was 90.08μA/cm2,the open circuit potential of304SS could be negatively shifted by 200 m V.In the dark,the open circuit potential of 304SS could be negatively shifted by 80 m V.The cathodic protection effect was continued to a certain degree,which indicated that sB₇W₁ had a certain energy storage effect and could continue cathodic protection in the dark.2.The flaky BiVO₄（fBiVO₄）was prepared by changing the synthesis parameters,and then the flaky BiVO₄/WO₃ composite（fB₇W₁）was prepared by in-situ synthesis to further enhance the performance ofBiVO₄ and its composite system.The basic properties of the materials were characterized by using SEM,XRD,and XPS.The specific surface area and oxygen vacancy signal of the materials were analyzed by using BET and EPR.The photoelectrochemical performance of sBiVO₄,sB₇W₁,fBiVO₄,and fB₇W₁was comparatively studied by using UV-DRS,FL,and electrochemical testing.The test results showed that fB₇W₁ had a wider light absorption range,higher electron-hole separation rate,and better photocathode protection performance.The maximum photocurrent density that could be generated by the fB₇W₁photoanode under illumination was 215.88μA/cm2,the open circuit potential of 304SS could be negatively shifted by 330 m V.In the dark,the open circuit potential of 304SS could be negatively shifted by 200 m V,which indicates that fB₇W₁ has a certain energy storage effect.fB₇W₁ has better photocathodic protection performance with and without light.3.sB₇W₁ and fB₇W₁ were used as functional fillers,respectively,and compounded with epoxy resin to prepare energy-storing photocathodic protection coatings.The coating was brushed onto the surface of 304SS to obtain photocathodic protection coatings（s EBW and f EBW）.The results of SEM,contact angle,and mechanical performance test show that the coating has good smoothness,wettability,and good overall mechanical properties.The results of the photocathodic protection performance tests showed that the maximum photocurrent densities that could be generated by the s EBW coating and the f EBW coating under illumination were 250μA/cm2and 550μA/cm2,respectively.The result of the OCP-t test over a short period showed that the s EBW coating and f EBW coating negatively shifted the open circuit potential of 304SS by 280 m V and 350 m V,respectively.The result of the OCP-t test over a long period showed that f EBW coating could continue the cathodic protection effect for 3 h on 304SS after 1 h of continuous light.Compared to s EBW coatings,f EBW coatings have better photocathodic protection performance with and without light.