Study On The Composite Design Of Iron Based Co-catalyst On The Surface Of BiVO₄ Photoanode And Its Photoelectric Performance Of Water Decomposition

Among many ways of using renewable energy to produce hydrogen,the use of solar energy is undoubtedly the most valuable and potential.The sun continuously radiates energy to the Earth’s surface through sunlight,saving manufacturing costs in other ways of producing hydrogen energy and avoiding secondary pollution to the environment.In this context,the technology of photoelectrochemical（PEC）water decomposition emerged,which simulates natural photosynthesis and uses semiconductors to directly convert solar energy into chemical energy and generate hydrogen and oxygen.Among numerous semiconductors,bismuth vanadate（Bi VO₄）,as a cheap and easily available semiconductor material with stable physicochemical properties and absorption response to visible light,has great potential for application in the field of PEC water decomposition.However,the slow water oxidation reaction kinetics and photo generated carrier recombination issues on the surface of Bi VO₄restrict its further application and development.To address the aforementioned bottleneck issues,this paper selects common transition metal iron-based oxides and hydroxides to construct a series of catalytic layers on the surface of Bi VO₄ semiconductors,effectively improving the efficiency of surface water oxidation evolution reaction（OER）.The specific work is divided into the following three parts:（1）We use solvothermal method to transform cubic crystalline phaseγ-Fe₂O₃ onto Bi VO₄substrate.Benefit by the rich catalytic active site and large catalytic area ofγ-Fe₂O₃nanoparticles,the PEC water oxidation activity of the composite photoanode has been significantly improved.Meanwhile,we introduce a conductive polymer with redox activity—poly（2,6-diaminoanthraquinone）（PDAAQ）into the catalytic system,quinone carbonyl groups in the polymer skeleton as proton acceptors can accelerate the proton coupled electron transfer（PCET）process and further promote the OER catalytic activity ofγ-Fe₂O₃.According to density functional theory calculations and electrochemical tests,the type II heterojunction formed between PDAAQ and Bi VO₄ can serve as a hole transport channel and inhibit photogenerated electrons and hole recombination.Tests have shown that the preparedγ-Fe₂O₃-PDAAQ@Bi VO₄ photoanode can reach 5.35 m A/cm² photocurrent density at 1.23 V_RHE.（2）Iron hydroxide（Fe（OH）_x）is an OER co-catalyst with excellent catalytic activity,which can be prepared through the self-hydrolysis reaction of potassium ferrate（K₂Fe O₄）.At 4℃（atmospheric pressure）,liquid water has the maximum density（approximately 999.972 kg/m³）,and there is a stronger hydrogen bonding effect inside it compared to other temperature states（such as 25℃）.This work utilized K₂Fe O₄ as the precursor and water as the reaction solvent to investigate the differences in the PEC performance of Fe（OH）_x@Bi VO₄ prepared under low temperature（4℃）and room temperature（25℃）conditions.The material characterization and catalytic test results indicate that the hydrogen bonding force of the aqueous solution can affect the crystal structure of Fe（OH）_x formed,and the Fe（OH）_x obtained from the reaction at 4℃has better OER activity due to its internal strong hydrogen bonding interaction.This work takes the density difference caused by temperature in water reaction systems as the research entry point,and conducts a theoretical study on the preparation process of Fe（OH）_x co-catalysts based on water systems.（3）On the basis of work 2,we added strong electronegative ions such as BO₃^3-,SO₄^2-,PO₄^3-and Cl^-into the reaction solution.These ions can be doped into the Fe（OH）_x structure through hydrogen bonding to obtain Fe（OH）_x-X@Bi VO₄ Core shell structured photoanode.The XPS results also demonstrate that there are stronger hydrogen and B-O bonds in the Fe（OH）_x-B co-catalytic layer.After PEC testing,The prepared Fe（OH）_x-B@Bi VO₄ photoanode exhibits photocurrent density of 6.31 m A/cm²@1.23 V_RHE.