Preparation And Photoelectrochemical Performances Of Co-Pi Modified TiO₂/BiVO₄ Inverse Opal Nanostructures

Energy is the material basis for human society to survive and develop.Global energy resources are currently mainly derived from the use of fossil fuels such as coal,oil and natural gas.As human energy consumption continues to grow,it is expected that there will be energy shortages in the near future.In addition,the large-scale use of fossil fuels has also brought serious environmental pollution and greenhouse effect to the entire planet.Therefore,in the long run,it is very necessary for human beings to seek a clean energy alternative to fossil fuels.This demand has become the consensus and pursuit of scientists.Photocatalytic hydrogen production can make full use of the energy of sunlight to continuously produce hydrogen,showing great possibilities in the future to alleviate human energy crisis and environmental problems.The use of semiconductor materials with good light absorption properties to drive photoelectrochemical reactions of water molecules represents an effective way to produce non-polluting hydrogen fuels,and to have great application prospects in the field of fuel cells.As a direct band gap semiconductor material,titanium dioxide has excellent photo-corrosion resistance and non-toxicity.It has been widely studied since it was discovered by Japanese scientist Fujishima in 1972 for photocatalytic decomposition of water to produce hydrogen.However,the band gap of TiO₂ is large?3.2 eV?,which is not conducive to the absorption of sunlight and energy conversion in the visible region.At the same time,the electron transport distance in the bulk material is short and it is easy to recombine,which is not conducive to the chemical reaction between solid and solution.Therefore,the preparation of a three-dimensional porous structure having a long period can provide sufficient transport channels for ion diffusion between electrodes/electrolytes,enhancing photo-generated charge transport efficiency.At the same time,the large surface area of the three-dimensional porous structure itself is advantageous for enhancing the multiple reflection absorption of sunlight and reducing the transmission of sunlight.These advantages make the three-dimensional ordered porous structure?TiO2 inverse opal?based on TiO2promising as the main material skeleton of the future photoelectric conversion device.In this paper,a three-dimensional TiO₂ composite inverse opal nanostructure was prepared by using polystyrene microspheres as template.Some aspects of TiO₂inverse opal nanostructures for visible light absorption and oxygen evolution catalysis were explored.The specific research contents are as follows:?1?The three-dimensional TiO₂ inverse opal structure was prepared by solution-gel method using 500 nm diameter polystyrene microspheres as a template,and the bismuth vanadate?BiVO4?light absorber was further loaded on the TiO2inverse opal by hydrothermal method.UV-visible absorption spectroscopy showed that the TiO₂/BiVO₄ inverse protein structure extended the absorption spectrum from380 nm to 510 nm compared with the original TiO₂ inverse opal,showing a significant enhancement in the visible light absorption region.?2?A layer of controlled Cobalt phosphate?Co-Pi?co-catalysts were deposited on the TiO₂/BiVO₄ inverse opal photoanode by photo-assisted electrodeposition.The effects of different content of Co-Pi on the photochemical performance of the TiO₂/BiVO₄ inverse opal photoanode were investigated.It was found that the surface modification of Co-Pi significantly enhanced the photocurrent of TiO₂/BiVO₄ inverse opal,especially when the applied bias voltage of the electrode was low.Mechanism analysis by means of electrochemical impedance spectroscopy and other means that the proper amount of Co-Pi can reduce the activation energy of water oxidation,effectively promote the reaction kinetic mechanism of the electrode/electrolyte interface,and lead to the improvement of photoelectrochemical decomposition water reaction performance.The experimental results show that the photoelectrochemical performance of the optimized TiO2/BiVO4/Co-Pi inverse opal structure is significantly enhanced compared to the single TiO₂ inverse opal photoanode and TiO₂/BiVO₄ composite inverse opal structure,which is 1.23 V vs.RHE.The photocurrent density of 4.96mA/cm² is produced,and the corresponding photoelectric conversion efficiency is 9.0times that of the ordinary TiO₂ inverse opal structure,and 2.3 times that of the TiO2/BiVO4 inverse opal structure photoelectrode.