Construction Of Cuprous Oxide Nanowires Photoelectrode And Their Photoelectrocatalytic Reduction Of Carbon Dioxide

Photoelectrichemical（PEC）conversion of carbon dioxide may be an effective way to solve the problem of greenhouse effect and energy shortage in the future.Among the p-type semiconductors for PEC CO₂reduction,cuprous oxide（Cu₂O）possess high carrier mobility,narrow band gap（2-2.2 e V）,and has a suitable energy band position for CO₂reduction.However,the serious photocorrosion of Cu₂O in aqueous solution results in the low solar energy conversion efficiency and poor selectivity.In view of this,this paper firstly used Cu₂O nanowires as a model photocathode to study its main corrosion behavior and analyse reasons.Based on the reasearch of the corrosion process,a suitable strategy is proposed to alleviate the photocorrosion by introducing metal nanoparticles as cocatalysts,which could effectively facilitate electron transfer and accelerate the CO₂ reduction reaction kinetics.The main research contents are as follows:（1）Considering the fact that the reason for Cu₂O photocorrosion is unclear,Cu₂O nanowires photocathode films were synthesized by anodization to investigate the corrosion behavior and pathway of Cu₂O during the photoelectrochemical CO₂ reduction.The evolution in microstructure and composition of the Cu₂O photoelectrode were analyzed by scanning electron microscope（SEM）,X-ray photoelectron spectroscopy（XPS）,etc.And the deactivation of photoelectrochemical properties was analyzed by relevant electrochemical measurements.The results show that the corrosion behavior is mainly embodied in the generation of copper and the collapse of the structure,leading to a decrease of charge transfer efficiency.Oxygen and sodium sulfite were added to the electrolyte as electron and hole sacrificial agents,respectively,to obtain photostablilty curves.The results show that the accumulation of electrons was the primary corrosion reasons of the Cu₂O photocathode,which is caused by the slow kinetics of the CO₂ reduction reaction,and the corresponding corrosion pathway is that Cu₂O reduce to Cu⁰ directly.（2）The work in the previous chapter shows that the photocorrosion of Cu₂O is mainly due to the slow kinetics of CO₂ reduction reaction,which leads to electron accumulation and self-reduction.In/Cu₂O core-shell nanowires photoelectrode is controllably synthesized by physical vapor deposition.The Cu₂O nanowires and the shell layer form a radial heterojunction,which promotes the transfer of photogenerated electrons to the surface to participate in the CO₂ reaction.Moreover,indium acts as a co-catalyst to accelerate the CO₂ reduction reaction of the Cu₂O photocathode.The results show that the current density of Cu O photocathode decorated with 15 nm thick indium film increases from 3.1mA cm^-2 to 4 mA cm^-2 at-0.7 V vs.RHE,and the selectivity（FE）for CO increases from 27.5%to 81.8%,the yield increased from 21.82μmol cm^-2 hr^-1 to 75.94μmol cm^-2 hr^-1,which was a 3.5-fold increasement.The reason for the improving the CO selectivity after introducing indium was elucidated by in situ infrared spectroscopy,which shows that indium could facilitate the adsorption of intermediates COOH*（the important intermediate for the formation of CO）to promote the generation of CO selectively.（3）In order to further improve the selectivity of multi-carbon（C₂）products,a series of Ag nanoparticles with different sizes were introduced on the surface of Cu₂O nanowire photoelectrode by vacuum thermal evaporation method for PEC CO₂ reduction.The research results show that the introduction of Ag sites improves the carrier separation efficiency,CO₂adsorption capacity as well as CO₂ catalytic activity of the Cu₂O photocathode.As a result,the selectivity of Ag/Cu₂O photocathode to acetic acid is significantly improved.The faradaic efficiency and yield of acetic acid is 47.7%and 212.67μmol cm^-2 hr^-1,respectively,and the product selectivity of C₂ is about 54%.The results of in situ infrared spectroscopy indicated that the interface constructed by Ag nanoparticles and Cu₂O nanowires enhanced the adsorption of the intermediate*CHO to promote the formation of acetic acid.