Preparation Of Novel Semiconductor Modified Electrodes And Property Research Of Photoelectrochemical Water Splitting

Artificial simulated photosynthesis,which converts solar energy into clean hydrogen through water splitting,is an ideal way to obtain storable and sustainable fuels.Building an effective photoelectrochemical cell is one of the most direct methods to achieve artificial photosynthesis.However,the water oxidation of the photoanode involves the transfer of multiple electrons and protons and is considered to be the bottleneck of the entire splitting water reaction.Therefore,the design and development of efficient and stable photoanode is the core of artificial photosynthesis system.In this study,we present WO₃ photoanode modified with the iridium complex[?H₄dphbpy?Ir^III?Cp*?Cl]Cl?Ir–PO₃H₂;H₄dphbpy=2,2'-bipyridine-4,4'-bisphosphonic acid,Cp*=pentamethylcyclopentadiene??WO₃+Ir–PO₃H₂?-for photoelectrochemical water oxidation.When Ir–PO₃H₂ was anchored to a WO₃ electrode,the photoanode showed a significant improvement in both photocurrent and faradaic efficiency compared to the bare WO₃photoanode.Under simulated solar irradiation(AM 1.5G,100 mW cm^-2)with a bias of 1.23 V?vs.reversible hydrogen electrode?,the photoanode exhibited a photocurrent of 1.16 mA cm^-2under acidic conditions,which was double that of the bare WO₃ photoanode.The faradaic efficiency reached 95%.Kinetic studies revealed that Ir–PO₃H₂ exhibited a different interfacial charge-transfer mechanism on the WO₃ photoanode for photoelectrochemical water oxidation compared to iridium oxide.Ir–PO₃H₂,as a water-oxidation catalyst,can accelerate the surface charge transfer through rapid surface kinetics.WO₃ photoanodes sensitized with different carbon quantum dots?CQDs?were successfully prepared by simple hydrothermal immersion under mild temperature.The photocurrent density of the electrodes modified with 1-CQDs,2-CQDs or 3-CQDs was higher than that of the WO₃ electrode without any cocatalysts or electron sacrificial agents.The enhancement of optical absorption and conductivity of WO₃ semiconductors is due to the introduction of CQDs,which makes the separation of photogenerated electron-hole pairs more efficient.Among them,the photocurrent density of WO₃/1-CQDs composite photoanode was increased by about 76%,and the applied bias photon-to-current efficiency was the highest.Notably,the high-efficiency sensitization of CQDs could provide a promising route to improve the light harvesting and photoelectrochemical performance of WO₃ photoanode.Cobalt phosphide?CoP?nanosheet was integrated on the nanoporous bismuth vanadate?BiVO₄?electrode by using the hydrothermal method.The introduction of CoP significantly improved the photoelectrochemical performance of the photoanode,with a photocurrent up to4.0 mA cm^-2 at 1.23 V?vs.RHE?under simulated 100 mW cm^-2 irradiation,a 3-fold enhancement over that obtained by the bare BiVO₄.The BiVO₄+CoP photoanode exhibited an impressive early onset of water oxidation,with a more than 220 mV cathodic shift of the onset potential,superior to the typical Co₃O₄ and Co-Pi cocatalysts-modified BiVO₄ photoanode.Systematic studies show that the improvement in photoelectrochemical performance by CoP is mainly due to the restraint of surface charge recombination and increase in photovoltage.The BiVO₄/CQDs+Ni?OH?₂ composite photoanode was constructed by introducing CQDs with fluorescence and optical properties.The BiVO₄/CQDs+Ni?OH?₂ photoanode exhibited a lower onset potential?⁰.2 V vs.RHE?toward water oxidation,and a photocurrent density of 3.05 mA cm^-2 at 1.23 V vs.RHE,which was about 2.5 times higher than that of the unmodified BiVO₄ electrode,and the charge injection efficiency was 65%.Surface kinetics measurements showed that BiVO₄/CQDs+Ni?OH?₂ photoanode had higher k_trans and lower k_recec values than BiVO₄ electrodes.It is indicated that Ni?OH?₂ as a water oxidation catalyst combined with CQDs can effectively improve the photoelectron and hole migration to improve the photoelectrochemical water oxidation activity.