Water Oxidation Performance Of Dye-sensitized Molecular Devices Based On Co(salen)Catalysts

At the moment,energy crisis and environmental pollution are serious challenges in current social development.Thus,the demand for clean,sustainable energy is becoming more and more urgent.Solar energy holds strong regional and timeliness characteristics.In addition,hydrogen has the advantages of pollution-free,renewable,low cost,which is considered to be one of the most ideal energy carriers for solar energy.Therefore,the artificial photosynthesis which simulates photosynthesis in the natural realized the conversion and utilization of solar energy.For example,Dye-Sensitized Photoelectrochemical Cells?DSPECs?as a feasible way to realize water splitting have been designed and assembled progressively in recent years.When the DSPEC was illuminated with visible light,it realizes the separation and delivery of charge,then two molecules H₂O are decomposed into four protons and one molecule of oxygen,finally the catalyst reduces protons into hydrogen under the condition that the electrolyte provides electrons.In this paper,a cheap cobalt complex Co?salen?,ruthenium complex([Ru?bpy?₂?4,4^?-?PO₃H₂?₂bpy₂]Cl₂?were prepared as water oxidation catalyst and the photosensitizer,a method was to incorporate both the catalyst and the photosensitizer on the surface of nanostructured FTO/TiO₂,then the co-adsorbed photoanode of a molecular dye-sensitized device was characterized by photoelectrochemistry.The photocurrent measurements of TiO₂/RuP+Co?salen?at pH 6.4 of sodium sulfate solution?pH 6.5 PBS and pH 5.8 silicate solution reached 400?A/cm²,380?A/cm²,and600?A/cm²,respectively.Duringsustainedlightillumination,TiO₂/RuP+Co?salen?demonstrated high photoactivity.The incident-photo-current conversion efficiency?IPCE?spectrum of it showed that the maximum absorption of the modified photoanode at 450 nm reached 1.9%.A molecular water oxidation catalyst Co?salen?has been synthesized and immobilized together with a molecular photosensitizer zinc porphyrin ZnPp on nanostructured TiO₂ particles on FTO conducting glass,forming a photoactive anode TiO₂/ZnPp+Co?salen?.The photocurrent density reached 50?A/cm² in 0.1 M pH 6.4sodium solution;a maximum IPCE value of 1.2%was obtained around 425 nm which accompanied with well stability.In order to suppress the electron recombination between the catalyst and the semiconductor and coordinate the electron transfer rate,another molecular DSPEC was assembled using Zr⁴⁺as linkage,a photosensitizer-Zr⁴⁺-catalyst chain photoanode TiO₂/ZnPp/Zr⁴⁺/Co?salen?was designed.The photocurrent density reached 75?A/cm²,has better photoelectric activity than co-adsorbed photoanode.A maximum IPCE value of 1.37%was obtained around 425 nm.The test results show that the chain photoanode,which was higher than that of the co-adsorbed photoanode.In this paper,two co-adsorbed photoanode systems were modified with Co?salen?complexes as a water oxidation catalyst and photosensitizer ruthenium complexes([Ru?bpy?₂?4,4^?-?PO₃H₂?₂bpy₂]Cl₂?or zinc porphyrin?ZnPp?complexes.The high photoactivies both of them were obtained.Compared to the photoanode which were decorated by the catalyst or photosensitizer respectively,increasement in photocurrent was obviously observed,which is of great significant for the development of cheap and efficient catalysts and photosensitizers apply to DSPECs.