| Simulating the photosynthesis of nature world that converts solar energy into chemical fuels is a promising counter-measure to address the current energy crisis and environmental concerns.Water oxidation is considered to be the bottleneck of the artificial synthesis system due to its high thermodynamic barriers and multi-electron transfer process.Therefore,the construction of highly efficient water oxidation system is crucial for the realization of solar energy conversion and storage.In this thesis,a hybrid system consisted of BiVO4-reduced graphene oxide(RGO)and cobalt cubane complex Col is developed for the first time to achieve the photocatalytic water oxidation.A 4-fold enhancement in the oxygen evolution rate and 100%chemical yield are obtained upon the introduction of Col to BiVO4-RGO in pure water under visible light irradiation.In addition,the RGO is found to play an important role in improving the lifetime of photogenerated charges and electron-transfer efficiency between Col and BiVO4.These findings may open a novel pathway to establish a molecular-based overall water splitting system.In order to remove the sacrificial reagents in the above system,the cobalt cubane catalysts were immobilized on the surface of BiVO4 photoanode.The results show that tuning the substituent groups on cobalt cubane allows the PEC properties of the final molecular catalyst/BiVO4 hybrid photoanodes to be tailored.Among them,a new cubane complex featuring alkoxy carboxylate bridging ligands(Co32)exhibits the best PEC performance.Under simulated sunlight(AM 1.5,100 mW/cm2)illumination,the photocurrent density of Co32/BiVO4 hybrid electrode prepared by drop-casting is up to 5 mA/cm2 at 1.23 V vs.RHE,which is higher than any other undoped BiVO4 photoanodes.A high solar-energy conversion efficiency of 1.84%is obtained for the integrated photoanode,a 6-fold enhancement over that of unmodified BiVO4.In addition,the fluorinated Co32 complex(Co33)modified BiVO4 exhibits excellent stability,which can achieve a constant photocurrent of 2.2 mA/cm2 for at least 4 h without decay.Intensity modulated photocurrent spectroscopy(IMPS)technique reveals that the high PEC performance of the above Co32/BiVO4 hybrid electrode is attributed to the suppression of surface charge recombination by molecular cocatalyst.While changing the adopted loading methodology from drop-casting to soaking also leads to high activity,however,the primary role of Co32 on PEC performance enhancement is altered from surface passivation to improving the hole transfer(water oxidation).In the last part,we assembled a two-electrode system consisted of Co33/BiVO4 photoanode and Co34 modified carbon cloth cathode,which was catalyzed by the precious metal-free complex for the first time,to realize the PEC CO2 reduction.Under simulated sunlight illumination,this device achieves a photocurrent density of 2.6 mA/cm2 at 1.4 V and the maximum ABPE of 0.52%at 0.7 V.Moreover,87%FEco and the highest ?sTC of 0.44%were also obtained.The above values are higher than those of the similar two-electrode PEC systems reported previously. |
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