| The consumption of fossil energy and the environmental pollution has compelled people to continuously develop renewable energy.As a kind of inexhaustible clean energy,the conversion and utilization of solar energy has aroused wide attention,particularly,solar water splitting for hydrogen production is simple,effective and environmentally friendly,which has aroused great interest in academia and industry.It is also known as the "Holy Grail" reaction in the field of chemical science.Solar water splitting to produce hydrogen by mimicking natural photosynthesis is one of the effective ways to solve the energy and environmental problems faced by human society.However,the energy conversion efficiency of the photocatalytic water splitting reaction is still low at present,and a key problem lies in poor charge separation and transfer efficiency.Based on the biomimetic concept,this thesis mainly describes the rational design and development of highly efficient and stable artificial photosynthetic system.and explores the mechanism of photogenerated charge separation and transfer during the catalytic reaction process.The main research contents and results are summarized as follows:(1)A new visible-light-driven water oxidation system was constructed using BiVO4 as a light harvester and cubic Co complex as the oxygen-evolving molecular catalyst.This system exhibits a high turnover frequency(TOF = 2.0 s-1)for photocatalytic water oxidation,with an apparent quantum efficiency(AQE)yield of 4.5%at 420 nm,which is ninefold that of bare BiVO4(0.5%).Furthermore,efficient interfacial hole transfer process was observed from photoexcited BiVO4 to Co complexes by Kelvin probe force microscopy(KPFM)and surface photovoltage(SPV)spectra,suggesting that the recombination of photoexcited carriers is effectively inhibited through loading Co complex catalyst.The hybrid system bridges the gap between homogeneous and heterogeneous photocatalysis for water oxidation and provides a new architecture for designing highly efficient catalyst with suitable ligands to promote charge separation and transfer from semiconductors to molecular catalysts.(2)An artificial photosynthesis system for photocatalytic water oxidation was assembled by mimicking the functions of photosystem ?,with SiO2-modified Ta3N5 semiconductor as a light harvester,cubic Co complex as the oxygen-evolving catalyst.A thin layer of silica grown on the surface of Ta3N5 by atomic layer deposition(ALD)not only greatly improves the hydrophilicity of the Ta3N5 surface,but also provides a large number of hydroxyl groups as a bridge connecting the molecular catalyst.It has been found that the adsorption model of molecular catalysts on the surface of the semiconductor is closely related to photogenerated charge separation and transfer.The system by chemical bonding exhibits a high turnover frequency(TOF)over 5.0 s-1 for photocatalytic water oxidation,with apparent quantum efficiency(AQE)of 2.5%under 500-600 nm illumination,which is 5-fold of bare Ta3N5.(3)A highly efficient photoelectrocatalytic system was designed and fabricated by mimicking the functions of photosystem II(PSII),with BiVO4 semiconductor as a light harvester protected by a layered double hydroxide(NiFeLDH)as a hole storage layer,a partially oxidized graphene(pGO)as biomimetic tyrosine for charge mediator,and molecular Co cubane as oxygen evolution complex.The integrated system exhibited an unprecedentedly low onset potential(0.17 V)and a high photocurrent(4.45 mA cm-2).with a 2.0%solar to hydrogen efficiency.Spectroscopic studies revealed that this photoelectrocatalytic system exhibited superiority in charge separation and transfer by benefiting from mimicking the key functions of PSII.The success of the biomimetic strategy opened up new ways for the rational design and assembly of artificial photosynthesis systems for efficient solar-to-fuel conversion. |
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