Nanomaterials For Photo（electro）chemical Water Splitting And CO₂ Reduction

Energy shortage and environmental pollution are becoming global issues and challenges facing the human society.Current world energy consumption is highly dependent upon fossil fuels.Concerns are growing that the increasing human activities would not only accelerate the consumption of fossil fuels,but also result in escalated greenhouse gas emission and breaks the carbon balance in the natural world.The rational utilization of solar energy is an important way to realize the sustainable development of energy and the ecological civilization of mankind in the future.Artificial photosynthesis by photocatalysis and photoelectrocatalysis is a feasible strategy for the large scale synthesis of fuel(through water splitting and carbon dioxide reduction).This paper contains four main studies that the author conducted on the applications of nanomaterials in photoelectrochemical water splitting and photocatalytic CO2 reduction.CuWO4 is an emerging candidate with suitable band gap and high chemical stability.Nevertheless,its overall solar-to-electricity remains low owing to the inefficient charge separation process.In the first work,we demonstrated that this problem can be partly alleviated through designing three-dimensional hierarchical nanostructures.Under illumination,our CuWO4 nanoflake array photoanodes demonstrate more than twice higher photocurrent density and incident photon-to-current efficiency(IPCE)than all existing CuWO4-based materials.In addition,we demonstrated that the coupling CuWO4 nanoflake arrays with solution-cast BiVO4 thin film in a heterojunction configuration is a possible resolution to the low charge separation efficiency problem.In the second work,we studied the application of Bi2WO6 as photoanode in PEC.The photocurrent density of the Bi2WO6 nanostructures was 0.34 mA/cm2(1.23 V vs.RHE).But Bi2WO6 nanostructured photoanode was very unstable.The reason might be due to the continuous dissolution of Bi2WO6.Another effective way to solve the energy problem can be through the employment of photochemical reduction method,recycling and using.So that it can convert to high value-added fuels.In the third work,ZnAl-Layered Double Hydroxide(LDH)was used as the object of photocatalytic CO2 reduction.The results show that ZnAl-LDH with layered structure also has the property of photocatalytic CO2 reduction,but its yield is too low and the product is mainly CO.Through the stripping,we successfully prepared a single layer of ZnAl-LDH nanoheets,and for the first time its application in the field of photocatalytic CO2 reduction.Photocatalytic tests show that the photocatalytic activity of the monolayer LDH is improved by nearly 100 times,and the product is mainly CH4.The results show that the monolayer LDH material is different from the precursor material in the product selectivity.In the fourth work,we designed ZnAl/C3N4 catalyst to further improve the performance of ZnAl-LDH photocatalytic CO2 reduction.Although ZnAl-LDH does not have visible light absorption property,but after its combination with C3N4,the synergistic effect of the two has greatly enhanced the photocatalytic reduction performance of CO2 under visible light.