| Energy crisis and environmental pollution are the main challenges in 21st century.Hence,the developments of the sustainable,efficient and clean energy sources and the corresponding energy conversion techniques are critical.Photo-/electro-catalytic energy conversion techniques are regarded as the moderator between energy and environment and receiving the extensive attentions.The core challenge for photo-/electro-catalysis is the development and applications of the highly low-cost,active and stable catalysts.Facing this circumstance,the key scientific problem is how to understand the structure-performance relationship.In this thesis,based on the photocatalytic water splitting and electrocatalytic CO2 reduction application oriented basic research,we develop the effective approach to synthesize superficial modification catalysts using carbon nitride and zinc-cadmium sulfide as the models in large amounts with controlled structure（multipores,ultrathin thickness and defects）and component（superficial functionalization and dopant）and then systematically explore their structure-performance relationship via various approaches,including synchrotron-based X-ray absorption spectroscopy,theory calculation and in-situ characterization technique.We successfully obtain the low-cost,active and stable catalysts.The main works of this thesis are shown as follows:1.A facile two-step continuous thermal-assisted air and ammonia treatment strategy is developed to obtain atomically-thin porous polymeric carbon nitride nanosheets with hydroxyl and amino groups modification（CNPS-NH2）.CNPS-NH2nanosheets with ultrathin 0.4 nm thickness,abundant micro/meso-pore and tri-s-triazine-based framework possess the huge surface area and strong hydrophilia.Based on the structure analysis of the intermediate,the unique structure formation mechanism of CNPS-NH2 can be deduced:abundant mesopore and superficial hydroxyl group modification are caused by thermal air etching;ultrathin thichness,mircopore and amino group modification are mainly created by thermal NH3treatment.CNPS-NH2 nanosheets possess highly active and stable photocatalytic hydrogen production performance.Synchrotron-based X-ray absorption spectroscopy reveals K edge 2p orbit of oxygen element plays a vital role in extending the lifetime of the photo-generated carriers and thus improves the photocatalytic performance.2.The utilization of our two-step thermal-assisted air and ammonia treatment and the low-cost urea as the precursor,polymeric carbon nitride with hydroxyl and amino groups modification is synthesized（OA-PCN）.We find that CO2 can be highly electro-converted to CO only under the existence of both hydroxyl and amino groups.A series of characterizations and density functional theory（DFT）calculations reveal that superficial hydroxyl and amino groups can synergistically decrease activation energy for CO2 electroreduction,optimize the reaction pathway and thus improve the catalytic performance.3.The coupling of amine modification with controllable Zn heteroatom doping into a rationally-designed ZnxCd1-xS-diethylenetriamine inorganic-organic hybrid(ZnxCd1-xS-Amine)electrocatalyst is synthesized.ZnxCd1-xS-Amine exhibits high activity for synthesizing syngas with tunable CO/H2 ratios in a wide range from 0 to19.7.Diethylenetriamine can enhance the adsorption and accelerate the activation of CO2 to form the key intermediate COOH*for CO formation.Zn substitution promotes the hydrogen evolution reaction（HER）,leading to tunable CO/H2ratios.Syngas and dihydroisoquinoline can be simultaneously synthesized by pairing with anodic semi-oxidation of tetrahydroisoquinoline in a ZnxCd1-xS-Amine||Ni2P two-electrode electrolyzer when the replacement of the kinetically-slow oxygen evolution reaction with a thermodynamically more favorable anodic organic reaction.Hence,the energy efficiency of the overall cell reaction is improved and the high value-added dihydroisoquinoline is simultaneously yielded. |
