Engineering The Interface Sites For Photocatalytic/Electrocatalytic CO₂ Reduction

The consumption on non-renewable fossil fuels has caused a rapid increase of carbon dioxide(CO2)concentration in atmospheric.Given the widely concerned severe energy crisis and ecology deterioration,numerous efforts have been made to address this challenge.Utilizing the harvestable solar energy-driven or low-cost electric energy to controllably transform the CO2 into value-added products may represent a promising approach to curb the anthropogenic CO2 emissions and alleviate the energy crisis.However,the catalysts for CO2 conversion generally face issues of limited catalytic sites,high recombination rates of carriers,and sluggish charge transport dynamics,which often result in lowered efficiency of CO2 reduction in catalytic process.As a result,exploring active catalysts is of paramount importance for making CO2 reduction into practical applications.The effective surface active sites,heterostructural interfaces,and dispersedly isolated metal sites structure were designed and constructed for tuning the physical,chemical and electronic features of the catalysts,and thus enhancing the photo/electro-reduction performance of CO2.The main research contents are presented as follows:(1)The 2D PbS nanosheets with abundant zigzag edges(e-PbS NS)were constructed and exhibited an excellent performance on CO2 photoconversion to CO while using Ru(bpy)3Cl2 as a photosensitizer.And the CO production yield of the e-PbS NS(11.3 umol/h)is much higher than that of bulk PbS(3.3 umol/h).The numerous edges in e-PbS NS with unsaturated dangling bonds are beneficial for exposing more active sites,promoting electrons transfer,strengthening CO2 absorption,thereby accelerating the kinetics processes of CO2 photoreduction.Meanwhile,the water-soluble e-PbS NS could also conveniently shorten the electronic transfer distances between Ru center and cocatalyst by intimately contacting with the homogeneous Ru dyes,which is another factor contributing to good photocatalytic CO2 reduction efficiency.(2)Engineering the metal node in MOFs,the 3D bimetallic Zn/Co-ZIFs with similarly topological structures were fabricated for photocatalytic CO2 conversion.Note that,a high photocatalytic CO2 reduction to CO of 24.42 umol/h and selectivity of 81.4%(vs.H2)were achieved under[Ru(bpy)3]Cl2 photosensitizer,which the activity of Zn/Co-ZIFs is 14 times higher than the original Zn-ZIF-8.This enhanced catalytic activity of Zn/Co-ZIFs was attributed to the optimized electronic structure of the synergistic effect sites in the bimetallic ZIFs structures by engineering of the dual metal nodes.MOFs possessed large surface area and high density of metal active sites,which was capable of supplying a wide place for breaking chemical bonds and minimizing electronic transfer limitations.(3)A hierarchical ZnIn2S4-CdS heterostructures were prepared through a facile two-step method,which confined CdS quantum dots uniformly on the surface of 3D ZnIn2S4 nanoflowers.ZnIn2S4-CdS composites presented an excellent catalytic performance for CO2 photoconversion to CO under visible-light irradiation.The obtained hierarchical heterostructure could significantly enhance the multiple light harvesting and shorten the migration distance of carriers,thus leading to a high efficiency on interfacial charge transfer.Besides,fs-TA demonstrated that the well-dispersed CdS QDs on the surface of ZnIn2S4 might open a preferential channel for the photoinduced carriers transfer in the hybrid system and boost the surface charge dynamics.(4)Constructing uniformly distributed Mn sites on two-dimensional nitrogen-doped carbon(2D Mn-N-C)can be realized by pyrolyzing the Mn-doped Zn-ZIF at high temperature with the assistance of NaCl.2D Mn-N-C achieved a high CO2 electroreduction activity and superior CO selectivity over 90%at an overpotential from-0.5 V to-0.7 V(vs.RHE),which was higher than the samples without Mn doping and NaCl assistance when other synthetic parameters were not changed.The distributed Mn sites decorating 2D structures could strength CO2 activation with interconnected nitrogen-doped carbon structure synergistic efect for CO2 electroreduction.