| The limited reserve of non-renewable fossil fuels and the global warming motivate people to find effective ways that can reduce depletion of the conventional fuels and mitigate CO2 emissions.Among the developing approaches,reduction of CO2 is the most attractive solution,which can change CO2 into useful fuels directly.However,the selectivity and efficiency of catalysts are very low,which prohibit the development of CO2 reduction.In addition,the reaction mechanisms of different products are still in debate since that the most promising pathways are not clear and the main active intermediates are controversial.It is well accepted that the reaction circumstance has an essential effect on the reactions.But the solid-liquid interfaces are unclear,which prohibit the development of CO2 reduction.Finding effective catalysts is the biggest chanllege.Understanding of the reaction mechanisms is basic study to find the effective catalysts.Effective descriptors can be evoluted based on the correct reaction mechanisms,which can accelerate the process to find effective catalysts.Although many excellent reseachers have devoted to study the reaction mechanisms,the effect of reaction circumstance,and effective decripotrs for CO2 reduction,there are still many issues to be addressed.We have built different models with solid-liquid interface.Further we studied the reaction mechanisms of different products for CO2 reduction based on these models.We give the most promising reaction pathway for different products and reveal the effect of reaction circumstance.Moreover,we have proposed the effecitive descriptors for CO2 reduction and did some predications for the promising alloy catalysts.This thesis expands these contents and are mainly divided into the following four parts:1.Mechanistic insights into the unique role of copper in CO2 electroreduction reactions.Cu has an unique capability towards CO2 electroreduction that can close the anthropogenic carbon cycle.However,its reaction mechanism remains elusive,owing to the obscurity of the solid-liquid interface on Cu surfaces where the electrochemical reactions occur.Using a genetic algorithm method,we explicitly identify the configuration of a water bilayer on Cu(211).These enable us to reveal a mechanistic picture for CO2 electroreduction,and find that the key intermediates are CCO* and CH* for the formation of C2H4 and CH4,and rationalize a series of experimental observations.Furthermore,we find that the interplay between the Cu surfaces,carbon monomers,and water network(but not the binding of CO*)essentially determine the unique capability of Cu towards CO2 electroreduction.Moreover we propose a new and effective descriptor for exploiting optimal catalysts.2.Electroreduction of CO2 to formic acid on Cu: Role of water bilayer in modeling electrochemical interface.Solid-liquid interface,which is the location that the electrochemical reaction occurs,is essential for CO2 reduction.However,different theoretical calculations often use different models and predict the conflicting mechanisms.To address this issue,we adopt different structures of solid-liquid interface to mimic the reaction circumstance.We find that the reaction barriers and energies are sensitive to the changes of reaction circumstance,such as the state of water molecules,the number of water molecules,whereas the selectivity of CO2 reduction can be hardly changed once a water bilayer network on Cu surface is used.In particular,a solid-liquid interface built from 4-6-4 water rings(5H2O/1H)can present an appropriate description of the solvent.The predicted pathway of HCOOH is consistent with the experimental results.3.Theoretical studies on the CO2 reduction to CH3 OH on Cu(211).Methanol synthesis from CO2 hydrogenation over Cu-based catalysts play an important role in the chemical industry.However,the reaction mechanism and key reaction intermediates of this process are still unclear.To address these issues,we studied the methanol formation process from CO2 hydrogenation process by using density functional theory(DFT),finding that the most effective pathway proceeds along the reaction series CO* → CHO* → CH2O* → CH2OH* → CH3OH* with the reactive intermediate CH2O*,which is consistent with experimental finding.Additionally,we find that water molecules play an inhibiting role in the reactions.These findings shed light on the reaction mechanism of CH3 OH formation from CO2 hydrogenation and reveal the effect of H2 O in this reaction.4.Effective descriptors for CO2 electroreduction on metal catalysts and predication of highly efficient and selective catalysts.CO2 electroreduction is an effective way to change the green-house gas,CO2,into value-added hydrocarbons.But the high overpotential prohibits the development and the practical application of CO2 electroreduction.Finding effective catalysts is the toughest challenge in this field.Effective descriptors give the useful and resultful direction to find the promising catalysts.Based on the experimental and theoretical results we propose two effective descriptors,the CO2/CO adsorption energy descriptor and the dynamic/thermic property of single C descriptor.The former one is a comprehensive descriptor for different products(CO,HCOOH,CH4/C2H4),while the latter one is special for the selectivity of CH4/C2H4.Coupling with the descriptors we did some predications of the alloy catalysts.These results shed lights on the development of CO2 reduction. |
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