Research On Reactive Hydrogen Regulation Using Water As A Hydrogen Source And Electrocatalytic Hydrogenation Performance Of Carbonyl Compounds

The catalytic hydrogenation of carbonyl compounds（such as biomass aldehydes/ketones,carbon dioxide,etc.）represents a significant pathway for upgrading carbon resources.The hydrogenation of carbonyl compounds predominantly depends on thermal catalytic approaches,commonly employing hydrogen gas as the source of hydrogen,often necessitating elevated temperatures and pressures.Recently,electrocatalytic hydrogenation technology,driven by renewable energy sources like solar and wind power and directly utilizing water as the hydrogen source,has garnered considerable attention.In electrocatalytic hydrogenation of carbonyl compounds,the the pivotal aspect resides in controlling the catalyst to activate water at the cathode into reactive hydrogen intermediates（H*）,while achieving selective hydrogenation through controllable adsorption of carbonyl groups in substrate molecules.Although there have been some reports in this field,several challenges persist:（1）The activation of water molecules on the cathode surface to produce H*often leads to the competitive hydrogen evolution reaction,reducing the Faradaic efficiency.Achieving precise control over H*on the cathode surface remains challenging.（2）In the electrocatalytic hydrogenation process of carbonyl compounds,the adsorption of carbonyl groups from reactants onto the catalyst surface dictates the selectivity of electrocatalytic hydrogenation products through the configuration and strength of adsorption.（3）Competition arises between the production of H*and the adsorption of substrates on a single catalyst surface.For instance,excessive adsorption of carbonyl groups may occlude H*production sites,thereby reducing the reaction rate.Balancing the production and reaction of reactants and H*on the catalyst surface generates a significant challenge as well.Addressing the aforementioned issue,this dissertation focuses on the design of water-based electrocatalytic hydrogenation catalysts for carbonyl compounds and undertakes innovative research involving two typical gas/liquid-phase reactants,carbon dioxide（CO₂）,and 5-hydroxymethylfurfural（HMF）.Firstly,by designing the structure of catalyst（including mesoporous and grain boundary structures）,we achieve the regulation of carbonyl adsorption and H*production capabilities,thereby enhancing selectivity and Faradaic efficiency in electrocatalytic CO₂/HMF hydrogenation.Furthermore,to address the competitive issues of substrate adsorption and H*generation on the catalyst surface during the reaction process,composite catalysts are constructed with a directed design of H*production sites and carbonyl adsorption sites,significantly boosting the reaction rate of CO₂/HMF electrocatalytic hydrogenation.Additionally,a series of electrochemical in situ experiments combined with DFT theoretical calculations reveal the regularities between H*generation,carbonyl adsorption,and product selectivity during the CO₂/HMF electrocatalytic hydrogenation process.The main research contents and results of this thesis are as follows:1.Research on the regulation of reactive hydrogen with water as hydrogen source and the performance of CO₂ electrocatalytic hydrogenation（1）Research on the performance of mesoporous bismuth subcarbonate for CO₂ electrocatalytic hydrogenation:CO₂,as a waste carbon resource,can be effectively transformed into formate through electrocatalytic hydrogenation（CO₂ER）,which is a valuable strategy to enhance its utilization.However,as a typical gaseous molecule,CO₂ has limited solubility in water,and the ability to adsorb CO₂ of catalyst significantly influences the reaction rate during CO₂ER.In this work,we synthesized a precursor of Bi-MOF via electrochemical deposition and further reconstructed it through in-situ electrochemical reduction to obtain mesoporous bismuth subcarbonate catalyst（MP-BOC）.The study indicates that the unique mesoporous structure of MP-BOC can effectively promote the adsorption of CO₂,and the exposed Bi sites can achieve selective adsorption of CO₂ carbonyl groups,thereby significantly enhancing the reaction rate of CO₂ER and the selectivity towards formate.The formate current density of MP-BOC is 1.6-fold higher than that with BOC.(55.74 m A cm^-2 vs.33.82 m A cm^-2@-1.16V vs.RHE).The MP-BOC catalyst exhibits a high formate FE of>80%in a wide potential window from-0.62 to-1.12 V vs.RHE.（2）Research on the performance of Ag/BOC composite catalyst for CO₂ electrocatalytic hydrogenation:In response to the competition between the generation of H*on the surface of a single catalyst and CO₂adsorption,this study prepared a composite catalyst of Ag nanoparticles loaded on bismuth subcarbonate carbonate（Ag/BOC）,where Ag acts as the site for water activation to produce H*,and BOC serves as the carbonyl adsorption site for CO₂.The CO₂ electroreduction（CO₂ER）reaction rate of Ag/BOC was 2-fold higher than the pure BOC catalyst,resulting in a formate Faradaic efficiency（FE）of over 98%.The formate FE could be maintained above 85%in a wide potential window（-0.86 to-1.26V vs.RHE）.Experimental and theoretical results show that Ag on the surface of the composite catalyst can promote the splitting of water to generate H*.Additionally,due to the low binding energy of Ag-H*bonds,it is advantageous to transfer H*to nearby Bi sites,promoting its hydrogenation process with CO₂ adsorbed on Bi sites to generate formate.Finally,a novel CO₂ER coupled glycerol electrooxidation reaction system was designed,achieving simultaneous production of formate（salt）at both cathode and anode in a homemade flow electrolysis cell.Compared to traditional CO₂ER coupled oxygen evolution reaction systems,the energy consumption per mole of formate（salt）produced can be reduced by 63%.2.Research on the regulation of reactive hydrogen with water as hydrogen source and the performance of HMF electrocatalytic hydrogenation（1）Resrarch on Cu-based catalysts rich in grain boundaries for HMF electrocatalytic hydrogenation:HMF is an important liquid-phase biomass platform compound,which can be transformed into high-value-added 2,5-dimethylfuran（DHMF）through electrocatalytic hydrogenation.However,current research still faces challenges such as low reaction rates and poor DHMF selectivity/FE.In this work,a strategy of alternating potential electrodeposition was employed to prepare Cu catalysts rich in grain boundaries（GB-Cu）,significantly enhancing the performance of HMF electrocatalytic hydrogenation to produce DHMF.The production rate of DHMF was increased by 3-8 times compared to pure Cu,and the FE of DHMF was increased by 3 times(90.23 m A cm^-2 vs 29.49 m A cm^-2@-0.62 V vs.RHE).Moreover,the GB-Cu catalyst exhibited excellent performance in selectively hydrogenating a series of aldehyde-ketone compounds and their derivatives to produce corresponding alcohol products.Series of electrochemical tests and in-situ characterization results demonstrated that grain boundaries in the GB-Cu catalyst promoted the splitting of water to generate H*.Additionally,GB-Cu facilitated the selective adsorption and activation of carbonyl groups in HMF,thereby catalyzing hydrogenation reactions with HMF via the Langmuir-Hinshelwood mechanism（L-H mechanism）.Furthermore,to address the deactivation issue of the catalyst after prolonged reaction time,a strategy of oxidative-reductive alternating potential cycling was further employed to achieve in-situ reconstruction of the surface grain boundary structure of the Cu catalyst,thereby restoring the electrocatalytic hydrogenation performance of HMF.（2）Research on Ag/SnO₂ composite catalyst for electrocatalytic hydrogenation of HMF:Addressing the issue of competition between H*generation and HMF adsorption on the surface of a single catalyst,this work parpared Ag nanoparticle-loaded and oxygen vacancy-rich tin oxide nanosheet arrays（Ag/SnO₂）,where Ag serves as the site for H*generation and oxygen vacancies on SnO₂ surface act as the adsorption sites for carbonyl groups in HMF.The Ag/SnO₂ composite catalyst achieved efficient electrocatalytic hydrogenation of HMF,with a reaction rate enhancement of 1.9 times(1276μmol cm^-2 h^-1 vs 650μmol cm^-2 h^-1m A cm^-2@-1.12 V vs.RHE),and maintained DHMF FE above 95%over a wide potential window（from-0.62 to-1.12 V vs.RHE）.Series of electrochemical tests and in-situ characterization results demonstrated that Ag could promote water splitting to generate H*,which then reacted with HMF adsorbed on the surface of SnO₂ via the L-H mechanism to produce DHMF.Additionally,Ag facilitated the formation of oxygen vacancies on SnO₂,which acted as electrophilic sites enabling selective adsorption and activation of carbonyl groups in HMF.Finally,to address the slow kinetics of the anodic OER process during HMF electrocatalytic hydrogenation,a coupled reaction system of HMF electrocatalytic hydrogenation and oxidation was designed,achieving co-production of DHMF and 2,5-furandicarboxylic acid（FDCA）,further enhancing the reaction’s economic viability...