Controllable Synthesis Of Pd/Cu-based Nanomaterials And Their Performance In Electrocatalytic Ethanol Oxidation And CO₂ Reduction

A roadmap for carbon neutrality using excess renewable electricity has attracted attention.To date,Cu-based catalysts have shown great potential for the electrochemical reduction of carbon dioxide（CO₂）to synthesize high-value polycarbon（C+）products.However,the selectivity and activity of Cu materials for electrocatalytic CO₂ reduction reactions（CO₂RR）are often difficult to control.The main obstacle to obtain high valueadded products from CO₂ is the coupling of C-C bonds,and the introduction of limiting effects to protect the Cu sites and reduce the loss of carbonaceous intermediates is considered to increase the C-C bond coupling and improve C2 selectivity.Meanwhile in recent years,providing clean energy through electrocatalysis is a popular way to optimize the energy mix.However the ethanol oxidation reaction（EOR）as the anode of direct ethanol fuel cells is usually incomplete and produces a large amount of byproducts instead of CO₂.the pathway that transfers only 4 electrons to produce CH3COOH/CH3COO-is called the C2 pathway.the presence of the C2 pathway greatly hinders the 12-electron transfer pathway that produces CO₂/CO32-（C1 pathway）.Optimizing the adsorption energy of the catalyst to the intermediate,or stabilizing OH adspecies（OHads）to accelerate the oxidation of the intermediate is a feasible option to improve C1 selectivity.The C1 selectivity of Pd-based materials can be optimized by introducing other metals（e.g.Au,Co,Bi,Ni,etc.）.This thesis focuses on improving the C2 selectivity of CO₂ RR by using mainly hollow mesoporous carbon spheres to provide protection to the active site Cu and provide a nano-limiting effect to confine the intermediates and thus promote the C-C bond coupling.Metal carbides are introduced into Pd-based materials through heterostructures,which stabilize the materials while providing Lewis acid-base pairs to change the adsorption energy of intermediates,accelerate the oxidative desorption of intermediates to improve C1 selectivity and improve EOR and electrocatalytic glycerol Oxidative（GOR）activity:1.We propose a method to probe the selectivity/activity of Cu-catalyzed CO₂ RR using the precise atomic ratio/valence of Cu clusters,and synthesize Cu12/HMCS material.The R-Cu12/HMCS,U-Cu12/HMCS and O-Cu12/HMCS materials were synthesized under different conditions of Ar/H2 mixed gas,Ar atmosphere and air oxidation,respectively.The proposed method to probe the selectivity/activity of Cu-catalyzed CO₂ RR using the precise atom/valence ratio of Cu clusters provides a new avenue to study the effect of Cu catalysis with different valence states on the selectivity/activity of CO₂ RR.2.We present a method to confine and protect the nano-Cu in HMCS while forming confinement effect nanocavities.This can better facilitate the selective production of C2 products from electrocatalytic CO₂ reduction.The C2 Faraday efficiency of Cu/HMCS5-20% can reach 88.7% at-1.0 V vs.RHE,where the Faraday efficiency of ethylene is 68.6%.The reaction process was compared using In situ Fourier Transform Infrared Spectroscopy（in situ FTIR）and it was found that the high loading of nano-Cu confined in hollow mesoporous carbon spheres facilitates the conversion of *CO to *CHO compared to Cu/HMCS5-10% materials and the synergistic effect of the nano-cavities provided by HMCS and copper atoms of different valence numbers facilitates the formation of C2H4 and C2H5 OH.The method proposed here using nano-Cu confined by hollow mesoporous carbon spheres to improve the C2 selectivity of CO₂ reduction not only protects the nano-Cu but also provides confinement effect nanocavities that reduce the Cu dosage.This approach not only develops a new strategy for protecting Cu states and constructing confinement effects to improve the selectivity of CO₂ reduction,but also provides an attractive method to reduce the amount of Cu used for electroreduction of CO₂ into high value-added products.3.A method is proposed for the first time to construct stable Lewis acid-base pairs with good EOR activity,stability,and C1 selectivity via heterostructures of SMSI and Pd-Mx C@CNT（M = W,Mo,and Cr）.Comparison of XPS spectra before and after long electrochemical cycles showed that the introduction of Mx C successfully acted as a stable electron donor and the electron transfers from Mx C to Pd formed a stable Lewis acid-base pair.Due to the introduction of Mx C and the generation of SMSI,the Pd-W2C@CNT nanomaterials exhibit the highest mass activity（13.9 A mg Pd-1）,stability（after 20,000 s of testing,there is still a mass activity of ⁷.1 A mg Pd-1,and after 20,000 CV cycles,still retains 89.7% of the initial activity）and C1 selectivity（74.15%）.Ex-situ electrochemical tests and in-situ FTIR tests show that the formed stable Lewis acid-base pair reduces the adsorption of Pd on carbonaceous intermediates（*CO）,and W2 C can better stabilize OHads to accelerate the oxidation of carbonaceous intermediates.The rapid oxidation,adsorption and desorption of the intermediates provide the possibility to use the active site more efficiently to promote C-C bond breaking,thus improving the C1 selectivity.It is worth mentioning that Pd-Mx C@CNT（M = W,Mo and Cr）nanomaterials with stable Lewis acidbase pairs formed by introducing heterostructures of Mx C and SMSI also exhibit better activity and stability in EOR and GOR than Pd Black.Pd@CNT.This work not only developed the first stable Lewis acid-base pairs for electrocatalysis,but also The introduction of stable Lewis acid-base pairs opens up new ideas for the design of catalysts for other catalytic reactions.