The Design,Synthesis And Application Study Of Non-precious Metal-based Electrocatalysts

Searching for new sustainable energy source is one of important ways to solve the resource and environment issues that arised during the chemical pruduction process.The mutual conversion between chemical energy and electrical energy provides a new way for boosting stable and portable renewable energy.Electrocatalytic reactions play a key role in the mutual conversion between chemical energy and electrical energy.However,most commercial electrocatalysts are precious metals which can not satisfy the wide applications of energy conversion devices because of the high price and scare resource.Therefore,it is urgent to develop efficient and stable non-precious metal electrocatalysts to replace the precious metal electrocatalysts.In this thesis,focused on non-precious metal electrocatalysts,such as,cobalt-based and copper-based materials,their electrocatalytic applications in oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）were investigated,and the relationship between the structure and catalytic performance of the electrocatalyst were explored.Moreover,the theoretical calculation method was applied to predict the application of cobalt-based catalyst in CO₂ electroreduction reaction.The main contents of this thesis are listed as follows:1.Core-shell ZIF-8@ZnCo-ZIF（op-ZnCo-ZIF）was chosen as the precursor to synthesize Co,N-doped hierarchical carbon catalysts op-ZnCo-950 through pyrolysis.During the pyrolysis,the low boiling point metal Zn in the core-shell template can serve as the activation agent,and Co in the shell is therefore dispersed well in the surface of as-synthesized carbons.The resultant op-ZnCo-950 exhibits a relatively high catalytic activity towards ORR with a half-wave potential of 0.846 V vs RHE,and shows higher methanol resistance and better stability than commercial Pt/C catalyst;2.Cobalt complexes were formed by cobalt ions with different proportions of S-containing ligands and calcined to obtain cobalt-based oxides.Comprehensive analysis was performed with the assistance of systematical characterizations for the precursors and the calcinated products.All the calcinated products are proved by XRD to possess C03O4 structure feature.And XPS analysis shows that the content of divalent cobalt and oxygen vacancies both increase with the proportion of S-containing ligands in the precursors.The OER electrochemical measurement results show that the cobalt-based oxide derived from the precursor with the highest proportion of sulfur-containing ligand has the highest OER activity.This work illustrates that divalent cobalt and oxygen vacancies are beneficial for OER activities,and the contents of divalent cobalt and oxygen vacancies in cobalt-based oxides can be tuned through controlling the proportions of S-containing ligands in precursors,resulting in improved OER activities;3.Cu,N-codoped hierarchical porous carbon（Cu-N-C）with high content of pyridinic N obtained by carbonizing Cu-ZIF-8 shows excellent ORR and OER electrocatalytic properties.Both the onset potential and limited current density of Cu-N-C are almost equal to those of commercial Pt/C catalyst,and the half-wave potential（0.857 V vs RHE）is not only～16 mV higher than that of commercial Pt/C catalyst,but also higher than that of Co-based electrocatalyst mentioned in this thesis.The reaction catalysized by Cu-N-C nearly follows four-electron route,and its electron transfer number reaches 3.92 at-0.4 V.More importantly,the Cu-N-C displays better stability and methanol tolerance than Pt/C catalyst.Besides,the OER activity of Cu-N-C is also higher than that of N-C.Through systematical structure characterizations and elemental analysis,it is found that the metal-N codoping strategy can significantly enhance the activity of electrocatalyst Cu-N-C because of the resulting hierarchical structure,high pyridinic N content and the synergism of Cu and N dopants;4.A heterostructure of Ag nanoparticles decorated Cu nanowire（CuNW@AgNPs）was synthesized by relatively simple non-aqueous method.The ORR activity of CuNW@AgNPs is significantly higher than that of CuNWs,and XRD and XPS demonstrates that CuNW@AgNPs displays better oxidation resistance than pure CuNWs,which means higher stability.In addition,after exposed in air for 12 months the electrocatalyst CuNW@AgNPs-12M exhibits enhanced electrocatalytic performances for oxygen reduction reaction.The rational redistribution of charge on CuNW@AgNPs-12M caused by the synergistic effect of mild oxidation and electronegativity difference is supposed to be responsible for the excellent performance;5.Spin-polarized density functional theory calculations were carried out to study the adsorption and dissociation properties of CO₂ on size-selected Co13,Co38 and Co55 nanoclusters,and to predict the catalytic performance and size-effect of cobalt-based catalysts in carbon dioxide reduction reaction.For the adsorption of Co2,CO and o on size-selected Co13,Co38 and Co55 nanoclusters,the lowest adsorption strength is found for all the different adsorbates on Co55 nanocluster.For the dissociation of CO₂ to CO on these three Co nanoclusters,the largest Co55 nanocluster possesses the smallest reaction barrier of 0.38 eV for the dissociation of CO₂,which means the greatest catalytic activity.Results in this thesis are of fundamental interest for the design of new cobalt-based electrocatalysts for the conversion of CO₂.