Study On The Electrocatalytic CO₂ Reduction Performance Of Carbon-supported Metal Single Atoms Regulated By Stress And Surface Functional Group

Electrocatalytic CO₂ reduction（ECR）is an effective way to convert CO₂ into high value-added chemicals using electricity as the driving force,and to achieve interstitial renewable electricity to chemical energy storage and maintain global carbon balance.Metal-atom materials based on the ligand stabilization of carbon carriers are promising ECR catalysts with maximum atom utilization and tunable electronic structure properties.At present,the modulation of the intrinsic activity of carbon-loaded single atoms is relatively single,mainly including heteroatom doping,introduction of defects,and construction of bimetallic atomic sites,etc.Different coordination numbers,different coordination spaces and interactions with reactants of single atoms can lead to different catalytic performance,and it is important to explore new means of activity modulation for the development of such catalysts.In this thesis,we develop new methods for the preparation of carbon-loaded monoatoms,explore the ways to modulate the intrinsic activity of monoatomic sites through the bending stress and surface functional groups of carbon carriers and reveal the mechanism of their performance enhancement,as follows:（1）A new method for the preparation of carbon-loaded Ni monatoms（Ni-N/CNT@CTF）based on the residual Ni particles in ultrathin covalent triazine framework（CTF）thermally activated carbon nanotubes（CNT）was developed.Theoretical calculations show that the compressive stress provided by the high curvature CNT surface can optimize the electron spin structure of Ni-Nx sites,promote the adsorption and desorption energy of Ni atoms to ECR reaction intermediates and enhance the electron transfer capability from Ni atom sites to CO₂,thus enhancing their ECR activity.The optimized Ni-N/CNT@CTF exhibited a stable FEco of 96%at a potential range between-0.6 V and-0.9 V.The performance of Ni-N/CNT@CTF electrolyzer was stable for 10 h at 21.54 m A cm^-2.The flow electrolytic cell prepared on the basis of CNT@CTF can obtain a high current density of 201 m A cm^-2 with a FEco of 92%.（2）A series of hydroxyl（OH）,and vertical pyridine N groups in different spatial positions were explored with functionalized reduced graphene oxide（RGO）immobilized cobalt phthalocyanine（CoPc）catalysts.The intrinsic activity of the non-homogeneous catalysts in the ECR reaction species was explored by means of secondary coordination modulation of the functionalized carbon carriers.The results show that OH with intercalation sites can stabilize the active medium by adsorption with synergistic sites compared to the absence of groups,while pyridine N increases the proton concentration around the active site as well as H-bonding promotes electron conduction to enhance the ECR performance（OH+N>OH>N）.It was shown that the Co-RGO-OH₃+N catalyst with dual synergistic sites exhibited a partial fractional current density of 22.5 m A cm^-2 and up to 97.8%FEco in the ECR reaction for CO,as well as a stable performance over 8 h.