Molecular Spacing Optimizes The Spatial Distribution Of Single Co Sites For Improving Electrocatalytic Oxygen Evolution

Using electrocatalytic water splitting to transform discontinuous renewable power resources into hydrogen energy,which is green and convenient for storage and transportation to alleviate the global energy crisis and environmental pollution,has become important research in the field of energy chemistry.Full realization of this promising energy conversion technology depends on the development of high performance electrocatalysts.The research progress of single atom（-site）catalysts（SACs）provides a new solution for the design of efficient electrocatalysts with atomic economy and accuracy.In addition to well-defined local coordination environment,controllable spatial active structure and durability under harsh conditions remain great challenges for SACs.Metal phthalocyanine（MPc）based compounds are a kind of natural SAC,with excellent electron transfer and mass transport ability,controllable structure and excellent stability.The Pc ring can coordinate with almost all metal atoms in the periodic table,and has a clear and uniform M-N4 central structure as well as excellent catalytic activity.Compared with SACs formed by traditional pyrolysis,MPc has more definite coordination structure and local electronic state,which is more conducive to the design of catalysts and mechanism analysis.In this thesis,cobalt tetraaminophthalocyanine（Co Pc-NH2）was used as a single-atom building block and pyromellitic dianhydride,1,4,5,8-naphthalenetetracarboxylic dianhydride and 3,4,9,10-perylenetetracarboxylic dianhydride were used as linking spacers.A series of molecule-spaced single atom site catalysts（ms SACs）have been reported to regulate the spatial distribution of discrete metal phthalocyanines with a single Co site.The molecular spacing strategy can significantly improve the effective activity density,mass transfer as well as electrocatalytic durability.At the same time,in situ polymerization with carbon nanotubes can significantly weaken the stacking effect,increase the overall charge transfer ability of the catalysts and regulate the intrinsic activity of metal single atomic sites.The experimental results show that shorter spacer molecules lead to exposing more active sites per unit area,that is higher activity density.The metal phthalocyanine-based catalyst ms SAC@CNT connected with pyromellitic dianhydride showed excellent OER performance on the glass carbon electrode,with an overpotentialη10=268.4±0.7 m V at 10 m A·cm^-2,and exhibited an outstanding mass activity of 162570.7±1370.6 A·g^-1 and TOF of 27.7±4.6 s^-1 at 1.58 V（versus RHE）.Even under simulated industrial conditions（6 M KOH,50^oC）,the catalyst can still maintain the ultra-high current density of 2.0 A·cm^-2 at a low overpotential of 0.32V for at least 105 h.DFT calculations show that ms SACs loaded on carbon nanotubes enhance electrocatalytic oxygen evolution performance with higher electron transport rates and optimized adsorption of the intermediate O*.Furthermore,a variety of spectral techniques and theoretical simulations showed that spacer molecules themselves did not have a significant effect on the electronic structures of the phthalocyanine core metal atoms,and the difference in catalytic performances mainly stems from the difference in the density of active sites caused by spacer molecules with different lengths.Therefore,this study demonstrates that the spatial distribution of single atom sites can be another important parameter to further enhance the overall performance of catalysts.