Construction,Application And Mechanism Clarification Of Confined Non-Precious Metal Electrocatalysts

Nowadays,single-atom catalysts(SACs)have achieved superior catalytic performance with maximum(100%)metal-utilization efficiency.However,the heat treatment process of these catalysts is much complex.In this case,their local configuration is rarely well-defined for the unpredictable transformation.Thus,SACs are not ideal models for clarifying the structure-function relationships.In this paper,we mainly focus on the confined electrocatalysts with clear structure and isolated active sites.To be more exactly,we have effectively disaggregated molecular aggregates through a facile and green synthesis,and actualized a series of heterogenized single-molecule catalysts with maximum molecule-utilization efficiency.Moreover,we have designed a synthetic method to control the structural transformation,which makes the pyrolysis process predictable.Besides,we largely overcome the shortcomings of traditional metal phosphate catalysts,such as crystal agglomeration,poor conductivity,and unsatisfactory catalytic specificity.The main research results are as follows:(1)The DNA has two functional building blocks of nucleobases and phosphate backbone.The nucleobases of adenine(A),guanine(G),cytosine(C)and thymine(T)bases can tightly bind to rGO through ?-? interaction,while the phosphate backbone can attract the central metal ions of metal complex.Based on such Janus property,we have utilized DNA as a mediator to indirectly anchor a single molecule onto the conductive graphene support(FePc-DNA-rGO).In addition,the one-step hydrothermal synthesis is quite facile and environmentally friendly.Notably,we have made a significant breakthrough in using aqueous poor solvent for inhibiting the secondary aggregation of dispersed single molecules.What's more,this heterogenized single-molecule catalyst has high activity in oxygen reduction reaction,and can achieve high power density comparable to commercial Pt/C(20 wt%),even if the metal loading is extremely low.Meanwhile,this model catalyst has well-defined structure and uniform catalytic sites.Moreover,the in-situ XANES spectra of Fe K-edge have revealed Fe3+/Fe2+redox potential is the driving force for oxygen activation.Furthermore,theoretical calculations indicate an unoccupied dz2 orbital of Fe center generate after the coordination by DNA group,which is favorable for O2 adsorption.In a word,this disaggregation mechanism indeed weakens the intrinsic ?-? interaction between molecular aggregates,and is also applicable in other metal complex,such as metallophthalocyanines and metalloporphyrins.Hence,these results are significant for other electrocatalysis to construct a single-molecule catalyst.(2)The phosphate group of DNA can attract the central metal ions.Based on this characteristic,we control DNA to absorb metal ions on graphene support and in-situ grows Fe2Co(PO4)2(OH)2 crystals.After heat treatment,Fe2Co(PO4)2 particles riveted on graphene support actualize.This synthetic method could control the structural transformation and further makes the heat treatment process predictable.Additionally,due to the strong absorption by DNA and steric effect,metal centers are confined in local part.Compared with other traditional metal phosphates,metal phosphates riveted on graphene support have overcome numerous problems,like crystal agglomeration,poor conductivity,and low catalytic specificity.To be more exact,metal phosphates confined on graphene support have isolated catalytic sites.Besides,the flower-like Fe2Co(PO4)2 crystals have more active area for catalysis.Furthermore,this composite has inherited the advantages of graphene and can achieve high specific surface area up to 540.3 m2 g-1.