Study On Preparation And Performance Of Oxygen Reduction Reaction Electrocatalysts From Different Raw Materials

The sluggish oxygen reduction reaction（ORR）at fuel cell cathode often relies on highly active electrocatalyst to be expedited.As can effectively activate oxygen-oxygen double bonds,platinum（Pt）-based materials are state of the art ORR electrocatalysts,but their high price,low reserves,and poor stability hinder the large-scale application of fuel cells.Therefore,it is meaningful to develop efficient non-noble metal electrocatalysts and to study their structure-activity relationship.Among them,the carbon-based non-noble metal electrocatalysts（CNPC）composed of conductive carbon networks,transition metals and heteroatoms have wide raw materials,easily constructed and adjusted active centers.To make full use of resources,herein,the inexpensive sulfonated cobalt phthalocyanine,Enteromorpha and coal/heavy oil co-refining residue（COVR）with transition metals or nitrogen（N）,sulfur（S）heteroatoms are selected as carbon-based raw materials to prepare highly efficient CNPC by reasonable activation and doping.The electrocatalysts are characterized by TEM,XRD,Raman,XPS,N₂ adsorption-desorption and electrochemical tests,and the relationship between electrocatalyst structure and ORR performance are studied.Firstly,sulfonated cobalt phthalocyanine（Co Pc-SO₃H）with clear molecular structure is coated on the outer wall of carbon nanotube（CNT）to prepare Co Pc-SO₃H/CNT electrocatalyst.The ORR half-wave potential（0.78 V）is higher than that of Co Pc/CNT（0.77V）without sulfonic acid group（-SO₃H）,and close to that of 20%Pt/C（0.85 V）.The research demonstrates that the CNT reduces the charge transfer resistance,while the S doping introduced by-SO₃H modulates the electronic structures of Co-N_x active centers,thus improving the ORR performance.To apply the above electronic regulation to general carbon-based raw materials,biomass Enteromorpha is selected to prepare HT-950 electrocatalyst with N,S self-doping,C-S-Zn coordination and rich micro/mesopores by zinc chloride（Zn Cl₂）activation.The ORR half-wave potentials（0.86/0.65 V）of HT-950 under alkaline and acidic conditions are higher than that of HTS-950（0.82/0.57 V）without C-S-Zn structures,and comparable to that of 20%Pt/C（0.85/0.80 V）.The research proves that the C-S-Zn structures provide abundant defect sites and regulate the electronic structures of active centers,thus enhancing the ORR activity.Based on the above experience in pore structure and active site construction,intractable COVR is selected to prepare Fe,N,and S-dopped CZ-MN-KOH-800 electrocatalyst with large specific surface and rich micro/mesopores by potassium hydroxide（KOH）activation and melamine doping.The ORR half-wave potentials（0.82/0.62 V）of COVR-based electrocatalyst under alkaline and acidic conditions are higher than that of its toluene solubles（0.78/0.53 V）or insolubles（0.79/0.60 V）-based electrocatalyst,and close to that of 20%Pt/C（0.85/0.80 V）.The research demonstrates that the asphaltenes in toluene solubles,the mineral templates and Fe-containing active species in insolubles have synergistic effects on the improvement of ORR performance.