Research On Preparation Of ZIF-12 Derived Materials And Electrocatalytic Properties

With the consumption of fossil energy and rising temperatures causing a series of environmental problems,fuel cells and metal-air cells are becoming highly regarded as low-carbon energy supply devices due to their high efficiency and low pollution characteristics.The oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）are the key electrochemical reactions in fuel cells and metal-air batteries.The use of expensive and limited reserves of precious metal electrocatalysts（Pt/C,Ru O₂）for both reactions have ultimately prevented their further commercial application.In this paper,ZIF-12-derived Co-N-C electrocatalysts with low cost,high activity and high stability were designed and prepared,and the relationship between the physicochemical properties of Co-N-C materials and their electrochemical performance was analyzed.The main research results are as follows:（1）A Na₂SO₄-assisted pyrolysis strategy with ZIF-12 as the precursor is reported for the synthesis of cobalt,sulfur,nitrogen,co-doped carbon（Co SNC-x Na₂SO₄-T）catalyst.Different from Co NC-800 derived from pure ZIF-12,with the presence of Na₂SO₄,the derived Co SNC-0.5Na₂SO₄-800 exhibits layered flake morphology with hierarchical meso-microporous structure.Besides,Co SNC-0.5Na₂SO₄-800 shows higher content of pyridinic-N and graphitic-N,higher relative intensity of Co-N_x,higher content of carbon defect,as well as larger specific surface area in comparison with Co NC-800,which results in higher activity of Co SNC-0.5Na₂SO₄-800.The Co SNC-0.5Na₂SO₄-800 displays a half-wave potential of 0.88 V,which is superior to that of20%Pt/C（0.86 V）.Moreover,Co SNC-0.5Na₂SO₄-800 demonstrates a better durability compared with Pt/C.（2）A simple compound-assisted pyrolyzing strategy is used to synthesize Co-N-C（Co NC-xcompound-800）materials by high-temperature annealing of ZIF-12.With the introduction of organic compound(i.e.,C₃H₆N₆,C₆H₁₄O₆,C₁₆H₃₂O₂,CH₃（CH₂）₁₆COOH,C₆H₅NO₃),the specific surface area,the carbon defect content,the content of pyridinic-N and graphitic-N,and the Co-N_x concentration of the obtained Co NC-0.5compound（organic）-800 are increased,which result in the improved activities of the 0.5compound（organic）-800 samples.Differently,with the addition of inorganic compound（i.e.,Na₃PO₄,KCl,K₂CO₃）,the carbon defect content,the content of pyridinic-N and graphitic-N,and the Co-N_x concentration of the obtained Co NC-0.5compound（inorganic）-800 are decreased,which lead to reduced activities of the0.5compound（inorganic）-800.Among these materials,the Co NC-0.5C₆H₁₄O₆-800shows satisfactory ORR performance with a half-wave potential of 0.89 V.Meanwhile,Co NC-0.5C₆H₁₄O₆-800 exhibits an optimal OER performance with an overpotential being only 425 m V at current density of 10 m A cm^-2.