Preparation And Catalyst Performance Of Polymer Metallo-phthalocyanine Catalysts

Direct methanol fuel cell (DMFC) as one kind of the fuel cells has become a hot spot because of its high energy density and non-polluting. But many problems limit its development. one of them is the high cost of Pt/C, and the other is the "methanol crossover" which is leading to the decay of the battery. Therefore the development of efficient methanol-tolerant cathode non-platinum catalyst is pivotal to resolve these problems. Highlyπ-conjugated macrocyclic system of phthalocyanine complexes provides the basic framework for the electron transfer, as non-platinum catalyst, it posesses very important significance in DMFC research. However, the correlated research shows that the monomer phthalocyanine is not stable in acidic conditions, and it is easy to break down.The search for a more active and stable TMM catalyst has thus become an important topic in this area.In this work, two kinds of metallo-polyphthalocyanine (MPPc) are synthesized, one is planar-conjugated metallo-polyphthalocyanine by polymerizing M(II)-4,4',4",4' phthalocyanine tetracarboxylic acid (TcPcM) in argon (Ar) atmosphere. The other is controllable-pore size metallo-polyphthalocyanine(CPMPPc). In the process of synthesis controllable pore size metallo-polyphthalocyanine,4-nitrophthalonitrile, bisphenol-A and hydroquinone are used as materials to synthesize two bridge structures of phthalonitrile. Two kinds of phthalonitrile, acetate cobalt and ammonium sulfate, acetaminophen are used to obtain corresponding metallo-polyphthalocyanine.Two kinds of novel catalysts are prepared by dispersing metallo-polyphthalocyanine (MPPc) a high surface area carbon powder (Vulcan XC-72), and then heat-treated in Ar atmosphere, all of these MPPc and MPPc/C catalysts are characterized systematically by a variety of methods, such as UV-Vis, FT-IR, TG, XRD, XPS and TEM. Results show that the MPPc obtained is stable below 600℃. The active site of MPPc/C was M-N4 in phthalocyanine ring, and the MPPc was dispersed homogeneously on the surface of XC-72. Electrocatalytic properties and electrochemical stability of the catalysts in 0.5 mol L-1 H2SO4 are evaluated by RDE measurements. The initial potential for O2 reduction in O2-saturated H2SO4 is 0.81 V and it catalyzed O2 reduction mainly through a 4-electron process. Almost no performance degradation is observed over continuous cyclic voltammetry (CV) at 10,000 cycles (4 days). Polarization curves obtained by linear sweep voltammetry (LSV) at 200 cycles also showed no change. MPPc/C catalysts displayed significant electrocatalytic performance for O2 reduction, tolerance towards methanol, and long-term stability. It is interesting that the PPcCo&Fe/C (TcPcFe:TcPcCo=1:1) catalyst show startling catalytic activity. The initial potential for O2 reduction is 0.93 V which is similar to Pt/C, the reason is the synergistic catalyst effect between different metal ion in a common conjugated system.The electrochemistry test result of CPMPPc/C catalyst indicates that CPMPPc/C heat-treated at 400℃, with the ratio (polyphthalocyanine:C) 1:1 possess the highest catalytic activity in 0.5 mol/L H2SO4. LSV at different electrode rotation rates led to determine the Koutecky-Levich plots from which it is shown that the kinetic parameters for the ORR are aroud 3.5 (mainly 4-electron process). Long-term test results show that this kind of catalyst also possess good long-term stability.