Research On Nickel Phthalocyanine-tetrasulfonic As Co-catalyst For Methanol Electro-oxidation On Pt/C

Pt-Ru catalysts are usually employed as anode catalyst in direct methanol fuel cell (DMFC). Though the Pt-Ru catalyst exhibited high methanol electro-oxidation activity, there is still room for improvements:(1) higher catalytic activity for methanol electro-oxidation and (2) replacement of expensive novel metals, Pt or Ru. Nickel phthalocyanine-tetrasulfonic acid (NiPcTs) was considered to be a candidate to replace Ru. In this paper, we illuminated the function of NiPcTs for methanol electro-oxidation on Pt/C and found that NiPcTs plays a major role by modifying Pt electronic density. Therefore, we should improve the preparation method and structure of catalyst to achieve higer avtivity. Then the Pt/C catalyst with NiPcTs-decorated was prepared by the colloid method. The structure and performance of the prepared catalysts were characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet visible detector (UV-vis) , X ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) respectively. The experimental results and conclusions are summarized as following:(1) NiPcTs has no activity for methanol electro-oxidation, but the presence of NiPcTs enhances the catalytic activity of Pt/C on methanol electro-oxidation. The promotion of CO_ads is electro-oxidation should be responsible for the methanol oxidation enhancement. The function of NiPcTs for the promotion of CO_ads electro-oxidation on Pt/C owes to that the presence of NiPcTs plays a major role by decreasing Pt electronic density, which will decrease the extent of back-donation of electron from Pt to anti-bonding orbital of C, resulting in the weaker Pt-CO bonding and easier CO_ads electro-oxidation.(2) Pt Nano-particles decorated with substituted phthalocyanine were successfully synthesized with chemical reduction. The test result of XPS showed that Pt particles were existed as Pt atoms. TEM showed that the resulting particles were homo-dispersed with support of NiPcTs, and its average diameter is about 3.7 run. It was detected by Uv-vis that there exist two processes of Pt⁴ reduction, the first process is reduction of Pt⁴ to Pt² and the second process is reduction of Pt² to Pt⁰. The appropriate reaction time for Pt⁴ reduction is 30 minutes.(3) The colloid of Pt Nano-particles decorated with NiPcTs was supported by XC-72 carbon. The better performance for methanol oxidation was achieved on the catalyst prepared by colloid method than by impregnate method, for the backward anodic peak was not appeared and the potential of methanol oxidation peak was decreased on the catalyst prepared by colloid method. The tafel slope of the two were equal in the rough, lower than the tafel slope of Pt/C. The electrochemical accelerated durability test showed that NiPcTs-Pt/C is stable in the electrochemical situation.(4) Density Functional Theory (DFT) calculations have been applied to investigate reaction mechanisms. It was found that the adsorption of CO on Ni-Pt alloy was weakened slightly as compared to pure Pt. CV was carried out in NiPcTs solution from 0.1 V to 1.2 V, NiPcTs was not electrolyzed. Hence, the function of NiPcTs is the essential element for the promotion of methanol electro-oxidation on Pt/C.