Bo-Qing Xu

A feasibility analysis for alkaline membrane direct methanol fuel cell: thermodynamic disadvantages versus kinetic advantages

As the proton exchange membrane direct methanol fuel cell (PEMDMFC) faces sustaining obstacles, alkaline membrane direct methanol fuel cell (AMDMFC) is attracting increasing attention. Although some advantages may be expected, the feasibility of AMDMFC does not seem well verified. In this paper, thermodynamic disadvantages and kinetic advantages of AMDMFC are elucidated. In thermodynamic aspect, a large voltage loss due to the pH difference across the membrane is predicted by theoretical calculation; in kinetic aspect, besides the well-known superiority of alkaline media for oxygen reduction, experimental data show much higher anodic performance in carbonate/bicarbonate than in acid. In-situ FTIR measurements indicate that methanol can be fully oxidized to carbon dioxide in carbonate/bicarbonate as in sulfuric acid. Taking into account all the foreseeable advantageous and disadvantageous factors, AMDMFC is worth study, and an alkaline membrane stable at elevated temperatures is the prerequisite for a successful AMDMFC.

Nitrogen-rich Fe-N-C materials derived from polyacrylonitrile as highly active and durable catalysts for the oxygen reduction reaction in both acidic and alkaline electrolytes

Fe-N-C catalyst with a core-graphitic shell nanostructure was synthesized by pyrolysis of polyacrylonitrile (PAN)-coated carbon black in the presence of iron salts. The attained catalyst exhibits high performance towards the oxygen reduction reaction (ORR) in both acid and alkaline electrolytes, with the half-wave potentials of 97mV negative and 39mV positive to Pt/C in 0.5M H2SO4 and 0.1M NaOH, respectively. Meanwhile, the catalyst shows high stability and remarkable tolerance towards methanol. The XRD analysis demonstrates that both the introduction of iron and an increase of the pyrolysis temperature promote the growth of layers in the graphitic shell. With the rise of pyrolysis temperature, increases of the catalytic activity and Fe3+ reduction potential are observed, as well as the relative content of nitrogen of Fe-Nx type and N 1s binding energy. Moreover, a linear relationship between the logarithm of ORR turnover number and the Fe3+ reduction potential is observed. Based on these findings, the enhanced ORR performance of the catalyst can be attributed to the growth of π-conjugated graphitic layers, which modulates the electronic structure of embedded Fe-N4 sites. In addition, the presence of an accessible core-graphitic shell nanostructure facilitates the mass transport of ORR-relevant species between the electrolyte and the catalytic sites.

Electrochemical Modification of Pt/C Catalyst by Silicomolybdic Acid

Abstract Modification of conventional Pt/C electrocatalyst with silicomolybdic acid (SiMoA) was performed using electrochemical cyclic voltammetry method. The modified and unmodified catalysts were tested under identical conditions for electrooxidation of CO, methanol, and ethanol. In the CO-stripping experiments, the modified catalyst was characterized by significant shifts (80 and 60 mV) to lower onset potential and peak potential for CO electrooxidation, suggesting better CO-tolerant property of the modified catalyst. In the electrooxidation of methanol and ethanol, the modified catalyst was featured by significantly increased current densities due to reduced residence time of the reaction intermediates, showing significantly higher electrocatalytic activity for the electrooxidation of alcohols.