Bin Hong Liu

A cobalt coordination compound with indole acetic acid for fabrication of a high performance cathode catalyst in fuel cells

As a catalyst precursor, a cobalt coordination compound with indole acetic acid (Co–IAA) was synthesized using the hydrothermal method. Pyrolysis significantly improved the catalytic activity of the carbon supported Co–IAA (Co–IAA/BP) toward the oxygen reduction reaction (ORR) due to the formation of nano-Co3O4. Both original and pyrolyzed Co–IAA/BP exhibited higher catalytic activity in an alkaline electrolyte than that in an acidic one because dioxygen and water were absorbed at the single electrophilic Co center in the alkaline electrolyte but dioxygen and proton were separately absorbed at the electrophilic Co center and nucleophilic center (O) in the acidic electrolyte. Construction of a coupling site where electrophilic and nucleophilic centers coexisted was the key to enhance the ORR in an acidic electrolyte. The pyrolyzed Co–IAA/BP exhibited excellent performance in the direct borohydride fuel cell, comparable to the commercialized 20 wt% Pt/XC-72. A peak power density as high as 186 mW cm−2 was achieved at ambient conditions.

Prevention of active-site destruction during the synthesis of high performance non-Pt cathode catalyst for fuel cells

Active-site destruction during the synthesis of porous non-Pt catalysts for the oxygen reduction reaction (ORR) is investigated in detail. Because of the carbon erosion caused by CO2 generated from the decomposition of CaCO3 template, active-sites are destroyed during the formation of the macroporous carbon-supported cobalt catalyst (Co/N-MPC) using Co-coordinated glucose–urea resin and a CaCO3 template. Removal of the CaCO3 template before its decomposition can effectively suppress this site destruction, thereby leading to a higher content of catalytic nitrogen species in the catalyst. Nitrogen-containing active-sites are unstable at temperatures over 800 °C. After optimizing the template removal and carbonization temperatures, the synthesized Co/N-MPC exhibits high catalytic activity towards ORR in both alkaline and acidic electrolytes. Its electron transfer number reaches 3.65 in alkaline and 3.75 in acidic electrolytes, respectively. The direct borohydride fuel cell with the synthesized Co/N-MPC shows a power density as high as 215 mW cm−2, which is comparable to that of the cell using 28.6 wt% Pt/C as a cathode catalyst under ambient conditions.