In the field of alkaline fuel cells, it is known that the performance of the cell is limited by the oxygen reduction reaction (ORR) rate at the cathode. Among the catalysts on cathodes, Ag nanoparticle (NP) catalysts have been found to have comparable overvoltages and similar activities to traditional Pt catalysts, but at a much lower cost. Developing an Ag-based electro-catalyst has aroused more and more attention. In parallel, the exciting electronic and mechanical properties of carbon nanotubes (CNTs) have generated broad and interdisciplinary attention. Thus the Ag/CNT nanohybrid materials have received particular attention in fuel cells due to their high catalytic performance in ORR in alkaline media. A typical protocol for synthesis of nanohybrids of metal NPs/CNTs was using organic or polymer linker molecules, which caused poor conductivity of the nanohybrid as the linker molecules may decrease the electron transfer.

A facile, one-pot synthesis of Ag NP-decorated CNTs was realized by researchers from Institute of Process Engineering (IPE) and Institute of Chemistry, Chinese Academy of Sciences. They presented a new strategy for the decoration of Ag NPs on CNTs using solely polyoxometalates (POMs) as both the reductant and bridging molecules and found that the prepared nanohybrid showed high electro-catalytic activities toward ORR.

To enhance the conductivity of the nanohybrid and electrocatalytic performance, they used a special reagent-POM, [PW12O40]3- (PW12) to reduce Ag+ into Ag NPs on the surface of CNTs. Compared to most of the literature work, an advantage of the present work is that surfactants were avoided on the Ag NPs surface or between Ag NPs and CNTs, improving the conductivity and electrocatalytic activity of the hybrid material, which showed efficient four-electron reaction. In addition, they demonstrated that different loading amounts of Ag NPs on CNT were readily achieved by controlling the concentrations of POM and AgNO3.

This work has been published on the J. Mater. Chem., 2011, 21, 14917-14924 and the related research work was supported by the National Natural Science Foundation of China (No.21071146, 51002155).

Contact: ZHANG Guangjin

Phone (Fax): 0086-10-62528935

Email: zhanggj@home.ipe.ac.cn

Schematic diagram indicating the preparation of Ag NP/POM/CNT tri-component hybrid for electro-catalytic activities toward ORR. (Image by IPE)