Direct liquid-fed fuel cell is a promising power device for applications, such as consumer electronic products. Formic acid and ethanol are considered to be good candidates as the fuels. Among the major technical hurdles in direct formic acid fuel cell (DFAFC) and direct ethanol fuel cell (DEFC), low activities of electrocatalysts are known to be one of the key factors that affect the performance of fuel cell systems. This thesis focuses on development of highly active catalysts for both formic acid and ethanol oxidation as well as on investigation of the reaction mechanisms....[ Read more ]

Direct liquid-fed fuel cell is a promising power device for applications, such as consumer electronic products. Formic acid and ethanol are considered to be good candidates as the fuels. Among the major technical hurdles in direct formic acid fuel cell (DFAFC) and direct ethanol fuel cell (DEFC), low activities of electrocatalysts are known to be one of the key factors that affect the performance of fuel cell systems. This thesis focuses on development of highly active catalysts for both formic acid and ethanol oxidation as well as on investigation of the reaction mechanisms.

This work starts with development of robust protocols for synthesis of Pd and Pd based binary catalyst. Without using “explicit” protective reagent, Pd nanoparticles with a controlled size ranging from 3.9 to 7.5 nm were produced. In addition, based on the idea of reaction engineering control, a novel protocol that enables the production of both alloy and non-alloy Pd-Au binary catalysts were developed. This strategy was demonstrated to be applicable for synthesis of other binary alloy catalyst, i.e., Pd-Rh. Interesting electrochemical properties of the as prepared Pd and Pd based binary (PdAu, PdRh) nanoparticles for formic acid oxidation were observed. Other than synthesizing binary catalyst, this approach ensured the production of well distributed Rh/C. Improved activity of Rh/C compared with conventional Pd/C for ethanol oxidation in alkaline medium was found.

Electrochemical impedance spectroscopy (EIS) was utilized for investigation of the reaction mechanisms. Our impedance study on formic acid oxidation suggest that unlike that on Pt/C, formic acid oxidation on Pd/C mainly follows the dehydrogenation pathway without generation of poisonous species, i.e. CO_ads. Moreover, distinct impedance behaviors of ethanol oxidation on Rh/C and Pd/C suggest that ethanol oxidation on these two catalysts could follow different reaction pathways, which could be the reason for the observed higher activity of Rh/C compared with Pd/C.

The development of the highly active nanocatalysts is believed to contribute to the improvement of the performance of fuel cell systems, while the study on the reaction mechanism provides better understanding and potential opportunities for the advancement of the fuel cell technologies.