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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. COads. 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

In this work, a simple co-deposition strategy for the synthesis of carbon-supported Pd-Au alloy was reported. Our approach involves the co-reduction of Au and Pd ions using ethylene glycol and sodium citrate as the reducing and stabilizing reagents. Both alloy and non-alloy bimetallic Pd-Au nanoparticles are produced using a right rate-limiting strategy. For example, when ethylene glycol and sodium citrate are the limiting reagent with Au and Pd ions in excess, the synthesis environment favors preferential nucleation and growth of Au nanoparticles followed by deposition of Pd either as the shell of Au core or as separate Pd clusters. On the other hand, if the supply of metal ions (not the reducing reagents) limits the reaction, it creates a synthesis condition for Pd-Au alloy particles. The as-prepared Pd-Au alloys exhibit higher Pd-specific activities towards formic acid oxidation compared with the non-alloy counterpart or individual Pd catalyst and an easier removal of adsorbed oxygen species (e.g., O(ads) or OH(ads)) was observed from the surface of Pd-Au alloy with a higher content of Au. (C) 2010 Elsevier Ltd. All rights reserved.

We report the synthesis and electrochemical characterization of rhodium/carbon (Rh/C) and palladium-rhodium/carbon (Pd-Rh/C) nanocatalysts for ethanol oxidation. Our results, for the first time. demonstrated that in an alkaline environment. Rh/C shows a much higher catalytic activity at low potential range than that of Pd-Rh/C and Pd/C. Intermediate species are produced during the oxidation process on Rh/C, as revealed by the complex impedance spectra (e.g., pseudo-inductive loop) at low potential range (i.e., -0.5 to -0.3 V). Adsorbed oxygen species, which are generated at high potentials, block active surface sires of Rh/C, resulting in the negative polarization resistance. (C) 2011 Elsevier B.V. All rights reserved.

This work provides a detailed electrochemical impedance study for formic acid electro-oxidation on size-controlled Pd/C nanoparticles, the synthesis of which was done by a simple protocol using ethylene glycol as a reducing agent. By controlling KOH concentration, this strategy provides a synthesis method for Pd nanoparticles with a selective size range of 3.9-7.5 nm. The as-prepared Pd nanoparticles exhibited size-dependent electrochemical property and electrochemical characterizations of four different Pd/C nanocatalysts (3.9, 5.2, 6.1, and 7.5 nm) showed that I'd particle with average size of 6.1 nm has the highest formic acid oxidation activity. Electrochemical impedance-based characterizations of formic acid oxidation on Pd/C suggested that at high potentials the adsorbed oxygen species could block the catalyst surface and inhibit the oxidation reaction, as reflected by the negative polarization resistance. Unlike Pd/C, the intermediate adsorbed CO species (COads) plays a critical role for formic oxidation on Pt/C and thus the impedance spectra of Pd/C and Pt/C appear different potential-dependent patterns in the second quadrant. The issue of CO was investigated by an impedance investigation of Pd/C in a mixture of formic acid containing dissolved CO. (C) 2009 Elsevier Ltd. All rights reserved.