Effects of the Addition of Antimony, Tin, and Lead to Palladium Catalyst Formulations for the Direct Formic Acid Fuel Cell

In an operating direct formic acid fuel cell (DFAFC), the palladium catalyst surface poisons and must be periodically regenerated by oxidative stripping. The objective of this paper is to analyze the effects of antimony, tin, and lead additions to the palladium black catalyst that is used in the DFAFC. We discovered that each adatom strongly promotes formic acid oxidation in an electrochemical cell and reduces the amount of CO poison that develops on the catalyst surface after one hour of oxidation, which suggests a steric effect due to the presence of the adatoms. However, after three hours of oxidation, the poisoning is nearly the same with each of the adatoms, which shows the limitations of the steric effect. We also used X-ray photoelectron spectroscopy to demonstrate a shift in the palladium binding energy due to the presence of the adatoms, which suggests an electronic effect is also present. We conclude that the steric and electronic effects cause a significant enhancement to oxidation in an electrochemical cell, although the enhancement is less in an operating fuel cell.