Date of Award
Doctor of Philosophy
Patricia A. Thiel
We have investigated the reaction of HCOOH with the (111) surface of platinum and its dependence on surface temperature, surface concentration (coverage), and the presence of other adspecies such as H[subscript]2O, CO, and atomic oxygen. The motivation for this investigation originates in the electrochemical community, where an interest in the development of fuel cells has existed for years. Small oxygen-containing hydrocarbons like HCOOH show potential as fuels in cells utilizing platinum as the electrode material. The desired reaction in such a cell is the decomposition of the formic acid to produce CO[subscript]2, which desorbs from the electrode surface; however, a competing reaction produces adspecies which do not desorb. The accumulation of these adspecies prevents continued adsorption and reaction of formic acid and eventually renders the cell useless;We have probed the reaction of formic acid with Pt(111) in ultrahigh vacuum via thermal desorption spectroscopy (TDS) and high resolution electron energy loss spectroscopy (HREELS). TDS experiments show HCOOH decomposes to produce CO[subscript]2 and H[subscript]2 for low exposures on clean Pt(111); at higher exposures molecular desorption, in several states, occurs. Coadsorption of atomic oxygen enhances decomposition, while coadsorption of CO retards it. Evidence also exists that CO may cause an alternate decomposition pathway. Interactions involving H[subscript]2O do not affect decomposition, but seem to involve hydrogen bonding formation and mutual displacement of HCOOH and H[subscript]2O from surface sites;HREELS experiments reveal that, on the clean surface, formic acid at 100 K appears to adsorb molecularly as hydrogen-bonded chains and exhibits a temperature- and coverage-dependent conversion to a bridged formate. Coadsorption of atomic oxygen lowers the temperature of conversion of HCOOH to formate as well as producing a second formate bonding configuration. The presence of CO retards the extent of conversion. Coadsorbed water is observed to undergo a reorientation, a possible result of hydrogen bonding with HCOOH.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Michael Ray Columbia
Columbia, Michael Ray, "The interaction of formic acid with Pt(111) and the effect of coadsorbed water, atomic oxygen, and carbon monoxide " (1991). Retrospective Theses and Dissertations. 9635.