(759f) Fundamental Aspects of Formic Acid Electro-Oxidation on Bimetallic Catalysts

Authors: 
Murray, E. A., University of Wisconsin-Madison
Elnabawy, A., University of Wisconsin-Madison
Mavrikakis, M., University of Wisconsin-Madison
Direct formic acid fuel cells (DFAFCs) have emerged as a viable power source as demands for alternative energy sources for transportation and portable energy storage have increased1. Formic acid (FA) is a carbon-neutral fuel that can be produced from biomass2 or via the reduction of CO23. DFAFCs have numerous advantages compared to other similar fuel cells4 because they have an equilibrium cell voltage (1.40 V) that is higher than that shown by hydrogen (1.23 V) and methanol (1.21 V) fuel cells among others5. Additionally, FA is liquid at room temperature (unlike hydrogen), is less toxic than methanol5,and shows less crossover through Nafion® membranes in fuel cells6. Despite these key advantages of DFAFCs, the best monometallic catalysts, platinum and palladium, are unstable in acidic media, are poisoned by CO during FA electro-oxidation, and are costly4. Alloying Pt and Pd with less elxpensive metals reduces the amount of Pt or Pd in the catalyst (and lowers the cost) and can improve both the stability and activity of the catalyst7,14. Here, we present a density functional theory (PW91-GGA) study of FA electro-oxidation on the (111) facet of bimetallic Pt or Pd catalysts alloyed with Au, Ag, Cu, Pt, Pd, Ir, Rh, Ru, and Re to better understand the activity of these catalysts. For each catalyst, we calculate free energy diagrams to investigate the interconversion between CO, OH, carboxyl (COOH), and formate (HCOO) on each surface. This allows us to calculate the onset potential of three key reaction mechanisms: direct oxidation of FA via COOH, direct oxidation of FA via HCOO, and the indirect oxidation of FA that forms CO for each surface. We then compare the onset potential of each mechanism to determine preferred reaction pathways and the propensity of each catalyst to be poisoned by CO.

References

  1. N. V. Rees and R. G. Compton, “Sustainable energy: a review of formic acid electrochemical fuel cells”, Journal of Solid State Electrochemistry 15, 2095 (2011).
  2. J. J. Bozell and G. R. Petersen, “Technology development for the production of biobased products from biorefinery carbohydrates-the US Department of Energy's "Top 10" revisited”, Green Chemistry 4, 539 (2010).
  3. S. Moret, P. J. Dyson, and G. Laurenczy, “Direct synthesis of formic acid from carbon dioxide by hydrogenation in acidic media”, Nature Communications 5, 4017 (2014).
  4. K. Jiang, H-X. Zhang, S. Zou, and W-B. Cai, “Electrocatalysis of formic acid on palladium and platinum surfaces: from fundamental mechanisms to fuel cell applications”, Physical Chemistry Chemical Physics 38, 20360 (2014).
  5. U. B. Demirci, “Direct liquid-feed fuel cells: Thermodynamic and environmental concerns”, Journal of Power Sources 169, 239 (2007).
  6. Y-W. Rhee, S. Y. Ha, and R. I. Masel, “Crossover of formic acid through Nafion((R)) membranes”, Journal of Power Sources 117, 35 (2003).
  7. Z. Zhang, Y. Wang, and X. Wang. “Nanoporous bimetallic Pt–Au alloy nanocomposites with superior catalytic activity towards electro-oxidation of methanol and formic acid” Nanoscale 3, 1663 (2011)
  8. S. Hu, F. Munoz, J. Noborikawa, J. Haan, L. Scudiero, and S. Ha, “Carbon supported Pd-based bimetallic and trimetallic catalyst for formic acid electrochemical oxidation”, Applied Catalysis B: Environmental 180, 758 (2016).
  9. X. Xia, S-I. Choi, J. A. Herron, N. Lu, J. Scaranto, H-C. Peng, J. Wang, M. Mavrikakis, M. J. Kim, and Y. Xia, “Facile Synthesis of Palladium Right Bipyramids and Their Use as Seeds for Overgrowth and as Catalysts for Formic Acid Oxidation”, Journal of the American Chemical Society 135, 15706 (2013).
  10. S. Singh, S. Li, R. Carrasquillo-Flores, A. C. Alba-Rubio, J. A. Dumesic, and M. Mavrikakis, “Formic Acid Decomposition on Au Catalysts: DFT, Microkinetic Modeling, and Reaction Kinetics Experiments”, AIChE Journal 60, 1303 (2014).
  11. 10. A. Herron, J. Scaranto, P. Ferrin, S. Li, and M. Mavrikakis, “Trends in Formic Acid Decomposition on Model Transition Metal Surfaces: A Density Functional Theory study”, ACS Catalysis 4, 4434 (2014).
  12. S. Choi, J. A. Herron, J. Scaranto, H. Huang, Y. Wang, X. Xia, T. Lv, J. Park, H. Peng, M. Mavrikakis, and Y. Xia, “A Comprehensive Study of Formic Acid Oxidation on Palladium Nanocrystals with Different Types of Facets and Twin Defects”, ChemCatChem 7, 2077 (2015).
  13. S. Li, J. Scaranto, and M. Mavrikakis, “On the Structure Sensitivity of Formic Acid Decomposition on Cu Catalysts”, Topics in Catalysis 59, 1580 (2016).
  14. R. Schimmenti, R. Cortese, D. Duca, and M. Mavrikakis, “Boron Nitride-supported Sub-nanometer Pd6 Clusters for Formic Acid Decomposition: A DFT Study”, ChemCatChem 9, 1610 (2017).
  15. A. O. Elnabawy, J. A. Herron, J. Scaranto, and M. Mavrikakis, “Structure Sensitivity of Formic Acid Electrooxidation on Transition Metal Surfaces: A First-Principles Study”, Journal of the Electrochemical Society 165, J3109 (2018).