In-silico screening of metal and bimetallic alloy catalysts for SOFC anode at high, intermediate and low temperature operations

Abstract

A microkinetic model (MKM), independent from the assumptions of surface coverage or rate determining steps, was developed to understand reactivity trends of several metal and bimetallic catalysts for application as a Solid Oxide Fuel Cell (SOFC) anode at operating conditions ranging from the low (673 K) to high (1273 K) temperatures. A 1:1 composition of H2: CO was used as the fuel, which may be obtained from internal or external reforming of a variety of hydrocarbon fuels fed to the SOFC anode. The reactivity of the catalysts was plotted as a volcano plot against two descriptors; the carbon and oxygen binding energies of all the surface intermediates, reactants and products species. While water production rates gave a direct indication of catalyst activity for the oxidation reaction, CO2 production rates were indirectly interpreted as its ability to oxidize surface adsorbed carbon to provide long-term stable operations. Following the interpolation principle, the volcano plot of the monometallic (Ag, Au, Cu, Pd, Pt, Ni, Co, Rh, Ru, and Re) catalysts dictated opportunities for alloying. A series of bimetallic catalysts containing Ni and other metals were screened for the same oxidation reaction. The results were significant in interpreting previously reported experimental trends on the reactivity of monometallic and bimetallic catalysts as well as in predicting novel compositions of bimetallic catalysts for achieving high catalyst activity and desired stability for a SOFC anode. Additionally, the effect of an applied electrode potential was studied on the activity of transition metal catalysts at SOFC conditions using volcano diagram. The MKM was constructed at an applied potential of U = 1.5 V with respect to a standard oxygen electrode (SOE) and analyzed at T = 873 K and T = 1073 K. Significant decrease in the H2 oxidation rates were observed, while CO oxidation rates remained unaffected at the applied potential.