First-Principles Analysis of the Activity of Transition and Noble Metals in the Direct Utilization of Hydrocarbon Fuels at Solid Oxide Fuel Cell Operating Conditions

Abstract

The direct on-cell use of hydrocarbon fuels in solid oxide fuel cells (SOFCs) involves many thermochemical and electrochemical reactions that occur on anode electrocatalysts, both at and away from the three-phase boundary. We have used first-principles density functional theory calculations and kinetic modeling to investigate relevant reactions associated with the direct utilization of methane on different electrocatalysts at SOFC operating conditions. The investigated reactions are steam and dry reforming of methane, electrochemical oxidation of and CO, and direct electrochemical oxidation of methane. These studies allowed us to compare the relative activity of different metals and to identify those metals that offer optimal performance. Our analysis shows that under relevant operating conditions, there exists a family of metals (mainly Ni, Co, Rh, Ru, and Ir) that offer maximum activity for all relevant reactions. The findings suggest that a fairly simple anode design including only one material in combination with yttria-stabilized zirconia performing multiple reactions should offer close to optimal performance. While we outline our results for methane in detail, we also comment on the direct utilization of other hydrocarbons.