Combined Experimental/Theoretical Approach Toward the Development of Carbon Tolerant Electrocatalysts for Solid Oxide Fuel Cell Anodes.

The main objective of this dissertation was to utilize a molecular approach combining DFT calculations and numerous experimental techniques to develop carbon tolerant electrocatalysts for solid oxide fuel cell (SOFC) anodes. SOFCs are solid-state electrochemical devices that can convert the chemical energy of hydrogen, CO, and hydrocarbons into electrical energy. One of the main issues associated with the direct operation of SOFCs using hydrocarbons is the deactivation of the conventional anode electrocatalysts, such as Ni on yttria-stabilized zirconia (YSZ) due to the formation of carbon deposits. To tackle the problem of carbon-induced deactivation of Ni, we have utilized DFT calculations to identify the chemical transformations that govern carbon poisoning of Ni. We found that the processes of C-C and C-O bond formation as well as carbon nucleation played an important role in the carbon-induced deactivation of the Ni catalysts. These insights led to the identification of the Ni surface alloys as promising carbon tolerant catalysts. Electrocatalysts containing Sn/Ni and Ni supported on YSZ were synthesized. The carbon tolerance of the Sn/Ni surface alloy and monometallic Ni was tested using reactor and electrochemical SOFC studies. We found that the Sn/Ni surface alloy exhibited a significantly improved carbon tolerance compared to monometallic Ni in hydrocarbons steam reforming reactions and as SOFC anode electrocatalyst. To advance our understanding of the chemistry that occurs on the Sn/Ni surface alloy, we have also performed kinetic studies in combination with DFT calculations to identify the critical elementary steps that govern the performance of Ni and Sn/Ni electrocatalysts. We have also utilized electron microscopy and spectroscopy to measure the electronic structure of the supported Ni and Ni alloys and have related that to their chemical and catalytic performance. These detailed atomistic studies led to the derivation of very general set of principles that allow us to identify novel carbon tolerant alloy catalysts for hydrocarbon reforming and electro-oxidation. The work described in this dissertation presents a rare example where DFT calculations combined with experimental techniques led to the bottom-up (based on molecular insights rather than on empirical trial and error testing) identification of improved electrocatalysts.PhDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/62356/1/erandan_1.pd