Maxim Shishkin, Post Doctoral Fellow

DEPARTMENT OF CHEMISTRY

CHEMISTRY 601/ 603

THEORETICAL SECTION

SPEAKER:            Maxim Shishkin, Post Doctoral Fellow

DATE:                     Thursday, November 12, 2009

TIME:                      3:00 pm

PLACE:                  SB 324

TITLE:                    Electrochemical reactions at the anode-electrolyte interface of solid oxide fuel cells (SOFC): DFT Study.

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Abstract.

Electrochemical oxidation of fuel molecules (H2, CH4, CO), which results in a transfer of electric charge from the electrolyte to the anode of SOFC, is known to occur at the interface where fuel, electrolyte and anode meet. Using DFT approach it is shown that oxidation of hydrogen molecules at such an interface (also known as a triple phase boundary, TPB) indeed results in a flow of charge from the electrolyte oxide (yttria-stabilized zirconia, YSZ) to the metallic part of the anode (Ni). Evaluated kinetic pathways of hydrogen oxidation on the Ni surface of the anode at the TPB are very similar to these on pure Ni surface. On the other hand, the electrolyte surface of TPB is inert for direct fuel adsorption, even for the case of oxygen-enriched oxide (YSZ+O), which is known to be active for fuel activation in the absence of Ni. It is also demonstrated that oxygen can migrate from YSZ+O to the Ni surface, accounting for fuel oxidation on the metal (oxygen spill over). Alternatively surface hydrogen species can migrate from Ni to YSZ+O with subsequent water formation and desorption (hydrogen spill over). By contrast, oxygen and hydrogen spill over reactions from/to stoichiometic YSZ surface are associated with high kinetic barriers and considered implausible. It is also shown that methane can be oxidized on Ni surface, whereas adsorption on YSZ+O surface in vicinity to TPB is energetically prohibitive.