A study of properties of palladium metal as a component of fuel cells

Abstract

Adsorptive studies focusing on palladium metal can model a situation in which some parts of platinum are replaced with palladium in a fuel cell, or some kind of PdPt alloy is used. Correspondingly thus, adsorptions of small molecules such as carbon monoxide and hydrogen are studied using density functional theory and the neural network method of generating higher dimensional potential energy surfaces. Various lower index surfaces of palladium metal are considered, and the adsorption energies appear to increase according to: Pd(211) ≃ Pd(110) >Pd(100) > Pd(111) with the adsorption of both molecules. The numerical values of these energies are in the range 0.52 to 1.86 eV with the adsorption of carbon monoxide while the values are between 0.28 to 1.76 eV with the adsorption of hydrogen. Exploring possible adsorption sites gives insight on better ways in which charge transfers are maximized while at the same time forming of the by-products, water and carbon dioxide, becomes efficient. Charge transfers give some insight into the study of electrification process in the system. These values are computed to be about 1.06e with the adsorption of hydrogen and upto 0.90e with the adsorption of carbon monoxide. It appears that (211) and (110) surfaces offer better catalytic role for the electrification process than (100) or (111) surfaces. Barriers of dissociations and combinations are calculated to confirm a possible reality of the assumed processes within the system. Electronic structure calculation using band structure and projected density of states reveals the d electrons of the surface palladium atoms are most affected by the adsorptions. Training of the system potential energies using the neural network method shows promising opportunity to study further complex problems in such systems.