First principle study of the electronic and catalytic properties of palladium-silver (PdAg) alloys catalyst for direct liquid fuel cells

Abstract

The alcohol fuel cell is a promising technology that will replace conventional energy production with higher energy conversion efficiency and less pollutant emission. However, the catalyst faces some challenges, and it requires modification. Among various modification methods, producing bimetallic alloys has delivered better performance than monometallic noble metal catalysts. Five catalyst models, Pd (111), Ag (111), Pd3Ag (111), PdAg (111), and PdAg3 (111), have been studied in this work in terms of structural, electronic, and adsorption molecules properties through density functional theory (DFT) studies. The structural and electronic properties of the modified catalyst model show the ligand and strain effect on the alloy with the addition of silver as second metal promotes the adsorption capability; however, the catalytic activity heavily depends on the alloy composition. Searching for active sites was also carried out by adsorption of selected atoms and molecules and used as a preliminary study to find possible active sites for alcohol electrochemical reaction at the anode in a direct liquid fuel cell (DLFC). The Pd3Ag (111) catalyst exhibits better adsorption ability on atomics, simple molecules, and alcohol/polyol molecules (methanol, ethanol, and glycerol). This work also carried out catalytic activities for ORR at the cathode. Pd3Ag (111) was found to be the most suitable for the ORR. The presence of the Ag atom showed theoretically a promising metal–metal combination for an excellent catalyst that might replace monometallic catalyst and produce a new tri-metallic catalyst in the future for the application in DLFCs, especially with glycerol. Even by replacing the 75% of Pd surface with Ag, the adsorption strength on the glycerol is remarkable, positively contributing to the oxidation reaction. The Ag metal is a suitable second metal candidate for the alloy to oxidize molecules with a longer carbon chain similar to or more than glycerol.