Factors controlling the energetics of the oxygen reduction reaction on the Pd-Co electro-catalysts: Insight from first principles

Abstract

We report here results of our density functional theory based computational studies of the electronic structure of the Pd-Co alloy electrocatalysts and energetics of the oxygen reduction reaction (ORR) on their surfaces. The calculations have been performed for the (111) surfaces of pure Pd, Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) alloys, as well as of the surface segregated Pd/Pd(0.75)Co(0.25) alloy. We find the hybridization of dPd and dCo electronic states to be the main factor controlling the electrocatalytic properties of Pd/Pd(0.75)Co(0.25). Namely the dPd-dCo hybridization causes low energy shift of the surface Pd d-band with respect to that for Pd(111). This shift weakens chemical bonds between the ORR intermediates and the Pd/Pd(0.75)Co(0.25) surface, which is favorable for the reaction. Non-segregated Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) surfaces are found to be too reactive for ORR due to bonding of the intermediates to the surface Co atoms. Analysis of the ORR free energy diagrams, built for the Pd and Pd/Pd(0.75)Co(0.25), shows that the co-adsorption of the ORR intermediates and water changes the ORR energetics significantly and makes ORR more favorable. We find the onset ORR potential estimated for the configurations with the O-OH and OH-OH co-adsorption to be in very good agreement with experiment. The relevance of this finding to the real reaction environment is discussed.

Ion‐Enhanced Conversion of CO2 into Formate on Porous Dendritic Bismuth Electrodes with High Efficiency and Durability

“…In the CO 2 reaction pathway, the free energy G for the CO 2 product was calculated as follows [Eq. ]: …”

Effects of Co Content in Pd-Skin/PdCo Alloys for Oxygen Reduction Reaction: Density Functional Theory Predictions

“…Manogaran and Hwang 45 studied the role of the surface-subsurface interlayer interaction in enhancing the oxygen hydrogenation towards water in Pd 3 Co alloy catalysts. Their work clarified that the subsurface Co atoms facilitate the ORR by lowering the activation barriers for O/OH hydrogenation; however, the Co atoms lying below the subsurface far from the surface layer have no significant involvement in the modification of the surface reactivity towards O hydrogenation.Experimental and theoretical works confirmed that the Pd-skin alloy catalysts are the key systems for improving the ORR activity 26,35,36,[39][40][41][42][43][44][45][46][47][48][49]. Many works have been performed to clarify the ORR activity versus the Co content for PdCo films and carbonsupport PdCo nanoparticles where Co atoms can be at the topmost surface layer [25][26][27][28][29][30][31][32].…”

“…Many works have been performed to clarify the ORR activity versus the Co content for PdCo films and carbonsupport PdCo nanoparticles where Co atoms can be at the topmost surface layer [25][26][27][28][29][30][31][32]. Despite the fact that the Pd-skin/PdCo electrocatalysts are very stable and active for the ORR,26,35,36,[39][40][41][42][43][44][45][46][47][48][49] no similar works are available in the literature for Pd-skin/PdCo alloy catalysts. Understanding the effects of the Co content on the ORR activity of Pd-…”

Hierarchical nanoporous PtTi alloy as highly active and durable electrocatalyst toward oxygen reduction reaction

“…Both the decreased O and OH adsorption energies on PtTi are beneficial for the reduction of O and OH intermediates to water as well as alleviating the surface poisoning from these species, thus generating the modified oxygen reaction kinetics [55]. The downshifts of the deband center of Pt relative to the Fermi level means the decrease of an electron backdonation from the Pt 5d orbital to the 2p* orbital of O and OH [54,56,57], consequently weakening the OePt and OHePt bonding. This is considered to be the possible origination for the higher ORR activities and catalytic durability of HNPePt 75 Ti 25 alloy than Pt/C and NPePt catalysts.…”