Pd-Cu Core/shell Nanoparticles as an Efficient Catalyst for Fuel Cell applications

Designing new materials for heterogeneous catalysis is interesting and challenging in surface science. For years, scientists have found out that bimetallic system can achieve better catalytic performance due to effects such as... [ view full abstract ]

Designing new materials for heterogeneous catalysis is interesting and challenging in surface science. For years, scientists have found out that bimetallic system can achieve better catalytic performance due to effects such as ligand effect and ensemble effect. Since the reactivity of bimetallic overlayer can be tailored by substrate, the bimetallic nanoparticle with core/shell structure is promising due to its easy way of the formation with the effect of phase separation. Recent studies have proved that Pd-based intermetallic nanoparticle has the potential to serve as an non-Pt catalyst for fuel oxidation and oxygen reduction reaction.¹

In this paper, we have studied the catalytic activity of PdCu nanoparticle for CO oxidation and oxygen reduction reaction by density functional theory calculations. Two structures have been proposed,including face-centered tetragonal (fct) PdCu/Pd nanoparticle and face-centered cubic (fcc) PdCu bimetallic surface alloy. Fct-Pd/Cu/Pd structure consists of ordered alloy distribution PdCu as core and thin overlayer Pd as shell;fcc-PdCu bimetallic surface alloy structure includes three-layer Cu(111)substrate as core and thin overlayer Pd as shell. 

We have found out that the adsorption energies and catalytic activities depend largely on the electronic structure of surface Pd atoms near the Fermi level which is affected and modified by core. A linear relationship is found between the adsorption energy (E_ad) and the d-band center (ɛ_d) for fcc-PdCu bimetallic alloy with increasing Pd overlayer up to three layers at most. With nudged elastic band method, we have calculated the energy barriers for O₂ dissociation on fct-PdCu/Pd nanoparticle and CO oxidation with atomic O on fcc-PdCu bimetallic alloy. With Sabatier principle and volcano curve, we have predicted the activity of ORR and CO oxidation for both structures by adopting the model proposed by Nǿrskov.² We hope our work can shed some lights on the design of bimetallic nanoparticles towards superior catalytic catalysis.

References

1. Wang, Chenyu, et al. "Size-dependent disorder–order transformation in the synthesis of monodisperse intermetallic PdCu nanocatalysts." ACS nano 10.6 (2016): 6345-6353.

2. Stamenkovic, Vojislav, et al. "Changing the activity of electrocatalysts for oxygen reduction by tuning the surface electronic structure." Angewandte Chemie 118.18 (2006): 2963-2967.