Core-shell and heterostructured silver-nickel nanocatalysts fabricated by γ-radiation induced synthesis for oxygen reduction in alkaline media.

Yi Yang,Pavel Anatolyevich Nikolaychuk,Gerard Montserrat-Sisó,Björn Wickman,Inna L Soroka

doi:10.1039/d1dt03897d

Abstract

To reach commercial viability for fuel cells, one needs to develop active and robust Pt-free electrocatalysts. Silver has great potential to replace Pt as the catalyst for the oxygen reduction reaction (ORR) in alkaline media due to its low cost and superior stability. However, its catalytic activity needs to be improved. One possible solution is to fabricate bimetallic nanostructures, which demonstrate a bifunctional enhancement in the electrochemical performance. Here, two types of bimetallic silver-nickel nanocatalysts, core-shells (Ag@NiO) and heterostructures (Ag/Ni), are fabricated using γ-radiation induced synthesis. The Ag@NiO nanoparticles consist of an amorphous, NiO layer as a shell and a facetted crystalline Ag particle as a core. Meanwhile, the Ag/Ni heterostructures comprise Ag particles decorated with Ni/Ni(oxy-hydro)-oxide clusters. Both materials demonstrate similar and increased alkaline ORR activity as compared to monometallic catalysts. It was revealed that the enhanced catalytic activity of the core-shells is mainly attributed to the electronic ligand effect. While in the Ag/Ni heterostructures, a lattice mismatch between the Ni-based clusters and Ag implies a significant lattice strain, which, in turn, is responsible for the increased activity of the catalyst. Also, the Ag/Ni samples exhibit good stability under operating conditions due to the existence of stable Ni3+ compounds on the surface.

Highlights

Anion exchange membrane fuel cells (AEMFCs) are considered as generation fuel cells and show great potential to be an alternative to acidic proton exchange membrane fuel cells (PEMFCs).[1]
In order to tune the redox conditions of the solution to either reductive or oxidative, the undesired radical needs to be scavenged
In the Ag@NiO sample, both electronic effects are assumed to contribute to the improved oxygen reduction reaction (ORR) activity, while the strong ligand effect induced by the amorphous Ni–O layers may play a prominent role

Summary

Introduction

Anion exchange membrane fuel cells (AEMFCs) are considered as generation fuel cells and show great potential to be an alternative to acidic proton exchange membrane fuel cells (PEMFCs).[1] Alkaline conditions in AEMFCs allow the usage of less expensive, Pt-free catalysts for the oxygen reduction reaction (ORR).[2] Potential candidates include many abundant transition metals, the use of which drastically reduces the cost per kilowatt of power in fuel cell devices.[3] One such candidate is Ag, whose market price is approximately 50 times lower than that of Pt and 90 times lower than the price of Pd and Au.[4] as it has been reported in a number of studies, Ag. It is believed that there are two dominant factors that govern the ORR activity in alkaline media: (i) adsorption strength of the oxygen species on the catalyst surface and (ii) O–O bond breakage tendency.[11,12] since the d-band of Ag is completely occupied, it is difficult for pure silver to provide unpaired electrons from the d-band to form bonds with oxygen, resulting in low oxygen coverage.[13] Ag shows slow kinetics of the O–O bond split.[12]

Results

Discussion

Conclusion