Multimetallic Core–Bishell Ni@Au@Pd nanoparticles with reduced graphene oxide as an efficient bifunctional electrocatalyst for oxygen reduction/evolution reactions

In this study, a multimetallic core–bishell electrocatalyst, Ni@Au@Pd was fabricated. The catalyst consisting of a Ni core and Au@Pd bishell was synthesized using reduced graphene oxide (rGO) as support via chemical reduction-replacement technique. For comparative analysis, the bimetallic core–shell electrocatalyst, Ni@Pd-rGO as a control was also synthesized. A test for electrochemical activity toward oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) was then conducted in an alkaline medium. The results showed that Ni@Au@Pd-rGO exhibited a half-wave potential (0.7713 V) similar to that of Ni@Pd-rGO, which is more positive than that of commercial carbon supported platinum (Pt/C). Furthermore, a higher limited current (5.6 mA cm−2) compared to Pt/C and Ni@Pd-rGO was obtained for ORRs. In OERs, Ni@Au@Pd-rGO exhibited the most negative onset potential (1.5663 V), the lowest overpotential (∼0.52 V), and the lowest Tafel slope (0.199 V decade−1) among these three materials. As a result, Ni@Au@Pd-rGO was confirmed to be an effective bifunctional electrocatalyst for ORRs and OERs. The enhanced activity is attributed to the geometric and electronic effect, the synergistic action of three metals, and the relatively stable Ni@Au@Pd system. All these factors result in an overall good performance as cathode catalyst in lithium-air batteries.