Exploring the Effect of Pd on the Oxygen Reduction Performance of Pt by In Situ Raman Spectroscopy

Abstract

Directly monitoring the oxygen reduction reaction (ORR) process in situ is very important to deeply understand the reaction mechanism and is a critical guideline for the design of high-efficiency catalysts, but there is still lack of definite in situ evidence to clarify the effect between adsorbed intermediates and the strain/electronic effect for enhanced ORR performance. Herein, in situ surface-enhanced Raman spectroscopy (SERS) was employed to detect the intermediates during the ORR process on the Au@Pd@Pt core/shell heterogeneous nanoparticles (NPs). Direct spectroscopic evidence of the *OOH intermediate was obtained, and an obvious red shift of the *OOH frequency was identified with the controllable shell thickness of Pd. Detailed experimental characterizations and density functional theory (DFT) calculations demonstrated that such improved ORR activity after inducing Pd into Au@Pt NPs can be attributed to the optimized adsorbate−substrate interaction due to the strain and electronic effect, leading to a higher Pt−O binding energy and a lower O−O binding energy, which was conducive to O−O dissociation and promoted the subsequent reaction. Notably, this work illustrates a relationship between the performance and strain/electronic effect via the intermediate detected by SERS and paves the way for the construction of ORR electrocatalysts with high performance.

Carbon-based material-supported single-atom catalysts for energy conversion

“…Surface-enhanced Raman scattering (SERS) is caused by electromagnetic and the charge transfer mechanism, which means that when the analyte is adsorbed on rough metal surface, its Raman signal will be enhanced ( Cialla et al., 2012 ). Sun and colleagues employed the in situ SERS to monitor the adsorbate-substrate interaction in the process of ORR on the Au@Pd@Pt core/shell nanoparticles, which provided the direct evidence of ∗OOH intermediate ( Sun et al., 2022 ). Furthermore, it is proved that the introduction of Pd shells affects the strain and electronic effect, leading to enhanced ORR activity.…”

Applications of In Situ Raman Spectroscopy on Rechargeable Batteries and Hydrogen Energy Systems

“…Tuning the thickness (content) of Pd led to a shift of the Raman peak of OOH* and a change in the ORR activity (Figure 7f). [47] In our other system, by alloying Ni with Pt to form PtNi alloy bimetallic nanocatalysts we also observed the ligand and/or strain effect in lowing the binding energy between Pt and oxygen by using Au@PtNi NPs. [48] Although the borrowing strategy worked well on in situ exploring the ORR process of Pt-based core-shell nanoparticles, conversational Pt-based catalysts are commonly finer nanoparticles (a few nanometers) compared to the morphology of the borrowing strategy.…”

“…Tuning the thickness (content) of Pd led to a shift of the Raman peak of OOH* and a change in the ORR activity (Figure 7f). [47] In our other system, by alloying Ni with Pt to form PtNi alloy bimetallic nanocatalysts we also observed the ligand and/or strain effect in lowing the binding energy between Pt and oxygen by using Au@PtNi NPs [48] …”

Why Does Pt Shell Bearing Tensile Strain Still Have Superior Activity for the Oxygen Reduction Reaction?

“…As the thickness of the Pt shell decreases from 2 to 1 ML, a red shift of the peak frequency of the *OOH band is observed. The red shift of *OOH indicates stronger OOH ad adsorption as a result of the increase in back-donation of electrons from Pt to the O–O antibond. − According to the scaling relationship, the adsorption strength of OOH ad scales with those of O ad and OH ad . In a word, the increase of ORR activity with the decrease of Pt shell thickness of Au@Pt x ML ( x ≈ 1, 2) follows well with the increase of binding strength of Pt-OOH ad /O ad /OH ad .…”