On the Role of Elastic Strain on Electrocatalysis of Oxygen Reduction Reaction on Pt

TL;DR

This study investigates how elastic strain in de-alloyed Pt-Cu thin films influences their catalytic activity for oxygen reduction, combining real-time stress measurements, nanogravimetric analysis, and DFT calculations to reveal strain effects on ORR performance.

Contribution

It provides the first direct measurement of elastic strain in de-alloyed Pt layers and links it to enhanced ORR activity through combined experimental and theoretical analysis.

Findings

De-alloyed Pt layers exhibit compressive stress of about 4.95 GPa.

Enhanced ORR activity observed in de-alloyed Pt compared to polycrystalline Pt.

DFT calculations confirm strain-induced shifts in ORR limiting potentials.

Abstract

The effect of elastic strain on catalytic activity of platinum (Pt) towards oxygen reduction reaction (ORR) is investigated through de-alloyed Pt-Cu thin films; stress evolution in the de-alloyed layer and the mass of the Cu removed are measured in real-time during electrochemical de-alloying of (111)-textured thin-film PtCu (1:1, atom %) electrodes. In situ stress measurements are made using the cantilever-deflection method and nano-gravimetric measurements are made using an electrochemical quartz crystal nanobalance. Upon de-alloying via successive voltammetric sweeps between -0.05 and 1.15 V vs. standard hydrogen electrode, compressive stress develops in the de-alloyed Pt layer at the surface of thin-film PtCu electrodes. The de-alloyed films also exhibit enhanced catalytic activity towards ORR compared to polycrystalline Pt. In situ nanogravimetric measurements reveal that the mass of de-alloyed Cu is approximately 210 +/- 46 ng/cm2, which corresponds to a de-alloyed layer thickness of 1.2 +/- 0.3 monolayers or 0.16 +/- 0.04 nm. The average biaxial stress in the de-alloyed layer is estimated to be 4.95 +/- 1.3 GPa, which corresponds to an elastic strain of 1.47 +/- 0.4%. In addition, density functional theory calculations have been carried out on biaxially strained Pt (111) surface to characterize the effect of strain on its ORR activity; the predicted shift in the limiting potentials due to elastic strain is found to be in good agreement with the experimental shift in the cyclic voltammograms for the dealloyed PtCu thin film electrodes.