Inducing Microstrain in Electrodeposited Pt through Polymer Addition for Highly Active Oxygen Reduction Catalysis

We investigate an approach to tune the d-band center and enhance the oxygen reduction reaction (ORR) activity of Pt material without relying on foreign metals or the process of alloying/dealloying. It is known that Pt exhibits suboptimal ORR catalytic activity due to its strong binding to oxygen, therefore requiring a downshift in the d-band center by approximately 0.2 eV to weaken the Pt-O binding energy and boost ORR kinetics. We found that the d-band center can be tuned by inducing microstrain in the Pt electrodeposit, simply achieved by introducing polymer into the electrodeposition bath. Pt electrodes (Pt-P1 and Pt-PLA) prepared with the addition of poly-N-(6-aminohexyl)acrylamide (P1) or poly-l-arginine (PLA) exhibit improved ORR activity compared to Pt electrodeposited without polymer addition (Pt-alone) in both acidic and basic environments, with the order of activity being Pt-P1 > Pt-PLA > Pt-alone. Pt-P1 exhibits a positive shift of E_1/2 by 90 mV vs Pt-alone in basic solution, comparable to other reported high-activity ORR catalysts. Scanning electron microscopy shows the presence of agglomerates with diameters between 5 and 20 μm and tip-splitting growth structure due to diffusion-limited aggregation on Pt-P1 and Pt-PLA. Characterization using X-ray photoemission spectroscopy and X-ray diffraction, combined with Rietveld refinement analysis reveal a trend of downshifted d-band center, increased microstrain, and slightly increased compressive strain as the ORR activity increased among the three catalysts. The presence of more defective sites on Pt-P1 and Pt-PLA is the cause of the increased microstrain, which further leads to the downshift of the Pt d-band center and enhancement of ORR activity.