Tailoring the Oxygen Reduction Activity of Pt Nanoparticles through Surface Defects: A Simple Top-Down Approach

Abstract

Results from Pt model catalyst surfaces have demonstrated that surface defects, in particular surface concavities, can improve the oxygen reduction reaction (ORR) kinetics. It is, however, a challenging task to synthesize nanostructured catalysts with such defective surfaces. Hence, we present a one-step and up-scalable top-down approach to produce Pt/C catalyst (with ~3 nm Pt nanoparticle diameter). Using high-resolution transmission electron microscopy and tomography, electrochemical techniques, high energy X-ray measurements and positron annihilation spectroscopy, we provide evidence of a high density of surface defects (including surface concavities). The ORR activity of the developed catalyst exceeds that of commercial Pt/C catalyst, at least 2.7-times in terms of specific (~1.62 mA/cm 2 Pt at 0.9 V vs the reversible hydrogen electrode) and at least 1.7-times in terms of mass activity (~712 mA/mg Pt), which can be correlated to the enhanced amount of surface defects. Besides, the technique used here reduces the Page 2 of 51 ACS Paragon Plus Environment ACS Catalysis 3 complexity of the synthesis (and therefore production costs) compared to state-of-the-art bottom-up techniques. This information is available free of charge on the ACS Publications website. Coincident Doppler broadening spectrum, WAXS measurements, Rietveld refinement data, Reference ORR polarization curve, Accelerated durability test, TEM analysis AUTHOR INFORMATION

Electrochemical top-down synthesis of C-supported Pt nano-particles with controllable shape and size: Mechanistic insights and application

“…4(a), all particles synthesized in the electrolytes with different cations (Cs + , Na + , Li + ) exhibit a strong degree of surface defects. As reported previously, such concave defects can be used to tailor the oxygen reduction reaction (ORR) activity of Pt nanoparticles, verifying the various application possibilities [4,27,28]. It has to be noted, that the depicted particles are not representative for the mean particle size, for accurate shape comparison larger particles with similar sizes were pre-selected.…”

“…The shape, size and composition of metallic nanoparticles (NPs) often play a decisive role in achieving specific surface functionality for various applications [1][2][3]. For instance, the properties of metal NPs can be tailored by changing the aforementioned parameters for their applications as heterogeneous, electro-and photo-catalysts as well as in biosensors [4][5][6][7][8][9]. Currently, most of the state-of-the-art synthetic procedures in nanochemistry are based on colloidal wet-chemical "bottom up" approaches, which often require complex steps.…”

Atomic Regulation of PGM Electrocatalysts for the Oxygen Reduction Reaction

“…Copyright 2017, American Chemical Society. (C) Reproduced with permission ( Fichtner et al, 2020 ). Copyright 2020, American Chemical Society.…”

“…Some novel defect engineering strategies have been developed for the Pt/C catalyst. Aliaksandr et al synthesized polycrystalline Pt/C catalyst with highly defective structures through an electrochemical method ( Fichtner et al, 2020 ). Alternating voltages were applied between two Pt wire electrodes to generate the dissolution and re-deposition of Pt.…”

“…The quantitative value of micro-strain can be obtained by subtracting the effects of instrument broadening and grain size ( Chattot et al, 2018 ). In addition, defects can also be visualized and analyzed by HRTEM( Fichtner et al, 2020 ) and three-dimensional STEM tomography ( Pfisterer et al, 2019 ; Fichtner et al, 2020 ). The positron annihilation technique is also found to be an effective method for quantitatively investigate the defects in materials.…”