Effects of Capping Agents on the Oxygen Reduction Reaction Activity and Shape Stability of Pt Nanocubes

Abstract

We investigated the formation of Pt nanocubes (NCs) and their electrocatalytic oxygen reduction reaction (ORR) properties and structural stability using two different capping agents, namely, polyvinylpyrrolidone (PVP) and oleylamine (OAm). The mono‐dispersity of the obtained Pt NCs and their interactions with PVP and OAm were analyzed by transmission electron microscopy (TEM), energy dispersive X‐ray spectroscopy (EDX), X‐ray photoelectron spectroscopy (XPS), Fourier‐transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The TEM data show a high mono‐dispersity (82 %) and a large mean particle size (9‐10 nm) for the Pt NCs obtained by the oleylamine‐assisted method compared to those prepared via the PVP‐assisted procedure (68 %, 6–7 nm). FTIR, XPS, and TGA data show that PVP and OAm still remain at the Pt surface, despite washing. Interestingly, the OAm‐capped Pt NCs show significantly higher electrochemically active surface area (ECSA) and ORR activity than the PVP‐capped ones. An accelerated stress protocol, however, reveals that the OAm‐capped NCs possess a poor structural stability during electrochemical cycling. The loss of a defined surface arrangement in the NCs is connected with a transformation into a near‐spherical particle shape. In contrast, the PVP‐capped NCs mainly retain their particle shape due to their strong capping behavior. In addition, we have developed a degradation model for NCs as a function of electrochemical parameters such as upper potential and cycle number. Altogether, we provide fundamental insights into the electronic interactions between capping agent and Pt NCs and the role of the adsorption strength of the capping agent in improving the electrochemical ORR performance as well as the structural stability of shape‐controlled nanoparticles.

Real-time imaging of nanoscale electrochemical Ni etching under thermal conditions

“… 44 A reasonable possibility is oxidation of the capping agent oleylamine, since it has been reported that oleylamine is unstable during electrochemical cycling at potentials higher than 1.0 V per RHE. 45 These results emphasize the benefits of operando imaging methods: electrochemical analysis alone does not readily distinguish between Ni dissolution and side reactions such as oxidation of capping agents, whereas images are most sensitive to the removal of metallic species, with changes in the surfactant not highly visible. The combination of electrochemical analysis and in situ imaging provides a more complete picture of the etching process.…”

Activation Matters: Hysteresis Effects during Electrochemical Looping of Colloidal Ag Nanowire Catalysts

“…This implies that only the product distribution (ratio of FECO and FEH2 values) is altered by this treatment, whereas the total current density normalized to the geometric surface area (total transferred charge) remains unaffected. This is an important distinction between the current study and previous studies on catalyst activation processes in which only a single electrocatalytic reaction needs to be considered (e.g., ORR 40,49,55 , OER 49 , or HER 37 ) and where increased reaction rates directly correlate with an increase of the electrochemically active surface area (ECSA). [53][54] In order to elaborate on which experimental factors contribute to the observed change in the product distribution (e.g.…”

Effect of Nanoparticle Size in Pt/SiO2 Catalyzed Nitrate Reduction in Liquid Phase

“…Chemisorbed PVP ligands were reported to enhance the catalytic activity in the liquid phase reaction by stabilizing the metal nanocrystals [ 57 ]. The pyrrolidone ring of chemisorbed PVP interacts with the Pt surface and that interaction can serve as the electron donor–acceptor media between PVP and the Pt surface [ 58 ]. However, the interaction of PVP ligands with the metal via the O atom in the ring can accompany the charge transfer from PVP to the metal, and the PVP interaction via the N atom in the ring can accompany the charge transfer from the metal to PVP [ 59 ].…”