Shape-controlled synthesis of Pt-Ir nanocubes with preferential (100) orientation and their unusual enhanced electrocatalytic activities

Abstract

Pt-Ir nanocubes with (100)-terminated facets were synthesized for the first time and their unusual high electrocatalytic activity for a model reaction (i.e., ammonia oxidation) was reported. The key parameters in controlling the shape of the PtIr nanocubes were systematically investigated by transmission electron microscopy (TEM). The electrocatalytic activities of the prepared Pt-Ir and pure Pt nanoparticles (NPs) were characterized by cyclic voltammetry (CV). The results showed that the amount of W(CO) 6 and the volume ratio of oleylamine and oleic acid play a significant role in the development of well-defined Pt-Ir nanocubes. The resultant Pt-Ir nanocubes exhibit (100) orientation, which has been confirmed by not only the structural characterization results from high-resolution TEM (HRTEM) and X-ray diffraction (XRD) but also hydrogen desorption profiles obtained from the CV measurements in H 2 SO 4 solution. Lattice contraction of the Pt-Ir nanocubes were suggested by HRTEM and XRD measurements, and the electronic interactions between Pt and Ir in the Pt-Ir nanocubes were demonstrated by X-ray photoelectron spectroscopy. The Pt-Ir nanocubes show higher specific activity than pure Pt nanocubes and much higher specific activity than the polycrystalline Pt-Ir NPs. The much improved specific activity of the Pt-Ir nanocubes could be attributed to the reason that the introduction of Ir in the Pt-Ir nanocubes largely maintains the highly active Pt (100) sites and thus a positive synergistic effect through the addition of Ir to Pt could be achieved due to the possible bifunctional mechanism and the electronic effect.

Nanostructured Pt Surfaces with Ir Submonolayers for Enhanced NH3 Electro‐oxidation

“…0.67 mA cm À2 , see Figure S8c) was rather unexpected. Similar enhancement was obtained for Pt-rich PtIr nanocubes with highly crystalline-oriented (100) structures, [41] and for Pt-rich PtIr alloyed electrodeposits (Pt 90 Ir 10 ) in low NH 3 concentrations electrolyte ( 0.01 M). Also, the deposition of the same amount of Ir atoms (Ir PD5 ) did not enhance the NH 3 activity of poly-oriented Pt ( Figure S8d).…”

A one-step, clean, capping-agent-free electrochemical approach to prepare Pt nanoparticles with preferential (100) orientation and their high electrocatalytic activities

“…To show the intrinsic activity, the current is normalized by the ECSA. There is an anodic current peak at − 0.36 V (SCE), corresponding to the electro-oxidation of ammonia [13,16,17]. Previous work from our group found that if the CV was measured in KOH solution without ammonia, there was no such characteristic current peak [22].…”

“…For example, Pt nanoparticles exposing (100) surfaces have been found to benefit a wide variety of catalytic reactions such as ammonia electro-oxidation [8], dimethyl ether electro-oxidation [10], methanol and ethanol electro-oxidation [11], oxygen reduction reaction in H 2 SO 4 medium [9], and electrocatalytic hydrogenation of 2-cyclohexenone [12]. Therefore, it has received great attention to prepare (100)-oriented Pt nanoparticles [7][8][9][10][11]13].…”

“…The effect of the preferential orientation of Pt nanoparticles on their electrocatalytic activity for ammonia electro-oxidation was investigated by cyclic voltammetry (CV). The ammonia electro-oxidation was selected as a model reaction since this reaction is highly sensitive to the Pt (100) sites [8,13,15,16]. Besides, the ammonia electro-oxidation has attracted considerable attention since it addresses not only the environmental protection but also the clean energy supply without CO x [1,17].…”

Understanding of the major reactions in solution synthesis of functional nanomaterials

“…The Pt nanocubes in a 8 nm size obtained by introducing trace amount of Fe(CO)5 in octadecene, with the combination of OAm/OAc, were consistently reported by several research groups [208][209][210]. Afterwards, Hu and co-authors [211] presented that the W(CO)6 can be used to generate the Pt-It nanocubes bounded with {100} facets. Absolutely, further endeavors should be made to better understand the kinetic effects of CO gas so as to achieve an efficiently utilization of CO gas in the synthesis of colloidal metal and metal alloy NCs.…”