Synthesis and Characterization of Diverse Pt Nanostructures in Nafion

Abstract

With the aid of TEM characterization, we describe two distinct Pt nanostructures generated via the electroless reduction of Pt(NH3)4(NO2)2 within Nafion. Under one set of conditions, we produce bundles of Pt nanorods that are 2 nm in diameter and 10-20 nm long. These bundled Pt nanorods, uniformly distributed within 5 μm of the Nafion surface, are strikingly similar to the proposed hydrated nanomorphology of Nafion, and therefore strongly suggestive of Nafion templating. By altering the reaction environment (pH, reductant strength, and Nafion hydration), we can also generate nonregular polyhedron Pt nanoparticles that range in size from a few nanometers in diameter up to 20 nm. These Pt nanoparticles form a dense Pt layer within 100-200 nm from the Nafion surface and show a power-law dependence of particle size and distribution on the distance from the Nafion membrane surface. Control over the distribution and the type of Pt nanostructures in the surface region may provide a cost-effective, simple, and scaleable pathway for enhancing manufacturability, activity, stability, and utilization efficiency of Pt catalysts for electrochemical devices.

Controlling Nanoparticle Interconnectivity in Thin-Film Platinum Catalyst Layers

“…An intense burst of nucleation is triggered by borohydride addition, then quenched after several minutes. Under these nucleation and growth conditions, extremely small crystallites are achieved (down to 1.5 nm in diameter) in contrast with high aspect ratio single-crystal Pt nanorods previously obtained using 1 h of slower, preferential growth . High-resolution field emission SEM shows dense clusters of white Pt nanoparticles in a band at the Nafion surface with a few scattered particles buried deeper into the membrane (Figure , top and middle).…”

“…Under these nucleation and growth conditions, extremely small crystallites are achieved (down to 1.5 nm in diameter) in contrast with high aspect ratio single-crystal Pt nanorods previously obtained using 1 h of slower, preferential growth. 10 Transmission X-ray diffraction (XRD) shows the broadened peaks expected for a highly nanostructured Pt film (Figure S1). Bright-field TEM on ultramicrotomed sections of the embedded Pt layer reveal a wide particle size distribution approximately in the 2−7 nm range (Figure 1, bottom and in Figures S2−S5).…”

“…Electroless Deposition. The electroless deposition followed the procedure detailed by us previously, 10 with several small modifications. A piece of Nafion is held clamped between two chambers, allowing different solutions to access each side.…”

“…In this work, we utilize an electrolessly deposited thin film of nanostructured Pt nanoparticles on Nafion membrane similar to our previously described process. 10 Briefly, a concentration gradient of cationic Pt species is established inside a divided cell separated with a Nafion membrane. This Pt species is reduced with borohydride, and Pt nanoparticles are formed at the solution interface of the membrane.…”

Influence of Pt Nanoparticle Electroless Deposition Parameters on the Electrochemical Characteristics of Nafion-Based Catalyst-Coated Membranes

“…The amount of Pt deposition on the membrane was determined by inductively coupled plasma−atomic emission spectroscopy (ICP-AES) after treatment of the membrane with aqua regia (a solution that contains a ratio of 1:3 mixtures of concentrated HNO 3 and HCl). 18 2.3. Physicochemical Characterization of the CCMs.…”