Carbon-based nanofibers decorated with metallic nanoparticles (NPs) as hierarchically structured electrodes offer significant opportunities for use in low-temperature fuel cells, electrolyzers, flow and air batteries, and electrochemical sensors. We present a facile and scalable method for preparing nanostructured electrodes composed of Pt NPs on graphitized carbon nanofibers. Electrospinning directly addresses the issues related to large-scale production of Pt-based fuel cell electrocatalysts. Through precursors containing polyacrylonitrile and Pt salt electrospinning along with an annealing protocol, we obtain approximately 180 nm thick graphitized nanofibers decorated with approximately 5 nm Pt NPs. By in situ annealing scanning transmission electron microscopy, we qualitatively resolve and quantitatively analyze the unique dynamics of Pt NP formation and movement. Interestingly, by very efficient thermal-induced segregation of all Pt from the inside to the surface of the nanofibers, we increase overall Pt utilization as electrocatalysis is a surface phenomenon. The obtained nanomaterials are also investigated by spatially resolved Raman spectroscopy, highlighting the higher structural order in nanofibers upon doping with Pt precursors. The rationalization of the observed phenomena of segregation and ordering mechanisms in complex carbon-based nanostructured systems is critically important for the effective utilization of all metal-containing catalysts, such as electrochemical oxygen reduction reactions, among many other applications.
COBISS.SI-ID: 27163395
Herein a modified floating electrode (MFE) approach for investigating the electrochemical phenomena at a gas/electrode/liquid reaction interface is introduced. Such investigation is in sharp contrast to conventional electrochemical techniques, which measure the properties of electrode/liquid interfaces. MFE is based on an apparatus that enables electrocatalytic conversion under enhanced mass transport of reactant gas. This is enabled by the floating regime of the working electrode that presents a low mass transport barrier for the gas. The present MFE is designed to take the advantage of transmission electron microscopy (TEM) grids with a deposited electrocatalyst of choice, to be used as working electrodes. The applicability of MFE is demonstrated on the example of oxygen reduction reaction (ORR), an essential segment in the sector of electrochemical energy conversion. The approach is validated on two state-of-the-art industrial benchmarks ORR electrocatalysts, a carbon-supported platinum (Pt/C) nanoparticulated electrocatalyst and an alloyed counterpart (Pt-Co/C). It is shown that MFE enables acquisition of the two most vital catalyst features in one measurement sequence. Firstly, it allows for rapid electrochemical performance measurements of potential ORR electrocatalysts under high oxygen transport, specifically high current densities. Secondly, it enables the local characterization of nanostructural events via identical location transmission electron microscopy (IL-TEM).
COBISS.SI-ID: 39249411