Abstract
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.
Highlights
Unsustainable methods to obtain utilizable energy are causing global warming because of the rising CO2 concentration in the earth’s atmosphere.[1]
The average diameter of the fibers is strongly reduced to φ = 130 nm, corresponding to an overall ∼50% shrinkage upon removal of non-carbon groups, which proceeds through the formation of different gases during relevant heating.[39]
By analyzing the evolution of the nanofiber in the recorded scanning transmission electron microscopy (STEM) in situ movie snapshots taken at different temperatures, we are able to monitor the change in the number of Pt NPs at the whole fiber as well as on the edge (Figure 6b and for more details, see the discussion, eqs S1−S4, and Figures S12−S15 in the Supporting Information)
Summary
Unsustainable methods to obtain utilizable energy are causing global warming because of the rising CO2 concentration in the earth’s atmosphere.[1]. Electrochemical techniques show limitations in terms of particle size distribution and uneven surface coverage.[26,28,29] Particles larger than 50 nm are generally obtained by this process, which is quite far from the sub 5 nm size range for optimal Pt utilization These issues may be addressed to some extent by the novel process known as controlled cathodic corrosion, which exploits electrochemical biasing at low potentials to break down metallic NPs.[30] On the other hand, forming Pt NPs in situ can lead to significant enhancement of particle stability,[7,31] including more efficient charge-transfer dynamics.[32] a challenge, in this case, is making Pt NPs properly available on carbonactive surfaces, without having them embedded inside the bulk carbon phase where they are inaccessible to reactants.[31,33,34] To date, exploring and studying these aspects has been complicated, on one hand, by no positive experimental evidence of such events that exist and, on the other hand, by the difficulty to observe in situ the Pt-NP synthesis dynamics. The study of the NP dynamics formation from precursors and the subsequent segregation in carbon-based nanomaterials is highly relevant for the improved design of nanocomposites and electrochemical devices (and other fields) and for elaborating suitable models that describe how temperature affects the active surface of Pt-based electrodes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
