Tailoring
of nanostructured materials with well-controlled morphologies
and their integration into valuable applications in a facile, cheap,
and green way remain a key challenge. Herein, platinum nanoparticles
as well as Pt–polymer nanocomposites with unique shapes, including
flower-, needle-, porous-, and worm-like structures, were synthesized
and simultaneously deposited on a three-dimensional carbon substrate
and carbon nanofibers in one step using a levitated, overheated water
drop as a green, rotating chemical reactor. Sprinkling of a metal
aqueous solution on a hot surface results in its sudden evaporation
and creates an overheated zone along with the water self-ionization
(i.e., charge separation) at the hot interface. These generated Leidenfrost
conditions are believed to induce a series of chemical reactions involving
the used solvent and counterions, resulting in the nanoparticles formation.
Besides, the in situ generated basic conditions in the vicinity of
the liquid–vapor interface due to the loss of hydronium ions
into the vapor layer could also play a role in the mechanism of the
nanoparticles formation, e.g., by discharging. The as-prepared Pt
nanostructures exhibited a superior catalytic activity and stability
toward the desired direct formic acid oxidation (essential anodic
reaction in fuel cells) into CO2 without generating CO
poisoning intermediates compared to the state-of-the-art commercial
PtC electrode. The addressed nanotailoring technique is believed to
be a promising, inexpensive, and scalable way for the sustainable
manufacture of well-designed nanomaterials for future applications.
To propel the commercial success of fuel cells, increased Pt catalyst utilization is preeminent. To achieve this, advanced 3D scaffold electrode architecture with controllable porosity, thickness, etc. should be developed. Here, we present a novel technique for the fabrication of electrode structures through electrospinning, which is not only tailorable, but inexpensive and scalable. The structure is freestanding and contains carbon nanotube‐enforced carbon nanofibers, which give the electrode its structure. Pt is decorated on the surface of the fiber structures through impregnation of a Pt precursor and successive reduction. The electrode structure is hot‐pressed by inserting it between a gas diffusion layer (GDL) and a membrane to form the cathode. The novel fabrication technique is versatile and can be used to prepare electrodes of different morphologies. In this work, we demonstrate the technique by preparing a highly porous network, which shows a very high Pt utilization of approximately 90% for a loading of 0.3 mgPt cm−2. In comparison, a standard electrode prepared via a hot‐spray technique has a catalyst utilization of 60% for the same loading.
High‐temperature polymer electrolyte membrane fuel cells are promising alternatives to low temperature fuel cells, owing to their higher operating temperatures, which allow for easier water management and enhanced catalytic activity. However, their performance suffers from low oxygen solubility in the electrolyte and phosphoric acid poisoning of catalytically active Pt sites. In this work, we developed new organic additives that provide π‐π stacking of the commercially applied carbon support materials as well as variable substitutable functionalities to interact with the Pt nanoparticles. Different electrochemical methods, such as cyclic voltammetry and linear sweep voltammetry, were performed to test the effect of these organic additives on the onset potential, limiting current, and the number of transferred electrons. It is observed that the limiting currents increase for the additive‐modified Pt/C samples, whereas the onset potential for significant oxygen reduction reaction activity remains unchanged. We conclude that enhanced oxygen solubility at the electrode/electrolyte interface is the reason for the observed behavior.
The Cover Feature illustrates planar additives with a large π network and functional groups for self‐assembly via π–π‐stacking on the carbon support in high‐temperature polymer electrolyte membrane fuel cells. The polyaromatic hydrocarbon fluoranthene consists of a naphthalene unit, which is fused to a benzene unit through a five membered ring. The fluoranthene framework can interact via π–π‐interaction with the carbon, whereas the functional groups can interact with the Pt particles anchored on the support. More information can be found in the Article by Ö. Delikaya et al. on page 3892 in Issue 15, 2019 (DOI: 10.1002/celc.201900251).
Production of energy through renewable and sustainable processes are important goals for the future in the context of depleting fossil fuels and environmental pollution. In this regard fuel cell technology offers an attractive combination of highly efficient fuel utilization and environmentally friendly operation. For successful commercialization of low temperature proton exchange membrane (PEM) fuel cells, they should have a long life and a high performance.
Recently, high performance fuel cell electrodes were obtained by electrospinning a solution containing proton conducting Nafion and commercial platinum catalyst powder along with PAA as electrospinning polymer. Electrospinning of the catalyst together with Nafion ionomer resulted in enhanced triple phase boundaries which resulted in high fuel cell performance. Moreover, it was also found that the stability of the electrodes is significantly higher than the electrodes prepared from the same catalyst by conventional methods. However, carbon corrosion still ensued.
In this work, we demonstrate the stability of polyacrylic acid (PAA) - Nafion composite as a stable support due to which the Pt after the carbon corrosion does not come out of the system. On the contrary, it stays entrapped in the membrane electrode assembly giving significance performance even after the corrosion protocols/measurements. Here, we first produce Pt nanoparticles that are produced by a photochemical reaction of the precursor induced by UV light. To this, PAA and Nafion (1:2 by weight) were added and stirred overnight. The resulting solution was electrospun. (Small amount of carbon was added in some cases to get the desired conductivity) to get a Pt/PAA-Nafion catalyst as shown in transmission electron micrograph. The electrodes are first tested for electrochemical stability by potential cycling and then in the fuel cell test bench using the FCCJ recommended cell evaluation protocol.
Figure 1
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