Article
Multi-Technique Characterization of PtNi Nanowires for Enhanced Durability and Efficiency
Surface Analysis Spotlight: XPS
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by Jennifer Mann Product Manager/Senior Staff Scientist |
Polymer electrolyte membrane (PEM) devices offer numerous benefits, including the production of clean hydrogen or electricity with no emissions. These devices have a high energy density and operate at low temperatures, making them highly efficient. Their versatility allows for a wide range of applications, from automotive to stationary and portable uses. Moreover, PEM fuel cells and water electrolyzers can work together in tandem, providing a clean, full-cycle production of hydrogen and its conversion into electricity. PEM fuel cells (PEMFCs) specifically can convert hydrogen into electricity, producing only water and heat as byproducts, which makes them environmentally friendly.
However, there are several challenges to overcome in the development and operation of PEM devices. The kinetics of the oxygen reduction reaction (ORR) at the cathode is a significant challenge, along with the high cost of platinum (Pt) catalysts. The primary goal in advancing PEM technology is to develop a novel catalyst that contains low Pt content while maintaining high activity and durability for extended device operation. Consequently, advancing PEMFCs requires progress in catalyst technologies to overcome these limitations. Previous studies have investigated the synthesis of extended-surface platinum-nickel (PtNi) nanowires (NWs) through atomic layer deposition (ALD) and examined their durability.1
In this work, we demonstrate how the composition and chemical states of the nanowires transform after a series of post-synthetic modifications aimed at maximizing their longevity as catalysts. The characteristics of the as synthesized, annealed, acid leached, and reannealed PtNi NWs were investigated using several techniques including X-ray photoelectron spectroscopy (XPS), hard X-ray photoelectron spectroscopy (HAXPES), and Auger electron spectroscopy (AES). After synthesis, there are multiple surface oxides of Ni present in all samples, with the least amount of oxidation occurring in the acid leached and reannealed samples. Comparison of the XPS and HAXPES results shows there is increased presence of Ni metal below the surface for all the samples. Through the integration of complementary surface analytical techniques, including XPS, HAXPES, and AES, we construct a more comprehensive model of the intricate chemical nature of these catalysts than any individual technique could achieve on its own. This approach accelerates the development of more durable and efficient PEMFC catalysts.
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Figure 1: PHI 710 SEM images of nanowires after each processing step. Each image shows a 10 um field of view. Hollow nanowires are clearly visible after the acid leaching step, indicating that acid leaching has successfully removed the nickel wire core, a critical step for improved durability during fuel cell operation.
For more information on how complementary analytical techniques can measure the properties of catalysts used in polymer electrolyte membrane fuel cells, please attend the upcoming talk at ECASIA 24 where Dr. Jennifer Mann will discuss the " Multi-Technique Characterization of PtNi Nanowires for Enhanced Durability and Efficiency.”