Event
Surface Analysis of PtNi Nanowires for Improved Catalytic Performance Webinar
Presented by Dr. Sarah Zaccarine
Polymer electrolyte membrane fuel cells (PEMFCs) are a promising technology for sustainable energy generation, offering high efficiency and minimal environmental impact -- by producing only water and heat as byproducts. However, widespread adoption has been hindered by challenges, such as the slow oxygen reduction reaction (ORR) kinetics at the cathode and the high cost of platinum (Pt) catalysts. Addressing these challenges requires the development of durable, low-Pt-content catalysts with high activity. Creating bi- and tri-metallic catalysts can improve both performance and stability by altering the d-band of the Pt metal while reducing the amount of Pt required, which also lowers cost. Atomic layer deposition (ALD) is one method to create controlled layers of metal shells on a nanowire core, and post-synthesis modifications can tune the properties of the metals to improve activity plus durability.
Characterizing these structures requires analysis of surface and subsurface composition, bonding, and distribution with high resolution both laterally and with depth. All three Surface analysis techniques available from Physical Electronics can be combined to obtain a more thorough understanding of these properties. Auger electron spectroscopy (AES) provides high-resolution imaging and elemental analysis to assess homogeneity of individual wires. X-ray photoelectron spectroscopy (XPS) adds chemical state analysis of multiple wires, which will infulence the reactivity of metals at the outermost surface. Hard X-ray photoelectron spectroscopy (HAXPES) with the use of Cr Ka extends the analysis depth threefold, to compare composition and chemistry beneath the surface. HAXPES is also highly suitable for mixed-transition-metal materials, which often have many overlapping peaks, complicating data interpretation. Finally, time-of-flight secondary ion mass spectrometry (TOF-SIMS) can be used to detect surface contamination from synthesis and post-synthesis treatments. Its high surface sensitivity can add information on what is at the extreme surface, where the electrocatalytic reaction will occur.
In this webinar, platinum nickel (PtNi) and platinum nickel cobalt (PtNiCo) nanowires (NWs) were investigated with AES, XPS, HAXPES, and TOF-SIMS. The ALD-synthesized NWs were exposed to annealing and acid leaching processes to improve electrocatalytic properties of the Pt as well as create more durable catalysts that can withstand device conditions. Results highlight a tradeoff in properties between initial annealing and acid leaching. The final catalysts have a blend of beneficial properties for high activity and longer-term stability. Integrating PHI's complementary analytical techniques allows a detailed understanding of the complex chemical nature of the catalysts, enabling the design of more robust and efficient PEMFC catalysts with reduced platinum content.