Gold nanoparticles improve fuel-cell reactions

Gold nanoparticles improve fuel-cell reactions

2:49 AM, 13th March 2012
Gold nanoparticles improve fuel-cell reactions
Gold atoms create orderly places for iron and platinum atoms, then retreat to the periphery of the fuel cell, where they scrub CO from fuel reactions. The tighter organization and cleaner reactions extend the cell’s performance life.

RHODE ISLAND, US: Advances in fuel-cell technology have been stymied by the inadequacy of metals studied as catalysts. The drawback to platinum is that it absorbs carbon monoxide (CO) in reactions involving fuel cells powered by organic materials like formic acid. A more recently tested metal, palladium, breaks down over time.

Chemists at Brown University have created a triple-headed metallic nanoparticle that outperforms and outlasts all others at the anode end in formic-acid fuel-cell reactions. Researchers report a 4-nanometre iron-platinum-gold nanoparticle (FePtAu), with a tetragonal crystal structure, generates higher current per unit of mass than any other nanoparticle catalyst tested. Moreover, the trimetallic nanoparticle performs nearly as well after 13 hours. By contrast, another nanoparticle assembly tested under identical conditions lost nearly 90 per cent of its performance in just one-quarter of the time.

“We’ve developed a formic acid fuel-cell catalyst that is the best to have been created and tested so far. It has good durability as well as good activity,” said Shouheng Sun, Professor, Brown University. Gold plays key roles in the reaction. First, it acts as a community organizer of sorts, leading the iron and platinum atoms into neat, uniform layers within the nanoparticle. The gold atoms then exit the stage, binding to the outer surface of the nanoparticle assembly. Gold is effective at ordering the iron and platinum atoms because the gold atoms create extra space within the nanoparticle sphere at the outset. When the gold atoms diffuse from the space upon heating, they create more room for the iron and platinum atoms to assemble themselves. Gold creates crystallization at lower temperature.

Gold also removes CO from the reaction by catalyzing its oxidation. Gold helps researchers get a crystal structure called ‘face-centered-tetragonal,’ a four-sided shape in which iron and platinum atoms essentially are forced to occupy specific positions in the structure, creating more order. By imposing atomic order, iron and platinum layers bind more tightly in the structure, thus making the assembly more stable and durable, essential to better-performing and longer-lasting catalysts.

In experiments, the FePtAu catalyst reached 2809.9 mA/mg Pt (current generated per milligram of platinum), which is the highest among all NP (nanoparticle) catalysts ever reported. After 13 hours, the FePtAu nanoparticle has a mass activity of 2600mA/mg Pt, or 93 per cent of its original performance value. In comparison, the well-received platinum-bismuth nanoparticle has a mass activity of about 1720mA/mg Pt under identical experiments, and is four times less active when measured for durability.

Sen Zhang, Student, Browm University, helped with the nanoparticle design and synthesis. Shaojun Guo, Postdoctoral Student, Brown University performed electrochemical oxidation experiments. Huiyuan Zhu, Student, Brown University synthesized the FePt nanoparticles and ran control experiments.

© Brown University News



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