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Materials

Ancient reaction inspires method for making porous catalysts

A nontoxic variation on the ‘pharaoh’s snakes’ reaction yields high-surface-area catalysts for fuel cells

by Katherine Bourzac, special to C&EN
April 22, 2018 | APPEARED IN VOLUME 96, ISSUE 17

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Credit: ACS Appl. Mater. Interfaces
When ignited, melamine, sugar, iron nitrate, and baking soda produce a snakelike, porous catalyst precursor.

A recipe for a new electrocatalyst takes inspiration from an ancient reaction used in fireworks for making the wispy, elongated char known as pharaoh’s snakes. The newly reported version of the reaction converts a simple mix of ingredients to a high-surface-area, nanostructured catalyst for oxygen reduction in fuel cells and zinc-air batteries (ACS Appl. Mater. Interfaces 2018, DOI: 10.1021/acsami.7b16936). The carbon-, nitrogen-, and iron-containing material is much cheaper than the platinum or ruthenium dioxide it would replace. Ying Zhu of Beihang University was inspired by a YouTube video demonstrating the pharaoh’s snake: When a small mound of mercury thiocyanate powder is ignited, a series of reactions releases large amounts of gas, and the material forms long, highly porous, foamy ropes of carbon nitride that rise from the flames like snakes rearing their heads. Applying this principle to electrocatalysts, Zhu, Liming Dai of Case Western Reserve University, and colleagues ignited a combination of melamine (the nitrogen source), iron nitrate, sugar (the carbon source), and baking soda. The material grew into a snaky rope as it burned. After annealing at 1,000 °C, the researchers crushed the catalyst and used it in a methanol fuel cell and a zinc-air battery. The fuel cell operated at 0.9 volts, slightly better than platinum-catalyzed fuel cells. In the zinc-air battery, the new material functioned comparably to the standard, ruthenium dioxide. To be practical for fuel cells, the material must outperform platinum not just in alkaline solutions, as in these experiments, but also in acid. That’s a goal for future work, Dai says.

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