Wet Method Grows Ultrathin Films

Researchers at the National Institute of Standards & Technology have developed a wet-phase analog of atomic layer deposition (ALD), a gas-phase thin-film growth method, and used it to prepare highly active iridium catalysts for water splitting (Energy Environ. Sci. 2015, DOI: 10.1039/c5ee02541a). ALD is touted for its ability to grow a predetermined number of atomic layers of a material only where the film is wanted, but the method requires costly, dedicated equipment. So NIST staff scientist Thomas P. Moffat and coworkers developed an inexpensive solution phase alternative. The team showed that its electrochemical layer-by-layer technique can be used to grow ultrathin films of iridium, a rare and expensive catalytic metal, by using an electrolyte solution containing K₃IrCl₆, Na₂SO₄, and H₂SO₄. The scientists grew films of iridium on gold, platinum, and nickel and evaluated them as catalysts for water splitting, a process that generates valuable hydrogen fuel. The team reports that the catalytic activity of its iridium films, just one monolayer thick, matches the top performing bulk polycrystalline iridium electrodes, demonstrating that the new deposition method provides a simple way to use this precious metal efficiently.