Friday, November 20, 2015

Liquid ALD by Self-terminated electrodeposition of iridium electrocatalysts

Here is an interesting report on liquid ALD from NIST covered by Nanowerk News: "Remember that pair of gold electroplated earrings you bought years ago at the mall? Key to crafting their allure was the ability to place an ever-so-thin layer of valuable metal atop a less costly base material. This same strategy will be central to building the “engines” of future hydrogen-powered cars, and scientists at the National Institute of Standards and Technology (NIST) have developed a way to do it more effectively with metals rarer than gold ("Self-terminated electrodeposition of iridium electrocatalysts")."

Gray center section shows individual atomic layers of iridium NIST scientists deposited, one layer at a time, atop a base of gold, with the boundary between the two metals clarified by the green/red image at right. A top view is shown at left in gold. The deposition technique, which also works with other important metals, could produce economical catalysts for hydrogen fuel cells and water electrolysis. (Picture and text from Nanowerk)

Self-terminated electrodeposition of iridium electrocatalysts

Sang Hyun Ahn,   Haiyan Tan,   Mareike Haensch,   Yihua Liu,   Leonid A. Bendersky and   Thomas P. Moffat.
Energy Environ. Sci., 2015, Advance Article
DOI: 10.1039/C5EE02541A

A simple electrochemical process for submonolayer deposition of ultrathin catalytic Ir films is demonstrated. This method enables effective utilization of one of nature's rarest elements while different substrates facilitate the exploration of promising bimetallic catalysts for a sustainable hydrogen economy. Semi-coherent Ir films were deposited on Au, Pt and Ni substrates using K3IrCl6–Na2SO4–H2SO4 electrolytes operated between 40 °C and 70 °C. However, the deposition reaction is quenched at the onset of H2 production where adsorbed H blocks the reduction of IrCl6−xH2Oxx−3 to Ir. The electrode can be reactivated for further deposition by pulsing the potential to more positive values where adsorbed H is oxidized. The electrocatalytic activity of ultrathin Ir and Pt films, and combinations thereof, were examined as function of the number of self-terminating deposition pulses. The ultrathin films match or exceed the best reported activity metrics for hydrogen oxidation in alkaline media and oxygen evolution in acid.