Noble metals have important applications in an array of fields including hydrogen storage and sensing, chemical catalysis, and fuel cells. They offer high volumetric power density in metal hydride batteries and pseudocapacitors. However, the kinetics of chemical reactions at their surfaces are often limited by the high stability of surface-bound species. Theoretical[1] and experimental[2],[3] reports suggest that adlayers of other metals can destabilize the surface species, which should increase chemical reaction rates.

We have developed a room-temperature electroless atomic layer deposition (ALD) technique in which we grow adlayers of other metals on palladium and platinum substrates.[4] The method contrasts with electrochemical ALD,[3] which requires applying a current to a substrate, and to gas-phase ALD, which requires elevated temperatures that can damage some substrates. Exposing a substrate to dilute hydrogen/nitrogen gas mixtures causes a surface hydride to form. Subsequent addition of a solution containing noble metal salts displaces the surface hydride with the reduced metal in a surface-limited reaction. This process can be repeated, and the thickness of the surface coverage increases, as shown by X-ray photoelectron spectroscopy. We have developed variations of the method that allow a nanoporous layer to be grown in a stepwise manner, and that use aqueous reducing agents to form the hydride instead of hydrogen gas.

This technique requires no specialized equipment, and makes use of benign reagents. It is surface-limited in nature, but is not limited to an electrode. This confers important advantages of high scalability and compatibility with complex surface topologies; conductive substrates are not required. We believe that this versatile technique could be widely applied by synthetic chemists to take advantage of enhanced catalytic properties of near-surface alloys.

This work was supported by the Laboratory-Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government. SAND2018-3092 A

[1] Greeley, J.; Mavrikakis, M. J. Phys. Chem. B 2005, 109, 3460−3471.

[2] Bartlett, P. N.; Marwan, J. Phys. Chem. Chem. Phys.2004, 6, 2895−2898.

[3] Sheridan, L. B.; Yates, V. M.; Benson, D. M.; Stickney, J. L.; Robinson, D. B. Electrochim. Acta 2014, 128, 400−405.

[4] Cappillino, P. J.; Sugar, J. D.; El Gabaly, F.; Cai, T. Y.; Liu, Z.; Stickney, J. L.; Robinson, D. B. Langmuir 2014, 30, 4820−4829.