Regular Article

Helium nanodroplets doped with copper and water^★,

¹ Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria
² Physics Department, University of New Hampshire, Durham NH 03824, USA

^a e-mail: paul.scheier@uibk.ac.at
^b e-mail: olof.echt@unh.edu

Received: 2 April 2018
Received in final form: 10 May 2018
Published online: 12 July 2018

Abstract

Copper nanoparticles are promising, low-cost candidates for the catalytic splitting of water and production of hydrogen gas. The present gas-phase study, based on the synthesis of copper-water complexes in ultracold helium nanodroplets followed by electron ionization, attempts to find evidence for dissociative water adsorption and H₂ formation. Mass spectra show that H₂O–Cu complexes containing dozens of copper and water molecules can be formed in the helium droplets. However, ions that would signal the production and escape of H₂, such as (H₂O)_n−2(OH)₂Cu_m⁺ or the isobaric (H₂O)_n−1OCu_m⁺, could not be detected. We do observe an interesting anomaly though: While the abundance of stoichiometric (H₂O)_nCu_m⁺ ions generally exceeds that of protonated or dehydrogenated ions, the trend is reversed for (H₂O)OHCu₂⁺ and (H₂O)₂OHCu₂⁺; these ions are more abundant than (H₂O)₂Cu₂⁺ and (H₂O)₃Cu₂⁺, respectively. Moreover, (H₂O)₂OHCu₂⁺ is much more abundant than other ions in the (H₂O)_n−1OHCu₂⁺ series. A byproduct of our experiment is the observation of enhanced stability of He₆Cu⁺, He₁₂Cu⁺, He₂₄Cu⁺, and He₂Cu₂⁺.