Helium nanodroplets doped with copper and water

Stefan Raggl,Paul Scheier,Paul Martini,Norbert Gitzl,Olof Echt

doi:10.1140/epjd/e2018-90150-7

Stefan Raggl, Paul Scheier + Show 3 more

Open Access

https://doi.org/10.1140/epjd/e2018-90150-7

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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)2Cum+ or the isobaric (H2O)n−1OCum+, could not be detected. We do observe an interesting anomaly though: While the abundance of stoichiometric (H2O)nCum+ 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+.Graphical abstract

Highlights

Copper nanoparticles dispersed in water or in the form of coatings have a range of promising uses, including lubrication, ink jet printing, as luminescent probes, exploiting their antimicrobial and antifungal activity, and in fuel cells [1,2,3,4,5,6]
Mass spectra show that H2 production would be the reaction (H2O)–Cu complexes containing dozens of copper and water molecules can be formed in the helium droplets
Splitting of water adsorbed on copper cluster ions followed by generation and escape of H2 would be described by the reaction (H2O)nCum+ → (H2O)n−2(OH)2Cum+ + H2, (1)

Summary

Introduction

Copper nanoparticles dispersed in water or in the form of coatings have a range of promising uses, including lubrication, ink jet printing, as luminescent probes, exploiting their antimicrobial and antifungal activity, and in fuel cells [1,2,3,4,5,6]. Theoretical studies of the reaction of water with surfaces of crystalline copper have been reported by Johansson et al [8] and Lousada et al [9]. Huseyinova et al have reported the synthesis of surfactant-free, nearly mono-disperse Cu5 clusters in water that are stable to UV irradiation, elevated temperature, and a wide range of pH [13] Their catalytic activity has not yet been measured, but several theoretical studies of water dissociation on Cu7 have been reported [14,15,16]. (H2O)nOHCu+ complexes have been characterized by vibrational spectroscopy and collision-induced dissociation [29,30,31,32] as well as theoretical modeling [31] In contrast to these numerous studies of (H2O)nCu+. The significance of those observations for our results will be discussed

Experiment

Experimental results

Copper-water complexes

Copper–helium complexes

Conclusion