Abstract
Anisotropic heterogenous Ni/NiO nanoparticles with controlled compositions are grown using a high-power pulsed hollow cathode process. These novel particles can be tuned to consist of single-phase Ni via two-phase Ni/NiO to fully oxidized NiO, with a size range of 5–25 nm for individual crystals. A novelty of this approach is the ability to assemble multiple particles of Ni and NiO into a single complex structure, increasing the Ni-NiO interface density. This type of particle growth is not seen before and is explained to be due to the fact that the process operates in a single-step approach, where both Ni and O can arrive at the formed nanoparticle nuclei and aid in the continuous particle growth. The finished particle will then be a consequence of the initially formed crystal, as well as the arrival rate ratio of the two species. These particles hold great potential for applications in fields, such as electro- and photocatalysis, where the ability to control the level of oxidation and/or interface density is of great importance.Graphical abstract
Highlights
Ni/NiO composite materials are of interest in a number of applications, including energy-related hydrogen evolution (Wang et al 2017), lithium ion batteries (Bell et al 2015), and supercapacitors (Liu et al 2017)
We demonstrate the ability to grow Ni/ NiO nanoparticles with interconnected interfaces and how to tune their composition ranging from pure Ni to pure NiO by using a hollow cathode pulsed plasma process (Pilch et al 2013)
There is a thin shell with a thickness of ~ 1–2 nm assumed to be NiO formed after exposing the pure Ni surface to air (Jesús et al 1996)
Summary
Ni/NiO composite materials are of interest in a number of applications, including energy-related hydrogen evolution (Wang et al 2017), lithium ion batteries (Bell et al 2015), and supercapacitors (Liu et al 2017). The existence of NiO shifts the d-states of surface Ni atoms down in energy and enhances the reactivity of the exposed Ni surface. This has been demonstrated experimentally using nanoparticles attached to a carbon nanotube network (Gong et al 2014). Common to all of these applications, the partially oxidized nanoparticles display the best results. This means that to synthesize the Bdualphase^ Ni/NiO material to perform at its best, it is important to be able to precisely control both the Ni/NiO composition and their amount of interfaces
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