Introducing copper ions into a host material (tantalum (IV) sulfide) with PDII. Hydrogen ions force out sodium ions from phosphate glass; these sodium ions then force out copper ions from CuI, shooting them into nanometer-level gaps in tantalum (IV) sulfide. Excessive copper ions crystalize around the tantalum (IV) sulfide as copper metal (right image). Images: Fujioka M. et al., Journal of the American Chemical Society, November 16, 2017.A team of researchers at Hokkaido University in Japan has developed a novel material synthesis method called proton-driven ion introduction (PDII) that utilizes a phenomenon similar to ‘ion billiards’. This new method could pave the way for creating numerous new materials, thus drastically advancing materials science.
The novel synthesis method is based on a liquid-free process for inserting guest ions into a host material, known as intercalation, and replacing existing ions in the host material with new ions, known as ion substitution, by driving the ions with protons. This study, led by Masaya Fujioka and Junji Nishii at Hokkaido University’s Research Institute for Electric Science, is described in a paper in the Journal of the American Chemical Society.
Conventionally, intercalation and ion substitution are conducted in an ion solution, but this liquid-based process is regarded as cumbersome and problematic. Solvent molecules can be inserted into the host materials along with the guest ions, degrading the crystal quality, while introducing ions into host materials homogeneously can be difficult and some host materials are simply not suitable for use with liquids.
The PDII method, by contrast, involves applying a voltage of several kilovolts to a needle-shaped anode placed in atmospheric hydrogen to generate protons (hydrogen ions) via the electrolytic disassociation of hydrogen. The protons migrate along the electric field and are shot into a source of the desired ions – similar to firing a cue ball at a group of balls in billiards. This drives the ions out of the source material and causes them to be introduced, or intercalated, into a nanometer-level gap in the host material.
With this process, the team succeeded in homogenously introducing lithium ions (Li+), sodium ions (Na+), potassium ions (K+), copper ions (Cu+) and silver ions (Ag+) into nanometer-level gaps in tantalum (IV) sulfide (TaS2), a layered material, while maintaining its crystallinity. Furthermore, the team successfully substituted sodium ions in Na3V2(PO4)3 with potassium ions, producing a thermodynamically metastable material that cannot be obtained with conventional solid-state reaction methods.
“At present, we have shown that hydrogen ions (H+), Li+, Na+, K+, Cu+ and Ag+ can be used to introduce ions in our method, and we expect a larger variety of ions will be usable. By combining them with various host materials, our method could enable the production of numerous new materials,” says Fujioka. “In particular, if a method to introduce negatively charged ions and multivalent ions is established, it will spur the development of new functional materials in the solid ion battery and electronics fields.”
This story is adapted from material from Hokkaido University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.