One-Dimensional Cuprous Selenide Nanostructures with Switchable Plasmonic and Super-ionic Phase Attributes

Metal selenide nanomaterials for biomedical applications

Metal selenide nanomaterials have received enormous attention as they possess diverse compositions, microstructures, and properties. The combination of selenium with various metallic elements gives the metal selenide nanomaterials distinctive optoelectronic and magnetic properties, such as strong near-infrared absorption, excellent imaging properties, good stability, and long in vivo circulation. This makes metal selenide nanomaterials advantageous and promising for biomedical applications. This paper summarizes the research progress in the last five years in the controlled synthesis of metal selenide nanomaterials in different dimensions and with different compositions and structures. Then we discuss how surface modification and functionalization strategies are well-suited for biomedical fields, including tumor therapy, biosensing, and antibacterial biological applications. The future trends and issues of metal selenide nanomaterials in the biomedical field are also discussed.

Superionic Conduction in One-Dimensional Nanostructures

Nanostructuring has become a powerful tool for tuning the electronic properties of materials and enhancing transport. As an example of relevance to next-generation battery technologies, nanocrystals have shown promise for realizing fast-ion conduction in solids; however, dissipationless ion transport over extended length scales is hindered by lossy interfaces formed between nanocrystals in a solid. Here we address this challenge by exploiting one-dimensional nanostructures for ion transport. Superionic conduction, with a record-high ionic conductivity of ∼4 S/cm at 150 °C, is demonstrated in solid electrolytes fabricated from nanowires of the earth-abundant solid copper selenide. This quasi-one-dimensional ionic conductivity is ∼5× higher than that in bulk cuprous selenide. Nanoscale dimensions in the radial direction lower ion-hopping barriers, while mesoscopically long, interface-free transport paths are available for ion transport in the axial direction. One-dimensional nanostructures can exceptionally boost solid-state devices that rely on ion transport.

Plasmon-Assisted Ammonia Electrosynthesis

Ammonia is a promising liquid-phase carrier for the storage, transport, and deployment of carbon-free energy. However, the realization of an ammonia economy is predicated on the availability of green methods for the production of ammonia powered by electricity from renewable sources or by solar energy. Here, we demonstrate the synthesis of ammonium from nitrate powered by a synergistic combination of electricity and light. We use an electrocatalyst composed of gold nanoparticles, which have dual attributes of electrochemical nitrate reduction activity and visible-light-harvesting ability due to their localized surface plasmon resonances. Plasmonic excitation of the electrocatalyst induces ammonium synthesis with up to a 15× boost in activity relative to conventional electrocatalysis. We devise a strategy to account for the effect of photothermal heating of the electrode surface, which allows the observed enhancement to be attributed to non-thermal effects such as energetic carriers and charged interfaces induced by plasmonic excitation. The synergy between electrochemical activation and plasmonic activation is the most optimal at a potential close to the onset of nitrate reduction. Plasmon-assisted electrochemistry presents an opportunity for conventional limits of electrocatalytic conversion to be surpassed due to non-equilibrium conditions generated by plasmonic excitation.

Motion of Defects in Ion-Conducting Nanowires

Superionic conductors are prime candidates for the electrolytes of all-solid-state batteries. Our understanding of the mechanism and performance of superionic conductors is largely based on their idealized lattice structures. But how do defects in the lattice affect ionic structure and transport in these materials? This is a question answered here by in situ transmission electron microscopy of copper selenide, a classic superionic conductor. Nanowires of copper selenide exhibit antiphase boundaries which are a form of a planar defect. We examine the lattice structure around an antiphase boundary and monitor with atomic resolution how this structure evolves in an ordered-to-superionic phase transition. Antiphase boundaries are found to act as barriers to the propagation of the superionic phase. Antiphase boundaries also undergo spatial diffusion and shape changes resulting from thermally activated fluctuations of the neighboring ionic structure. These spatiotemporal insights highlight the importance of collective ionic transport and the role of defects in superionic conduction.