Quantum Confinement and Its Related Effects on the Critical Size of GeO₂ Nanoparticles Anodes for Lithium Batteries

This work has been performed to determine the critical size of the GeO₂ nanoparticle for lithium battery anode applications and identify its quantum confinement and its related effects on the electrochemical performance. GeO₂ nanoparticles with different sizes of ∼2, ∼6, ∼10, and ∼35 nm were prepared by adjusting the reaction rate, controlling the reaction temperature and reactant concentration, and using different solvents. Among the different sizes of the GeO₂ nanoparticles, the ∼6 nm sized GeO₂ showed the best electrochemical performance. Unexpectedly smaller particles of the ∼2 nm sized GeO₂ showed the inferior electrochemical performances compared to those of the ∼6 nm sized one. This was due to the low electrical conductivity of the ∼2 nm sized GeO₂ caused by its quantum confinement effect, which is also related to the increase in the charge transfer resistance. Those characteristics of the smaller nanoparticles led to poor electrochemical performances, and their relationships were discussed

Control of Architecture in Rhombic Dodecahedral Pt–Ni Nanoframe Electrocatalysts

Platinum-based alloys are known to demonstrate advanced properties in electrochemical reactions that are relevant for proton exchange membrane fuel cells and electrolyzers. Further development of Pt alloy electrocatalysts relies on the design of architectures with highly active surfaces and optimized utilization of the expensive element, Pt. Here, we show that the three-dimensional Pt anisotropy of Pt–Ni rhombic dodecahedra can be tuned by controlling the ratio between Pt and Ni precursors such that either a completely hollow nanoframe or a new architecture, the excavated nanoframe, can be obtained. The excavated nanoframe showed ∼10 times higher specific and ∼6 times higher mass activity for the oxygen reduction reaction than Pt/C, and twice the mass activity of the hollow nanoframe. The high activity is attributed to enhanced Ni content in the near-surface region and the extended two-dimensional sheet structure within the nanoframe that minimizes the number of buried Pt sites