Nucleation of nanoparticles using
the exsolution phenomenon is
a promising pathway to design durable and active materials for catalysis
and renewable energy. Here, we focus on the impact of surface orientation
of the host lattice on the nucleation dynamics to resolve questions
with regards to “preferential nucleation sites”. For
this, we carried out a systematic model study on three differently
oriented perovskite thin films. Remarkably, in contrast to the previous
bulk powder-based study suggesting that the (110)-surface is a preferred
plane for exsolution, we identify that other planes such as (001)-
and (111)-facets also reveal vigorous exsolution. Moreover, particle
size and surface coverage vary significantly depending on the surface
orientation. Exsolution of (111)-oriented film produces the largest
number of particles, the smallest particle size, the deepest embedment,
and the smallest and most uniform interparticle distance among the
oriented films. Based on classic nucleation theory, we elucidate that
the differences in interfacial energies as a function of substrate
orientation play a crucial role in controlling the distinct morphology
and nucleation behavior of exsolved nanoparticles. Our finding suggests
new design principles for tunable solid-state catalyst or nanoscale
metal decoration.
Cathode materials are usually active in the range of 2–4.3 V, but the decomposition of the electrolytic salt above 4 V versus Na+/Na is common. Arguably, the greatest concern is the formation of HF after the reaction of the salts with water molecules, which are present as an impurity in the electrolyte. This HF ceaselessly attacks the active materials and gradually causes the failure of the electrode via electric isolation of the active materials. In this study, a bioinspired β‐NaCaPO4 nanolayer is reported on a P2‐type layered Na2/3[Ni1/3Mn2/3]O2 cathode material. The coating layers successfully scavenge HF and H2O, and excellent capacity retention is achieved with the β‐NaCaPO4‐coated Na2/3[Ni1/3Mn2/3]O2 electrode. This retention is possible because a less acidic environment is produced in the Na cells during prolonged cycling. The intrinsic stability of the coating layer also assists in delaying the exothermic decomposition reaction of the desodiated electrodes. Formation and reaction mechanisms are suggested for the coating layers responsible for the excellent electrode performance. The suggested technology is promising for use with cathode materials in rechargeable sodium batteries to mitigate the effects of acidic conditions in Na cells.
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