Smart Windows Get Boost from Novel Self-Assembled Porous Yolk-Shell NiO Nanospheres Exhibiting Impressive Electrochromic Capabilities

Researchers from Tsinghua University synthesized porous yolk-shell NiO nanospheres (PYS-NiO NSs) via a solvent thermal calcination and subsequent calcination process of Ni-MOF. Because the large specific surface areas and hollow porous nanostructures were favorable for ion transport, PYS-NiO NS showed fast coloration/bleaching speed (3.6/3.9 s per coloration/bleaching cycle) and excellent rotational stability (82% holding power thereafter). 3000 cycles). These superior electronegativity (EC) properties indicated that PYS-NiO NSs were a promising candidate for high-performance EC devices.

The team published their work in the journal particle science.

Electrochromic materials (ECMs) are defined as materials that have reversible changes in their colors and optical properties (transmittance, reflectance, and absorption) under different external voltages. Over the past decades, ECM has shown promising advantages and application prospects in many fields such as smart windows, adaptive camouflage, electronic displays, energy storage, etc., due to its excellent optical modulation capabilities.

Transition metal oxides (TMOs) are one of the most important and extensively studied ECMs. They have many advantages such as rich nanoscale design, simple synthesis process, high security, etc. Among them, nickel oxide (NiO) is an attractive ECM anode and has attracted widespread research attention due to its high optical contrast, high staining efficiency, low cost, etc.

However, NiO-based ECMs still face the challenges of long EC switching times and poor cycling lives caused by poor ionic/electronic diffusion kinetics and low electrical conductivity.

Metal-organic frameworks (MOFs) have received much attention, due to their high porosity and large surface areas, and they can be modified to achieve different properties by selecting different metal ions and organic bridge bonds.

Due to their porosity and long-range order, MOFs can provide fast and convenient channels for small molecules and ions to enter and extract during the transformation process. Therefore, MOFs can be used as efficient templates to prepare hollow, porous TMO systems with high ion transfer efficiency, excellent specific capacitance, and electrochemical activities.

Therefore, the authors proposed a new strategy to design a type of NiO with hollow and porous structure to obtain excellent EC performance and cyclic stability. As a proof-of-concept, the authors successfully synthesized porous yolk-derived MOF-derived NiO NSs (PYS-NiO NSs) that showed excellent EC performance.

The nickel organic framework pellets were prepared by a simple thermosolvent method and then converted into PYS-NiO NSs by thermal decomposition. The PYS-NiO NSs exhibited relatively high specific surface areas and stable hollow nanostructures, which not only provided a large contact area between the active sites and electrolyte ions in the EC process but also helped the NiO to accommodate large size changes without fracture.

In addition, the PYS-NiO NS also shortened the ionic diffusion length and provided efficient channels for the transport of electrons and ions. In addition, carbon coupling also made the PYS-NiO NSs with improved electronic conductivity and obtained better EC performance. The PYS-NiO NSs exhibited a fast staining/bleaching speed (3.6/3.9 s).

PYS-NiO NS also showed excellent cycling stability (82% holding capacity after 3000 cycles). The superior EC properties indicate that PYS-NiO NSs are a promising candidate for high-performance EC devices. The as-prepared PYS-NiO NSs are believed to be a promising candidate for smart windows, displays, anti-glare rear-view mirrors, etc. periodic stability.