Designing TiO₂/Au/Prussian blue heterostructures nanorod arrays for ultra-stable cycle and ultra-fast response electrochromism

Prussian blue (PB) is an anodic coloring candidate in the wide area of electrochromic (EC) applications. However, the co-influence of weak adhesion and low electrical conductivity leads to the poor stability and slow switching speed. To tackle this bottleneck, a novel TiO₂/Au/PB nanorod array is designed through hydrothermal and electrodeposition approaches on fluorine-doped tin oxide (FTO) glass. Such a designed ternary array structure could not only increase reactive site and conductivity, but also improve ion storage capacity and promote charge transfer, attributed to the synergistic effect of TiO₂/Au/PB core–shell heterostructure and the localized surface plasmon resonance (LSPR) effect of Au nanoparticles. Besides, density functional theory (DFT) calculation confirms the strong interaction between rutile TiO₂ and FTO substrate, which contributes to the improvement of EC cycle stability. Benefiting from these effects, the TiO₂/Au/PB film shows a fast coloration/bleaching response of 1.08/2.01 s (2.17/4.48 s, PB film) and ultra-stable EC performance of 86.8% after 20,000 cycles (50% after 600 cycles, PB film). Furthermore, the high-intensity light source can be shot clearly by the designed and assembled EC iris device (ECID) with TiO₂/Au/PB film as an EC layer, while the photograph without an ECID is blurry, confirming the feasibility of the material in portable digital products.