Stimuli‐responsive smart optical materials hold great promise for applications in active optics, display, sensing, energy conversion, military camouflage, and artificial intelligence. However, their applications are greatly restricted by the difficulty of tuning different optical properties within the same material, especially by a single stimulus. Here, magnetic modulations of multiple optical properties are demonstrated in a crystalline colloidal array (CCA) of magnetic nanorods. Small‐angle X‐ray scattering studies reveal that these nanorods form an unusual monoclinic crystal in concentrated suspensions. The CCA exhibits optical anisotropy in the form of a photonic bandgap and birefringence, thus enabling magnetic tuning of the structural color and transmittance at a rate of 50 Hz. As a proof‐of‐concept, it is further demonstrated that the fabrication of a multifunctional device for display, anticounterfeiting, and smart‐window applications based on this multiple magneto‐optical effect. The study not only provides a new model system for understanding colloidal assembly, but also opens up opportunities for new applications of smart optical materials for various purposes.
Increasing attention has now been focused on the photoelectrochemical (PEC) hydrogen evolution as a promising route to transforming solar energy into chemical fuels. Silicon is one of the most studied PEC electrode materials, but its performance is still limited by its inherent PEC instability and electrochemical inertness toward water splitting. To achieve significant PEC activities, silicon-based photoelectrodes usually have to be coupled with proper cocatalysts, and thus, the formed semiconductor-cocatalyst interface presents a critical structural parameter in the rational design of efficient PEC devices. In this study, we directly grow nanostructured pyrite-phase nickel phosphide (NiP) cocatalyst films on textured pn-Si photocathodes via on-surface reaction at high temperatures. The areal loading of the cocatalyst film can be tailored to achieve an optimal balance between its optical transparency and electrocatalytic activity. As a result, our pn-Si/Ti/NiP photocathodes demonstrate a great PEC onset potential of 0.41 V versus reversible hydrogen electrode (RHE), a decent photocurrent density of ∼12 mA/cm at the thermodynamic potential of hydrogen evolution, and an impressive operation durability for at least 6 h in 0.5 M HSO. Comparable PEC performance is also observed in 1 M potassium borate buffer (pH = 9.5) using this device.
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