Facile synthesis of porous transition metal hydroxides from a poly(4-vinyl pyridine) film by controlling pH.

Non-noble transition metal hydroxides have been widely used in electrochemical devices because of low cost and multiple redox states. In particular, self-supported porous transition metal hydroxides are used to improve the electrical conductivity, as well as achieving fast electron and mass transfer and a large effective surface area. Herein, we introduce facile synthesis of self-supported porous transition metal hydroxides using a poly(4-vinyl pyridine) (P4VP) film. We used metal cyanide as a transition metal precursor capable of forming metal hydroxide anions in aqueous solution, which is the seed for transition metal hydroxides. To increase the coordination between P4VP and the transition metal cyanide precursors, we dissolved the precursors in buffer solutions with various pH. When the P4VP film was immersed in the precursor solution with lower pH, the metal cyanide precursors were sufficiently coordinated with the protonated nitrogen in P4VP. When reactive ion etching was performed on the precursor-containing P4VP film, the P4VP region without coordination was etched out and became pores. Then, the coordinated precursors were aggregated as metal hydroxide seeds and became the metal hydroxide backbone, resulting in the formation of porous transition metal hydroxide structures. We successfully fabricated various self-supported porous transition metal hydroxides (Ni(OH)2, Co(OH)2, and FeOOH). Finally, we prepared a pseudo-capacitor based on self-supported porous Ni(OH)2, which showed a good specific capacitance (780 F g-1 at 5 A g-1).

AlGaN Deep-Ultraviolet Light-Emitting Diodes with Localized Surface Plasmon Resonance by a High-Density Array of 40 nm Al Nanoparticles.

We present a remarkable improvement in the efficiency of AlGaN deep-ultraviolet light-emitting diodes (LEDs) enabled by the coupling of localized surface plasmon resonance (LSPR) mediated by a high-density array of Al nanoparticles (NPs). The Al NPs with an average diameter of ∼40 nm were uniformly distributed near the Al0.43Ga0.57N/Al0.50Ga0.50N multiple quantum well active region for coupling 285 nm emission by block copolymer lithography. The internal quantum efficiency is enhanced by 57.7% because of the decreased radiative recombination lifetime by the LSPR. As a consequence, the AlGaN LEDs with an array of Al NPs show 33.3% enhanced electroluminescence with comparable electrical properties to those of reference LEDs without Al NPs.