This Review article explores the use of illumination to direct the growth of metal and semiconductor nanostructures.

Photoexcitation can be used to control the composition and nanoscale morphology of inorganic materials. Here we report the photoinduced transformation of faceted cuprous oxide (Cu 2 O) microcrystals to hollow particles consisting of an inner region of cuprous oxide and an outer shell of copper metal. When cuprous oxide microcrystals with mixed {100} and {111} facets are held at a negative bias (−1.0 V vs Ag/AgCl) in a solution of sodium hydroxide (NaOH), light mediates the growth of copper metal selectively on the {100} facets while the crystal interior is etched at {111} facets. Conformal Cu layers grow to connect at vertices of the cuboctahedral microcrystals and form a hollow shell. This process is only observed in the presence of illumination. Without an applied bias the {100} facets are preferentially etched under illumination in the same NaOH solution. We propose this light-driven, facet-selective transformation arises from the potential-dependent structure and energetics of the semiconductor/electrolyte interface, which lead to facet-selective extraction of photogenerated electrons from the {100} facets when the applied bias is more negative than the flat-band potential of the Cu 2 O microcrystals. Growth of the Cu shell protects the {100} facets while the {111} facets are chemically etched in the presence of oxygen and hydroxide.

Direct methanol fuel cells (DMFCs) have been the focus of future research because of their simple structure, abundant fuel sources, high energy conversion efficiency and low cost. Among the components in DMFC, the activity and stability of the cathode catalyst is the key to the performance and lifetime of the DMFCs. Oxygen reduction reaction (ORR) is an important electrode reaction on DMFC cathode. It is known that Pt is widely used in the fabrication of ORR catalysts, but the limited earth storage of Pt and its high price limit the use of Pt-based commercial catalysts in DMFCs. To overcome these problems, advances have been made on new low Pt-based catalysts and Pt-free catalysts in recent years. In this article, the development of novel ORR catalysts and the carbon supports is reviewed and discussed.

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