Nanostructuring offers a pathway toward achieving new material properties that can radically enhance their energy storage and conversion abilities. We focus on two examples that utilize the nanoscale properties to modulate and enhance their energy storage and conversion functionalities. In the first example, we use the plasmonic properties of Au nanoparticles to sensitize and enhance the photocatalytic activities of SrTiO3, a wide band gap semiconductor. SrTiO3 has long been known to be an active photocatalyst for solar-driven water splitting. However, its large band gap (3.2 eV) renders only the UV portion of the solar spectrum usable for photocatalysis. To extend the usability to the visible, we take advantage of the work function and the plasmonic properties of the Au nanoparticle to form a Schottky junction that can capture the visible light-induced hot electron from Au, effectively sensitizing the SrTiO3 substrate. We demonstrate that such junction is capable of conducting photo-electro-oxidation of water, ferrocyanide, hydrogen, and methanol, using excitation in the visible range. In another example, we utilize few nanometer-thick manganese oxides (LaMnO3) that have been epitaxially grown on a SrTiO-3 substrate for the oxygen reduction reaction (ORR). We demonstrate that the ORR activities of the LaMnO3 films can be modulated by changing the thickness of the manganite layer, which can be attributed to the competing interactions between SrTiO3, LaMnO3, and the electrolyte. In the thinnest LaMnO3 film, the interaction between SrTiO3 and the electrolyte is the strongest, causing a charge transfer to LaMnO3. This disrupts its ability to inject electron to the O2 and turns off the film's ORR activity. With thicker LaMnO3 film (> 10 nm), the interactions between SrTiO3 and LaMnO3, and LaMnO3 and the electrolyte become stronger. This reduces the charge transfer effect and consequently, the ORR activity approaches the bulk LaMnO3 value.

Modulation of electrocatalytic and photocatalytic properties of transition metal oxides by nanostructuring

246th National Meeting (2013)

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