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D7.11 - Porous Ca-Containing MnO2 Nanorod Bundles with Superior Photoelectrochemical Activity 
April 24, 2014   4:45pm - 5:00pm

Global climate warming and environment pollution have spurred scientists to develop new high-efficient and environmental-friendly energy technologies. Hydrogen is an ideal fuel for fuel cell applications. Hydrogen has to be produced from renewable and carbon-free resources using nature energies such as sunlight if one thinks of clean energy and environmental issues. In this regard, a photoelectrochemical (PEC) cell consisting of semiconductor photoelectrodes that can harvest light and use this energy directly for splitting water is a more promising way for hydrogen generation. In the past, there has been a major research effort studying the synthesis of various manganese compounds aimed at mimicking the oxygen evolving complex of photosystem II. Of these manganese compounds, particular attention has been given to the manganese oxides, which have been shown to be multifunctional for applications of battery, supercapacitors, oxygen electrochemistry, and especially visible light-driven catalysis. Therefore, the low costs of manganese and the envisioned biomimetic character make the development of manganese oxide-based photoelectrodes for solar water splitting especially desirable. However, to date, the PEC activity of manganese oxide is still low due to poor carrier separation and transport. Recently, we report the first demonstration of hierarchically porous Ca-containing MnO2 nanorod bundles as visible-light-sensitive photofunctional nanoelectrodes to fundamentally improve the performance of MnO2 for PEC hydrogen generation. A substantial amount of Ca (up to 7.8 at%) can be in-situ incorporated into the MnO2 lattice via simple electroplating technique because of the exceptionally small feature sizes of quantum rods. The maximum photocurrent could be successfully achieved as high as 0.42 mA cm-2, which is the best value for a MnO2 photoanode. Significantly, Ca-containing MnO2 photoanodes illustrated striking PEC activity in response to visible light with a high incident photon to current conversion efficiency (IPCE) of 7% at a monochromatic wavelength of 450 nm, which is comparable to that from hematite. The improvement in photoactivity of PEC response may be attributed to the enhanced visible-light absorption, increased charge-carrier densities, and large contact area with electrolyte due to the synergistic effects of Ca incorporation and specific mesopore networks, thus contributing to photocatalysis. The new design of constructing highly photoactive Ca-containing MnO2 nanostructures sheds light on developing high efficiency photoelectrodes for solar-hydrogen field.

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Keynote Address
Panel Discussion - Different Approaches to Commercializing Materials Research
Business Challenges to Starting a Materials-Based Company
Fred Kavli Distinguished Lectureship in Nanoscience
Application of In-situ X-ray Absorption, Emission and Powder Diffraction Studies in Nanomaterials Research - From the Design of an In-situ Experiment to Data Analysis