On the Theoretical and Experimental Control of Defect Chemistry and Electrical and Photoelectrochemical Properties of Hematite Nanostructures.

Hematite (α-FeO) is regarded as one of the most promising cost-effective and stable anode materials in photoelectrochemical applications, and its performance, like other transition-metal oxides, depends strongly on its electrical and defect properties. In this work, the electrical and thermomechanical properties of undoped and Sn-doped α-FeO nanoscale powders were characterized in situ at controlled temperatures ( T = 250 to 400 °C) and atmospheres ( pO = 10 to 1 atm O) to investigate their transport and defect properties. Frequency-dependent complex impedance spectra show that interfacial resistance between particles is negligible in comparison with particle resistance.

In Situ/Operando X-ray Spectroscopies for Advanced Investigation of Energy Materials.

Issues related to energy and the environment have now become of central and crucial importance in our societies. Low-carbon green energy will have a critical role in a necessary third industrial revolution. To reduce global greenhouse gas emissions in response to globalization and increasingly stringent carbon emission policies, large scale green energy production technologies must be established worldwide.

Stability and Performance of Sulfide-, Nitride-, and Phosphide-Based Electrodes for Photocatalytic Solar Water Splitting.

With the past decade of worldwide sustained efforts on artificial photosynthesis for photocatalytic solar water splitting and clean hydrogen generation by dedicated researchers and engineers from different disciplines, substantial progress has been achieved in raising its overall efficiency along with finding new photocatalysts. Various materials, systems, devices, and better fundamental understandings of the interplay between interfacial chemistry, electronic structure, and photogenerated charge dynamics involved have been developed. Nevertheless, the overall photocatalytic performance is yet to achieve its maximum theoretical limit.

Atomic-Scale Origin of Long-Term Stability and High Performance of p-GaN Nanowire Arrays for Photocatalytic Overall Pure Water Splitting.

The atomic-scale origin of the unusually high performance and long-term stability of wurtzite p-GaN oriented nanowire arrays is revealed. Nitrogen termination of both the polar (0001¯) top face and the nonpolar (101¯0) side faces of the nanowires is essential for long-term stability and high efficiency. Such a distinct atomic configuration ensures not only stability against (photo) oxidation in air and in water/electrolyte but, as importantly, also provides the necessary overall reverse crystal polarization needed for efficient hole extraction in p-GaN.

On the orbital anisotropy in hematite nanorod-based photoanodes.

The orbital anisotropy of hematite (α-Fe2O3) nanorod arrays, an engineered structure commonly investigated for applications in solar water oxidation photoanodes, is probed using polarization-dependent soft X-ray absorption spectroscopy at the O K-edge and at the Fe L2,3-edge. Thereby the unoccupied states of α-Fe2O3 are examined. In the lowest energy region these are found to be strongly-hybridized Fe 3d (a1g) orbitals and O(2-) ligand 2p orbitals, oriented along the c-axis.

Electron enrichment in 3d transition metal oxide hetero-nanostructures.

Direct experimental observation of spontaneous electron enrichment of metal d orbitals in a new transition metal oxide heterostructure with nanoscale dimensionality is reported. Aqueous chemical synthesis and vapor phase deposition are combined to fabricate oriented arrays of high-interfacial-area hetero-nanostructures comprised of titanium oxide and iron oxide nanomaterials. Synchrotron-based soft X-ray spectroscopy techniques with high spectral resolution are utilized to directly probe the titanium and oxygen orbital character of the interfacial region's occupied and unoccupied densities of states.