Effect of Tin Doping on α-Fe₂O₃ Photoanodes for Water Splitting

Sputter-deposited films of α-Fe₂O₃ of thickness 600 nm were investigated as photoanodes for solar water splitting and found to have photocurrents as high as 0.8 mA/cm² at 1.23 V vs the reversible hydrogen electrode (RHE). Sputter-deposited films, relative to nanostructured samples produced by hydrothermal synthesis,, permit facile characterization of the role and placement of dopants. The Sn dopant concentration in the α-Fe₂O₃ varies as a function of distance from the fluorine-doped tin oxide (FTO) interface and was quantified using secondary ion mass spectrometry (SIMS) to give a mole fraction of cations of approximately 0.02% at the electrolyte interface. Additional techniques for determining dopant density, including energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), electrochemical impedance spectroscopy (EIS), and conductivity measurements, are compared and discussed. Based on this multifaceted data set, we conclude that not all dopants present in the α-Fe₂O₃ are active. Dopant activation, rather than just increasing surface area or dopant concentration, is critical for improving metal oxide performance in water splitting. A more complete understanding of dopant activation will lead to further improvements in the design and response of nanostructured photoanodes

Robust Composite-Shell Microcapsules via Pickering Emulsification

Microencapsulation technology has been increasingly applied toward the development of self-healing paints. Added to paint as a dry powder prior to spraying, the microcapsules store a liquid that can repair the protective barrier layer if released into a scratch. However, self-healing will not occur unless the microcapsules can withstand spray-painting, aggressive solvents in the paint, and long-term exposure to the elements. We have therefore developed a one-pot synthesis for the production of Pickering microcapsules with outstanding strength, solvent resistance, and barrier properties. Octadecyltrimethoxysilane-filled (OTS) microcapsules form via standard interfacial polycondensation, except that silica nanopowder (10–20 nm diameter) replaces the conventional surfactant or hydrocolloid emulsifier. Isophorone diisocyanate (IPDI) in the OTS core reacts with diethylenetriamine, polyethylenimine, and water to form a hard polymer shell along the interface. Compared to pure polyurea, the silica-polyurea composite improves the shelf life of the OTS by 10 times. The addition of SiO₂ prevents leaching of OTS into xylenes and hexanes for up to 80 days, and the resulting microcapsules survive nebulization through a spray gun at 620 kPa in a 500 cSt fluid