RESUMEN
A careful design of the nanocrystal architecture can strongly enhance the nanocrystal function. So far, this strategy has faced a synthetic bottleneck in the case of refractory oxides. Here we demonstrate the epitaxial growth of hafnia shells onto zirconia cores and pure zirconia shells onto europium-doped zirconia cores. The core/shell structures are fully crystalline. Upon shelling, the optical properties of the europium dopant are dramatically improved (featuring a more uniform coordination and a longer photoluminescence lifetime), indicating the suppression of nonradiative pathways. These results launch the stable zirconium and hafnium oxide hosts as alternatives for the established NaYF4 systems.
RESUMEN
The investigation of high-efficiency and sustainable electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media is critical for renewable energy technologies. Here, we report a low-cost and high-yield method to obtain ZnOHF-ZnO-based 2D nanostars (NSs) by means of chemical bath deposition (CBD). The obtained NSs, cast onto graphene paper substrates, were used as active materials for the development of a full water splitting cell. For the HER, NSs were decorated with an ultralow amount of Pt nanoparticles (11.2 µg cm-2), demonstrating an overpotential of 181 mV at a current density of 10 mA cm-2. The intrinsic activity of Pt was optimized, thanks to the ZnO supporting nanostructures, as outlined by the mass activity of Pt (0.9 mA mgPt-1) and its turnover frequency (0.27 s-1 for a Pt loading of 11.2 µg cm-2). For the OER, bare NSs showed a remarkable result of 355 mV at 10 mA cm-2 in alkaline media. Pt-decorated and bare NSs were used as the cathode and anode, respectively, for alkaline electrochemical water splitting, assessing a stable overpotential of 1.7 V at a current density of 10 mA cm-2. The reported data pave the way toward large-scale production of low-cost electrocatalysts for green hydrogen production.
