Facets and vertices regulate hydrogen uptake and release in palladium nanocrystals.

Crystal facets, vertices and edges govern the energy landscape of metal surfaces and thus the chemical interactions on the surface1,2. The facile absorption and desorption of hydrogen at a palladium surface provides a useful platform for defining how metal-solute interactions impact properties relevant to energy storage, catalysis and sensing3-5. Recent advances in in operando and in situ techniques have enabled the phase transitions of single palladium nanocrystals to be temporally and spatially tracked during hydrogen absorption6-11. We demonstrate herein that in situ X-ray diffraction can be used to track both hydrogen absorption and desorption in palladium nanocrystals. This ensemble measurement enabled us to delineate distinctive absorption and desorption mechanisms for nanocrystals containing exclusively (111) or (100) facets. We show that the rate of hydrogen absorption is higher for those nanocrystals containing a higher number of vertices, consistent with hydrogen absorption occurring quickly after ß-phase nucleation at lattice-strained vertices9,10. Tracking hydrogen desorption revealed initial desorption rates to be nearly tenfold faster for samples with (100) facets, presumably due to the faster recombination of surface hydrogen atoms. These results inspired us to make nanocrystals with a high number of vertices and (100) facets, which were found to accommodate fast hydrogen uptake and release.

Solution-Deposited Solid-State Electrochromic Windows.

Commercially available electrochromic (EC) windows are based on solid-state devices in which WO3 and NiOx films commonly serve as the EC and counter electrode layers, respectively. These metal oxide layers are typically physically deposited under vacuum, a time- and capital-intensive process when using rigid substrates. Herein we report a facile solution deposition method for producing amorphous WO3 and NiOx layers that prove to be effective materials for a solid-state EC device. The full device containing these solution-processed layers demonstrates performance metrics that meet or exceed the benchmark set by devices containing physically deposited layers of the same compositions. The superior EC performance measured for our devices is attributed to the amorphous nature of the NiOx produced by the solution-based photodeposition method, which yields a more effective ion storage counter electrode relative to the crystalline NiOx layers that are more widely used. This versatile method yields a distinctive approach for constructing EC windows.

Ammonia-Containing Species Formed in Cu-Chabazite As Per In Situ EPR, Solid-State NMR, and DFT Calculations.

Nowadays, the most attractive technology for the elimination of nitric oxides from the exhaust gas of diesel vehicles is the selective catalytic reduction with ammonia (NH3-SCR-NOx) using Cu zeolite with the chabazite structure as the catalyst. Isolated copper species are the active sites, but the reaction intermediates and the overall reaction mechanism are still under debate. Here, we study the interaction of ammonia with zeolite Cu-SSZ-13 (CHA topology) with a uniform distribution of Cu(2+) sites prepared in one pot and a conventional Cu-ZSM-5 (MFI topology) for comparison. In situ EPR and solid-state NMR spectroscopies combined with DFT calculations have allowed the identification of NH4(+), [Cu(NH3)5](2+), [Cu(Of)2(NH3)2](2+), [Cu(Of)3NH3](2+), [Cu(NH3)2](+), and [CuOf(NH3)](+) (Of being framework oxygen) under different conditions. The results demonstrate that ammonia is able to reduce Cu(2+) to Cu(+) and provide new information on the species formed in Cu-SSZ-13, which have important implications for the elucidation of the SCR reaction mechanism.