Chemical Imaging of Hierarchical Porosity Formation within a Zeolite Crystal Visualized by Small-Angle X-Ray Scattering and In-Situ Fluorescence Microscopy.

Introducing hierarchical porosity to zeolites is vital for providing molecular access to microporous domains. Yet, the dynamics of meso- and macropore formation has remained elusive and pore space ill-characterized by a lack of (in situ) microscopic tools sensitive to nanoporosity. Here, we probe hierarchical porosity formation within a zeolite ZSM-5 crystal in real-time by in situ fluorescence microscopy during desilication. In addition, we introduce small-angle X-ray scattering microscopy as novel characterization tool to map intracrystal meso- and macropore properties. It is shown that hierarchical porosity formation initiates at the crystal surface and propagates to the crystal core via a pore front with decreasing rate. Also, hierarchical porosity only establishes in specific (segments of) subunits which constitute ZSM-5. Such space-dependent meso- and macroporosity implies local discrepancies in diffusion, performance and deactivation behaviors even within a zeolite crystal.

Basicity and Electrolyte Composition Dependent Stability of Ni-Fe-S and Ni-Mo Electrodes during Water Splitting.

Non-noble metal electro-catalysts for water splitting are highly desired when we are moving towards a society where green electrons are becoming abundantly available, offering clear prospects to make our society more sustainable. In this work, Ni-Fe-S is reported as a high performing anode material for the water splitting reaction, operating at low overpotentials and showing high apparent stability. Furthermore, Ni-Mo electrodes are developed on metallic foam substrates and optimized in terms of their performance. The Ni-Fe-S material as anode, combined and integrated with Ni-Mo as cathode in a cell configuration, splits water at 10 mA cm-2 and a potential of 1.55 V. Similar to previous reports, we confirm that Mo leaches from Ni-Mo/Ni foam electrodes. Cycling tests and ICP-AES measurements show that the stability of Ni-Fe-S is apparent, and that in reality S is leaching from the material as was already suggested in literature. We expand on this knowledge and show that the leaching of S is dependent on both pH and the cation used during electrocatalysis. Furthermore, we find that applying an oxidative potential is in truth stabilizing towards S and that the alkalinity causes leaching. S was furthermore mobile and found to segregate towards the surface. Finally, using too low pH values (11 and lower) result in the passivating hydroxide metal layers being destroyed and the Ni-Fe-S dissolving completely.

Template-Free Nanostructured Fluorine-Doped Tin Oxide Scaffolds for Photoelectrochemical Water Splitting.

The synthesis and characterization of highly stable and conductive F:SnO2 (FTO) nanopyramid arrays are investigated, and their use as scaffolds for water splitting is demonstrated. Current densities during the oxygen evolution reaction with a NiFeOx catalyst at 2 V vs reversible hydrogen electrode were increased 5-fold when substituting commercial FTO (TEC 15) by nanostructured FTO scaffolds. In addition, thin α-Fe2O3 films (∼50 nm thick) were employed as a proof of concept to show the effect of our nanostructured scaffolds during photoelectrochemical water splitting. Double-layer capacitance measurements showed a drastic increase of the relative electrochemically active surface area for the nanostructured samples, in agreement with the observed photocurrent enhancement, whereas UV-vis spectroscopy indicates full absorption of visible light at wavelengths below 600 nm.