The Ni/NiO core/shell structure is one of the most efficient co-catalysts for solar water splitting when coupled with suitable semiconducting oxides. It has been shown that pretreated Ni/NiO core/shell structures are more active than pure Ni metal, pure NiO or mixed dispersion of Ni metal and NiO nanoparticles. However, Ni/NiO core/shell structures on TiO 2 are only able to generate H 2 but not O 2 in aqueous water. The nature of the hydrogen evolution reaction in these systems was investigated by correlating photochemical H 2 production with atomic resolution structure determined with aberration corrected electron microscopy. It was found that the core/shell structure plays an important role for H 2 generation but the system undergoes deactivation due to a loss of metallic Ni. During the H 2 evolution reaction, the metal core initially formed partial voids which grew and eventually all the Ni diffused out of the coreshell into solution leaving an inactive hollow NiO void structure. The H 2 evolution was generated by a photochemical reaction involving photocorrosion of Ni metal.3

Ni-NiO core-shell co-catalyst structures on Ta 2 O 5 have been investigated for solar H 2 production. Core-shell co-catalysts with different morphologies resulted in large changes in photocatalytic activity. Increased H 2 production was found to be related to an increase in the thickness of NiO shell due to suppression of the back reaction.Atomic level transmission electron microscopy showed that the core-shell co-catalyst structures deactivated primarily due to a loss of metallic Ni from the core structure.During deactivation, the catalyst transformed either to structures consisting of NiO nanoblocks or hollow NiO shells. The phase transformations occurring during deactivation were associated with Ni diffusion processes that are driven by light illumination.

Understanding the role of water, hydrate and hydroxyl species on nanoparticle surfaces and interfaces is very important in both physical and life sciences. Detecting the presence of oxygen-hydrogen species with nanometer resolution is extremely challenging at present. Here we show that the recently developed vibrational electron energy-loss spectroscopy using subnanometer focused electron beams can be employed to spectroscopically identify the local presence and variation of OH species on nanoscale surfaces. The hydrogen-oxygen fingerprint can be correlated with highly localized structural and morphological information obtained from electron imaging. Moreover, the current approach exploits the aloof beam mode of spectral acquisition which does not require direct electron irradiation of the sample thus greatly reducing beam damage to the OH bond. These findings open the door for using electron microscopy to probe local hydroxyl and hydrate species on nanoscale organic and inorganic structures.

This paper reports the effects of synthesis time, temperature, and reactant ratio on ZIF-71 particle size and the effect of particle size on membrane performance. Temperature has the greatest effect on particle size, as the synthesis temperature varies from −20 °C to 35 °C. The synthesized ZIF-71 has particle diameters ranging from 150 nm to 1 μm. ZIF-71 particle size is critical in ZIF-71/PDMS composite membrane performance for ethanol and 1-butanol removal from water through pervaporation. The membranes that are made with micrometer-sized ZIF-71 particles exhibit higher alcohol/ water selectivity than those with smaller particles. Both alcohol and water permeability increase when larger-sized ZIF-71 particles are incorporated, because the pathways through the membranes are less tortuous.

Strategies for protecting unstable semiconductors include the utilization of surface layers composed of thin films deposited using atomic layer deposition (ALD). The protective layer is expected to (1) be stable against reaction with photogenerated holes, (2) prevent direct contact of the unstable semiconductor with the electrolyte, and (3) prevent the migration of ions through the semiconductor/electrolyte interface, while still allowing photogenerated carriers to transport to the interface and participate in the desired redox reactions. Zinc oxide (ZnO) is an attractive photocatalyst material due to its high absorption coefficient and high carrier mobilities. However, ZnO is chemically unstable and undergoes photocorrosion, which limits its use in applications such as in photoelectrochemical cells for water splitting or photocatalytic water purification. This article describes an investigation of the band alignment, electrochemical properties, and interfacial structure of ZnO coated with AlO and SiO ALD layers. The interface electronic properties were determined using in situ X-ray and UV photoemission spectroscopy, and the photochemical response and stability under voltage bias were determined using linear sweep voltammetry and chronoamperometry. The resulting surface structure and degradation processes were identified using atomic force, scanning electron, and transmission electron microscopy. The suite of characterization tools enable the failure mechanisms to be more clearly discerned. The results show that the rapid photocorrosion of ZnO thin films is only slightly slowed by use of an AlO ALD coating. A 4 nm SiO layer proved to be more effective, but its protection capability could be affected by the diffusion of ions from the electrolyte.