Atomic Replacement of PtNi Nanoalloys within Zn-ZIF-8 for the Fabrication of a Multisite CO2 Reduction Electrocatalyst.

Exploring the transformation/interconversion pathways of catalytic active metal species (single atoms, clusters, nanoparticles) on a support is crucial for the fabrication of high-efficiency catalysts, the investigation of how catalysts are deactivated, and the regeneration of spent catalysts. Sintering and redispersion represent the two main transformation modes for metal active components in heterogeneous catalysts. Herein, we established a novel solid-state atomic replacement transformation for metal catalysts, through which metal atoms exchanged between single atoms and nanoalloys to form a new set of nanoalloys and single atoms. Specifically, we found that the Ni of the PtNi nanoalloy and the Zn of the ZIF-8-derived Zn1 on nitrogen-doped carbon (Zn1-CN) experienced metal interchange to produce PtZn nanocrystals and Ni single atoms (Ni1-CN) at high temperature. The elemental migration and chemical bond evolution during the atomic replacement displayed a Ni and Zn mutual migration feature. Density functional theory calculations revealed that the atomic replacement was realized by endothermically stretching Zn from the CN support into the nanoalloy and exothermically trapping Ni with defects on the CN support. Owing to the synergistic effect of the PtZn nanocrystal and Ni1-CN, the obtained (PtZn)n/Ni1-CN multisite catalyst showed a lower energy barrier of CO2 protonation and CO desorption than that of the reference catalysts in the CO2 reduction reaction (CO2RR), resulting in a much enhanced CO2RR catalytic performance. This unique atomic replacement transformation was also applicable to other metal alloys such as PtPd.

High-efficiency CO2 separation using hybrid LDH-polymer membranes.

Membrane-based gas separation exhibits many advantages over other conventional techniques; however, the construction of membranes with simultaneous high selectivity and permeability remains a major challenge. Herein, (LDH/FAS)n-PDMS hybrid membranes, containing two-dimensional sub-nanometre channels were fabricated via self-assembly of unilamellar layered double hydroxide (LDH) nanosheets and formamidine sulfinic acid (FAS), followed by spray-coating with a poly(dimethylsiloxane) (PDMS) layer. A CO2 transmission rate for (LDH/FAS)25-PDMS of 7748 GPU together with CO2 selectivity factors (SF) for SF(CO2/H2), SF(CO2/N2) and SF(CO2/CH4) mixtures as high as 43, 86 and 62 respectively are observed. The CO2 permselectivity outperforms most reported systems and is higher than the Robeson or Freeman upper bound limits. These (LDH/FAS)n-PDMS membranes are both thermally and mechanically robust maintaining their highly selective CO2 separation performance during long-term operational testing. We believe this highly-efficient CO2 separation performance is based on the synergy of enhanced solubility, diffusivity and chemical affinity for CO2 in the sub-nanometre channels.

Alkali-Etched Ni(II)-Based Metal-Organic Framework Nanosheet Arrays for Electrocatalytic Overall Water Splitting.

The exploration of efficient electrocatalysts is the central issue for boosting the overall efficiency of water splitting. Herein, pertinently creating active sites and improving conductivity for metal-organic frameworks (MOFs) is proposed to tailor electrocatalytic properties for overall water splitting. An Ni(II)-MOF nanosheet array is presented as an ideal material model and a facile alkali-etched strategy is developed to break its NiO bonds accompanied with the introduction of extra-framework K cations, which contribute to creating highly active open metal sites and largely improving the electrical conductivity. As a result, the assembled defect-Ni-MOF||defect-Ni-MOF electrolyte cell delivers a lower and stable voltage of 1.50 V at 10 mA cm-2 in alkaline medium for overall water splitting, comparable to the combination of iridium and platinum as benchmark catalysts.

Rational Localization of Metal Nanoparticles in Yolk-Shell MOFs for Enhancing Catalytic Performance in Selective Hydrogenation of Cinnamaldehyde.

The development of sustainable catalysts to simultaneously improve activity and selectivity remains a challenge. Herein, it is demonstrated that metal nanoparticles (MNPs) can be encapsulated into a yolk-shell metal-organic framework (MOF) with controllable spatial localization to optimize catalytic performance. When the MNPs are located in the void space between the shell and the core of the MOF, the resulting MNPs@MOF composites show both high catalytic activity and selectivity toward the hydrogenation of α,ß-unsaturated aldehydes. In particular, the easily recoverable and stable Ptvoid @MOF(Y) shows an exceptionally high selectivity of 98.2 % for cinnamyl alcohol at a high conversion of 97 %. The excellent performance can be attributed to easy diffusion of the reactants to access highly exposed MNPs in the MOF support, as well as the improved adsorption of the reactant and desorption of the product due to the appropriate metal-support interaction and rich void space between core and shell.

Partial Sulfurization of a 2D MOF Array for Highly Efficient Oxygen Evolution Reaction.

A feasible strategy for the in situ growth of two-dimensional (2D) [Ni3(OH)2(1,4-BDC)2-(H2O)4]·2H2O (Ni-BDC; 1,4-BDC = 1,4-benzenedicarboxylate) and the subsequent partial sulfurization treatment for the decoration of nickle sulfide (NiS) is developed. The fabricated hierarchically structured Ni-BDC@NiS as a synergistic electrocatalyst shows extremely high activity toward the oxygen evolution reaction (OER). The optimal Ni-BDC@NiS catalyst acquires a current density of 20 mA cm-2 at a lower overpotential of 330 mV and low Tafel slope of 62 mV dec-1, outperforming most previously reported Ni-based sulfide catalysts. Clearly, the combination of the NiS and Ni-BDC array contributed to the improvement of electron transfer, promotion of water adsorption, and increase of rich active species. In addition, the in situ created hierarchical structure not only affords feasible access for mass transport but also strengthens structural integrity, contributing to efficient and stable OER performance. This general and effective strategy anchoring conductive active species on a porous metal-organic framework (MOF) thus provides an efficient way to fabricate synergistic electrocatalysts for the OER.

Ultrafast switching of an electrochromic device based on layered double hydroxide/Prussian blue multilayered films.

Electrochromic materials are the most important and essential components in an electrochromic device. Herein, we fabricated high-performance electrochromic films based on exfoliated layered double hydroxide (LDH) nanosheets and Prussian blue (PB) nanoparticles via the layer-by-layer assembly technique. X-ray diffraction and UV-vis absorption spectroscopy indicate a periodic layered structure with uniform and regular growth of (LDH/PB)n ultrathin films (UTFs). The resulting (LDH/PB)n UTF electrodes exhibit electrochromic behavior arising from the reversible K(+) ion migration into/out of the PB lattice, which induces a change in the optical properties of the UTFs. Furthermore, an electrochromic device (ECD) based on the (LDH/PB)n-ITO/0.1 M KCl electrolyte/ITO sandwich structure displays superior response properties (0.91/1.21 s for coloration/bleaching), a comparable coloration efficiency (68 cm(2) C(-1)) and satisfactory optical contrast (45% at 700 nm), in comparison with other inorganic material-based ECDs reported previously. Therefore, this work presents a facile and cost-effective strategy to immobilize electrochemically active nanoparticles in a 2D inorganic matrix for potential application in displays, smart windows and optoelectronic devices.

Humidity-triggered self-healing films with excellent oxygen barrier performance.

Hybrid films were fabricated via layer-by-layer assembly of layered double hydroxide (LDH) nanoplatelets and poly(sodium styrene-4-sulfonate) (PSS) followed by subsequent permeation of poly(vinyl alcohol) (PVA), which show excellent oxygen barrier performance with humidity-triggered self-healing capability.

Reversible thermally-responsive electrochemical energy storage based on smart LDH@P(NIPAM-co-SPMA) films.

A smart supercapacitor was fabricated by loading a thermosensitive polymer P(NIPAM-co-SPMA) onto the surface of NiAl-layered double hydroxide (LDH) nanowalls grown on a flexible Ni foil substrate, which displays temperature-triggered on-off ion channels for controlling the electrochemical behavior.