Alkali-induced Transformation of Ni-MOF into Ni(OH)2 Nanostructured Flowers for Efficient Electrocatalytic Methanol Oxidation Reaction

Zirconium-based metal-organic frameworks and their roles in electrocatalysis

Due to their exceptional chemical stability in water and high structural tunability, zirconium(IV)-based MOFs (Zr-MOFs) have been considered attractive materials in the broad fields of electrocatalysis. Numerous studies published since 2015 have attempted to utilise Zr-MOFs in electrocatalysis, with the porous framework serving as either the active electrocatalyst or the scaffold or surface coating to further enhance the performance of the actual electrocatalyst. Herein, the roles of Zr-MOFs in electrocatalytic processes are discussed, and some selected examples reporting the applications of Zr-MOFs in various electrocatalytic reactions, including several studies from our group, are overviewed. Challenges, limitations and opportunities in using Zr-MOFs in electrocatalysis in future studies are discussed.

Fabrication of Flower-like Rhodium-Doped β-Ni(OH)2 as an Efficient Electrocatalyst for Methanol Oxidation Reaction in Alkaline Media

In this study, β-Ni(OH)₂ with a unique flower-like morphology was synthesized through a hydrothermal method. The doping of Rh in β-Ni(OH)₂ was achieved by a reduction method. The as-synthesized catalysts were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy for the crystal structure, morphology, composition, and chemical state analysis. The electrochemical tests revealed that the doping of Rh can significantly increase the electrocatalytic performance of β-Ni(OH)₂ in 1.0 M KOH solution. The methanol oxidation peak current density of Rh-doped β-Ni(OH)₂ reached 95 mA cm^-2 with a Tafel slope of 40 mV dec^-1. The reason for these improvements is that Rh can suppress the phase transformation of NiOOH from β to α. Meanwhile, the electronic structure change of nickel in β-Ni(OH)₂ and the defect ratio increase caused by Rh doping are beneficial to methanol oxidation reaction (MOR) catalytic activity. Furthermore, the synergistic effect between Rh and Ni(OH)₂ improved the surface activity of β-NiOOH. The doping of Rh in β-Ni(OH)₂ is initiative in this work, which provides a new strategy to design highly efficient and cost-effective MOR electrocatalysts for alkaline DMFCs.

Metal-Organic Framework Reinforced Acrylic Polymer Marine Coatings

Metal-organic frameworks (MOFs), a class of crystalline, porous, 3D materials synthesized by the linking of metal nodes and organic linkers are rapidly emerging as attractive materials in gas storage, electrodes in batteries, super-capacitors, sensors, water treatment, and medicine etc. However the utility of MOFs in coatings, especially in marine coatings, has not been thoroughly investigated. In this manuscript we report the first study on silver MOF (Ag-MOF) functionalized acrylic polymers for marine coatings. A simple and rapid microwave technique was used to synthesize a two-dimensional platelet structured Ag-MOF. Field tests on the MOF reinforced marine coatings exhibited an antifouling performance, which can be attributed to the inhibition of marine organisms to settle as evidenced by the anti-bacterial activity of Ag-MOFs. Our results indicate that MOF based coatings are highly promising candidates for marine coatings.

Strong Ligand Stabilization Based on π-Extension in a Series of Ruthenium Terpyridine Water Oxidation Catalysts

The substitution behavior of the monodentate Cl ligand of a series of ruthenium(II) terpyridine complexes (terpyridine (tpy)=2,2′:6′,2′′‐terpyridine) has been investigated. ¹H NMR kinetic experiments of the dissociation of the chloro ligand in D₂O for the complexes [Ru(tpy)(bpy)Cl]Cl (1, bpy=2,2’‐bipyridine) and [Ru(tpy)(dppz)Cl]Cl (2, dppz=dipyrido[3,2‐a:2′,3′‐c]phenazine) as well as the binuclear complex [Ru(bpy)₂(tpphz)Ru(tpy)Cl]Cl₃ (3  b, tpphz=tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h:2′′′,3′′′‐j]phenazine) were conducted, showing increased stability of the chloride ligand for compounds 2 and 3 due to the extended π‐system. Compounds 1–5 (4=[Ru(tbbpy)₂(tpphz)Ru(tpy)Cl](PF₆)₃, 5=[Ru(bpy)₂(tpphz)Ru(tpy)(C₃H₈OS)/(H₂O)](PF₆)₃, tbbpy=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine) are tested for their ability to run water oxidation catalysis (WOC) using cerium(IV) as sacrificial oxidant. The WOC experiments suggest that the stability of monodentate (chloride) ligand strongly correlates to catalytic performance, which follows the trend 1>2>5≥3>4. This is also substantiated by quantum chemical calculations, which indicate a stronger binding for the chloride ligand based on the extended π‐systems in compounds 2 and 3. Additionally, a theoretical model of the mechanism of the oxygen evolution of compounds 1 and 2 is presented; this suggests no differences in the elementary steps of the catalytic cycle within the bpy to the dppz complex, thus suggesting that differences in the catalytic performance are indeed based on ligand stability. Due to the presence of a photosensitizer and a catalytic unit, binuclear complexes 3 and 4 were tested for photocatalytic water oxidation. The bridging ligand architecture, however, inhibits the effective electron‐transfer cascade that would allow photocatalysis to run efficiently. The findings of this study can elucidate critical factors in catalyst design.