The catalytic alkylation of amines with alcohols is a highly atom-economical approach that produces water as the sole by-product. Existing catalytic systems lack generality and are primarily applicable to electron-poor amines or to non-oxidizable amines, such as anilines. The outstanding effectiveness of an Ir-NHC catalyst in forming C−N bonds from alcohols and amines, both aliphatic and aromatic, is presented here. The catalyst performs remarkably under mild conditions, even at room temperature, attaining complete selectivity in all tested cases toward monoalkylation, even for challenging aliphatic amines, and under base-free conditions. Thorough mechanistic investigation to understand the outstanding activity and selectivity, combining experimental, theoretical, and both in situ and ex situ X-ray absorption spectroscopy (XAS) studies, are presented.

Two-dimensional (2D) metal–organic frameworks (MOFs) have become a hot topic recently due to their high surface area, larger number of exposed active sites, and improved conductivity. Combining different 2D MOFs could introduce new physical and chemical properties. Here, we have synthesized a heteroepitaxially grown 2D zeolitic imidazolate framework with a leaf-like morphology (ZIF-L). ZIF-L has a layer-by-layer dense structure, which possesses a high content of N and metal ions as active sites. ZIF-L-Co is heteroepitaxially grown on ZIF-L-Zn, while ZIF-L-Zn@ZIF-Co has been successfully prepared. After pyrolysis, the heteroepitaxially grown MOF derived ultra-small Co nanoparticle immobilized nitrogen doped carbon (NC) material (HM-Co@NC) exhibits superior oxygen reduction reaction (ORR) activity (Eonset = 0.998 V, E1/2 = 0.905 V) and better stability than Pt/C, achieving well-qualified assemblies for use in rechargeable Zn–air batteries.

Water oxidation is an important reaction for multiple renewable energy conversion and storage-related devices and technologies. High-performance and stable electrocatalysts for the oxygen evolution reaction (OER) are urgently required. Bimetallic (oxy)hydroxides have been widely used in alkaline OER as electrocatalysts, but their activity is still not satisfactory due to insufficient active sites. In this research, A unique and efficient approach of sacrificial W to prepare CoFe (oxy)hydroxides with abundant active species for OER is presented. Multiple ex situ and operando/in situ characterizations have validated the self-reconstruction of the as-prepared CoFeW sulfides to CoFe (oxy)hydroxides in alkaline OER with synchronous W etching. Experiments and theoretical calculations show that the sacrificial W in this process induces metal cation vacancies, which facilitates the in situ transformation of the intermediate metal hydroxide to CoFe-OOH with more high-valence Co(III), thus creating abundant active species for OER. The Co(III)-rich environment endows the in situ formed CoFe oxyhydroxide with high catalytic activity for OER on a simple flat glassy carbon electrode, outperforming those not treated by the sacrificial W procedure. This research demonstrates the influence of etching W on the electrocatalytic performance, and provides a low-cost means to improve the active sites of the in situ self-reconstructed bimetallic oxyhydroxides for OER.

Catalysts for photochemical reactions underlie many foundations in our lives, from natural light harvesting to modern energy storage and conversion, including processes such as water photolysis by TiO₂. Recently, metal–organic frameworks (MOFs) have attracted large interest within the chemical research community, as their structural variety and tunability yield advantages in designing photocatalysts to address energy and environmental challenges. Here, we report a series of novel multivariate metal–organic frameworks (MTV-MOFs), denoted as MTV-MIL-100. They are constructed by linking aromatic carboxylates and AB₂OX₃ bimetallic clusters, which have ordered atomic arrangements. Synthesized through a solvent-assisted approach, these ordered and multivariate metal clusters offer an opportunity to enhance and fine-tune the electronic structures of the crystalline materials. Moreover, mass transport is improved by taking advantage of the high porosity of the MOF structure. Combining these key advantages, MTV-MIL-100(Ti,Co) exhibits a high photoactivity with a turnover frequency of 113.7 mol_H2 g_cat.^–1 min^–1, a quantum efficiency of 4.25%, and a space time yield of 4.96 × 10^–5 in the photocatalytic hydrolysis of ammonia borane. Bridging the fields of perovskites and MOFs, this work provides a novel platform for the design of highly active photocatalysts.

Electrocatalytic water splitting is an efficient means of producing energy carriers, such as H-2. The hydrogen evolution reaction (HER) requires high-efficiency electrocatalysts. Understanding the active site structures of the HER electrocatalysts is essential for the rational design and development of water splitting devices. In this study, porous CoW sulfides were employed as model electrocatalysts for pH-universal HER. Multiple characterization studies, such as X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and operando X-ray diffraction, were systematically used to investigate the reconstruction of the active species at the surface and in the bulk. The results show that during the HER, the structural transformation of the species CoW sulfides is strongly dependent on the pH of the electrolyte. Electrolytes of varying pH lead to varied reconstruction and influence the true catalytically active species responsible for the HER. The surface and the bulk of the electrocatalysts transform to different oxides/hydroxides when subjected to the HER. This is the first time that the pH-dependent bulk and surface structural evolution in the HER has been revealed. This study reveals the reconstruction and potential active site evolution of mixed-metal sulfides for the HER. We believe that the present study not only provides an idealized pre-catalyst for pH-universal highly-efficient HER, but also provides a thorough understanding about the identification of the real active sites and the mechanism of the structural evolution of the electrocatalysts during hydrogen evolution.

The development of highly active and durable catalysts for water oxidation under acidic conditions is necessary but challenging for renewable energy conversion. Ir-based catalysts are highly efficient for water oxidation in acid, but their large scale application is hindered by the high cost and scarcity of iridium. Herein, we use an amorphous WO3 induced lattice distortion (AWILD) strategy to reduce the Ir content to only 2 wt% in the final material. The optimized hybrid nitrogen-doped carbon (NC)/WO3/IrO2 can efficiently catalyze water oxidation with a low overpotential of 270 mV at 10 mA cm(-2) current density (eta (10)) and a high turnover frequency of over 2 s(-1) at 300 mV overpotential in 0.5 M H2SO4, a performance that surpasses that of commercial IrO2 significantly. Introducing the layer of amorphous WO3 between IrO2 nanoparticles and NC can distort the lattice of IrO2, exposing more highly active sites for water oxidation. The AWILD effect compensates for the lower Ir content and dramatically reduces the cost of the catalyst without sacrificing the catalytic activity. Additionally, this catalyst also exhibits high activity in acid for hydrogen evolution with only 65 mV of eta (10) attributed to the AWILD effect, exhibiting efficient bifunctionality as a Janus catalyst for overall water splitting. The AWILD approach provides a novel and efficient strategy for low-cost and highly efficient electrocatalysts for acidic overall water splitting with an extremely low content of noble metals.

Tuning the local environment of nanomaterial-based catalysts has emerged as an effective approach to optimize their oxygen evolution reaction (OER) performance, yet the controlled electronic modulation around surface active sites remains a great challenge. Herein, directed electronic modulation of NiO nanoparticles was achieved by simple surface molecular modification with small organic molecules. By adjusting the electronic properties of modifying molecules, the local electronic structure was rationally tailored and a close electronic structure-activity relationship was discovered: the increasing electron-withdrawing modification readily decreased the electron density around surface Ni sites, accelerating the reaction kinetics and improving OER activity, and vice versa. Detailed investigation by operando Raman spectroelectrochemistry revealed that the electron-withdrawing modification facilitates the charge-transfer kinetics, stimulates the catalyst reconstruction, and promotes abundant high-valent gamma-NiOOH reactive species generation. The NiO-C(6)F(5)catalyst, with the optimized electronic environment, exhibited superior performance towards water oxidation. This work provides a well-designed and effective approach for heterogeneous catalyst fabrication under the molecular level.

Fe is considered as a promising alternative for OER catalysts owing to its high natural abundance and low cost. Due to the low conductivity and sluggish catalytic kinetics, the catalytic efficiency of Fe-rich catalysts is far from less abundant Ni, Co-rich alternatives and has been hardly improved without the involvement of Ni or Co. The lower activity of Fe-rich catalysts renders the real active center of state-of-the-art NiFe, CoFe catalyst in long-term scientific debate, despite of detection of Fe-based active intermediates in these catalysts during catalytic process. In the present work, we fabricated a series of sub-5 nm Fe1-yCryOx nanocatalysts via a simple solvothermal method, achieving systematically promoted high-valent Fe(VI) species generation by structural and electronic modulation, displaying highly active OER performance without involvement of Ni or Co. Detailed investigation revealed that the high OER activity is related to the ultrasmall nanoparticle size that promotes abundant edge- and corner-site exposure at catalyst surface, which involves in OER as highly reactive site; and the incorporated Cr ions that remarkably accelerate the charge transfer kinetics, providing an effective conduit as well as suitable host for high-valent active intermediate. This work reveals the structural prerequisites for efficient Fe-rich OER catalyst fabrication, inspiring deeper understanding of the structure-activity relationship as well as OER mechanism of Fe-based catalysts.