Hydroxylation of arenes via activation of aromatic C
-H bond has attracted great attention for decades but remains a huge challenge. Herein, we achieve the ring hydroxylation of various arenes with ...stoichiometric hydrogen peroxide (H
O
) into the corresponding phenols on a robust heterogeneous catalyst series of V-Si-ZSM-22 (TON type vanadium silicalite zeolites) that is straightforward synthesized from an unusual ionic liquid involved dry-gel-conversion route. For benzene hydroxylation, the phenol yield is 30.8% (selectivity >99%). Ring hydroxylation of mono-/di-alkylbenzenes and halogenated aromatic hydrocarbons cause the yields up to 26.2% and selectivities above 90%. The reaction is completed within 30 s, the fastest occasion so far, resulting in ultra-high turnover frequencies (TOFs). Systematic characterization including
V NMR and X-ray absorption fine structure (XAFS) analyses suggest that such high activity associates with the unique non-radical hydroxylation mechanism arising from the in situ created diperoxo V(IV) state.
Artificial nitrogen fixation through the nitrogen reduction reaction (NRR) under ambient conditions is a potentially promising alternative to the traditional energy-intensive Haber–Bosch process. For ...this purpose, efficient catalysts are urgently required to activate and reduce nitrogen into ammonia. Herein, by the combination of experiments and first-principles calculations, we demonstrate that copper single atoms, attached in a porous nitrogen-doped carbon network, provide highly efficient NRR electrocatalysis, which compares favorably with those previously reported. Benefiting from the high density of exposed active sites and the high level of porosity, the Cu SAC exhibits high NH3 yield rate and Faradaic efficiency (FE), specifically ∼53.3 μgNH3 h–1 mgcat –1 and 13.8% under 0.1 M KOH, ∼49.3 μgNH3 h–1 mgcat –1 and 11.7% under 0.1 M HCl, making them truly pH-universal. They also show good stability with little current attenuation over 12 h of continuous operation. Cu–N2 coordination is identified as the efficient active sites for the NRR catalysis.
Lithium–sulfur (Li–S) batteries are strong contenders among lithium batteries due to superior capacity and energy density, but the polysulfide shuttling effect limits the cycle life and reduces ...energy efficiency due to a voltage gap between charge and discharge. Here, we demonstrate that graphene foam impregnated with single-atom catalysts (SACs) can be coated on a commercial polypropylene separator to catalyze polysulfide conversion, leading to a reduced voltage gap and a much improved cycle life. Also, among Fe/Co/Ni SACs, Fe SACs may be a better option to be used in Li–S systems. By deploying SACs in the battery separator, cycling stability improves hugely, especially considering relatively high sulfur loading and ultralow SAC contents. Even at a metal loading of ∼2 μg in the whole cell, an Fe SAC-modified separator delivers superior Li–S battery performance even at high sulfur loading (891.6 mAh g–1, 83.7% retention after 750 cycles at 0.5C). Our work further enriches and expands the application of SACs catalyzing polysulfide blocking and conversion and improving round trip efficiencies in batteries, without side effects such as electrolyte and electrode decomposition.
Oxygen vacancies (OVs) have emerged as an important strategy to modulate the electronic structures, conductivity, and catalytic performance of transition metal oxides (TMOs). A few studies reported ...that OVs could be formed in N-doped TMOs during ammonia treatment. However, the OV-enriched TMOs without N-doping obtained through ammonia treatment are still unreported and their mechanism is unclear. Herein, we adopt experimental and theoretical investigations to demonstrate the mechanism of ammonia treatment. Based on this mechanism, we develop a facile method to synthesize OV-enriched blue WO3−x porous nanorods (OBWPN) without N-doping. OBWPN exhibit promising performance for photothermal reduction of CO2-H2O to CH4 without any external cocatalysts or sacrificial agents. In addition, the low-temperature ammonia-assisted reduction treatment is a universal strategy to generate OVs in other TMOs with enhanced performance of photocatalytic hydrogen generation. This work is significant for understanding the nature of ammonia treatment and promoting the wide application of OV-enriched TMOs.
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•Combining experimental and theoretical studies to reveal OV formation mechanism•A general low-temperature ammonia-assisted reduction strategy to create OVs in TMOs•The sample is highly active for photothermal CO2 conversion without sacrificial agents
Ammonia, as an abundant and cheap resource, is often adopted in the nitridation process. In addition, a few studies reported that oxygen vacancies (OVs) could be formed in N-doping transition metal oxides (TMOs) during ammonia treatment. However, the mechanism still lacks fundamental understanding. Thus, it is of interest to study the nature of ammonia treatment. Herein, we reveal that the H and N atoms can extract O atoms in WO3 to form H2O, N2, N2O, and NO in ammonia treatment. Meanwhile, WO3 are converted sequentially into WO3−x and WN. Based on this mechanism, we present a universal low-temperature ammonia-assisted reduction strategy to synthesize OV-enriched TMOs without N-doping. Interestingly, the as-prepared OV-enriched blue WO3−x porous nanorods (OBWPN) and Nb2O5−x show enhanced photocatalytic performance owing to the existence of OVs. This work provides a fundamental mechanism study of ammonia treatment and opens a new perspective on the design of OV-enriched TMOs with enhanced performance.
This work raises a universal low-temperature ammonia-assisted reduction strategy to synthesize OV-enriched TMOs without N-doping. The H and N atoms can extract O atoms in TMOs to form H2O and N2O at low temperature, and thus lead to OV-rich TMO including OV-enriched blue WO3−x porous nanorods (OBWPN). Compared with the corresponding yellow WO3 porous nanorods and N-doped WO3−x porous nanorods, OBWPN exhibits greatly enhanced photothermal CO2 conversion performance.
Fundamental insight into the surface charging mechanism of TiO2(B) nanomaterials is limited due to the complicated nature of lithiation behavior, as well as the limitations of available ...characterization tools that can directly probe surface charging process. Here, an in situ approach is reported to monitor the dynamic valence state of TiO2(B) nanotube electrodes, which utilizes in situ X‐ray absorption spectroscopy (XAS) to identify the origin and contribution of surface storage. A real‐time correlation is elucidated between the rate‐dependent electrode performance and dynamic Ti valence‐state change. A continuous Ti valence state change is directly observed through the whole charging/discharging process regardless of charging rates, which proves that along with the well‐known non‐faradaic reaction, the surface charging process also originates from a faradaic reaction. The quantification of these two surface storage contributions at different charging rates is further realized through in situ dynamic valence state monitoring combined with traditional cyclic voltammetry measurement. The methodology reported here can also be applied to other electrode materials for the real‐time probing of valence state change during electrochemical reactions, the quantification of the faradaic and non‐faradaic reactions, and the eventual elucidation of electrochemical surface charging mechanisms.
The origin and contribution of surface storage in a prototype TiO2(B) nanotube electrode by an in situ dynamic valence state monitoring approach are identified. Benefited from this, non‐faradaic and faradaic capacity from the surface reaction are identified and quantified in conjunction with a cyclic voltammetry measurement, putting an end to the long‐time question on surface reaction over distinguishing its non‐faradaic and faradaic contributions.
The ability to tune both local and global environments of a single-metal active center on a support is crucial for the development of highly robust and efficient single-atom electrocatalysts (SAECs) ...that can surmount both thermodynamic and kinetic constraints in electrocatalysis. Here, we designed a core–shell-structured SAEC (Co1-SAC) with superior oxygen reduction reaction (ORR) performance. Co1-SAC consists of a locally engineered single Co-N3C1 site on a N-doped microporous amorphous carbon support enveloped by a globally engineered highly conductive mesoporous graphitic carbon shell. Theoretical calculations reveal that Co-N3C1 exhibits near-Fermi electronic states distinct from those of Co-N2C2 and Co-N4, which facilitate both the electronic hybridization with O2 and the subsequent protonation of adsorbed O2* toward the formation of OOH*. Engineering Co-N3C1-SAC into a micro/mesoporous core–shell structure dramatically enhances the mass transport and electron transfer, which further boosts the ORR and Zn-air battery performance (slightly outperforming Pt/C). Our findings open an avenue toward engineering of the local and global environment of SACs for a wide range of efficient electrochemical conversions.
We report one-pot synthesis of Fe(III)–polydopamine (PDA) complex nanospheres, their structures, morphology evolution, and underlying mechanism. The complex nanospheres were synthesized by ...introducing ferric ions into the reaction mixture used for polymerization of dopamine. It is verified that both the oxidative polymerization of dopamine and Fe(III)–PDA complexation contribute to the “polymerization” process, in which the ferric ions form coordination bonds with both oxygen and nitrogen, as indicated by X-ray absorption fine-structure spectroscopy. In the “polymerization” process, the morphology of the complex nanostructures is gradually transformed from sheetlike to spherical at the feed Fe(III)/dopamine molar ratio of 1/3. The final size of the complex spheres is much smaller than its neat PDA counterpart. At higher feed Fe(III)/dopamine molar ratios, the final morphology of the “polymerization” products is sheetlike. The results suggest that the formation of spherical morphology is likely to be driven by covalent polymerization-induced decrease of hydrophilic functional groups, which causes reself-assembly of the PDA oligomers to reduce surface area. We also demonstrate that this one-pot synthesis route for hybrid nanospheres enables the facile construction of carbonized PDA (C-PDA) nanospheres uniformly embedded with Fe3O4 nanoparticles of only 3–5 nm in size. The C-PDA/Fe3O4 nanospheres exhibit catalytic activity toward oxygen reduction reaction and deliver a stable discharge voltage for over 200 h when utilized as the cathode in a primary Zn–air battery and are also good recyclable catalyst supports.
The catalytic and magnetic properties of molybdenum disulfide (MoS2) are significantly enhanced by the presence of edge sites. One way to obtain a high density of edge sites in a two-dimensional (2D) ...film is by introducing porosity. However, the large-scale bottom-up synthesis of a porous 2D MoS2 film remains challenging and the correlation of growth conditions to the atomic structures of the edges is not well understood. Here, using molecular beam epitaxy, we prepare wafer-scale nanoporous MoS2 films under conditions of high Mo flux and study their catalytic and magnetic properties. Atomic-resolution electron microscopy imaging of the pores reveals two new types of reconstructed Mo-terminated edges, namely, a distorted 1T (DT) edge and the Mo-Klein edge. Nanoporous MoS2 films are magnetic up to 400 K, which is attributed to the presence of Mo-terminated edges with unpaired electrons, as confirmed by density functional theory calculation. The small hydrogen adsorption free energy at these Mo-terminated edges leads to excellent activity for the hydrogen evolution reaction.
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