Highly exposed metal atomic active sites in Al2O3/CoNC: Modify reaction pathways by coupling oxygen species

The catalytic oxidation of formaldehyde (HCHO) at ambient temperature is a highly efficient, cost-effective and environmentally friendly approach for formaldehyde removal. Reactive oxygen (O*) and reactive hydroxyl groups (OH*) are the main active species in the catalytic oxidation reaction of HCHO. Therefore, it is crucial to design catalysts that can simultaneously enhance the surface concentrations of O* and OH*, thereby improving their overall catalytic performance. The present study aimed to design an Al2O3/CoNC catalyst featuring layered carbon nitride coupled with metal oxides possessing domain-limited cobalt (Co) metal active sites, to efficiently remove HCHO (≈100 %, 100 ppm, RH=50 %, GSHV=20,000 mL/(g h)) and ensure stability (more than 90 % formaldehyde removal within 450 h) at ambient temperature. The characterization revealed that the interaction between Al2O3-supported metal and CoNC resulted in enhanced confinement of Co, leading to a higher abundance of edge structures exposing more active sites. Additionally, the presence of highly dispersed Co-NX active sites and increased oxygen vacancies effectively facilitated the adsorption and activation processes of HCHO and O2, as well as the adsorption and desorption dynamics of intermediates during the reaction. These factors collectively contributed to an improved catalytic activity. The results of in situ infrared spectroscopy revealed that the catalyst improved the adsorption and activation of O2 and H2O, leading to the rapid generation of substantial amounts of O* and OH*. This synergistic interaction between Al2O3 and CoNC plays a crucial role in the sustained production of O* and OH*, promoting efficient of intermediate decomposition, and ensuring excellent catalytic activity and stability for HCHO.

Floating Bimetallic Catalysts for Growing 30 cm-Long Carbon Nanotube Arrays with High Yields and Uniformity

Ultralong carbon nanotubes (CNTs) are considered as promising candidates for many cutting-edge applications. However, restricted by the extremely low yields of ultralong CNTs, their practical applications can hardly be realized. Therefore, new methodologies shall be developed to boost the growth efficiency of ultralong CNTs and alleviate their areal density decay at the macroscale level. Herein, a facile, universal, and controllable method for the in situ synthesis of floating bimetallic catalysts (FBCs) is proposed to grow ultralong CNT arrays with high yields and uniformity. Ferrocene and metal acetylacetonates serve as catalyst precursors, affording the successful synthesis of a series of FBCs with controllable compositions. Among these FBCs, the optimized FeCu catalyst increases the areal density of ultralong CNT arrays to a record-breaking value of ≈8100 CNTs mm-1 and exhibits a lifetime 3.40 times longer than that of Fe, thus achieving both high yields and uniformity. A 30-centimeters-long and high-density ultralong CNT array is also successfully grown with the assistance of FeCu catalysts. As evidenced by this kinetic model and molecular dynamics simulations, the introduction of Cu into Fe can simultaneously improve the catalyst fluidity and decrease carbon solubility, and an optimal catalytic performance will be achieved by balancing this tradeoff.

Highly Active and Sintering-Resistant Pt Clusters Supported on FeOx-Hydroxyapatite Achieved by Tailoring Strong Metal-Support Interactions

The catalytic performance of supported metal catalysts is closely related to their structure. While Pt-based catalysts are widely used in many catalytic reactions because of their exceptional intrinsic activity, they tend to deactivate in high-temperature reactions, requiring a tedious and expensive regeneration process. The strong metal-support interaction (SMSI) is a promising strategy to improve the stability of supported metal nanoparticles, but often at the price of the activity due to either the coverage of the active sites by support overlay and/or the too-strong metal-support bonding. Herein, we newly constructed a supported Pt cluster catalyst by introducing FeOx into hydroxyapatite (HAP) support to fine-tune the SMSIs. The catalyst exhibited not only high catalytic activity but also sintering resistance, without deactivation in a 100 h test for catalytic CO oxidation. Detailed characterizations reveal that FeOx introduced into HAP weaken the strong covalent metal-support interaction (CMSI) between Pt and FeOx while simultaneously inhibiting the oxidative strong metal-support interaction (OMSI) between Pt and HAP, giving rise to both high activity and thermal stability of the supported Pt clusters.

Carbon Encapsulation of Supported Metallic Iridium Nanoparticles: An in Situ Transmission Electron Microscopy Study and Implications for Hydrogen Evolution Reaction

Carbon-supported metal nanoparticles (NPs) comprise an important class of heterogeneous catalysts. The interaction between the metal and carbon support influences the overall material properties, viz., the catalytic performance. Herein we use in situ and ex situ transmission electron microscopy (TEM) in combination with in situ X-ray spectroscopy (XPS) to investigate the encapsulation of metallic iridium NPs by carbon in an Ir/C catalyst. Real-time atomic-scale imaging visualizes particle reshaping and increased graphitization of the carbon support upon heating of Ir/C in vacuum. According to in situ TEM results, carbon overcoating grows over Ir NPs during the heating process, starting from ca. 550 °C. With the carbon overlayers formed, no sintering and migration of Ir NPs is observed at 800 °C, yet the initial Ir NPs sinter at or below 550 °C, i.e., at a temperature associated with an incomplete particle encapsulation. The carbon overlayer corrugates when the temperature is decreased from 800 to 200 °C and this process is associated with the particle surface reconstruction and is reversible, such that the corrugated carbon overlayer can be smoothed out by increasing the temperature back to 800 °C. The catalytic performance (activity and stability) of the encapsulated Ir NPs in the hydrogen evolution reaction (HER) is higher than that of the initial (nonencapsulated) state of Ir/C. Overall, this work highlights microscopic details of the currently understudied phenomenon of the carbon encapsulation of supported noble metal NPs and demonstrates additionally that the encapsulation by carbon is an effective measure for tuning the catalytic performance.

Regulating the Spin State of Metal and Metal Carbide Heterojunctions for Efficient Oxygen Evolution

Developing high-performance electrocatalysts for oxygen evolution reaction (OER) is of importance for improving the overall efficiency of water splitting. Herein, the CoFe/(Co_xFe_1-x)₃Mo₃C heterojunction is purposely designed as an OER catalyst, which displays a low overpotential of 293 mV for affording a current density of 10 mA cm^-2 and a small Tafel slope of 48 mV/dec. Various characterization results demonstrate that the significant work-function difference between CoFe and (Co_xFe_1-x)₃Mo₃C can induce interfacial charge redistribution, which results in the formation of Co and Fe sites with a high-spin state, thus stimulating the surface phase reconstruction of CoFe/(Co_xFe_1-x)₃Mo₃C to corresponding active oxyhydroxide. Meanwhile, the electrochemical leaching of Mo ions from the initial structure can contribute to the formation of defective sites, further benefiting OH^- adsorption and surface oxidation. Moreover, the remaining CoFe can accelerate electron migration during the electrocatalytic process. This study presents new insights into constructing efficient OER electrocatalysts with an optimized spin-state configuration via interfacial engineering.

FeCo alloy encased in nitrogen-doped carbon for efficient formaldehyde removal: Preparation, electronic structure, and d-band center tailoring

Formaldehyde is a typical indoor air pollutant that has posed severely adverse effects on human health. Herein, a novel FeCo alloy nanoparticle-embedded nitrogen-doped carbon (FeCo@NC) was synthesized with the aim of tailoring the transition-metal d-band structure toward an improved formaldehyde oxidation activity for the first time. A unique core@shell metal-organic frameworks (MOFs) architecture with a Fe-based Prussian blue analogue core and Co-containing zeolite imidazole framework shell was firstly fabricated. Then, Fe and Co ion alloying was readily achieved owing to the inherent MOF porosity and interionic nonequilibrium diffusion occurring during pyrolysis. High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectra confirm that small FeCo alloys in situ form in FeCo@NC, which exhibits a higher formaldehyde removal efficiency (93%) than the monometallic Fe-based catalyst and a remarkable CO₂ selectivity (85%) at room temperature. Density functional theory calculations indicate the number of electrons transferred from the metal core to the outer carbon layer is altered by alloying Fe and Co. More importantly, a downshift in the d-band center relative to the Fermi level occurs from - 0.93 to - 1.04 eV after introducing Co, which could alleviate the adsorption of reaction intermediates and greatly improve the catalytic performance.

In Situ Construction of FeCo Alloy Nanoparticles Embedded in Nitrogen‑Doped Bamboo-like Carbon Nanotubes as a Bifunctional Electrocatalyst for Zn-Air Battery

The rational design and exploration of low-cost, highly efficient, and robust bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts are essential for the application of zinc-air batteries....

Catalyst overcoating engineering towards high-performance electrocatalysis

Clean and sustainable energy needs the development of advanced heterogeneous catalysts as they are of vital importance for electrochemical transformation reactions in renewable energy conversion and storage devices. Advances in nanoscience and material chemistry have afforded great opportunities for the design and optimization of nanostructured electrocatalysts with high efficiency and practical durability. In this review article, we specifically emphasize the synthetic methodologies for the versatile surface overcoating engineering reported to date for optimal electrocatalysts. We discuss the recent progress in the development of surface overcoating-derived electrocatalysts potentially applied in polymer electrolyte fuel cells and water electrolyzers by correlating catalyst intrinsic structures with electrocatalytic properties. Finally, we present the opportunities and perspectives of surface overcoating engineering for the design of advanced (electro)catalysts and their deep exploitation in a broad scope of applications.

Electrocatalysis in confined spaces: interplay between well-defined materials and the microenvironment

Catalysis in a confined space has attracted much attention due to the simultaneously designable nature of active sites and their microenvironment, leading to a broad spectrum of highly efficient chemical conversion schemes. Recent work has extended the scope of confined catalysis to electrochemical reactions. Mechanistic studies suggest that the confined environment in electrocatalysis can modulate mechanical, electronic, and geometric effects, stabilizing important charge-transfer intermediates and promoting reaction kinetics. In this minireview, we first discuss the fundamental concepts of confined catalysis by summarizing density functional theory (DFT) calculations and experimental investigations. We then present the rational design and applications of space-confined electrocatalysts with emphasis on the confined environment provided by carbon-based materials. We specifically focus on metal-based materials confined in carbon nanotubes (CNTs) and their applications in emerging electrochemical reactions including the oxygen reduction reaction (ORR), water-splitting reactions, carbon dioxide reduction reaction (CO2RR), and nitrogen reduction reaction (NRR). Finally, the existing challenges, opportunities, and future directions of electrocatalysis in confined spaces are highlighted.

Rational design of FeOx-MoP@MWCNT composite electrocatalysts toward efficient overall water splitting

Herein, a series of FeOx-MoP@MWCNT composite electrocatalysts was designed and prepared to investigate the influence of the content of FeOx on the water splitting performance. The optimized FeOx-MoP@MWCNTs-2 exhibits excellent hydrogen and oxygen evolution reaction activity while a cell voltage of 1.51 V with outstanding stability is attained, attributed to the synergistic effect of each component, as evidenced by the experimental and density functional theory results. The observed electrocatalytic activity outperforms current state-of-the-art non-precious metal electrocatalysts.

A highly efficient bifunctional electrocatalyst (ORR/OER) derived from GO functionalized with carbonyl, hydroxyl and epoxy groups for rechargeable zinc–air batteries

A highly efficient bifunctional electrocatalyst, Co–N/S/rGO, was prepared via modifying the surface functional groups of GO, and it showed good application prospects in zinc–air batteries.