Carbon-Doped Boron Nitride Nanosheet: An Efficient Metal-Free Electrocatalyst for the Oxygen Reduction Reaction

Replacing precious Pt-based catalysts with cheap and earth-abundant materials to facilitate the sluggish oxygen reduction reaction (ORR) at the cathode is critical to realize the commercialization of fuel cells. In this work, we explored the potential of utilizing the experimentally available carbon (C)-doped boron nitride (BN) nanosheet as an ORR electrocatalyst by means of comprehensive density functional theory (DFT) computations. Our computations revealed that C-singly doping into <i>h</i>-BN nanosheets can cause high spin density and charge density and reduce the energy gap, resulting in the enhancement of O₂ adsorption. In particular, the C_N sheet (substituting N by C atom) exhibits appropriate chemical reactivity toward O₂ activation and promotes the subsequent ORR steps to take place though a four-electron OOH hydrogenation pathway with the largest activation barrier of 0.61 eV, which is lower than that of the Pt-based catalyst (0.79 eV). Therefore, the C_N-based BN sheet is a promising metal-free ORR catalyst for fuel cells

Single Mo Atom Supported on Defective Boron Nitride Monolayer as an Efficient Electrocatalyst for Nitrogen Fixation: A Computational Study

The production of ammonia (NH₃) from molecular dinitrogen (N₂) under mild conditions is one of the most attractive and challenging processes in chemistry. Here by means of density functional theory (DFT) computations, we systematically investigated the potential of single transition metal atoms (Sc to Zn, Mo, Ru, Rh, Pd, and Ag) supported on the experimentally available defective boron nitride (TM–BN) monolayer with a boron monovacancy as a N₂ fixation electrocatalyst. Our computations revealed that the single Mo atom supported by a defective BN nanosheet exhibits the highest catalytic activity for N₂ fixation at room temperature through an enzymatic mechanism with a quite low overpotential of 0.19 V. The high spin-polarization, selective stabilization of N₂H* species, or destabilizing NH₂* species are responsible for the high activity of the Mo-embedded BN nanosheet for N₂ fixation. This finding opens a new avenue of NH₃ production by single-atom electrocatalysts under ambient conditions

Frustrated Lewis Pair Catalysts in Two Dimensions: B/Al-Doped Phosphorenes as Promising Catalysts for Hydrogenation of Small Unsaturated Molecules

Using comprehensive density functional theory (DFT) computations, we designed two promising two-dimensional (2D) metal-free heterogeneous frustrated Lewis pair (FLP) catalysts for the hydrogenation of small unsaturated molecules (such as ketone, nitrile, and ethylene). The catalyst consists of a phosphorene monolayer that is doped with B or Al impurity to form a frustrated B/P or Al/P Lewis pair without the need for steric hindrance. The hydrogenations of ketones, nitrile, and ethylene on the B- or Al-doped phosphorene prefer to proceed through a two-step mechanism: the heterolytic dissociation of H₂ molecule, followed by the concerted hydrogen transfer. This study not only identifies two promising catalysts, namely B/Al-doped phosphorenes, for the hydrogenations of small unsaturated molecules, but also provides a useful strategy to develop FLP catalysts in 2D materials

Metal–Organic-Framework-Derived Fe-N/C Electrocatalyst with Five-Coordinated Fe‑N_<i>x</i> Sites for Advanced Oxygen Reduction in Acid Media

Even though Fe-N/C electrocatalysts with abundant Fe-N_<i>x</i> active sites have been developed as one of the most promising alternatives to precious metal materials for oxygen reduction reaction (ORR), further improvement of their performance requires precise control over Fe-N_<i>x</i> sites at the molecular level and deep understanding of the catalytic mechanism associated with each particular structure. Herein, we report a host–guest chemistry strategy to construct Fe-mIm nanocluster (NC) (guest)@zeolite imidazole framework-8 (ZIF-8) (host) precursors that can be transformed into Fe-N/C electrocatalysts with controllable structures. The ZIF-8 host network exhibits a significant host–guest relationship dependent confinement effect for the Fe-mIm NCs during the pyrolysis process, resulting in different types of Fe-N_<i>x</i> sites with two- to five-coordinated configurations on the porous carbon matrix confirmed by X-ray absorption near edge structure (XANES) and Fourier transform (FT) extended X-ray absorption fine structure (EXAFS) spectra. Electrochemical tests reveal that the five-coordinated Fe-N_<i>x</i> sites can significantly promote the reaction rate in acid media, due to the small ORR energy barrier and the low adsorption energy of intermediate OH on these sites suggested by density functional theory (DFT) calculations. Such a synthesis strategy provides an effective route to realize the controllable construction of highly active sites for ORR at the molecular level

Reclamation of Acid Pickling Waste: Preparation of Nano α‑Fe₂O₃ and Its Catalytic Performance

Nano α-Fe₂O₃ materials with various size and morphology were prepared from acid pickling waste using nonionic surfactant polyethylene glycol (PEG-400) as dispersant and ultrasonic enhancement, as proved by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis, and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The results showed that high purity (96.89%) α-Fe₂O₃ nanoparticles were well-crystallized with different size and morphology, mainly including a web-like structure linked by about 25 nm spherical particles (Fe-w), a nanorod with about a 45 nm width diameter (Fe-r), and daylily bud-like materials with a 50 nm width leaf (Fe-l). The Fe-w, as well as other nanosized α-Fe₂O₃, was found to be very active for benzylation of aromatics by benzyl chloride, exhibiting turn over frequency (TOF) of 35.2 h^–1 for anisole, 65.1 h^–1 for aniline, 33.3 h^–1 for phenol, and 1776 h^–1 for benzene, respectively. The catalyst could be recycled at least three times without appreciable loss of catalytic activity

Metal-Doped C₃B Monolayer as the Promising Electrocatalyst for Hydrogen/Oxygen Evolution Reaction: A Combined Density Functional Theory and Machine Learning Study

The development of high-efficiency electrocatalysts for hydrogen evolution reduction (HER)/oxygen evolution reduction (OER) is highly desirable. In particular, metal borides have attracted much attention because of their excellent performances. In this study, we designed a series of metal borides by doping of a transition metal (TM) in a C3B monolayer and further explored their potential applications for HER/OER via density functional theory (DFT) calculations and machine learning (ML) analysis. Our results revealed that the |ΔG*H| values of Fe-, Ag-, Re-, and Ir-doped C3B are approximately 0.00 eV, indicating their excellent HER performances. On the other hand, among all the considered TM atoms, the Ni- and Pt-doped C3B exhibit excellent OER activities with the overpotentials smaller than 0.44 V. Together with their low overpotentials for HER (3B and Pt/C3B could be the potential bifunctional electrocatalysts for water splitting. In addition, the ML method was employed to identify the important factors to affect the performance of the TM/C3B electrocatalyst. Interestingly, the results showed that the OER performance is closely related to the inherent properties of TM atoms, i.e., the number of d electrons, electronegativity, atomic radius, and first ionization energy; all these values could be directly obtained without DFT calculations. Our results not only proposed several promising electrocatalysts for HER/OER but also suggested a guidance to design the potential TM–boron (TM–B)-based electrocatalysts

Rapid Decolorization of Phenolic Azo Dyes by Immobilized Laccase with Fe₃O₄/SiO₂ Nanoparticles as Support

Fe₃O₄/SiO₂ nanoparticles with particle size below 30 nm were used as the support for laccase immobilization through glutaraldehyde coupling. Investigation of the immobilized laccase was carried out by X-ray diffractometry (XRD), transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), vibrating sample magnetometry (VSM), UV–vis spectrophotometry, and cyclic voltammogram (CV) measurements. Two phenolic azo dyes, Procion Red MX-5B and azophloxine, were selected to investigate the enzyme activity of the immobilized laccase toward degradation of phenolic azo dyes. The immobilized laccase presents unusual performance for dye decolorization and easy separation with an external magnetic field. Finally, the possible mechanism for the unusual decolorization of phenolic azo dyes by the immobilized laccase is discussed

Component Matters: Paving the Roadmap toward Enhanced Electrocatalytic Performance of Graphitic C₃N₄‑Based Catalysts <i>via</i> Atomic Tuning

Atomically precise understanding of componential influences is crucial for looking into the reaction mechanism and controlled synthesis of efficient electrocatalysts. Herein, by means of comprehensive experimental and theoretical studies, we carefully examine the effects of component dopants on the catalytic performance of graphitic C₃N₄ (g-C₃N₄)-based electrocatalysts. The g-C₃N₄ monoliths with three types of dopant elements (B, P, and S) embedded in different sites (either C or N) of the C–N skeleton are rationally designed and synthesized. The kinetics, intrinsic activity, charge-transfer process, and intermediate adsorption/desorption free energy of the selected catalysts in oxygen reduction reaction and hydrogen evolution reaction are investigated both experimentally and theoretically. We demonstrate that the component aspect within the g-C₃N₄ motifs has distinct and substantial effects on the corresponding electroactivities, and proper component element engineering can be a viable yet efficient protocol to render the metal-free composites as competent catalysts rivaling the metallic counterparts. We hope that this study may shed light on the empirical trial-and-error exploration in design and development of g-C₃N₄-based materials as well as other metal-free catalysts for energy-related electrocatalytic reactions