Template-Free Synthesis of Two-Dimensional Fe/N Codoped Carbon Networks as Efficient Oxygen Reduction Reaction Electrocatalysts

Tunable Syngas Formation at Industrially Relevant Current Densities via CO2 Electroreduction and Hydrogen Evolution over Ni and Fe-derived Catalysts obtained via One-Step Pyrolysis of Polybenzoxazine Based Composites

Simultaneous electroreduction of CO2 and H2O to syngas can provide a sustainable feed for established processes used to synthesize carbon-based chemicals. The synthesis of MOx/M-N-Cs (M = Ni, Fe) electrocatalysts reported via one-step pyrolysis that shows increased performance during syngas electrosynthesis at high current densities with adaptable H2/CO ratios, e.g., for the Fischer-Tropsch process. When embedded in gas diffusion electrodes (GDEs) with optimized hydrophobicity, the NiOx/Ni-N-C catalyst produces syngas (H2/CO = 0.67) at -200 mA cm-2 while for the FeOx/Fe-N-C syngas production occurs at ≈-150 mA cm-2. By tuning the electrocatalyst's microenvironment, stable operation for >3 h at -200 mA cm-2 is achieved with the NiOx/Ni-N-C GDE. Post-electrolysis characterization revealed that the restructuring of the catalyst via reduction of NiOx to metallic Ni NPs still enables stable operation of the electrode at -200 mA cm-2, when embedded in an optimized microenvironment. The ionomer and additives used in the catalyst layer are important for the observed stable operation. Operando Raman measurements confirm the presence of NiOx during CO formation and indicate weak adsorption of CO on the catalyst surface.

Enhanced adsorption of roxarsone on iron-nitrogen co-doped biochar from peanut shell: Synthesis, performance and mechanism

Efficient removal of organic arsenic (roxarsone, ROX) from wastewater is highly demanded on the purpose of human health and environmental protection. This work aims to prepare Fe-N co-doped biochar (Fe-N-BC) via one-pot hydrothermal method using waste peanut shell, FeCl3·6H2O and urea, followed by pyrolysis. The effect of Fe-N co-doping on biochar's physicochemical properties, and adsorption performance for ROX were systematically investigated. At the pyrolysis temperature of 650 °C, Fe-N-BC-650 shows a significantly increased specific surface area of 358.53 m2/g with well-developed micro-mesoporous structure. Its adsorption capacity for ROX reaches as high as 197.32 mg/g at 25 °C, with > 90 % regeneration efficiency after multiple adsorption-desorption cycles. Correlation and spectral analysis revealed that the pore filling, π-π interactions, as well as hydrogen bonding play the dominant role in ROX adsorption. These results suggest that the Fe-N co-doped biochar shows great potential in the ROX removal from wastewater with high efficiency.

In situ anchoring strategy to enhance dual nonradical degradation of sulfamethoxazole with high loading manganese doped carbon nitride

A low-cost catalyst with high metal loading and unique catalytic activities is highly desired for peroxymonosulfate (PMS) activation in environmental remediation. Herein, in situ anchoring strategy using 1,10-phenanthroline is reported to construct manganese doped carbon nitride (PMCN) with 8.2 wt% manganese loading and dramatically enhanced PMS adsorption and sulfamethoxazole (SMX) removal efficiency. Our study revealed that the PMCN/PMS system readily reacted with contaminants with electron-rich groups, where complete degradation of sulfamethoxazole (SMX) was achieved within 60 min. Combining quenching experiments, EPR tests, and electrochemical analysis, we proposed a dual nonradical pathway dominated by high-valent manganese oxygen species (Mn(V) = O) and electron transfer. Systematic investigation elucidated that the introduction of 1,10-phenanthroline constructed denser catalyst active sites, and identified the manganese center and pyridine nitrogen as the active sites for PMS activation. Furthermore, PMCN exhibited excellent pH anti-interference ability and good reusability, achieving more than 90% SMX degradation efficiency after four cycles. This study provides new insights into the regulation of Mn-N active sites and promotes the mechanistic understanding of the synergistic effect of manganese and pyridine nitrogen in PMS activation.

Single-Atom (Iron-Based) Catalysts: Synthesis and Applications

Supported single-metal atom catalysts (SACs) are constituted of isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and metal oxides. Their thermal stability, electronic properties, and catalytic activities can be controlled via interactions between the single-metal atom center and neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomic dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased, thus offering new possibilities to control the selectivity of a given transformation as well as to improve catalyst turnover frequencies and turnover numbers. This review aims to comprehensively summarize the synthesis of Fe-SACs with a focus on anchoring single atoms (SA) on carbon/graphene supports. The characterization of these advanced materials using various spectroscopic techniques and their applications in diverse research areas are described. When applicable, mechanistic investigations conducted to understand the specific behavior of Fe-SACs-based catalysts are highlighted, including the use of theoretical models.

Fe-N4 Doped Carbon Nanotube Cathode Catalyst for PEM Fuel Cells

The earth-abundant iron and nitrogen doped carbon (Fe-N-C) catalyst has great potential to substitute noble metal catalysts for oxygen reduction reaction (ORR) in H₂-O₂ proton exchange membrane fuel cells (PEMFCs). Herein, we report the preparation of Fe-N₄ moiety doped carbon nanotubes (CNTs) by ball milling and two-step pyrolysis with dual metal-organic frameworks (MOFs) as the precursor. This catalyst shows high ORR catalytic performance and stability. Different from traditional inorganic iron sources, the MOF structure can effectively prevent the iron metal from aggregating during pyrolysis. In PEMFC, the catalyst shows high current density (0.39 A/cm² at 0.7 V) and power density (850 mW/cm²). Such a method brings inspiration for the reasonable design of FeNC catalysts with high catalytic activity for H₂-O₂ PEMFCs.