Axial Chlorine Induced Electron Delocalization in Atomically Dispersed FeN4 Electrocatalyst for Oxygen Reduction Reaction with Improved Hydrogen Peroxide Tolerance.

Atomically dispersed iron sites on nitrogen-doped carbon (Fe-NC) are the most active Pt-group-metal-free catalysts for oxygen reduction reaction (ORR). However, due to oxidative corrosion and the Fenton reaction, Fe-NC catalysts are insufficiently active and stable. Herein, w e demonstrated that the axial Cl-modified Fe-NC (Cl-Fe-NC) electrocatalyst is active and stable for the ORR in acidic conditions with high H2 O2 tolerance. The Cl-Fe-NC exhibits excellent ORR activity, with a high half-wave potential (E1/2 ) of 0.82 V versus a reversible hydrogen electrode (RHE), comparable to Pt/C (E1/2 = 0.85 V versus RHE) and better than Fe-NC (E1/2 = 0.79 V versus RHE). X-ray absorption spectroscopy analysis confirms that chlorine is axially integrated into the FeN4. More interestingly, compared to Fe-NC, the Fenton reaction is markedly suppressed in Cl-Fe-NC. In situ electrochemical impedance spectroscopy reveals that Cl-Fe-NC provides efficient electron transfer and faster reaction kinetics than Fe-NC. Density functional theory calculations reveal that incorporating Cl into FeN4 can drive the electron density delocalization of the FeN4 site, leading to a moderate adsorption free energy of OH* (∆GOH* ), d-band center, and a high onset potential, and promotes the direct four-electron-transfer ORR with weak H2 O2 binding ability compared to Cl-free FeN4, indicating superior intrinsic ORR activity.

Synergistic Electronic Interaction of Nitrogen Coordinated Fe-Sn Double-Atom Sites: An Efficient Electrocatalyst for Oxygen Reduction Reaction.

Double-atom site catalysts (DASs) have emerged as a recent trend in the oxygen reduction reaction (ORR), thereby modifying the intermediate adsorption energies and increasing the activity. However, the lack of an efficient dual atom site to improve activity and durability has limited these catalysts from widespread application. Herein, the nitrogen-coordinated iron and tin-based DASs (Fe-Sn-N/C) catalyst are synthesized for ORR. This catalyst has a high activity with ORR half-wave potentials (E1/2 ) of 0.92 V in alkaline, which is higher than those of the state-of-the-art Pt/C (E1/2  = 0.83 V), Fe-N/C (E1/2  = 0.83 V), and Sn-N/C (E1/2  = 0.77 V). Scanning electron transmission microscopy analysis confirmed the atomically distributed Fe and Sn sites on the N-doped carbon network. X-ray absorption spectroscopy analysis revealed the charge transfer between Fe and Sn. Both experimental and theoretical results indicate that the Sn with Fe-NC (Fe-Sn-N/C) induces charge redistribution, weakening the binding strength of oxygenated intermediates and leading to improved ORR activity. This study provides the synergistic effects of DASs catalysts and addresses the impacts of P-block elements on d-block transition metals in ORR.

Mimicking Metalloenzyme Microenvironments in the Transition Metal-Single Atom Catalysts for Electrochemical Hydrogen Peroxide Synthesis in an Acidic Medium.

Electrochemical reduction of oxygen into hydrogen peroxide in an acidic medium offers an energy-efficient and green H2 O2 synthesis as an alternative to the energy-intensive anthraquinone process. Unfortunately, high overpotential, low production rates, and fierce competition from traditional four-electron reduction limit it. In this study, a metalloenzyme-like active structure is mimicked in carbon-based single-atom electrocatalysts for oxygen reduction to H2 O2 . Using a carbonization strategy, the primary electronic structure of the metal center with nitrogen and oxygen coordination is modulated, followed by epoxy oxygen functionalities close to the metal active sites. In an acidic medium, CoNOC active structures proceed with greater than 98% H2 O2 selectivity (2e- /2H+ ) rather than CoNC active sites that are selective to H2 O (4e- /4H+ ). Among all MNOC (M = Fe, Co, Mn, and Ni) single-atom electrocatalysts, the CoNOC is the most selective (> 98%) for H2 O2 production, with a mass activity of 10 A g-1 at 0.60 V vs. RHE. X-ray absorption spectroscopy is used to identify the formation of unsymmetrical MNOC active structures. Experimental results are also compared to density functional theory calculations, which revealed that the structure-activity relationship of the epoxy-surrounded CoNOC active structure reaches optimum (ΔG*OOH ) binding energies for high selectivity.

Tailoring the Co4+/Co3+ active sites in a single perovskite as a bifunctional catalyst for the oxygen electrode reactions.

Developing a non-precious metal electrocatalyst for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is desirable for low-cost energy conversion devices. Herein, we designed and developed a new class of layered cation ordered single perovskite oxides (Pr0.9Ca0.1Co0.8Fe0.2O3-δ) with an optimum ratio of the Co4+/Co3+ oxidation state and oxygen vacancy for oxygen electrode reactions. Catalytic activities are investigated as a function of electronic structure and surface composition. A moderate amount of Ca and Fe dopants keeps the B-site Co cations at a higher oxidation state (Co4+) and generates a vast amount of an oxygen defect rich structure. The improved performance in the ORR and OER is explained by the increase in the sites of Co4+ cations, a state responsible for enhanced catalytic activity. A hypothesis for how doped Ca fraction affects the adsorbed oxygen species and contributes to catalytic activity is discussed. This work sheds light on the influence of crystal structure on the catalytic property and reports that ORR and OER activities are affected not only by oxygen vacancy concentration but also by the oxidation state of the transition metal in the perovskite oxide.

Physiochemical and biological characterization of novel exopolysaccharide produced by Bacillus tequilensis FR9 isolated from chicken.

Hetero-exopolysaccharide secreted by Bacillus tequilensis FR9 (BtqEPS), was produced and fractioned on DEAE-Sepharose and phenyl sepharose CL-6B column. HPLC analysis revealed the existence of five monosaccharides including glucose, galactose, mannose, arabinose and xylose. FT-IR spectroscopy confirmed the presence of carboxyl and hydroxyl groups. 1H NMR and 13C NMR spectra analysis showed the presence of α and ß-d-(+)-glucose residues and glycosidic linkages. The fibrous, porous nature and elemental composition (C, O, N, Cl, Na, P, S) of BtqEPS was inferred from SEM and EDX analysis. AFM proved that the micro-structure of BtqEPS is compact and rough. XRD analysis confirmed the amorphous nature of BtqEPS with 15.6% crystallinity index. TGA curve indicated the degradation temperature (Td) of 239.72°C. Furthermore, BtqEPS exhibited antioxidant effects by scavenging reactive oxygen species (ROS) and demonstrated strong reducing power. All the above findings on BtqEPS paves way to find novel insights of its potential applications in industries.