Unveiling Low Temperature Assembly of Dense Fe-N4 Active Sites via Hydrogenation in Advanced Oxygen Reduction Catalysts.

The single-atom Fe-N-C is a prominent material with exceptional reactivity in areas of sustainable energy and catalysis research. It is challenging to obtain the dense Fe-N4 site without the Fe nanoparticles (NPs) sintering during the Fe-N-C synthesis via high-temperature pyrolysis. Thus, a novel approach is devised for the Fe-N-C synthesis at low temperatures. Taking FeCl2 as Fe source, a hydrogen environment can facilitate oxygen removal and dichlorination processes in the synthesis, efficiently favouring Fe-N4 site formation without Fe NPs clustering at as low as 360 °C. We shed light on the reaction mechanism about hydrogen promoting Fe-N4 formation in the synthesis. By adjusting the temperature and duration, the Fe-N4 structural evolution and site density can be precisely tuned to directly influence the catalytic behaviour of the Fe-N-C material. The FeNC-H2-360 catalyst demonstrates a remarkable Fe dispersion (8.3 wt %) and superior acid ORR activity with a half-wave potential of 0.85 V and a peak power density of 1.21 W cm-2 in fuel cell. This method also generally facilitates the synthesis of various high-performance M-N-C materials (M=Fe, Co, Mn, Ni, Zn, Ru) with elevated single-atom loadings.

Regulating Au coverage for the direct oxidation of methane to methanol.

The direct oxidation of methane to methanol under mild conditions is challenging owing to its inadequate activity and low selectivity. A key objective is improving the selective oxidation of the first carbon-hydrogen bond of methane, while inhibiting the oxidation of the remaining carbon-hydrogen bonds to ensure high yield and selectivity of methanol. Here we design ultrathin PdxAuy nanosheets and revealed a volcano-type relationship between the binding strength of hydroxyl radical on the catalyst surface and catalytic performance using experimental and density functional theory results. Our investigations indicate a trade-off relationship between the reaction-triggering and reaction-conversion steps in the reaction process. The optimized Pd3Au1 nanosheets exhibits a methanol production rate of 147.8 millimoles per gram of Pd per hour, with a selectivity of 98% at 70 °C, representing one of the most efficient catalysts for the direct oxidation of methane to methanol.

Electrochemical coverage of reduced graphene oxide layers on sulfur supported by biochar for enhancing performance of Li-S battery.

To improve the electrochemical performance of Li-S batteries, a cathodic material (rGO150/S/CF-75) was fabricated for Li-S batteries by adopting a melt-flow method to load sulfur on biomass-derived carbon fibers, then the reduced graphene oxide was electrochemically covered on the outside surface of the sulfur. The coverage of reduced graphite oxide layers endows the performance of S/CF-75 multiple improvements. The specific capacity of rGO150/S/CF-75 cathode delivers a specific capacity of 1451.4 mAh g-1 at 0.1 A g-1. The specific capacity of rGO150/S/CF-75 cathode can still maintain 537.3 mAh g-1 after 1000 cycles at 5 A g-1 (109 % capacity retention). The excellent performance of rGO150/S/CF-75 cathode is benefit from not only the conductive paths of reduced graphene oxide layers and protective function of reduced graphene oxide layers inhibiting that the soluble sulfur diffuse into bulk electrolyte, but also the redistribution of sulfur on conductive carbon components during the cycling process.

Novel synergistically effects of palladium-iron bimetal and manganese carbonate carrier for catalytic oxidation of formaldehyde at room temperature.

The elimination of formaldehyde at room temperature holds immense potential for various applications, and the incorporation of a catalyst rich in surface hydroxyl groups and oxygen significantly enhances its catalytic activity towards formaldehyde oxidation. By employing a coprecipitation method, we successfully achieved a palladium domain confined within the manganese carbonate lattice and doped with iron. This synergistic effect between highly dispersed palladium and iron greatly amplifies the concentration of surface hydroxyl groups and oxygen on the catalyst, thereby enabling complete oxidation of formaldehyde at ambient conditions. The proposed method facilitates the formation of domain-limited palladium within the MnCO3 lattice, thereby enhancing the dispersion of palladium and facilitating its partial incorporation into the MnCO3 lattice. Consequently, this approach promotes increased exposure of active sites and enhances the catalyst's capacity for oxygen activation. The co-doping of iron effectively splits the doping sites of palladium to further enhance its dispersion, while simultaneously modifying the electronic modification of the catalyst to alter formaldehyde's adsorption strength on it. Manganese carbonate exhibits superior adsorption capability for activated surface hydroxyl groups due to the presence of carbonate. In situ infrared testing revealed that dioxymethylene and formate are primary products resulting from catalytic oxidation of formaldehyde, with catalyst surface oxygen and hydroxyl groups playing a crucial role in intermediate product decomposition and oxidation. This study provides novel insights for designing palladium-based catalysts.

Instantaneous Free Radical Scavenging by CeO2 Nanoparticles Adjacent to the Fe-N4 Active Sites for Durable Fuel Cells.

To achieve the Fe-N-C materials with both high activity and durability in proton exchange membrane fuel cells, the attack of free radicals on Fe-N4 sites must be overcome. Herein, we report a strategy to effectively eliminate radicals at the source to mitigate the degradation by anchoring CeO2 nanoparticles as radicals scavengers adjacent (Scaad-CeO2 ) to the Fe-N4 sites. Radicals such as ⋅OH and HO2 ⋅ that form at Fe-N4 sites can be instantaneously eliminated by adjacent CeO2 , which shortens the survival time of radicals and the regional space of their damage. As a result, the CeO2 scavengers in Fe-NC/Scaad-CeO2 achieved ∼80 % elimination of the radicals generated at the Fe-N4 sites. A fuel cell prepared with the Fe-NC/Scaad-CeO2 showed a smaller peak power density decay after 30,000 cycles determined with US DOE PGM-relevant AST, increasing the decay of Fe-NCPhen from 69 % to 28 % decay.

Surface modification using heptafluorobutyric acid to produce highly stable Li metal anodes.

The Li metal is an ideal anode material owing to its high theoretical specific capacity and low electrode potential. However, its high reactivity and dendritic growth in carbonate-based electrolytes limit its application. To address these issues, we propose a novel surface modification technique using heptafluorobutyric acid. In-situ spontaneous reaction between Li and the organic acid generates a lithiophilic interface of lithium heptafluorobutyrate for dendrite-free uniform Li deposition, which significantly improves the cycle stability (Li/Li symmetric cells >1200 h at 1.0 mA cm-2) and Coulombic efficiency (>99.3%) in conventional carbonate-based electrolytes. This lithiophilic interface also enables full batteries to achieve 83.2% capacity retention over 300 cycles under realistic testing condition. Lithium heptafluorobutyrate interface acts as an electrical bridge for uniform lithium-ion flux between Li anode and plating Li, which minimizes the occurrence of tortuous lithium dendrites and lowers interface impedance.

A plasma-assisted approach to enhance density of accessible FeN4 sites for proton exchange membrane fuel cells.

Enhancing the density and utilization of FeN4 sites can serve as a viable approach to enhance the catalytic efficacy of iron nitrogen carbon (FeNC) catalysts for oxygen reduction reaction (ORR). Herein, we present a plasma-assisted method for enhancing the porosity of nitrogen-doped carbon. Our findings indicate that the ideal ratio of mesopore to micropore area is 0.463. This ratio not only promotes the diffusion of Fe3+ but also creates additional active sites for Fe3+ loading, leading to an increase in the number of available FeN4 sites in FeNC electrocatalysts during pyrolysis. The density (76.5 µmol g-1) and utilization (21.08 %) of d-FeNC-30 are significantly higher than those of FeNC without plasma treatment, with a 2.8-fold and 2-fold increase, respectively. Remarkably, it displays outstanding performance, evidenced by a half-wave potential of 0.835 V (vs. RHE) in a 0.1 M HClO4 solution and a power density of 0.860 W cm-2 in proton exchange membrane fuel cells (PEMFCs). The developed plasma-assisted approach for improving the site density (SD) and utilization of FeN4 provides a new perspective for high-performance ORR FeNC catalysts.

Ultrathin Nitrogen-Doped Carbon Encapsulated Ni Nanoparticles for Highly Efficient Electrochemical CO2 Reduction and Aqueous Zn-CO2 Batteries.

Electrochemical CO2 reduction reaction (CO2 RR), powered by renewable electricity, has attracted great attention for producing high value-added fuels and chemicals, as well as feasibly mitigating CO2 emission problem. Here, this work reports a facile hard template strategy to prepare the Ni@N-C catalyst with core-shell structure, where nickel nanoparticles (Ni NPs) are encapsulated by thin nitrogen-doped carbon shells (N-C shells). The Ni@N-C catalyst has demonstrated a promising industrial current density of 236.7 mA cm-2 with the superb FECO of 97% at -1.1 V versus RHE. Moreover, Ni@N-C can drive the reversible Zn-CO2 battery with the largest power density of 1.64 mW cm-2 , and endure a tough cycling durability. These excellent performances are ascribed to the synergistic effect of Ni@N-C that Ni NPs can regulate the electronic microenvironment of N-doped carbon shells, which favor to enhance the CO2 adsorption capacity and the electron transfer capacity. Density functional theory calculations prove that the binding configuration of N-C located on the top of Ni slabs (Top-Ni@N-C) is the most thermodynamically stable and possess a lowest thermodynamic barrier for the formation of COOH* and the desorption of CO. This work may pioneer a new method on seeking high-efficiency and worthwhile electrocatalysts for CO2 RR and Zn-CO2 battery.

Adsorption of BiOBr microspheres to rhodamine B and its influence on photocatalytic reaction.

Adsorption and its influence are often neglected during photocatalytic degradation of organic pollutants. To call attention to these issues, a novel bismuth oxybromide (BiOBr) microsphere with hierarchical flower-like structure was fabricated through a facile hydrothermal process using polyvinyl pyrrolidone (PVP) as additive in this work, and then the adsorption of the BiOBr microspheres to RhB and its influence on the photocatalytic degradation of RhB were investigated in detail. Experimental results show that the BiOBr microspheres have a very strong adsorption capacity to RhB. The adsorption behavior follows the Langmuir model and the quasi second order kinetic equation. Tests of the photocatalytic degradation of RhB under visible irradiation verify that the adsorption of the BiOBr microspheres to RhB greatly boosts the degradation of RhB due to the "enriching effect", and a complete degradation of 20 mg L-1 RhB only requires 37 min.

Amidinothiourea as a new deposition-regulating additive for dendrite-free lithium metal anodes.

Lithium (Li) dendrite growth seriously hinders the practical application of Li metal batteries. Here, we report molecular amidinothiourea (ATU) as a new electrolyte additive to regulate Li stripping/plating behaviors of Li metal anodes. The molecular ATU in the electrolyte can act as a shielding layer on the Li metal surface to suppress the decomposition of electrolytes as verified by XPS and adsorption energy calculation, which improves the electrochemical reversibility of the Li plating/stripping behaviors and inhibits lithium dendrite growth.

Plasma-induced defect engineering: Boosted the reverse water gas shift reaction performance with electron trap.

The reverse water gas shift reaction is a promising approach to solve the problem of excessive CO2 emission and energy shortage. However, insufficient charge separation efficiency of numerous semiconductor photocatalysts hamper their CO2 photoreduction performance. Defect engineering is considered as a desired method to tackle that shortcoming by the boosting the electron capture process. Herein, the sulfur vacancies-rich CdIn2S4 (VS-CdIn2S4) was synthesized by an efficient low-temperature plasma-enhanced technology. The outstanding VS-CdIn2S4 shows a more excellent CO formation rate of 103.6 µmol g-1 h-1 comparing that of traditional CdIn2S4 (31.36 µmol g-1 h-1). The density function theory (DFT) calculation reveals the sulfur vacancy is the center of electron capture. Moreover, the formed defect level after introduce of surface vacancy effectively optimizes the light absorption propertie of the prepared material. Thus, the enhanced photocatalytic CO2 reduction performance can be attributed to the double improvement of light absorption and carrier separation. This work provides a novel and facile strategy to mediate carriers' movement behavior via defect engineering for high-efficient CO2 photoreduction.

Rechargeable Zinc-Air Battery with Ultrahigh Power Density Based on Uniform N, Co Codoped Carbon Nanospheres.

Highly efficient catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key to the commercialization of rechargeable zinc-air batteries (ZABs). In this work, a catalyst with uniform nanospherical morphology was prepared from cobalt nitrate, acetylacetone, and hydrazine hydrate. The final catalyst possesses high ORR and OER performances, with a half-wave potential of 0.911 V [vs reversible hydrogen electrode (RHE)] for ORR and a low potential of 1.57 V (vs RHE) at 10 mA cm-2 for OER in 0.1 M KOH solution. Specially, a ZAB based on the catalyst demonstrates an ultrahigh power density of 479.1 mW cm-2, as well as excellent stability, and potential in practical applications.

Microwave synthesis and photocatalytic activity of Tb(3+) doped BiVO4 microcrystals.

Tb(3+) doped BiVO4 has been successfully synthesized by a simple microwave-assisted hydrothermal method at 140°C for 30min. The structure, morphology and optical property of the Tb(3+) doped BiVO4 products have been systematically investigated. This study indicates that the incorporation of Tb(3+) could induce the conversion of structure from monoclinic to tetragonal for BiVO4. Furthermore, the as-obtained Tb(3+) doped BiVO4 samples showed an obvious morphological change: the hollow square rod-like BiVO4 crystal gradually changed to spindle-like crystal. The Tb(3+) doped BiVO4 products exhibited extraordinary photocatalytic activity for Methylene Blue (MB) degradation under visible light irradiation. The doped BiVO4 at a molar ratio of 2at% (Tb and Bi) with a mixture of monoclinic and tetragonal phases showed and prominent photocatalytic degradation rate, which reached 99.9% in 120min. The results suggest that the differences in the photocatalytic activity of these BiVO4 crystals with different Tb(3+) doping concentrations can be attributed to the change of crystalline phases, and the coexistence of the monoclinic/tetragonal phases in BiVO4 products, which improve the efficient charge separation and transportation.

High pressure synthesis, structure, and multiferroic properties of two perovskite compounds Y2FeMnO6 and Y2CrMnO6.

High purity crystals of Y2FeMnO6 (YFMO) and Y2CrMnO6 (YCMO) have been synthesized for the first time using a flux method under a high temperature of 1573 K and high pressure of 6 GPa. Both YFMO and YCMO have orthorhombic structures in space group Pnma. The temperature-dependent magnetization and the nonlinear M-H hysteresis loops of both materials indicate that an antiferromagnetic transition occurs at the Néel temperature of 328 K for YFMO, and a ferrimagnetic transition occurs at 74 K for YCMO. YFMO is a relaxor ferroelectric in which three dielectric relaxations were observed at 245, 328 and 358 K, respectively. The first relaxation process is due to Maxwell-Wagner polarization at the grain boundary whereas the second and the third relaxation behaviours arise from the beginning and the ending of antiferromagnetic ordering, respectively. The presence of the dielectric anomaly near TN indicates the magnetoelectric effect. Ferroelectric hysteresis loops and PUND (positive-up & negative-down) pulse data reveal weak ferroelectric behavior of YFMO at 77 K. Otherwise one dielectric constant anomaly has been found for YCMO at about 390 K. But no ferroelectric polarization was observed in YCMO.