Single Atomic State Research Articles

Candle flame generated Co and Fe single atoms supported in soot as novel host for lithium-sulfur batteries with excellent electrochemical performance

By simply introducing metal salts into paraffin, Co and Fe single atoms dispersed in candle soot (CS) can be directly collected from the flame of home-made candles without any byproducts. STEM, XRD and XANES analysis demonstrate that Co and Fe exist in single atom state. The prepared Co-CS and Fe-CS, with high specific area and excellent sulfur loading capability, can be used as innovative host for cathode to assemble Li-S pouch cells, and exhibit excellent electrochemical performance with higher specific capacities (approximately 1250 mAh/g at 0.1 C with 7.5 mg/cm² sulfur loading) and improved cycling stability (retaining about 63 % of capacity after 50 cycles) than bare CS host. Meanwhile, density functional theory (DFT) calculations demonstrate that Fe-CS/Co-CS decrease the energy barriers of conversion reactions from Li2S8 to Li2S due to the increased binding energy between Co-CS/Fe-CS and LiPSs, therefore effectively mitigating the polysulfides shuttle effect. Such a strategy holds promise for practical cell-level designs in Li-S batteries.

Efficient activation of peroxymonosulfate by Mn single-atom: Critical role of Mn-N4 coordination for generating singlet oxygen

Single-atom catalysts with high catalytic efficiency and simple preparation methods are critical for activation of peroxymonosulfate (PMS) to degrade emerging contaminants in aqueous solution. Herein, manganese single-atom nitrogen-doped carbon catalyst (SA-Mn-NC) was synthesized by precisely controlled catalytic carbonization using small-molecule organic compounds as precursors, and Mn was uniformly dispersed in a single-atom state and existed in the ligand structure of Mn-N4. Thus, the SA-Mn-NC had considerable catalytic activity and can realize 100% bisphenol A degradation within 3 min with kobs of 1.56 min−1, which was 4.7 and 9.2 times higher than that of NC (0.33 min−1) and Mn-NC (0.17 min−1). Moreover, SA-Mn-NC has excellent environmental adaptability, negligible metal leaching concentration, good cycling stability, and selectivity to electron-rich compounds. EPR tests, quenching experiments, electrochemical measurements, and selective degradation results together confirmed that singlet oxygen (1O2) was the main active species in the SA-Mn-NC/PMS system. The coupled N-active sites of Mn-N4 contribute to the efficient activation of PMS to generate 1O2 and achieve high catalytic turnover frequency. This work provides a simple strategy for the preparation of single-atom catalysts with considerable PMS catalytic efficiency and negligible metal leaching toxicity, which is of guiding importance for the design of single-atom catalysts for high-efficiency water treatment.

(Keynote) Single Atom Co-Catalysts in Photocatalytic H2 Generation

Photocatalytic H2 generation has been a highly investigated topic ever since Fujishima und Honda (1972) reported on the use of TiO2 as a solar-illuminated semiconductor for the splitting of water into H2 and O2. Generally, in a fully photocatalytic setting (when photogenerated electron and hole are transferred from a solution-suspended TiO2 nanoparticle to an aqueous electrolyte), a reasonable electron transfer rate can only be established when a noble metal co-catalyst is attached to the TiO2. Mostly this is a Pt nanoparticle that is deposited onto the TiO2 by various reductive treatments. Over the years numerous efforts have been devoted to the shrinkage of the particle to enhance the usage of the noble metal. Evidently the most extreme case shrinkage is the use of an insulated single atom of Pt. The use of such isolated atoms as a co-catalyst in photocatalysis has in recent years attracted strong interest, not only because the single atom state represents a maximized surface to volume efficiency, but also because single atom reactivity allows for unprecedented reaction pathways. In the presentation we discuss the use of Pt dispersed and anchored as single atoms on TiO2 nanocrystallites, powders and nanotubes as a co-catalyst in photocatalytic H2 generation. We discuss various trapping and stabilization approaches of SAs on photocatalysts and report on a SA-Pt photocatalyst with a higher photocatalytic activity than observed for classic arrangements of co-catalyst on the semiconductive substrate. Moreover, we show that a small fraction of the totally deposited Pt that is stably trapped SAs provides virtually all photocatalytic reactivity of a Pt decorated catalyst. References 1) C. Gao, J. Low, R. Long, T. Kong, J. Zhu and Y. Xiong, Chem. Rev., 2020, 120, 12175-12216.2) N. Denisov, S. Qin, J. Will,, T. Yokosawa, .. and P. Schmuki, Adv. Mater., 2022, n/a, 2206569.3) S. Hejazi, ..O. Tomanec, S. Kment, and P. Schmuki, Adv. Mater., 2020, 32, 1908505.4) S. Qin, N. Denisov, J. Will, ..E. Spiecker and P. Schmuki, Solar RRL, 2022, 6, 2101026.5) S. Qin, J. Will, H. Kim, N. Denisov, S. Carl, E. Spiecker and P. Schmuki, ACS Energy Lett., 2023, DOI: 10.1021/acsenergylett.2c02801, 1209-1214.6) I. Hwang, A. Mazare, ..and P. Schmuki, Adv. Funct. Mater., 2022, n/a, 2207849.

An Erythrocyte-Templated Iron Single-Atom Nanozyme for Wound Healing.

Iron single-atom nanozymes represent a promising artificial enzyme with superior activity owing to uniform active sites that can precisely mimic active center of nature enzymes. However, current synthetic strategies are hard to guarantee each active site at single-atom state. In this work, an erythrocyte-templated strategy by utilizing intrinsic hemin active center of hemoglobin as sing-atom source for nanozyme formation is developed. By combining cell fixation, porous salinization, and high-temperature carbonization, erythrocytes are successfully served as uniform templates to synthesize nanozymes with fully single-atom FeN4 active sites which derived from hemin of hemoglobin, resulting in an enhanced peroxidase (POD)-like activity. Interestingly, the catalytic activity of erythrocyte-templated nanozyme (ETN) shows dependence on animal species, among which murine ETN performed superior catalytic efficiency. In addition, the as-prepared ETNs display a honeycomb-like network structure, serving as a sponge to accelerate hemostasis based on the interactions with prothrombin and fibrinogen. These features enable ETN to effectively kill methicillin-resistant Staphylococcus aureus (MRSA) by combining POD-like catalysis with near-infrared (NIR) induced photothermal effect, and subsequently suitable to promote wound healing. This study provides a proof-of-concept for facile fabrication of multifunctional nanozymes with uniform single-atom active sites by utilizing intrinsic iron structure characteristics of biogenic source like erythrocytes.

Triethylenediamine cobalt complex encapsulated in a metal–organic framework cage to prepare a cobalt single-atom catalyst with a high Co-N4 density for an efficient oxygen reduction reaction

Transition metal single atom catalysts (TM SACs) are the most promising oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs) and metal-air batteries. However, the low density of M-Nx active sites seriously hinders further improvement of the ORR electrocatalytic activity. Here, a strategy for encapsulating nitrogen-rich guest molecules (triethylenediamine cobalt complex, [Co(en)3]3+) was proposed to construct a high-performance cobalt single-atom catalyst (Co-encapsulated SAC/NC). With this strategy, the guest molecules are encapsulated into metal–organic framework (MOF) cages as an additional cobalt source to boost cobalt loading, while abundant nitrogen from guest molecules contributes to the formation of Co-N4 active sites. Remarkably, the resulting Co-encapsulated SAC/NC has a high cobalt loading amount of 4.03 wt%, and spherical aberration-corrected transmission electron microscopy (AC-TEM) has confirmed that most cobalt exists in a single-atom state. As a result, the Co-encapsulated SAC/NC exhibits excellent ORR catalytic performance with a half-wave potential of 0.88 V. Furthermore, Zn-air batteries employing Co-encapsulated SAC/NC as air cathode show high peak power density and excellent cycling stability. Density functional theory (DFT) calculations reveal that adjacent active sites have different rate-determining steps and lower reaction energy barriers than a single active site.

Effect of palladium chemical states on CO2 photocatalytic reduction over g-C3N4: Distinct role of single-atomic state in boosting CH4 production

Cocatalyst decoration has been recognized as an effective strategy in photocatalysis, yet the critical role of sing-atomic state on CO2 photocatalytic reduction, distinguished from the oxide and elemental states, remains a mystery hitherto. Herein, single-atom Pd (Pd-SA), Pd oxides (PdOx), and Pd nanoparticles (Pd-NP), were homogeneously anchored on g-C3N4 (CN) to investigate their CO2 reduction behaviors under visible-light irradiation. Performance tests showed Pd species decoration improved the CH4 production of CN, with Pd/CN-SA exhibiting the optimum yields (2.25 μmol g–1), markedly higher than that of PdOx/CN (1.08 μmol g–1) and Pd/CN-NP (0.44 μmol g–1). After comprehensive mechanism analysis with various characterization techniques, in-situ DRIFT spectra and DFT calculations, it was found that the conducive activation of CO2, negative conduction band potentials, and excellent •H utilization efficiency, collaboratively contributed to the superior CH4 production of Pd/CN-SA. Despite the larger electron density of Pd/CN-NP and PdOx/CN, the moderate reduction ability of their photogenerated electrons restricted the further reduction of adsorbed CO2 species and CO intermediate, limiting the enhancement of CO2 reduction activity. Furthermore, the CH4 evolutions of Pd/CN-NP and PdOx/CN were also limited by the poor •H supply and inferior •H utilization efficiency, respectively. It is expected that the effect of chemical states, especially the critical role of single-atomic state, revealed in this work can inspire the rational design of more advanced photocatalysts for CO2 reduction.

Synergism of Ultrasmall Pt Clusters and Basic La2O2CO3 Supports Boosts the Reverse Water Gas Reaction Efficiency

AbstractThe reverse water‐gas shift reaction (RWGS) has been regarded as a promising approach for fighting climate change caused by the excessive emission of the greenhouse gas CO2, but it still suffers from relatively poor low‐temperature reactivity. Herein, a high‐performance RWGS catalyst composed of ultrasmall Pt clusters (1.38 nm on average) anchored by La2O2CO3 support (PtNC/LOC), which possesses a record CO production rate of 2678 molCO molPt−1 h−1 with nearly 100% CO selectivity at 300 °C, is reported. The specific activity is nearly 1.5 and 7.9 fold higher than that of Pt single atoms and nanoparticles on La2O2CO3, respectively. More importantly, over 87.7% of the initial activity of PtNC/LOC remains after 80 h constant operation at 380 °C, firmly verifying the structural robustness. LOC support is essential, because of not only the moderate basicity that can boost the reaction efficiency but also the strong interaction with Pt species that can stabilize the ultrasmall particle size. Further investigations also point out the key role of the Pt clusters. The two key steps, CO2 adsorption, and CO desorption, individually prefer electron‐rich and electron‐deficient Pt species. Ultrasmall Pt clusters successfully integrate the unique surface states of single atoms and nanoparticles, thus achieving excellent low‐temperature RWGS performance.

Ultimate Localization

We report approaches to grow directly noble-metal-(NM)-decorated nanotubes by self-organized anodization. Key to obtain highly defined tubes is an optimized and controlled anodization of Ti-Pt (or other NM) alloys in fluoride containing solutions. In general, the morphology of porous TiO2 and of the tubular layers is affected strongly by the electrochemical growth parameters. NM-decorated titanium-dioxide is a highly functional material that has numerous interesting properties, for example, in solar energy conversion, catalysis of the decomposition of organic compounds (self-cleaning). Therefore this simple approach to produce this highly defined nanoscopic form of NM-TiO2 bears a high potential for technological exploitation. Over the years numerous efforts have been devoted to the shrinkage of the NM-particles to enhance the usage of the noble metal. Evidently the most extreme case of shrinkage is the use of an isolated single atoms of Pt. The use of single atoms as a co-catalyst in photocatalysis has in recent years attracted strong interest, not only because the single atom state represents a maximized surface to volume efficiency, but also because single atom reactivity allows for unprecedented reaction pathways.In the presentation we discuss the formation of Pt dispersed and anchored as single atoms on TiO2 nanotubes and the use of such tubes in highly effective photocatalysis.

(Invited) Single Atom Co-Catalysts in Photocatalytic H2 Generation

Photocatalytic H2 generation has been a highly investigated topic ever since Fujishima und Honda (1972) reported on the use of TiO2 as a solar-illuminated semiconductor for the splitting of water into H2 and O2. Generally, in a fully photocatalytic setting (when photogenerated electron and hole are transferred from a solution-suspended TiO2 nanoparticle to an aqueous electrolyte), a reasonable electron transfer rate can only be established when a noble metal co-catalyst is attached to the TiO2. Mostly this is a Pt nanoparticle that is deposited onto the TiO2 by various reductive treatments.Over the years numerous efforts have been devoted to the shrinkage of the particle to enhance the usage of the noble metal. Evidently the most extreme case shrinkage is the use of an insulated single atom of Pt. The use of such isolated atoms as a co-catalyst in photocatalysis has in recent years attracted strong interest, not only because the single atom state represents a maximized surface to volume efficiency, but also because single atom reactivity allows for unprecedented reaction pathways.In the presentation we discuss the use of Pt dispersed and anchored as single atoms on TiO2 nanocrystallites, powders and nanotubes as a co-catalyst in photocatalytic H2 generation.We discuss various trapping and stabilization approaches of SAs on photocatalysts and report on a SA-Pt photocatalyst with a higher photocatalytic activity than observed for classic arrangements of co-catalyst on the semiconductive substrate. Moreover, we show that a small fraction of the totally deposited Pt that is stably trapped SAs provides virtually all photocatalytic reactivity of a Pt decorated catalyst.

Ultra-deep photocatalytic desulfurization of dibenzothiophene over hollow Core-shell N-doped graphene nanospheres anchored bimetallic single atoms under visible light

HCS-NG-Ni/Cu nanospheres composed of the 100–120 nm hollow core- shell N-doped graphene with lattice spacing d = 0.25 nm were prepared by a facile method and their surfaces were decorated with d = 0.14 nm Ni and d = 0.12 nm Cu single atoms. Characterization of HAADF-STEM, XPS, Raman, and photoelectron-chemi- cal showed the morphology of Ni/Cu was a single atomic state on the hollow core- shell N-doped graphene, which could effectively inhibit the photoelectron-hole pair recombination leading to improve the efficiency of photocatalytic desulfurization. The influence of metal loading, Ni:Cu ratios, time, catalyst amount, and different catalysts on the removal of DBT were investigated. Results indicated the hollow core–shell N-doped graphene decorated with Ni/Cu had higher photocatalytic removal ratios (>99.1%) than the others under the mild conditions and had a high activity even after 10 cycles because of the synergism of single Ni/Cu atoms and the hollow core–shell N-doping-graphene under visible light. The energy barrier and the removal rate constant of DBT were 78 kJ/mol and 3.79*10-2, respectively, and the photocatalytic mechanism was assumed. Researches provided not only a high-efficiency desulfurization catalyst to produce clean fuel, but also a new idea on designing bimetallic single-atom catalysts.

Operando Cooperated Catalytic Mechanism of Atomically Dispersed Cu-N4 and Zn-N4 for Promoting Oxygen Reduction Reaction.

Dual-metal single-atom catalysts exhibit superior performance for oxygen reduction reaction (ORR), however, the synergistic catalytic mechanism is not deeply understood. Herein, we report a dual-metal single-atom catalyst consisted of Cu-N4 and Zn-N4 on the N-doped carbon support (Cu/Zn-NC). It exhibits high-efficiency ORR activity with an Eonset of 0.98 V and an E1/2 of 0.83 V, excellent stability (no degradation after 10 000 cycles), surpassing state-of-the-art Pt/C and great mass of Pt-free single atom catalysts. Operando XANES demonstrates that the Cu-N4 as active center experiences the change from atomic dispersion to cluster with the cooperation of Zn-N4 during ORR process, and then turns to single atom state again after reaction. DFT calculation further indicates that the adjustment effect of Zn on the d-orbital electron distribution of Cu could benefit to the stretch and cleavage of O-O on Cu active center, speeding up the process of rate determining step of OOH*.

Operando Cooperated Catalytic Mechanism of Atomically Dispersed Cu−N4 and Zn−N4 for Promoting Oxygen Reduction Reaction

AbstractDual‐metal single‐atom catalysts exhibit superior performance for oxygen reduction reaction (ORR), however, the synergistic catalytic mechanism is not deeply understood. Herein, we report a dual‐metal single‐atom catalyst consisted of Cu−N4 and Zn−N4 on the N‐doped carbon support (Cu/Zn−NC). It exhibits high‐efficiency ORR activity with an Eonset of 0.98 V and an E1/2 of 0.83 V, excellent stability (no degradation after 10 000 cycles), surpassing state‐of‐the‐art Pt/C and great mass of Pt‐free single atom catalysts. Operando XANES demonstrates that the Cu−N4 as active center experiences the change from atomic dispersion to cluster with the cooperation of Zn−N4 during ORR process, and then turns to single atom state again after reaction. DFT calculation further indicates that the adjustment effect of Zn on the d‐orbital electron distribution of Cu could benefit to the stretch and cleavage of O‐O on Cu active center, speeding up the process of rate determining step of OOH*.

Boosted peroxidase-like activity of metal-organic framework nanoparticles with single atom Fe(Ⅲ) sites at low substrate concentration

Single atom nanomaterials possess catalytic activity like natural enzymes are termed as SAzymes which have gained great attention during last two years because of the maximal utilization of atoms and the benefit of understanding structure-property relationship. However, most of SAzymes are fabricated based on hydrophobic carbon, which disperse poorly in water and exhibit inferior affinity towards substrates, which may limit their biomedical applications. Here, we report a peroxidase-like SAzyme through the post-modification route based on hydrophilic defective metal-organic frameworks. Hydrochloric acid (HCl) is employed as ligand modulator to fabricate defective NH2-UiO-66 nanoparticles (HCl–NH2-UiO-66 NPs). Compared with the NPs fabricated through acetic acid modulation method (Ac-NH2-UiO-66 NPs), HCl–NH2-UiO-66 NPs have more missing linkers. Hence, more Fe(Ⅲ) ions can be successfully doped onto Zr6 clusters in HCl–NH2-UiO-66 NPs in a single atom state via formation of Fe–O–Zr bridge. The HCl–NH2-UiO-66 NPs doped with Fe(Ⅲ) ions (Fe–HCl–NH2-UiO-66 NPs) possess higher peroxidase-like activity than Fe-Ac-NH2-UiO-66 NPs due to the higher loading amount of Fe. Besides, both Fe–HCl–NH2-UiO-66 NPs and Fe-Ac-NH2-UiO-66 NPs exhibit lower Michaelis-Menten constants (Km) for hydrogen peroxide (H2O2) than most reported nanomaterials, indicating their higher affinity to H2O2. Due to their excellent catalytic activity to low concentration of substrates, Fe–HCl–NH2-UiO-66 NPs can detect H2O2 with a limit of detection (LOD) of 1.0 μM. Thus, our system can be used to detect the low cellular H2O2 concentration. With high peroxidase-like activity induced by plenty of single atom Fe(Ⅲ) sites, Fe–HCl–NH2-UiO-66 NPs can also find wide applications in other fields including nanomedicine, pollution degradation and catalysis.

High-temperature treatment to engineer the single-atom Pt coordination environment towards highly efficient hydrogen evolution

The coordination environment of Pt is regulated through appropriate high-temperature treatment to further improve the HER performance of the single-atom Pt-catalyst. • High-t emperature induces new coordination environment for Pt single atom catalyst. • The obtained Pt 0.8 @CN-1000 shows superior HER performances to the pristine Pt 0.8 @CN. • The optimized Pt electronic state accounts for the enhanced HER performances. Development of high-performance and cost-effective catalysts for electrocatalytic hydrogen evolution reaction (HER) play crucial role in the growing hydrogen economy. Recently, the atomically dispersed metal catalysts have attracted increasing attention due to their ultimate atom utilization and great potential for highly cost-effective and high-efficiency HER electrocatalyst. Herein, we propose a high-temperature treatment strategy to furtherly improve the HER performance of atomically dispersed Pt-based catalyst. Interestingly, after appropriate high-temperature treatment on the atomically dispersed Pt 0.8 @CN, the Pt species on the designed N-doped porous carbon substrate with rich defect sites can be re-dispersed to single atom state with new coordination environment. The obtained Pt 0.8 @CN-1000 shows superior HER performance with overpotential of 13 mV at 10 mA cm −2 and mass activity of 11,284 mA/mg Pt at −0.1 V, much higher than that of the pristine Pt 0.8 @CN and commercial Pt/C catalyst. The experimental and theoretical investigations indicate that the high-temperature treatment induces the restructuring of coordination environment and then the optimized Pt electronic state leads to the enhanced HER performances. This work affords new strategy and insights to develop the atomically dispersed high-efficiency catalysts.

Quantum coherence and speed limit in the mean-field Dicke model of superradiance

Dicke superrandiance is a cooperative phenomenon which arises from the collective coupling of an ensemble of atoms to the electromagnetic radiation. Here we discuss the quantifying of quantum coherence for the Dicke model of superradiance in the mean-field approximation. We found the single-atom $l_1$-norm of coherence is given by the square root of the normalized average intensity of radiation emitted by the superradiant system. This validates quantum coherence as a useful figure of merit towards the understanding of superradiance phenomenon in the mean-field approach. In particular, this result suggests probing the single-atom coherence through the radiation intensity in superradiant systems, which might be useful in experimental realizations where is unfeasible to address atoms individually. Furthermore, given the nonlinear unitary dynamics of the time-dependent single-atom state that effectively describes the system of $N$ atoms, we analyze the quantum speed limit time and its interplay with the $l_1$-norm of coherence. We verify the quantum coherence speeds up the evolution of the superradiant system, i.e., the more coherence stored on the single-atom state, the faster the evolution. These findings unveil the role played by quantum coherence in superradiant systems, which in turn could be of interest for communities of both condensed matter physics and quantum optics.

Single-Atom Catalysts Based on the Metal-Oxide Interaction.

Metal atoms dispersed on the oxide supports constitute a large category of single-atom catalysts. In this review, oxide supported single-atom catalysts are discussed about their synthetic procedures, characterizations, and reaction mechanism in thermocatalysis, such as water-gas shift reaction, selective oxidation/hydrogenation, and coupling reactions. Some typical oxide materials, including ferric oxide, cerium oxide, titanium dioxide, aluminum oxide, and so on, are intentionally mentioned for the unique roles as supports in anchoring metal atoms and taking part in the catalytic reactions. The interactions between metal atoms and oxide supports are summarized to give a picture on how to stabilize the atomic metal centers, and rationally tune the geometric structures and electronic states of single atoms. Furthermore, several directions in fabricating single-atom catalysts with improved performance are proposed on the basis of state-of-the-art understanding in metal-oxide interactions.

Large array of Schr\xf6dinger cat states facilitated by an optical waveguide

Quantum engineering using photonic structures offer new capabilities for atom-photon interactions for quantum optics and atomic physics, which could eventually lead to integrated quantum devices. Despite the rapid progress in the variety of structures, coherent excitation of the motional states of atoms in a photonic waveguide using guided modes has yet to be demonstrated. Here, we use the waveguide mode of a hollow-core photonic crystal fibre to manipulate the mechanical Fock states of single atoms in a harmonic potential inside the fibre. We create a large array of Schrödinger cat states, a quintessential feature of quantum physics and a key element in quantum information processing and metrology, of approximately 15000 atoms along the fibre by entangling the electronic state with the coherent harmonic oscillator state of each individual atom. Our results provide a useful step for quantum information and simulation with a wide range of photonic waveguide systems.

High-Fidelity Manipulation of the Quantized Motion of a Single Atom via Stern–Gerlach Splitting**Supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0304501, 2016YFA0302800 and 2016YFA0302002), the Key Research Program of Frontier Science of the Chinese Academy of Sciences (CAS) (Grant No. ZDBSLY- SLH012), the National Natural Science Foundation of China (Grant No. 11774389), the Strategic Priority

We demonstrate high-fidelity manipulation of the quantized motion of a single 87Rb atom in an optical tweezer via microwave couplings induced by Stern–Gerlach splitting. The Stern–Gerlach splitting is mediated by polarization gradient of a strongly focused tweezer beam that functions as fictitious magnetic field gradient. The spatial splitting removes the orthogonality of the atomic spatial wavefunctions, thus enables the microwave couplings between the motional states. We obtain coherent Rabi oscillations for up to third-order sideband transitions, in which a high fidelity of larger than 0.99 is obtained for the spin-flip transition on the first order sideband after subtraction of the state preparation and detection error. The Stern–Gerlach splitting is measured at a precision of better than 0.05 nm. This work paves the way for quantum engineering of motional states of single atoms, and may have wide applications in few body physics and ultracold chemistry.

Electrospun single iron atoms dispersed carbon nanofibers as high performance electrocatalysts toward oxygen reduction reaction in acid and alkaline media

The metal (Fe/Co), nitrogen co-doped carbon represent an important class of oxygen reduction reaction (ORR), which can be obtained via the thermal treatment of transition-metal macrocycles (TMMs). However, the N4-chelate complex with metal atom (M-N4) moieties as major activity site for ORR are easily destroyed to form inorganic metal species during simple pyrolysis of TMMs. In this report, polyacrylonitrile (PAN) nanofibers were prepared by electrospinning containing a small amount of hemin (chloroprotoporphyrin IX iron(III), TMMs). The electrospun nanofibers were converted into Fe, N co-doped carbon nanofibers (Fe-N-CNFs) through preoxidized and thermal treatment. The PAN macromolecules can prevent hemin from aggregation during the process of pyrolysis. The Fe elemental mapping demonstrated that Fe species probably existed in a single atom state. The Fe K-edge X-ray absorption fine structure spectrum of Fe-N-CNFs proved that the Fe-N4 moieties have been successfully reserved. The X-ray photoelectron spectra of Fe-N-CNFs indicated that the amount of Fe-N4 moieties increased with the increased percent of hemin. Therefore, the Fe-N-CNFs exhibited the higher catalytic activity for ORR compared with Pt electrocatalysts. Furthermore, the Fe1-N-CNFs displayed higher stability and methanol tolerance than Pt/C.

Incorporating Mn cation as anchor to atomically disperse Pt on TiO2 for low-temperature removal of formaldehyde

The redox-driven hydrolysis precipitation is developed to atomically disperse Pt on TiO2 by involving high-valence Mn cations as the “anchor” into TiO2. With multiple characterizations including Cs-HAADF-STEM and XAFS, single-atom state of Pt on the surface of support is evidenced. Due to high dispersion of Pt and strong interaction between Pt and MnOx-TiO2 (Mn-TiO2), the physicochemical properties of catalysts are obviously improved. With combination of theoretical calculation and characterization, it is revealed that metallic Pt atom is stabilized by lattice oxygen of support. As observed, only 0.5% nominal amount of Pt loading (actual amount = 0.47%) on Mn-TiO2 support can meet the demands of complete removal of HCHO with high/low concentrations and severe space velocity at low temperature. Through analysis of in-situ DRIFTS of HCHO, the catalytic oxidation of HCHO over Pt/Mn-TiO2 obeys Mars-van-Krevelen mechanism. By associating with H-D exchange, it is found that introduction of water vapor can inhibit side-reactions and facilitate deep oxidation of HCHO.