Atomically dispersed Fe sites on hierarchically porous carbon nanoplates for oxygen reduction reaction

Developing cost-effective,robust and stable non-precious metal catalysts for oxygen reduction reaction(ORR) is of paramount importance for electrochemical energy conversion devices such as fuel cells and metal-air batteries.Although Fe-N-C single atom catalysts(SACs) have been hailed as the most promising candidate due to the optimal binding strength of ORR intermediates on the Fe-N_(4) sites,they suffer from serious mass transport limitations as microporous templates/substrates,i.e.,zeolitic imidazolate frameworks(ZIFs),are usually employed to host the active sites.Motivated by this challenge,we herein develop a hydrogen-bonded organic framework(HOF)-assisted pyrolysis strategy to construct hierarchical micro/mesoporous carbon nanoplates for the deposition of atomically dispersed Fe-N_(4) sites.Such a design is accomplished by employing HOF nanoplates assembled from 2-aminoterephthalic acid(NH_(2)-BDC) and p-phenylenediamine(PDA) as both soft templates and C,N precursors.Benefitting from the structural merits inherited from HOF templates,the optimized catalyst(denoted as Fe-N-C SAC-950) displays outstanding ORR activity with a high half-wave potential of 0.895 V(vs.reversible hydrogen electrode(RHE)) and a small overpotential of 356 mV at 10 mA cm^(-2) for the oxygen evolution reaction(OER).More excitingly,its application potential is further verified by delivering superb rechargeability and cycling stability with a nearly unfading charge-discharge gap of 0.72 V after 160 h.Molecular dynamics(MD) simulations reveal that micro/mesoporous structure is conducive to the rapid mass transfer of O_(2),thus enhancing the ORR performance.In situ Raman results further indicate that the conversion of O_(2) to~*O_(2)-the rate-determining step(RDS) for Fe-N-C SAC-950.This work will provide a versatile strategy to construct single atom catalysts with desirable catalytic properties.

利用空间位阻和氢溢流协同作用促进5-羟甲基糠醛选择性加氢制备5-甲基糠醛

化学工业生产中,用氢气为还原剂,通过选择性加氢可以制备多种重要化学品。5-羟甲基糠醛是重要的生物质基平台化合物,而5-甲基糠醛是用途广泛的化学品。由5-羟甲基糠醛加氢得到5-甲基糠醛是一条非常理想的路径,但是选择性活化C―OH非常困难。本文设计并制备了Pt@PVP/Nb_(2)O_(5)(PVP:聚乙烯吡咯烷酮)催化剂,该催化体系巧妙地结合了位阻效应、氢溢流和催化剂界面的电子效应,系统研究了该催化剂对5-羟甲基糠醛选择性加氢制备5-甲基糠醛催化性能,在最优条件下,5-甲基糠醛的选择性可达92%。利用密度泛函理论计算研究了5-羟甲基糠醛选择性加氢制备5-甲基糠醛反应路径。

采用薄层氮化碳促进的高性能钯基催化剂用于甲酸分解制氢

自第一次工业革命以来,传统的化石能源(煤炭,石油等)一直是能源消费的主体。但是,随着社会的进步和技术的发展,能耗不断增加。但是化石能源不仅储量有限,而且还会引起严重的环境问题(环境污染和温室效应)。因此,清洁和可持续能源的研究与开发尤为重要,氢能是研究的重点之一。由于氢具有高能量密度、清洁和可持续性的特点,因而成为了最有前景的能源载体。然而,氢气的储存和运输困难严重限制了其在质子交换膜燃料电池中的实际应用。作为液态氢存储材料之一,甲酸在催化剂存在下于室温下即可分解。另外,甲酸分解制氢的反应中不会释放有毒有害气体,对环境友好。用于甲酸分解(FAD)的高效催化剂是制氢的关键材料。本文制备了由薄层氮化碳促进的高性能钯(Pd)基催化剂,用于甲酸分解。首先,通过一步法直接煅烧三聚硫氰酸,以获得氮化碳(C_(3)N_(4)-S),然后制备以C_(3)N_(4)-S为载体的Pd基FAD催化剂(Pd/C_(3)N_(4)-S)。在三聚硫氰酸的热解过程中,―SH基团的溢出具有剥离作用,因此形成的C_(3)N_(4)为破碎的薄层,具有较大的比表面积和孔体积。由于改善的比表面积和孔体积以及大量的缺陷附着位点,C_(3)N_(4)-S载体可以有效地分散Pd纳米颗粒。此外,由于载体和金属之间的电子效应,该载体可以有效地调节催化剂表面上的Pd^(2+)含量。因此,Pd/C_(3)N_(4)-S表现优异的FAD性能。在30°C下,该催化剂可将甲酸有效分解为CO_(2)和H_(2),转换频率(TOF值)和质量比活性分别达到了2083 h−1和19.52 mol·g−1·h−1。并且气相色谱测试结果表明,气体产物中不含CO,表明Pd/C_(3)N_(4)-S催化剂具有优异的选择性。另外,Pd/C3N4-S催化剂也具有良好的稳定性。经过4次循环测试,催化性能仅下降了不到10%。该研究为研究高性价比、制备方法简单的甲酸制氢催化剂提供了一定的指导作用。

Acute Toxicity of Four Drugs to Larvae of Channa argus

The acute toxicity of 4 drugs,dipterex,potassium permanganate,copper sulfate and formaldehyde to larvae of black-spot hybrid snakehead was tested with the semi hydrostatic test method under water temperature of( 28. 3 ± 1. 5) ℃,pH of( 8. 01 ± 0. 12) and dissolved oxygen of( 4. 6 ± 0. 5) mg / L. The results showed that 96 h median-lethal concentration( LC_(50)) of copper sulphate was the lowest,1. 586 mg/L,while 96 h LC50 of formaldehyde was the highest,115. 159 mg / L. The toxicity of the 4 drugs ranked in the order of copper sulphate,dipterex,potassium permanganate and formaldehyde from high to low. The safe concentrations( SCs) of the 4 drugs were in order of formaldehyde( 35. 529 mg / L),potassium permanganate( 1. 277 mg / L),dipterex( 1. 450 mg / L) and copper sulphate( 0. 882 mg / L). According to the results,the SCs of dipterex,formaldehyde and copper sulphate were higher than the conventional dosage,they were safe to be used for control of corresponding diseases of Channa argus by the conventional dosage. The SC of potassium permanganate was in the conventional dosage range,so it could be used for control of diseases in accordance with the SC of C. argus to the drug in production.

A new pathway for formic acid electro-oxidation:The electro-chemically decomposed hydrogen as a reaction intermediate

Formic acid electro-oxidation reaction(FAOR)is generally believed that follows a two-pathway mechanism.Herein,we resorted to in situ electrochemical mass spectrometry and successfully captured the trace of H_(2),as the new intermediate species,during the process of FAOR on both Pt based catalyst and two single atom catalysts(Rh-N-C and Ir-N-C).Inspired by this,we proposed a new reaction path named hydrogen oxidation pathway:at the oxidation potential,formic acid will break the C–H bond and combine with the protons in the solution to form H_(2) species,then hydrogen oxidation reaction(HOR)will occur to generate two protons.This process is accompanied by electron transfer and contributes currently to the whole reaction.

Investigation of Phylogenetic Relationship among Three Species of Channa Based on ITS Sequence Analysis

Objective This study aimed to analyze genetic variation of ribosomal ITS region sequences in Channa argus,C. maculata and C. asiatica,and to investigate the phylogenetic relationship among Channa species based on ITS sequences. Method ITS sequences of three Channa species were amplified by PCR,cloned and assembled to obtain the full length of ITS sequences. Result The full length of ITS sequences of C. argus,C. maculata and C. asiatica was 902,927,and 902 /903 bp,respectively. ITS sequences of C. argus,C. maculata and C. asiatica exhibited higher G + C( 72%) than A + T. Interspecific nucleotide differences were significantly greater than intraspecific differences of these three Channa species. Thus,these remarkably differential ITS fragments could be used to identify C. argus,C. maculata and C. asiatica. Phylogenetic tree constructed by Neighbor-joining and Maximum Likehood methods showed that C. argus shared the lowest genetic distance with C. maculata and the highest genetic distance with C. asiatica. [Conclusion] This study provided reference for classification,identification,phylogenetic analysis and interspecific hybridization of Channa species.

High-Performance Magnetic-core Coils for Targeted Rodent Brain Stimulations

Objective and Impact Statement.There is a need to develop rodent coils capable of targeted brain stimulation for treating neuropsychiatric disorders and understanding brain mechanisms.We describe a novel rodent coil design to improve the focality for targeted stimulations in small rodent brains.Introduction.Transcranial magnetic stimulation(TMS)is becoming increasingly important for treating neuropsychiatric disorders and understanding brain mechanisms.Preclinical studies permit invasive manipulations and are essential for the mechanistic understanding of TMS effects and explorations of therapeutic outcomes in disease models.However,existing TMS tools lack focality for targeted stimulations.Notably,there has been limited fundamental research on developing coils capable of focal stimulation at deep brain regions on small animals like rodents.Methods.In this study,ferromagnetic cores are added to a novel angle-tuned coil design to enhance the coil performance regarding penetration depth and focality.Numerical simulations and experimental electric field measurements were conducted to optimize the coil design.Results.The proposed coil system demonstrated a significantly smaller stimulation spot size and enhanced electric field decay rate in comparison to existing coils.Adding the ferromagnetic core reduces the energy requirements up to 60%for rodent brain stimulation.The simulated results are validated with experimental measurements and demonstration of suprathreshold rodent limb excitation through targeted motor cortex activation.Conclusion.The newly developed coils are suitable tools for focal stimulations of the rodent brain due to their smaller stimulation spot size and improved electric field decay rate.

Microenvironment regulation of M-N-C single-atom catalysts towards oxygen reduction reaction

The development of cost-effective,robust,and durable electrocatalysts to replace the expensive Pt-based catalysts towards oxygen reduction reaction(ORR)is the trending frontier research topic in renewable energy and electrocatalysis.Particular attention has been paid to metal-nitrogen-carbon(M-N-C)single atom catalysts(SACs)due to their maximized atom utilization efficiency,biomimetic active site,and distinct electronic structure.More importantly,their catalytic properties can be further tailored by rationally regulating the microenvironment of active sites(i.e.,M-N coordination number,heteroatom doping and substitution.Herein,we present a comprehensive summary of the recent advancement in the microenvironment regulation of MN-C SACs towards improved ORR performance.The coordination environment manipulation regarding central metal and coordinated atoms is first discussed,focusing on the structure-function relationship.Apart from the near-range coordination,longrange substrate modulation including heteroatom doping,defect engineering is discussed as well.Besides,the synergy mechanism of nanoparticles and single atom sites to tune the electron cloud density at the active sites is summarized.Finally,we provide the challenges and outlook of the development of M-N-C SACs.

Revealing the true origin of size-dependent Pd/C catalytic behavior towards formic acid decomposition

Formic acid decomposition(FAD)is considered a promising hydrogen production route to facilitate the ambient storage and on demand release of hydrogen energy.To optimize the catalysts for FAD,efforts have been paid to explore the underlying reason for the varied catalytic activity among catalysts with similar composition but differed structure.However,such endeavors are highly challenging due to the deeply intermingled effects of electronic structure,particle size,and facets,etc.Herein,to separately evaluate the respective effects of these factors,a series of catalysts with the same surface electronic structure and different particle size was prepared by cation dipole adjustment method.The performance and characterization results showed that the catalysts with different sizes and facets exhibited similar intrinsic activity with deviation of less than 5%.However,they showed 252%deviation of site stability,indicating that only the optimized electronic structure could enhance the intrinsic activity and a smaller particle size could extend the catalyst’s life.

Recent Advances in Stability Improvement Strategies of M-N_(x)/C Catalysts Towards Oxygen Reduction Reaction

Although fuel cells possess advantages of high energy conversion efficiency and zero-carbon emission,their large-scale commercialization is restricted by expensive and scarce platinum(Pt)catalysts.Metal-nitrogen-carbon(M-Nx/C)catalysts are hailed as the most promising candidates to replace Pt due to their considerable oxygen reduction reaction(ORR)activity and low cost.Despite tremendous progress in terms of active site identification and activity improvement being achieved in the past few decades,the M-Nx/C catalysts still suffer from insufficient durability,which drastically limits their practical application.In this regard,understanding degradation mechanisms and customizing stabilization strategies are of significant importance yet challengeable.In this review,we summarize the recent advances in the stability improvement of M-Nx/C catalysts.The stability test protocols of the M-Nx/C are firstly introduced.Subsequently,with the combination of advanced ex situ and in situ characterization techniques and density functional theory calculation,we present a comprehensive overview of the main degradation mechanisms during ORR process.Aiming at these deactivation issues,a variety of novel improvement strategies are developed to enhance the stability of M-Nx/C.Finally,the current challenges and prospects to design highly stable M-Nx/C catalysts are also proposed.

Fe,Cu-codoped metal-nitrogen-carbon catalysts with high selectivity and stability for the oxygen reduction reaction

Metal-nitrogen-carbon materials(M-N-C) are non-noble-metal-based alternatives to platinum-based catalysts and have attracted tremendous attention due to their low-cost,high abundance,and efficient catalytic performance towards the oxygen reduction reaction(ORR).Among them,Fe-based materials show remarkable ORR activity,but they are limited by low selectivity and low stability.To address these issues,herein,we have synthesized FeCu-based M-N-C catalysts,inspired by the bimetal center of cytochrome c oxidase(CcO).In acidic media,the selectivity was notably improved compared with Febased materials,with peroxide yields less than 1.2%(<1/3 of the hydrogen peroxide yields of Fe-N-C catalysts).In addition to Cu-N-C catalysts which can catalytically reduce hydrogen peroxide,the reduction current of hydrogen peroxide using FeCu-N-C-20 exceeded that of Fe-N-C by about 6% when the potential was greater than 0.4 V.Furthermore,FeCu-based M-N-C catalysts suffered from only a15 mV attenuation in their half-wave potentials after 10,000 cycles of accelerated degradation tests(ADT),while there was a 30 mV negative shift for Fe-N-C.Therefore,we propose that the H_(2)O_(2) released from Fe-Nx sites or N-doped carbon sites would be reduced by adjacent Cu-Nx sites,re sulting in low H_(2)O_(2) yields and high stability.