石墨烯负载Pt-Co纳米粒子及其在氧化还原反应中的应用

采用微波-乙二醇方法还原氧化石墨烯和Pt(v)、Co(Ⅱ)粒子混合物,再经300℃H2还原,制备了石墨烯负载Pt-Co合金催化剂(Pt-Co/G).利用透射电镜、X-射线能谱、X-射线衍射和光电子能谱对所制催化剂进行表征.Pt-Co合金的粒径为3nm～8 nm,均匀地分散在石墨烯片上.与单金属的Pt/G和商品化的Pt/C催化剂相比,所制合金化的Pt-Co/G催化剂对氧还原反应展现出高的催化活性和可比拟的稳定性,显示了其在燃料电池中的应用潜力.     

Cobalt Phosphide Coupled with Heteroatom‐Doped Nanocarbon Hybrid Electroctalysts for Efficient,Long‐Life Rechargeable Zinc–Air Batteries

Metal phosphides and heteroatom‐doped carbons have been regarded as promising candidates as bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). However, both have suffered from stability issues during repeated ORR and OER operations in zinc–air batteries (ZABs). Herein, this study reports a versatile cobalt‐based hybrid catalyst with a 1D structure by integrating the metal‐organic framework‐derived conversion approach and an in situ crosslinking method. Among them, the 1D hybrid catalyst composed of ultrasmall cobalt phosphide nanoparticles supported by nitrogen‐, sulfur‐, phosphorus‐doped carbon matrix shows remarkable bifunctional activity close to that of the benchmark precious‐metal catalysts along with an excellent durability in the full potential range covering both the OER and ORR. The overall overpotential of the rechargeable ZABs can be greatly reduced with this bifunctional hybrid catalyst as an air‐electrode, and the cycling stability outperforms the commercial Pt/C catalyst. It is revealed that the cobalt phosphide nanoparticles are in situ converted to cobalt oxide under the accelerated conditions during OER (and/or ORR) of the ZABs and reduces the anodic current applied to the carbon. This contributes to the stability of the carbon material and in maintaining the high initial catalytic properties of the hybrid catalyst.     

A simple synthesis method for nanostructured Co-WC/carbon composites with enhanced oxygen reduction reaction activity

Co nanoparticles (Co NPs) and nanoscale tungsten carbide (WC) are successfully synthesized simultaneously with mesoporous structured carbon black (C) using an innovative simple method, which is known as solution plasma processing (SPP), and NPs are also loaded onto carbon black at the same time by SPP. The introduction of Co NPs led to not only superior oxygen reduction reaction (ORR) activity in terms of onset potential and peak potential, but also to a more efficient electron transfer process compared to that of pure WC. Co-WC/C also showed durability for long-term operation better than that of commercial Pt/C. These results clearly demonstrate that the presence of Co NPs significantly enhanced the ORR and charge transfer number of neighboring WC NPs in ORR activities. In addition, it was proved that SPP is a simple method (from synthesis of NPs and carbon black to loading on carbon black) for the large-scale synthesis of NP-carbon composite. Therefore, SPP holds great potential as a candidate for next-generation synthetic methods for the production of NP-carbon composites.     

Nitrogen-doped graphite encapsulated Fe/Fe_3C nanoparticles and carbon black for enhanced performance towards oxygen reduction

Non-noble metal(NNM) catalysts have recently attracted intensive interest for their high catalytic performance towards oxygen reduction reaction(ORR) at low cost.Herein,a novel NNM catalyst was synthesized by the simple pyrolysis of carbon black,urea and a Fe-containing precursor,which exhibits excellent ORR catalytic activity,superior durability and methanol tolerance versus the Pt/C catalyst in both alkaline and acidic solutions.Scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray diffraction(XRD) characterizations demonstrate that the product is a nitrogen-doped hybrid of graphite encapsulated Fe/Fe_3C nanoparticles and carbon black.X-ray photoelectron spectrum(XPS) and electrochemical analyses indicate that the catalytic performance and chemical stability correlate closely with a nitrogen-rich layer on the Fe/Fe_3C nanoparticle after pyrolysis with presence of urea,leading to the same four-electron pathway towards ORR as the Pt/C catalyst.The hybrid is prospective to be an efficient ORR electrocatalyst for direct methanol fuel cells with high catalytic performance at low cost.     

Mass production of highly loaded and highly dispersed PtRu/C catalysts for methanol oxidation using an electron-beam irradiation reduction method

An electron-beam irradiation reduction method (EBIRM) is a technique to reduce metal ions in an aqueous solution via irradiation with a high-energy electron beam. In this study, an EBIRM is improved to develop a technique for the mass production of highly loaded and highly dispersed PtRu/C catalysts for use as direct methanol fuel cell anodes. An increase in the Pt and Ru input concentrations increased the loading weight from 9 to 37 wt%; however, the dispersibility of the PtRu nanoparticles on the carbon particles decreased. To improve the low dispersibility, sodium phosphinate was added to the precursor solution and the input amount of carbon particles was decreased. These changes resulted in not only highly loaded but also highly dispersed PtRu/C catalysts. The catalytic activity of the highly loaded and highly dispersed PtRu/C catalysts for methanol oxidation was at least 1.6 times higher than that of the lowly loaded and lowly dispersed PtRu/C catalysts in all voltage range. More than 6000 mg of highly loaded and highly dispersed PtRu/C catalysts were relatively easily obtained, and the average particle size of the PtRu nanoparticles was 1.8 nm. These results demonstrated that the improved EBIRM is effective for the mass production of carbon-supported, highly loaded, and highly dispersed metal nanoparticles.     

Active Sites Engineering toward Superior Carbon‐Based Oxygen Reduction Catalysts via Confinement Pyrolysis

Developing efficient and low‐cost defective carbon‐based catalysts for the oxygen reduction reaction (ORR) is essential to metal–air batteries and fuel cells. Active sites engineering toward these catalysts is highly desirable but challenging to realize boosted catalytic performance. Herein, a sandwich‐like confinement route to achieve the controllable regulation of active sites for carbon‐based catalysts is reported. In particular, three distinct catalysts including metal‐free N‐doped carbon (NC), single Co atoms dispersed NC (Co–N–C), and Co nanoparticles‐contained Co–N–C (Co/Co–N–C) are controllably realized and clearly identified by synchrotron radiation‐based X‐ray spectroscopy. Electrochemical measurements suggest that the Co/Co–N–C catalyst delivers optimized ORR performance due to the rich Co–N_x active sites and their synergistic effect with metallic Co nanoparticles. This work provides deep insight for rationally designing efficient ORR catalyst based on active sites engineering.     

乙二醇法制备负载型钴基-堇青石催化剂及其催化燃烧甲苯的活性

用乙二醇法和浸渍法制备两种负载在堇青石上的钴基负载催化剂,并用XRD、XPS、TPR和TPD对制备的催化剂进行表征,比较两种催化剂催化氧化(燃烧)甲苯的活性。研究结果表明,与浸渍法制备的Co/cord催化剂相比,乙二醇法制备的催化剂Co/cord-EG对甲苯催化燃烧活性明显提高。应用乙二醇法制备Co/cord-EG负载型催化剂,Co元素主要以Co2+存在于载体表面;而传统浸渍法制备的Co/cord催化剂,Co元素是以Co2+与Co3+的两种化学状态存在于载体表面。应用乙二醇法制备Co/cord-EG负载型催化剂,有助于在载体表面形成比较均匀的吸附活性位。应用乙二醇法制备的Co/cord-EG催化剂,催化活性组分能在载体表面上以更小颗粒而且更高的分散度存在,从而能明显提高其催化活性。     

Electrochemical characterization of nano-sized Pd-based catalysts as cathode materials in direct methanol fuel cells

To improve the catalytic activity of palladium (Pd) as a cathode catalyst in direct methanol fuel cells (DMFCs), we prepared palladium-titanium oxide (Pd-TiO2) catalysts which the Pd and TiO2 nanoparticles were simultaneously impregnated on carbon. We selected Pd and TiO2 as catalytic materials because of their electrochemical stability in acid solution. The crystal structure and the loading amount of Pd and TiO2 on carbon were characterized by X-ray diffraction (XRD) and energy dispersive X-ray microanalysis (EDX). The electrochemical characterization of Pd-TiO2/C catalysts for the oxygen reduction reaction was carried out in half and single cell systems. The catalytic activities of the Pd-TiO2 catalysts were strongly influenced by the TiO2 content. In the single cell test, the Pd-TiO2 catalysts showed very comparable performance to the Pt catalyst.     

PGM‐Free Cathode Catalysts for PEM Fuel Cells: A Mini‐Review on Stability Challenges

In recent years, significant progress has been achieved in the development of platinum group metal‐free (PGM‐free) oxygen reduction reaction (ORR) catalysts for proton exchange membrane (PEM) fuel cells. At the same time the limited durability of these catalysts remains a great challenge that needs to be addressed. This mini‐review summarizes the recent progress in understanding the main causes of instability of PGM‐free ORR catalysts in acidic environments, focusing on transition metal/nitrogen codoped systems (M‐N‐C catalysts, M: Fe, Co, Mn), particularly MN_x moiety active sites. Of several possible degradation mechanisms, demetalation and carbon oxidation are found to be the most likely reasons for M‐N‐C catalysts/cathodes degradation.     

恒压电沉积Pt-Fe合金催化剂及在PEMFC阴极的应用

利用循环伏安法探究Pt与Fe共沉积的还原电位, 并在此电位下在多孔碳布表面恒压电沉积制备Pt-Fe合金, 研究其作为质子交换膜燃料电池 (PEMFC)阴极催化剂的电催化活性。通过X射线衍射 (XRD)、扫描电子显微镜(SEM)及场发射扫描电子显微镜 (FESEM)、能量色散谱 (EDS)、循环伏安 (CV)、单电池极化、电化学交流阻抗谱 (EIS)等测试技术对所得催化剂进行物理及电化学性能表征。实验表明, 在0.075 V电位下可还原得到Pt-Fe合金, 其颗粒在碳布表面呈空心球状且分散均匀; 共沉积时间对Pt-Fe合金催化剂成分组成有显著的影响, 随着时间的增加, 合金中Pt与Fe原子比增加, Fe相对含量下降。Fe可与Pt形成稳定的合金催化剂, 显著提高铂对氧还原的催化活性。电沉积30 min制得的合金催化剂具有最佳的催化活性。     

Characterization of Pt-Cu binary catalysts for oxygen reduction for fuel cell applications

Nanostructured Pt-Cu/C alloy catalysts synthesized by a reduction procedure with different reducing agents are investigated to find the origin of the enhanced activity of the oxygen reduction reaction for fuel cell applications. Prepared catalysts are characterized by various techniques, such as energy dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy (TEM) and cyclic voltammetry. XRD analysis shows that all prepared catalysts exhibit face-centered cubic structures and have smaller lattice parameters than pure Pt catalyst. TEM images show that the particle size of the catalysts increases with the heat treatment temperature, and that different reducing agent causes different particle size and dispersion of the binary catalysts on XC-72R. Using the polyol method with CuSO₄ as the precursor, the Pt-Cu/C sample is found to have good dispersion and high Cu loading. The Pt-Cu/C sample has a slightly higher specific activity value than that of Pt/C. The catalytic activity can be enhanced greatly with hydrogen reduction at 300 °C. Higher reduction temperatures cause the catalytic particles to agglomerate and therefore decreased catalytic activity.     

Single Cobalt Sites Dispersed in Hierarchically Porous Nanofiber Networks for Durable and High-Power PGM-Free Cathodes in Fuel Cells

Increasing catalytic activity and durability of atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts for the oxygen reduction reaction (ORR) cathode in proton-exchange-membrane fuel cells remains a grand challenge. Here, a high-power and durable Co–N–C nanofiber catalyst synthesized through electrospinning cobalt-doped zeolitic imidazolate frameworks into selected polyacrylonitrile and poly(vinylpyrrolidone) polymers is reported. The distinct porous fibrous morphology and hierarchical structures play a vital role in boosting electrode performance by exposing more accessible active sites, providing facile electron conductivity, and facilitating the mass transport of reactant. The enhanced intrinsic activity is attributed to the extra graphitic N dopants surrounding the CoN₄ moieties. The highly graphitized carbon matrix in the catalyst is beneficial for enhancing the carbon corrosion resistance, thereby promoting catalyst stability. The unique nanoscale X-ray computed tomography verifies the well-distributed ionomer coverage throughout the fibrous carbon network in the catalyst. The membrane electrode assembly achieves a power density of 0.40 W cm⁻² in a practical H₂/air cell (1.0 bar) and demonstrates significantly enhanced durability under accelerated stability tests. The combination of the intrinsic activity and stability of single Co sites, along with unique catalyst architecture, provide new insight into designing efficient PGM-free electrodes with improved performance and durability.     

过渡金属和磷共掺杂多孔碳作为氧气还原电催化剂

碳基材料作为非贵金属催化剂具有导电性能高、稳定性能好、价格低廉、环境友好等优点,在燃料电池阴极催化剂领域中引起了广泛的关注,尤其是过渡金属和异原子共掺杂能够显著提高碳材料的氧气还原催化活性。本文采用聚醚(F127)作为软模版,苯酚、甲醛作为碳源,四苯基溴化膦作为磷源,硝酸盐作为过渡金属来源,通过挥发溶剂自组装及高温煅烧过程制备了过渡金属(Co、Fe、Ni、Mn)和磷(P)共掺杂多孔碳材料(TM-P-C)。通过旋转环盘电极研究了TM-P-C在0.1 mol/L KOH电解液中的氧气还原电催化性能。研究结果表明：TM-P-C催化剂具有较高的氧化还原反应(ORR)电催化性能,其ORR活性为P-Co-C>P-NiC>P-Fe-C>P-Mn-C,其中P-Co-C的ORR电催化性能可与商业20wt%Pt/C催化剂相媲美,其电流密度与20wt%Pt/C催化剂的电流密度相当,与20wt%Pt/C仅存在66 mV的半波电位差,表现为ORR的4e–转移途径。制备的TM-P-C催化剂所具有的较高氧气还原电催化活性主要来自于过渡金属和P原子之间的协同作用。此外,TM-P-C催化剂表现出优异的...     

Double perovskite oxides Sr2MMoO6 (M = Fe and Co) as cathode materials for oxygen reduction in alkaline medium

The oxygen reduction reaction (ORR) was studied on Sr₂MMoO₆ (M = Fe and Co) double perovskites, prepared by a solid-state reaction, in 0.5 M NaOH at 25 °C with a rotating disk electrode (RDE). The two oxide powders were characterized by X-ray diffraction, scanning electron microscopy and BET analysis. The electrochemical techniques considered are linear voltammetry, steady state polarization and ac impedance spectroscopy. The electrocatalysts (SFMO/C, SCMO/C) consisting of the double perovskite oxides and carbon (Vulcan XC-72) were mixed and spread out into a thin layer on a glassy carbon substrate. At room temperature, a significantly electrocatalytic activity is observed for both electrocatalysts. Compared to SFMO/C, the SCMO/C electrocatalyst was found to show a relatively high electrocatalytic activity for O₂ reduction, which agrees well with the results obtained using the ac impedance spectroscopy.     

Co₃O₄ nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction

Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable-energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low cost remains a great challenge. Here, we report a hybrid material consisting of Co?O? nanocrystals grown on reduced graphene oxide as a high-performance bi-functional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Although Co?O? or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR activity that is further enhanced by nitrogen doping of graphene. The Co?O?/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions. The same hybrid is also highly active for OER, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER. The unusual catalytic activity arises from synergetic chemical coupling effects between Co?O? and graphene.     

Well‐Defined Cobalt Catalyst with N‐Doped Carbon Layers Enwrapping: The Correlation between Surface Atomic Structure and Electrocatalytic Property

Admittedly, the surface atomic structure of heterogenous catalysts toward the electrochemical oxygen reduction reaction (ORR) are accepted as the important features that can tune catalytic activity and even catalytic pathway. Herein, a surface engineering strategy to controllably synthesize a carbon‐layer‐wrapped cobalt‐catalyst from 2D cobalt‐based metal–organic frameworks is elaborately demonstrated. Combined with synchrotron radiation X‐ray photoelectron spectroscopy, the soft X‐ray absorption near‐edge structure results confirmed that rich covalent interfacial Co? N? C bonds are efficiently formed between cobalt nanoparticles and wrapped carbon‐layers during the polydopamine‐assisted pyrolysis process. The X‐ray absorption fine structure and corresponding extended X‐ray absorption fine structure spectra further reveal that the wrapped cobalt with Co–N coordinations shows distinct surface distortion and atomic environmental change of Co‐based active sites. In contrast to the control sample without coating layers, the 800 °C‐annealed cobalt catalyst with N‐doped carbon layers enwrapping achieves significantly enhanced ORR activity with onset and half‐wave potentials of 0.923 and 0.816 V (vs reversible hydrogen electrode), highlighting the important correlation between surface atomic structure and catalytic property.     

ZIF‐8/ZIF‐67‐Derived Co‐Nx‐Embedded 1D Porous Carbon Nanofibers with Graphitic Carbon‐Encased Co Nanoparticles as an Efficient Bifunctional Electrocatalyst

Herein, an approach is reported for fabrication of Co‐N_x‐embedded 1D porous carbon nanofibers (CNFs) with graphitic carbon‐encased Co nanoparticles originated from metal–organic frameworks (MOFs), which is further explored as a bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Electrochemical results reveal that the electrocatalyst prepared by pyrolysis at 1000 °C (CoNC‐CNF‐1000) exhibits excellent catalytic activity toward ORR that favors the four‐electron ORR process and outstanding long‐term stability with 86% current retention after 40 000 s. Meanwhile, it also shows superior electrocatalytic activity toward OER, reaching a lower potential of 1.68 V at 10 mA cm^?2 and a potential gap of 0.88 V between the OER potential (at 10 mA cm^?2) and the ORR half‐wave potential. The ORR and OER performance of CoNC‐CNF‐1000 have outperformed commercial Pt/C and most nonprecious‐metal catalysts reported to date. The remarkable ORR and OER catalytic performance can be mainly attributable to the unique 1D structure, such as higher graphitization degree beneficial for electronic mobility, hierarchical porosity facilitating the mass transport, and highly dispersed CoN_xC active sites functionalized carbon framework. This strategy will shed light on the development of other MOF‐based carbon nanofibers for energy storage and electrochemical devices.     

Ultrathin Co-N-C Layer Modified Pt–Co Intermetallic Nanoparticles Leading to a High-Performance Electrocatalyst toward Oxygen Reduction and Methanol Oxidation

The development of low platinum-based alloy electrocatalysts is crucial to accelerate the commercialization of fuel cells, yet remains a synthetic challenge and an incompatibility between activity and stability. Herein, a facile procedure to fabricate a high-performance composite that comprises Pt–Co intermetallic nanoparticles (IMNs) and Co, N co-doped carbon (Co-N-C) electrocatalyst is proposed. It is prepared by direct annealing of homemade carbon black-supported Pt nanoparticles (Pt/KB) covered with a Co-phenanthroline complex. During this process, most of Co atoms in the complex are alloyed with Pt to form ordered Pt–Co IMNs, while some Co atoms are atomically dispersed and doped in the framework of superthin carbon layer derived from phenanthroline, which is coordinated with N to form Co–N_x moieties. Moreover, the Co-N-C film obtained from complex is observed to cover the surface of Pt–Co IMNs, which prevent the dissolution and agglomeration of nanoparticles. The composite catalyst exhibits high activity and stability toward oxygen reduction reactions (ORR) and methanol oxidation reactions (MOR), delivering outstanding mass activities of 1.96 and 2.92 A mg_Pt⁻¹ for ORR and MOR respectively, owing to the synergistic effect of Pt–Co IMNs and Co-N-C film. This study may provide a promising strategy to improve the electrocatalytic performance of Pt-based catalysts.     

氮掺杂石墨烯的制备及其电催化氧气还原性能

通过改良Hummers法制备氧化石墨(Graphite oxide,GO),采用爆炸辅助还原法将GO还原剥离并原位掺杂得到氮掺杂石墨烯(Nitrogen-doped graphene,N-RGO)。采用TEM、SEM、FI-IR、XPS、XRD及Raman等分析手段对N-RGO的形貌、组成以及结构进行了表征,利用旋转环盘电极技术测试了其电催化氧气还原活性。TEM和SEM结果表明,爆炸条件下GO被很好地剥离开来,得到只有几层厚度的石墨烯;FI-IR及XPS结果表明,GO中大部分含氧官能团被脱除,C/O原子比达到26.2,是目前所得GO还原程度非常高的方法之一,且氮元素成功掺杂进石墨烯晶格中,掺杂氮的原子质量分数约为2.11%;电化学测试结果显示,氧气还原的极限扩散电流由非氮掺杂石墨烯(Reduced graphene oxide,RGO)的0.24mA提高到N-RGO的0.49 mA,尽管爆炸辅助还原得到的RGO对氧气还原也显示出较好的催化活性,但掺杂之后的N-RGO具有更高的催化活性。     

Co Nanoislands Rooted on Co–N–C Nanosheets as Efficient Oxygen Electrocatalyst for Zn–Air Batteries

Developing non‐precious‐metal bifunctional oxygen reduction and evolution reaction (ORR/OER) catalysts is a major task for promoting the reaction efficiency of Zn–air batteries. Co‐based catalysts have been regarded as promising ORR and OER catalysts owing to the multivalence characteristic of cobalt element. Herein, the synthesis of Co nanoislands rooted on Co–N–C nanosheets supported by carbon felts (Co/Co–N–C) is reported. Co nanosheets rooted on the carbon felt derived from electrodeposition are applied as the self‐template and cobalt source. The synergistic effect of metal Co islands with OER activity and Co–N–C nanosheets with superior ORR performance leads to good bifuctional catalytic performances. Wavelet transform extended X‐ray absorption fine spectroscopy and X‐ray photoelectron spectroscopy certify the formation of Co (mainly Co⁰) and the Co–N–C (mainly Co²⁺ and Co³⁺) structure. As the air‐cathode, the assembled aqueous Zn–air battery exhibits a small charge–discharge voltage gap (0.82 V@10 mA cm^?2) and high power density of 132 mW cm^?2, outperforming the commercial Pt/C catalyst. Additionally, the cable flexible rechargeable Zn–air battery exhibits excellent bendable and durability. Density functional theory calculation is combined with operando X‐ray absorption spectroscopy to further elucidate the active sites of oxygen reactions at the Co/Co–N–C cathode in Zn–air battery.