Enhanced activity and stability of Pt catalysts on functionalized graphene sheets for electrocatalytic oxygen reduction

Electrocatalysis of oxygen reduction using Pt nanoparticles supported on functionalized graphene sheets (FGSs) was studied. FGSs were prepared by thermal expansion of graphite oxide. Pt nanoparticles with average diameter of 2 nm were uniformly loaded on FGSs by impregnation methods. Pt-FGS showed a higher electrochemical surface area and oxygen reduction activity with improved stability as compared with the commercial catalyst. Transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical characterization suggest that the improved performance of Pt-FGS can be attributed to smaller particle size and less aggregation of Pt nanoparticles on the functionalized graphene sheets.     

石墨烯载Pt纳米粒子的原位还原制备及氧还原电催化性能

采用改进的化学氧化还原法(Hummers法)氧化鳞片石墨, 再超声振荡剥离得到氧化石墨烯(GO)水溶液. 通过聚二烯丙基二甲基氯化铵(PDDA)分子对GO表面功能化, 由于带正电荷的PDDA分子功能化的GO与带负电荷的^2-离子间的静电作用, 使Pt离子组装到GO表面, 再通过原位还原被束缚的Pt离子, 同时GO被还原成石墨烯片(GNs), 得Pt/PDDA-GNs催化剂. 相对空白GNs负载的Pt纳米粒子和商业化Pt/C(JM), Pt/PDDA-GNs催化剂有较高的氧还原活性和稳定性. 前者可归因于Pt颗粒尺寸细小和分散度较高, 后者是由于PDDA分子与Pt原子间的电子作用及对Pt颗粒的钉扎作用, 从而减缓了Pt的氧化和迁移.     

石墨烯量子点负载银纳米粒子制备及氧还原电催化活性

银基氧还原电催化剂具有较高的电催化活性且价格相对低廉,因而受到广泛关注. 本文采用简单、预先合成的石墨烯量子点作为载体和还原剂,制得了负载于石墨烯量子点、且无保护剂和表面活性剂的表面洁净银纳米粒子（Ag NPs/GQDs）. 电化学研究表明,Ag NPs/GQDs复合电催化剂的氧还原有较高的电催化活性,氧在碱性溶液中可经4电子途径还原为水. 与商业铂碳电极（Pt/C）相比,AgNPs/GQDs电极具有高催化电流密度、良好稳定性和极佳抗甲醇性能. 该银纳米粒子对开发高性能和低成本的非铂氧还原电催化剂有潜在的应用前景.     

铁氮掺杂对石墨烯担载铂催化剂氧还原反应活性的影响

高氧还原活性担载铂催化剂的研发是加快质子交换膜燃料电池商业化进程的主要手段之一。以石墨烯为碳源,1,10-菲啰啉为氮源,FeCl3为铁源,用浸渍法制备铁氮掺杂石墨烯(Fe/N-G)载体,并通过乙二醇还原法获得PtFe/N-G催化剂,探究铁氮原子的引入对石墨烯担载铂催化剂氧还原反应催化活性的影响。采用X射线衍射、比表面积和孔径分布测试、X射线光电子能谱等表征手段对载体及催化剂结构进行表征,使用电化学方法对载体和催化剂的氧还原反应活性进行测试。结果表明,PtFe/N-G催化剂的氧还原反应起始电位及半波电位分别为0.96 V、0.83 V,优于相同Pt担载量的商业20%Pt/C催化剂。铁氮掺杂后,石墨烯载体具有较大的孔径更有利于氧还原反应过程中生成物与反应物的传递,PtFe/N-G催化剂中存在吡啶氮和Fe-N型氮与铂纳米颗粒的协同催化,以及铂纳米颗粒与铁氮掺杂石墨烯载体间的相互作用,是PtFe/N-G催化剂具有优异的氧还原催化活性的可能原因。     

高活性、可循环的Pt-Cu@3D石墨烯复合催化剂的制备和催化性能

A composite hydrogel consisting of well-dispersed Pt-Cu nanoparticles (NPs) supported on three-dimensional (3D) graphene (Pt-Cu@3DG) was successfully prepared by mild chemical reduction. The 3D interconnected macroporous structure of the graphene framework not only possesses large specific surface area that allows high metal loadings, but also facilitates mass transfer during the catalytic reaction. The Pt-Cu bimetallic alloy NPs show good catalytic activity compared with Pt NPs and reduce the content of Pt NPs used, thereby lowering costs. The morphology and composition of the Pt-Cu@3DG composite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). The catalysis studies indicate that the resulting composites can be used as an efficient, inexpensive, recyclable, and stable catalyst for the reduction of 4-nitrophenol to 4-aminophenol under mild conditions.     

In-Situ Electrodeposition of Rhodium nanoparticles Anchored on Reduced Graphene Oxide nanosheets as an Efficient Oxygen Reduction Electrocatalyst

A simple, versatile, and cost-effective one-pot electrochemical deposition is used to fabricate rhodium (Rh) nanoparticles decorated surface of reduced graphene oxide (rGO) functionalized glassy carbon electrode (GCE) for oxygen reduction reaction (ORR) in alkaline media. The chemical and physical structure of the sample is probed via transmission electron microscopy, rotating disk electrode (RDE), X-ray photoelectron spectroscopy, linear sweep voltammetry, and Raman spectroscopy. The synergistic effects between the unique properties of Rh nanoparticles and rGO creates such innovative hybrid that exhibits a catalytic activity comparable to that of the commercial platinum electrocatalyst (Pt/C). As a result, the as-electrodeposited Rh@rGO hybrid exhibits outstanding ORR activity in alkaline media, as evidenced by a larger diffusion-limited current, greater positive onset potential, much better stability and methanol tolerance than Pt/C under the same conditions.     

The MOF/GO-based derivatives with Co@CoO core-shell structure supported on the N-doped graphene as electrocatalyst for oxygen reduction reaction

The development of nonprecious catalyst for oxygen reduction reaction (ORR) is important for the commercialization of the alkaline fuel cells (AFCs). Herein, we prepared a kind of Co-based nanoparticles (NPs) with a core-shell (Co@CoO) structure supported on the N-doped graphene (Co@CoO/NG) as an efficient ORR catalyst via simply pyrolyzing the ZIF-67 anchored on the synthesized graphene oxide (GO). The catalytic activity for ORR of the obtained Co@CoO/NG is comparable with the state-of-art Pt/C catalyst in terms of the onset and half-wave potential in the alkaline solution. In addition, the Co@CoO/NG exhibited an excellent ORR durability and antimethanol activity compared to the commercial Pt/C. This research would provide a simple strategy to prepare the high-performance nonprecious metal-based catalysts for AFCs.     

“Metal‐Free” Catalytic Oxygen Reduction Reaction on Heteroatom‐Doped Graphene is Caused by Trace Metal Impurities

The oxygen reduction reaction (ORR) is of high industrial importance. There is a large body of literature showing that metal‐based catalytic nanoparticles (e.g. Co, Mn, Fe or hybrid Mn/Co‐based nanoparticles) supported on graphene act as efficient catalysts for the ORR. A significant research effort is also directed to the so‐called “metal‐free” oxygen reduction reaction on heteroatom‐doped graphene surfaces. While such studies of the ORR on nonmetallic heteroatom‐doped graphene are advertised as “metal‐free” there is typically no sufficient effort to characterize the doped materials to verify that they are indeed free of any trace metal. Here we argue that the claimed “metal‐free” electrocatalysis of the oxygen reduction reaction on heteroatom‐doped graphene is caused by metallic impurities present within the graphene materials.     

微波辅助溶剂热法制备Pt/石墨烯-TiO2及其催化性能

质子交换膜燃料电池具有比能量高、结构简单、工作温度低、高效清洁和安静无摩擦等优点,是一种非常具有发展前景的电源.燃料电池借用电催化剂把燃料与氧化剂中的化学能转化为电能,通常采用碳粉负载的Pt催化剂.在燃料电池的工作环境下,碳粉载体容易腐蚀和团聚,降低了催化剂活性和稳定性,进而降低了燃料电池的使用寿命.因此,探索高稳定性的催化剂载体有利于提高催化剂的稳定性,促进燃料电池的实用化进程.为增强催化剂载体的抗腐蚀能力,一些金属氧化物如SnO2,WO3,CeO2和TiO2等被用作催化剂载体.其中,TiO2因具有稳定的化学性能以及与金属之间的"强相互作用"而备受研究者关注.但TiO2载体比表面积小和导电能力弱等缺点限制了它在燃料电池中的应用.石墨烯具有卓越的导电性和比表面积,却容易发生团聚.利用TiO2与碳材料间存在的协同作用,将TiO2与石墨烯复合来制备复合载体,能够增强TiO2的导电能力,抑制石墨烯的团聚,提高催化剂载体的化学稳定性和比表面积.本文采用微波辅助溶剂热法制备了石墨烯-TiO2复合载体和Pt/石墨烯-TiO2催化剂,研究了TiO2含量对催化剂活性和稳定性的影响.采用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对制备的样品进行了微观结构和成分表征.结果表明,Pt/石墨烯-TiO2催化剂中TiO2为立方状纳米颗粒,粒径约为60 nm,均匀地分布在石墨烯上;Pt纳米粒子倾向于锚定在TiO2与石墨烯之间,而且分布均匀.采用线性伏安扫描(LSV)和循环伏安法(CV)测试了不同TiO2含量的Pt/石墨烯-TiO2催化剂的活性和稳定性.发现TiO2的加入确实能够提高催化剂的稳定性,随着TiO2含量的提高,催化剂稳定性增加.当TiO2含量为20%时,催化剂的起始电压与极限电流均与Pt/C催化剂接近.经过循环伏安扫描3000圈的快速老化测试后,Pt/石墨烯-TiO2催化剂起始电压的负移明显低于Pt/C催化剂,呈现了优良的稳定性和催化活性.     

Tuning Nanoparticle Catalysis for the Oxygen Reduction Reaction

Advances in chemical syntheses have led to the formation of various kinds of nanoparticles (NPs) with more rational control of size, shape, composition, structure and catalysis. This review highlights recent efforts in the development of Pt and non‐Pt based NPs into advanced nanocatalysts for efficient oxygen reduction reaction (ORR) under fuel‐cell reaction conditions. It first outlines the shape controlled synthesis of Pt NPs and their shape‐dependent ORR. Then it summarizes the studies of alloy and core–shell NPs with controlled electronic (alloying) and strain (geometric) effects for tuning ORR catalysis. It further provides a brief overview of ORR catalytic enhancement with Pt‐based NPs supported on graphene and coated with an ionic liquid. The review finally introduces some non‐Pt NPs as a new generation of catalysts for ORR. The reported new syntheses with NP parameter‐tuning capability should pave the way for future development of highly efficient catalysts for applications in fuel cells, metal‐air batteries, and even in other important chemical reactions.     

高分散直接甲醇燃料电池Pt／C阴极电催化剂的制备过程机理与表征

 通过调变的多元醇法制备了40％Pt／C直接甲醇燃料电池阴极电催化剂，应用透射电镜（TEM）及X射线衍射（XRD）方法表征催化剂．结果表明，由该制备方法可得到高分散，金属粒子粒径分布窄的高载量贵金属催化剂．TEM统计结果表明，调变多元醇法制备的40％Pt／C催化剂的金属粒子平均粒径约为2．9nm．直接甲醇燃料电池单池性能测试表明，该方法制得的40％Pt／C的电催化氧还原能力比同型商品催化剂更好．另外，利用UV－Vis光谱研究了催化剂的制备过程．结果表明，在调变的多元醇法中，Pt4＋的还原是一步完成的．     

一步法制备还原态氧化石墨烯载铂纳米粒子及其对甲醇氧化的电催化性能

以天然石墨为原料,采用改进的Hummers法制备氧化石墨.然后采用简单的一步化学还原法在乙二醇(EG)中同时还原氧化石墨烯(GO)和H₂PtCl₆制备高分散的铂/还原态氧化石墨烯(Pt/RGO)催化剂.采用傅里叶变换红外(FTIR)光谱、X射线衍射(XRD)和透射电子显微镜(TEM)对催化剂的微结构、组成和形貌进行表征.结果表明, GO已被还原成RGO, Pt纳米粒子均匀分散在RGO表面,粒径约为2.3 nm.采用循环伏安法和计时电流法评价催化剂对甲醇氧化的电催化性能,测试结果表明, Pt/RGO催化剂对甲醇氧化的电催化活性和稳定性与Pt/C和Pt/CNT相比有了很大提高.另外其对甲醇电催化氧化的循环伏安图中正扫峰电流密度(I_f)和反扫峰电流密度(I_b)的比值高达1.3,分别是Pt/C和Pt/CNT催化剂的2.2和1.9倍,表明Pt/RGO催化剂具有高的抗甲醇氧化中间体CO_ad的中毒能力.     

3D nitrogen-doped graphene aerogel-supported Fe3O4 nanoparticles as efficient electrocatalysts for the oxygen reduction reaction

Three-dimensional (3D) N-doped graphene aerogel (N-GA)-supported Fe(3)O(4) nanoparticles (Fe(3)O(4)/N-GAs) as efficient cathode catalysts for the oxygen reduction reaction (ORR) are reported. The graphene hybrids exhibit an interconnected macroporous framework of graphene sheets with uniform dispersion of Fe(3)O(4) nanoparticles (NPs). In studying the effects of the carbon support on the Fe(3)O(4) NPs for the ORR, we found that Fe(3)O(4)/N-GAs show a more positive onset potential, higher cathodic density, lower H(2)O(2) yield, and higher electron transfer number for the ORR in alkaline media than Fe(3)O(4) NPs supported on N-doped carbon black or N-doped graphene sheets, highlighting the importance of the 3D macropores and high specific surface area of the GA support for improving the ORR performance. Furthermore, Fe(3)O(4)/N-GAs show better durability than the commercial Pt/C catalyst.     

Fabrication of graphene-supported tetraferrocenylporphyrin electrocatalyst for oxygen reduction and its unique electrochemical response in both alkaline and acid media

A novel high-performance non-noble metal electrocatalyst for the oxygen reduction reaction (ORR) was fabricated by anchoring cobalt tetraferrocenylporphyrin (CoFcP) onto poly(sodium-p-styrenesulfonate) modified graphene (PSS-Gr) through solvothermally assisted π–π assembling method. The morphology of the assembled composite was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The interactions between CoFcP moieties and graphene sheets were confirmed by UV–Vis absorption spectroscopy and X-ray photoelectron spectroscopy. The electrocatalytic properties of the CoFcP/PSS-Gr catalyst towards the oxygen reduction reaction were assessed using rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) measurements in both alkaline and acidic media. In addition, cyclic voltammetry and chronoamperometric measurements were utilized to evaluate the catalytic activity and stability of the CoFcP/PSS-Gr composite in alkaline solution. The results showed that CoFcP supported on graphene exhibited an outstanding electrocatalytic performance towards the ORR comparable with commercial Pt/C catalyst in alkaline media, such as high onset potential (0.889 V vs. reversible hydrogen electrode, RHE), half wave potential (0.789 V vs. RHE), better tolerance to methanol, excellent stability (84.1 %, retention after 10000 s), and efficient four-electron pathway. Moreover, the proposed hybrid presented excellent catalytic activity in terms of onset potential (0.72 V vs. RHE) and high-electron transfer number compared with Pt/C in acidic media.     

碳纳米管电极上原位沉积Pt纳米颗粒

 本文利用原位离子交换法制备了碳纳米管(CNTs)载铂(Pt/CNTs)电极. X射线光电子能谱分析表明, Pt通过离子交换载于电化学功能化的CNTs表面. 扫描电镜照片显示, Pt高度分散于CNTs表面. X射线衍射分析表明, Pt的粒径约为4.0 nm. 离子交换法所制Pt/CNTs电极的电化学表面积和Pt的利用率均大于传统Pt/CNTs电极(Pt粒径约为2.5 nm), 其对氧还原的催化活性高于传统电极. 这归因于离子交换法所制电极的特殊结构,即Pt普遍载于电化学活性位上.     

Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Electrochemical oxygen reduction on nitrogen doped graphene sheets in acid media

Nitrogen doped graphene were prepared via exfoliated graphite oxide. This graphene exhibited significantly high oxygen reduction activity. High electric conductivity, high surface area, large amount of edge sites and pyridinic N site in rGS (reduced graphene sheets) contribute to the high ORR (oxygen reduction reaction) activity. The rGS showed a potential to replace expensive Pt for oxygen reduction reaction in PEMFC.     

铂/石墨烯氧还原电催化剂的共还原法制备及表征

使用硼氢化钠共还原法制备40% (w)铂/石墨烯电催化剂用于氧还原反应. 通过循环伏安测试发现, 这种方法制备所得铂/石墨烯催化剂对氧还原反应活性较铂/碳催化剂差, 但稳定性有所提高. 在稳定性测试中,铂/石墨烯电催化性能衰减为50%, 较铂/碳(79%)好. X射线衍射(XRD)和透射电子显微镜(TEM)表征发现在铂/石墨烯催化剂中两者存在明显交互作用, 这可能是阻止石墨烯再堆垛和防止铂颗粒团聚的主要原因. 通过对单电池性能测试也发现铂/石墨烯催化剂更有利于电池长期稳定.     

石墨烯衍生物负载的纳米催化剂用于氧还原反应

综述了用于燃料电池中氧还原反应(ORR)的石墨烯衍生物负载的各种纳米催化剂的最新进展。介绍了用于表征石墨烯基电催化剂的常规电化学技术以及石墨烯基电催化剂最新的研究进展。负载于还原氧化石墨烯(RGO)上的Pt催化剂的电化学活性和稳定性均得到显著提高。其它贵金属催化剂,如Pd, Au和Ag也表现出较高的催化活性。当以RGO或少层石墨烯为载体时, Pd催化剂的稳定性提高。讨论了氧化石墨烯负载Au或Ag催化剂的合成方法。另外,以N4螯合络合物形式存在的非贵过渡金属可降低氧的电化学性能。 Fe和Co是可替代的廉价ORR催化剂。在大多数情况下,这些催化剂稳定性和耐受性的问题均可得到解决,但其整体性能还很难超越Pt/C催化剂。     

One-step synthesis of Pt nanoparticles/reduced graphene oxide composite with enhanced electrochemical catalytic activity

A one-step electrochemical approach for synthesis of Pt nanoparticles/reduced graphene oxide(Pt/RGO) was demonstrated.Graphene oxide(GO) and chloroplatinic acid were reduced to RGO and Pt nanoparticles(Pt NPs) simultaneously,and Pt/RGO composite was deposited on the fluorine doped SnO 2 glass during the electrochemical reduction.The Pt/RGO composite was characterized by field emission-scanning electron microscopy,Raman spectroscopy and X-ray photoelectron spectroscopy,which confirmed the reduction of GO and chloroplatinic acid and the formation of Pt/RGO composite.In comparison with Pt NPs and RGO electrodes obtained by the same method,results of cyclic voltammetry and electrochemical impedance spectroscopy measurements showed that the composite electrode had higher catalytic activity and charge transfer rate.In addition,the composite electrode had proved to have better performance in DSSCs than the Pt NPs electrode,which showed the potential application in energy conversion.