Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts

Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co(3)O(4) nanoparticles, a manganese-cobalt spinel MnCo(2)O(4)/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near-edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrids results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge XANES suggested substitution of Co(3+) sites by Mn(3+), which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared with the pure cobalt oxide hybrid. The covalently bonded hybrid afforded much greater activity and durability than the physical mixture of nanoparticles and carbon materials including N-rmGO. At the same mass loading, the MnCo(2)O(4)/N-graphene hybrid can outperform Pt/C in ORR current density at medium overpotentials with stability superior to Pt/C in alkaline solutions.     

溶液相合成卤化石墨烯及其对氧化还原反应的电催化活性(英文)

Metal-free carbon electrocatalyts for the oxygen reduction reaction (ORR) are attractive for their high activity and economic advantages. However, the origin of the activity has never been clearly elucidated in a systematic manner. Halogen group elements are good candidates for elucidating the effect, although it has been a difficult task due to safety issues. In this report, we demonstrate the synthesis of Cl-, Br- and I-doped reduced graphene oxide through two solution phase syntheses. We have evaluated the effectiveness of doping and performed electrochemical measurements of the ORR activity on these halogenated graphene materials. Our results suggest that the high electroneg-ativity of the dopant is not the key factor for high ORR activity; both Br- and I-doped graphene promoted ORR more efficiently than Cl-doped graphene. Furthermore, an unexpected sulfur-doping in acidic conditions suggests that a high level of sulfide can degrade the ORR activity of the graphene material.     

Stabilization of high-performance oxygen reduction reaction pt electrocatalyst supported on reduced graphene oxide/carbon black composite

Oxygen reduction reaction (ORR) catalyst supported by hybrid composite materials is prepared by well-mixing carbon black (CB) with Pt-loaded reduced graphene oxide (RGO). With the insertion of CB particles between RGO sheets, stacking of RGO can be effectively prevented, promoting diffusion of oxygen molecules through the RGO sheets and enhancing the ORR electrocatalytic activity. The accelerated durability test (ADT) demonstrates that the hybrid supporting material can dramatically enhance the durability of the catalyst and retain the electrochemical surface area (ECSA) of Pt: the final ECSA of the Pt nanocrystal on the hybrid support after 20?000 ADT cycles is retained at >95%, much higher than the commercially available catalyst. We suggest that the unique 2D profile of the RGO functions as a barrier, preventing leaching of Pt into the electrolyte, and the CB in the vicinity acts as active sites to recapture/renucleate the dissolved Pt species. We furthermore demonstrate that the working mechanism can be applied to the commercial Pt/C product to greatly enhance its durability.     

Cuprous oxide nanoparticles dispersed on reduced graphene oxide as an efficient electrocatalyst for oxygen reduction reaction

Cuprous oxide (Cu(2)O) nanoparticles dispersed on reduced graphene oxide (RGO) were prepared by reducing copper acetate supported on graphite oxide using diethylene glycol as both solvent and reducing agent. The Cu(2)O/RGO composite exhibits excellent catalytic activity and remarkable tolerance to methanol and CO in the oxygen reduction reaction.     

电化学还原氧化石墨烯用于四环素电催化检测

四环素(TTC)因其广泛的抗菌性和低生产成本等特点而成为应用最广泛的兽医药物. TTC的大量使用不可避免地导致其进入地表水、地下水和污水处理厂.迄今,已有许多方法用于TTC检测,包括免疫测定法、微生物检测法和化学-物理法等.然而,这些方法费用高,耗时长或需要复杂的样品预处理过程,不适合现场测量或常规分析.电化学分析法具有操作简单、成本低廉、选择性和灵敏度较高、易实现在线检测等特点,在检测领域具有重要优势.石墨烯在电化学传感器领域表现出优越的应用性能,但有关石墨烯材料应用于电分析和电催化方面的报道仍然有限.石墨烯的前驱体氧化石墨烯(GO)片层底面上具有各种类型的含氧官能团和层状边缘,导致其绝缘并具有很多缺陷,使GO包含了sp2和sp3杂化碳原子,为GO提供了独特的具有化学功能的异构电子结构.通过对GO进行还原,可以生成新的sp2域或者改变含氧官能团的数量和类型,从而为GO提供更多的特殊性质.研究表明,电化学还原是一种绿色快速的还原方法,可以控制GO的还原程度和还原过程.本文利用电化学还原法来调整GO表面的官能团和缺陷度,利用在–0.8 V还原电位下得到的电化学还原氧化石墨烯(ERGO-0.8V)修饰玻碳电极(GC)为工作电极(GC/ERGO-0.8V),采用循环伏安法对溶解在pH=3的缓冲溶液中的TTC进行电化学检测,发现ERGO-0.8V对TTC具有电催化性能.利用红外光谱(FT-IR)、X射线光电子能谱(XPS)和拉曼光谱对ERGO-0.8V, ERGO-1.2V, GO及化学还原得到的石墨烯(CRGO)表面官能团和缺陷程度进行了表征,考察了TTC在ERGO-0.8V/GC上的电化学行为,对其电催化还原机理进行了推测.结果表明,与GO, ERGO-1.2V及CRGO修饰电极相比, GC/ERGO-0.8V修饰电极的催化还原峰在0–0.5 V,对TTC表现出独特的电催化性能, GC/ERGO-0.8V电极对浓度为0.1–120 mg/L的TTC溶液具有良好的检测性能,在不同浓度范围内其氧化峰峰电流与峰电位的线性关系不同. FT-IR和XPS结果显示,在–0.8 V还原电位下得到的ERGO-0.8V,其官能团类型和数量发生变化,但仍存在大量官能团,主要是羧基、羟基和环氧基.同时,拉曼表征显示ERGO-0.8V的缺陷密度增大,同时新生成的sp2域减小而使得ERGO的sp2域减小.对比GO等其他材料的表征结果推测,官能团变化是影响ERGO独特电催化性质的主要因素,除此之外还有材料的缺陷度和sp2域.推测GC/ERGO-0.8V修饰电极对TTC可能的催化机理为： TTC在GC/ERGO电极上的还原与氢醌和醌之间的转换有关;而对于ERGO,则可能对应于羧基和羟基之间的转化.然而,同样具有羧基和羟基的ERGO-1.2V则对TTC没有产生电催化作用.其原因可能是在–0.8到–1.2 V还原电位下,形成的羧基位于石墨烯片层内部,而片层内的电子传递较慢.     

Synthesis of reduced graphene oxide and its electrocatalytic properties

The method of the chemical synthesis of reduced graphene oxide was developed. Sodium hypophosphite and sulfi te were used as reducing agents. The formation of reduced graphene oxide was confi rmed by several methods. Volt-ampere characteristics of electrodes based on reduced graphene oxide were investigated in an experimental model of an oxygen fuel cell with an alkaline electrolyte. Characteristics of oxygen electrodes based on reduced graphene oxide were stable over semiannual tests. The resulting reduced graphene oxide is a promising material for oxygen electrodes of chemical current sources.     

Electrografting of amino-TEMPO on graphene oxide and electrochemically reduced graphene oxide for electrocatalytic applications

4-Amino-2,2,6,6-tetramethyl-1-piperridine N-oxyl (4-amino-TEMPO), an electroactive nitroxide radical, was attached to the surface of graphene oxide (GO) and electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode by a simple, rapid and green electrografting method. The electroactive interfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The calculated surface coverage for 4-amino-TEMPO is up to 1.55 × 10^− 9 mol·cm^− 2. The modified electroactive interface exhibited excellent electrocatalytic activity towards the electro-oxidation of reduced glutathione (GSH) and hydrogen peroxide (H₂O₂).     

Synthesis of dendritic platinum nanoparticles/lucigenin/reduced graphene oxide hybrid with chemiluminescence activity

Multifunctional hybrid: A dendritic platinum nanoparticle/lucigenin/reduced graphene oxide (RGO) hybrid with chemiluminescence (CL) activity was prepared for the first time by using lucigenin as a linker through simultaneous reduction of H(2) PtCl(4) and a lucigenin-functionalized graphene oxide composite by sodium borohydride (see scheme). The hybrid may have potential applications as a CL sensor, in catalysis, energy conversion, and opto-electronic systems.     

Electrocatalytic activity of starch/Fe3O4/zeolite bionanocomposite for oxygen reduction reaction

The present work demonstrated an eco-friendly and facile method for the preparation of starch/Fe₃O₄/zeolite-bionanocomposite (BNC) at moderate temperature. Zeolite and starch were used as solid support and stabilizer, respectively. The analysis of UV–vis showed the appearance of surface plasmon resonance. From PXRD analysis, the incorporation of magnetite nanoparticles (NPs) in zeolite substrate results in reducing of intensities and broadening of the zeolite peaks of BNC. The TEM analysis showed the formation of highly distributed Fe₃O₄-NPs with an average diameter and standard deviation of 9.24 ± 3.57 nm. The FESEM and EDX analyses imply that Fe₃O₄-NPs were homogeneously formed on the surface of the zeolite substrate. VSM analysis illustrated the as prepared BNC possessed magnetic behaviour with a saturation magnetization and coercivity of 1.84 emu g⁻¹ and 17.76 G, respectively. The prepared BNC showed potential applicability in energy as low-cost electrode material. The BNC was used as a non-precious catalyst for oxygen reduction reaction (ORR) in the alkaline medium. The presence of starch and zeolite promoted long term stability up to 1000 cycles and avoid the dissolution and agglomeration of iron oxide. The ORR commences at the onset potential of 0 V follows by the two successive reduction peaks at −0.48 V and −1.00 V.     

Synthesis of poly(N-vinyl-2-pyrrolidone) adsorbed-AuPt/C bimetallic nanoparticles and their unusual electrocatalytic activity towards methanol tolerant oxygen reduction reaction

Journal of Solid State Electrochemistry - It has been suggested that the presence of adsorbed impurities, such as capping agent or organic reaction products adsorbed on the metallic nanoparticles,...     

Dealloyed carbon-supported PtAg nanostructures: Enhanced electrocatalytic activity for oxygen reduction reaction

Dealloyed PtAg/C nanostructures, prepared by selective electrochemical etching of Ag in 0.5 M H₂SO₄ from a series of alloyed Pt_mAg/C samples with atomic Pt/Ag ratio m = 0.1, 0.5, 1.0 and 1.5, were employed as cathode electrocatalysts for oxygen reduction reaction (ORR) in 0.5 M KOH. Compared with their as-prepared counterpart alloy catalysts, the dealloyed catalysts showed higher half-wave potentials (E_1/2) and significantly higher Pt mass-specific activity (MSA) data. The intrinsic activity (IA) of Pt increased more or less after the dealloying treatment but was strongly dependent on the composition (m) of the alloyed sample. The Pt IA numbers were comparable for the dealloyed catalysts derived from Pt_mAg/C of m = 0.5, 1.0 and 1.5, which were nearly twice that for E-TEK Pt/C catalyst and 3 times that for the dealloyed catalyst derived from Pt_0.1Ag/C.     

Co3O4/聚吡咯/石墨烯碱性溶液中电化学还原氧

燃料电池具有较高的能量密度和发电效率,以清洁能源为原料,零污染排放,是一种具有发展前景的能量储存和转化装置.阴极氧还原反应(ORR)在燃料电池中起着关键作用.ORR广泛采用贵金属铂基催化剂,但是它们价格昂贵,电子动力学转移速率慢,碱性条件下易团聚,这些亟需解决的问题阻碍了燃料电池商业化进程.近期,一些非贵金属催化剂被广泛研究,例如氮掺杂碳材料、Fe/N/C和Co/N/C材料等,它们有可能在未来替代铂基催化剂.我们的目标是合成新型高催化活性的Co/N/C及其衍生非贵金属材料,用于ORR催化反应.由于石墨烯具有独特的形貌、较大的比表面积和良好的导电性,其表面含有功能化的官能团,所以我们选择石墨烯作为碳载体.首先,用改性休克尔方法合成了氧化石墨烯(GO),为了提高其催化活性,采用聚吡咯作为氮源对其进行了氮掺杂,制备了聚吡咯/氧化石墨烯(Ppy/GO).通过ORR催化性能测试发现,GO对ORR具有一定的催化活性,它的起始电位和阴极电流电位分别为–0.31 V vs SCE和–0.38 V vs SCE;Ppy/GO的起始电位和阴极电流电位分别为–0.20 V vs SCE和–0.38 V vs SCE,氮掺杂对GO的催化活性有所提高.采用水热法沉积氧化钴合成了Co3O4/聚吡咯/氧化石墨烯(Co3O4/Ppy/GO).其形貌为Co3O4分散在氮掺杂GO表面.在KOH电解质(0.1 mol/L)中测试,Co3O4/Ppy/GO的起始电位和阴极电流电位分别为–0.20 V和–0.38 V vs SCE.经过800℃高温煅烧处理后,Co3O4/Ppy/GO-800的催化活性明显提高,起始电位和阴极电流电位分别达到–0.10 V和–0.18 V vs SCE.ORR电子转移数为3.4,接近于4电子反应途径.Co3O4/Ppy/GO对ORR的催化活性及4电子催化选择性较高,可能是由于纳米形态的Co3O4和Ppy/GO之间具有较强的表面作用力,聚吡咯掺杂的氧化石墨烯具有较强的电子储存及释放能力.综上,我们通过水热法制备了钴、氮共掺杂的GO,并研究了其对ORR的催化活性和电子转移选择性.结果表明Co3O4/Ppy/GO是一种高效的非贵金属电催化剂,在碱性电解质中具有很高的ORR催化活性,在燃料电池阴极催化剂方面很有前景.     

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.     

Bimetallic Pt-Au nanocatalysts electrochemically deposited on graphene and their electrocatalytic characteristics towards oxygen reduction and methanol oxidation

The burgeoning demand for clean and energy-efficient fuel cell system requires electrocatalysts to deliver greater activity and selectivity. Bimetallic catalysts have proven superior to single metal catalysts in this respect. This work reports the preparation, characterization, and electrocatalytic characteristics of a new bimetallic nanocatalyst. The catalyst, Pt-Au-graphene, was synthesized by electrodeposition of Pt-Au nanostructures on the surface of graphene sheets, and characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and voltammetry. The morphology and composition of the nanocatalyst can be easily controlled by adjusting the molar ratio between Pt and Au precursors. The electrocatalytic characteristics of the nanocatalysts for the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) were systematically investigated by cyclic voltammetry. The Pt-Au-graphene catalysts exhibits higher catalytic activity than Au-graphene and Pt-graphene catalysts for both the ORR and the MOR, and the highest activity is obtained at a Pt/Au molar ratio of 2:1. Moreover, graphene can significantly enhance the long-term stability of the nanocatalyst toward the MOR by effectively removing the accumulated carbonaceous species formed in the oxidation of methanol from the surface of the catalyst. Therefore, this work has demonstrated that a higher performance of ORR and the MOR could be realized at the Pt-Au-graphene electrocatalyst while Pt utilization also could be greatly diminished. This method may open a general approach for the morphology-controlled synthesis of bimetallic Pt-M nanocatalysts, which can be expected to have promising applications in fuel cells.     

Construction of a novel ZnCo2O4/Bi2O3 heterojunction photocatalyst with enhanced visible light photocatalytic activity

A novel ZnCo₂O₄/Bi₂O₃ heterojunction photocatalyst was prepared via balling method. The enhanced photocatalytic activity is mainly attributed to the broad photoabsorption and low recombination rate of photogenerated electron-hole pairs, which is driven by the photogenerated potential difference formed at the ZnCo₂O₄/Bi₂O₃ heterojunction interface.     

调控碳材料的功函数以大幅度提升其电催化氧还原性能

氧的电催化还原反应是燃料电池装置与金属空气电池的阴极反应, 具有重大的研究意义. 在众多的非铂催化剂中,碳材料因其低廉的价格以及独特的物理化学性质受到了广泛的关注. 自从发现氮掺杂的碳纳米阵列具有优异的氧还原活性后, 不同类型的氮掺杂的碳也得到了深入研究. 例如近年来兴起的由金属有机框架衍生的氮掺杂的碳材料, 兼具丰富...     

Sulphur-doped ordered mesoporous carbon with enhanced electrocatalytic activity for the oxygen reduction reaction

Metal-free,heteroatom functionalized carbon-based catalysts have made remarkable progress in recent years in a wide range of applications related to energy storage and energy generation.In this study,high surface area mesoporous ordered sulphur doped carbon materials are obtained via one-pot hydrothermal synthesis of carbon/SBA-15 composite after removal of in-situ synthesized hard template Si O₂.2-thiophenecarboxy acid as sulphur source gives rise to sulphur doping level of 5.5 wt%.Comparing with pristine carbon,the sulphur doped mesoporous ordered carbon demonstrates improved electro-catalytic activity in the oxygen reduction reaction in alkaline solution.     

Double laminated reduced graphene/Cu_2S/reduced graphene/graphene oxide nanofilms and their photoelectrochemical properties

In this work,an efficient photocatalytic material was prepared directly on Indium tin oxide(ITO)glass substrates by fabricating Cu_2 S and graphene oxide onto graphene for photoelectrochemical(PEC) water splitting.The double laminated reduced graphene/Cu_2S/reduced graphene/graphene oxide(RG/Cu_2S/RG/GO) nanofilms were characterized,and an enhanced photoelectrochemical response in the visible region was discovered.The photocurrent density of the nanofilms for PEC water splitting was measured to be up to 1.98 m A/cm~2,which could be ascribed to the followings:(i) a higher efficiency of light-harvesting because of GO coupling with Cu_2 S that could broaden the absorbing solar spectrum and enhance the light utilization efficiency;(ii) a stepwise structure of band-edge levels in the Cu_2S/GO electrode was constructed;(iii) double laminated electron accelerator(RG) was used in the Cu_2S/GO materials to get better electron-injecting efficiency.     

Synthesis and characterization of a novel binuclear iron phthalocyanine/reduced graphene oxide nanocomposite for non-precious electrocatalyst for oxygen reduction

Binuclear iron phthalocyanine/reduced graphene oxide(bi-Fe Pc/RGO) nanocomposite with good electrocatalytic activity for ORR in alkaline medium was prepared in one step. High angle annular dark field image scanning transmission electron microscopy(HAADF-STEM) and energy dispersive X-ray spectroscopy element mapping results show bi-Fe Pc was uniformly distributed on RGO. An obvious cathodic peak located at about-0.23 V(vs. SCE) in CV and an onset potential of-0.004 V(vs. SCE) in LSV indicate the as-prepared bi-Fe Pc/RGO nanocomposite possesses high activity which is closed to Pt/C for ORR. The ORR on bi-Fe Pc/RGO nanocomposite follows four-electron transfer pathway in alkaline medium. Compared with Pt/C, there is only a slight decrease(about 0.02 V vs. SCE) for bi-Fe Pc/RGO nanocomposite when the methanol exists. The excellent activity and methanol tolerance in alkaline solutions proves that bi-Fe Pc/RGO nanocomposite could be considered as a promising cathode catalyst for alkaline fuel cells.     

Relationship between polypyrrole morphology and electrochemical activity towards oxygen reduction reaction

The relationship between the morphology of polypyrrole and their electrocatalytic performances towards the oxygen reduction reaction (ORR) in alkaline media is described; annealed polypyrrole with granular- and tubules-like morphology exhibited different catalytic efficiencies.