利用生物质材料合成高性能氢氧燃料电池氧还原催化剂（英文）

制备廉价、高活性氧还原催化剂对于发展氢氧燃料电池清洁能源极为重要.在本论文中,我们利用黑木耳作为生物质材料,通过一种便捷的方法合成了高活性氧还原催化剂.黑木耳经水热和热解两个步骤,碳化形成BF-N-950催化剂.该催化剂在酸性和碱性溶液中的半波电势分别为0.77和0.91 V.采用BF-N-950催化剂作为膜电极得到的氢氧燃料单电池,峰值功率可达255 mW cm^-2.本文提出了使用生物质材料合成高性能氧还原催化剂的方法,为氢氧燃料电池的应用提供了有益探索.     

One-step scalable preparation of N-doped nanoporous carbon as a high-performance electrocatalyst for the oxygen reduction reaction

N-doped porous carbon materials have been prepared by a simple one-step pyrolysis of ethylenediaminetetraacetic acid (EDTA) and melamine in the presence of KOH and Co(NO₃)₂·6H₂O. The combination of the high specific area (1485 m²·g^?1), high nitrogen content (10.8%) and suitable graphitic degree results in catalysts exhibiting high activity (with onset and half-wave potentials of 0.88 and 0.79 V vs the reversible hydrogen electrode (RHE), respectively) and four-electron selectivity for the oxygen reduction reaction (ORR) in alkaline medium—comparable to a commercial Pt/C catalyst, but far exceeding Pt/C in stability and durability. Owing to their superb ORR performance, low cost and facile preparation, the catalysts have great potential applications in fuel cells, metal-air batteries, and ORR-related electrochemical industries.      

N-doped carbon shell encapsulated PtZn intermetallic nanoparticles as highly efficient catalysts for fuel cells

Nano Research - The high cost and poor durability of Pt nanoparticles (NPs) have always been great challenges to the commercialization of proton exchange membrane fuel cells (PEMFCs). Pt-based...     

Zeolite-templated mesocellular graphene foam with adjustable defects as highly efficient catalysts for oxygen reduction reaction

In this study, zeolite-templated mesocellular graphene foam was facilely synthesized by pyrolysis under different temperatures for oxygen reduction reaction. Investigations found that MGF can be regulated with different structure properties by controlling the pyrolysis temperature, where the MGF-900 (pyrolyzed under 900 °C) possessed a large BET specific surface area (619 m² g^?1), a hierarchically micro–meso–macroporous carbon framework, and a better balance between conductivity and active sites than the other counterparts (MGF-800 and MGF-1000). As a result, MGF-900 had the most excellent catalytic activity, the most positive onset potential of ??0.1 V and the highest current density of 5.01 mA cm^?2 among the different samples and many other reported carbon-based catalysts. More importantly, despite no heterogeneous atoms doping, the catalytic activity of MGF-900 was nearly equal to that of commercial Pt/C catalyst. Regarding tolerance and stability, MGF-900 behaved even better. Therefore, as a superior metal-free electrocatalyst, MGF-900 is proved to be well applied in highly efficient oxygen reduction reaction.

     

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。     

Symmetric growth of Pt ultrathin nanowires from dumbbell nuclei for use as oxygen reduction catalysts

This work demonstrates the synthesis of Pt ultrathin nanowires assisted by chromium hexacarbonyl [Cr(CO)₆]. The nanowires exhibit a uniform diameter of 2–3 nm. The length can reach up to several microns. It was found that Cr species produced dumbbell-like nuclei which play a pivotal role in the formation of the Pt nanowires. Such Pt nanowires can be tuned to nanocubes by simply decreasing the concentration of [Cr(CO)₆]. Compared to a commercial Pt/C catalyst (45 wt%, Vulcan, Tanaka) and Pt black (fuel cell grade, Sigma), the synthesized Pt nanowires exhibit superior performance in electrocatalytic oxygen reduction with a specific activity of 0.368 mA/cm², which was 2.7 and 1.8 times greater than that of Pt/C (0.138 mA/cm²) and Pt black (0.202 mA/cm²), respectively. The mass activity of Pt nanowires (0.088 mA/μg) is 2.3 times that of Pt black (0.038 mA/μg) and comparable to that of Pt/C (0.085 mA/μg).      

Ketjenblack carbon supported amorphous manganese oxides nanowires as highly efficient electrocatalyst for oxygen reduction reaction in alkaline solutions

A composite air electrode consisting of Ketjenblack carbon (KB) supported amorphous manganese oxide (MnOx) nanowires, synthesized via a polyol method, is highly efficient for the oxygen reduction reaction (ORR) in a Zn-air battery. The low-cost and highly conductive KB in this composite electrode overcomes the limitations due to low electrical conductivity of MnOx while acting as a supporting matrix for the catalyst. The large surface area of the amorphous MnOx nanowires, together with other microscopic features (e.g., high density of surface defects), potentially offers more active sites for oxygen adsorption, thus significantly enhancing ORR activity. In particular, a Zn-air battery based on this composite air electrode exhibits a peak power density of ～190 mW/cm2, which is far superior to those based on a commercial air cathode with Mn3O4 catalysts.     

Materials for high-temperature oxygen reduction in solid oxide fuel cells

Solid state ionic devices such as fuel cells and oxygen separation membranes require the adsorption of oxygen molecules, their dissociation into oxygen atoms, oxidation by charge exchange and entry of the resultant ion into the solid phase. The cathodes capable of sustaining these processes must themselves be stable in the high temperature environment of air with a significant water vapour content, and compatible chemically and mechanically with the contacting solid phase, normally an electrolyte. As charge transfer materials obviously a high electronic conductivity is imperative, and some degree of ionic conductivity can serve to delocalise the oxidation process, thus reducing polarisation. In the present review the evolution of these cathode materials and their present status will be presented.     

Carbon-encapsulated heazlewoodite nanoparticles as highly efficient and durable electrocatalysts for oxygen evolution reactions

The activity and durability of electrocatalysts are important factors in their practical applications,such as electrocatalytic oxygen evolution reactions (OERs)used in water splitting cells and metal-air batteries.In this study,a novel electrocatalyst,comprising few-layered graphitic carbon (～5 atomic layers) encapsulated heazlewoodite (Ni3S2@C) nanoparticles (NPs),was designed and synthesized using a one-step solid phase pyrolysis method.In the OER test,the Ni3S2@C catalyst exhibited an overpotential of 298 mV at a current density of 10 mA·cm-2,a Tafel slope of 51.3 mV·dec-1,and charge transfer resistance of 22.0 Ω,which were better than those of benchmark RuO2 and most nickelsulfide-based catalysts previously reported.This improved performance was ascribed to the high electronic conductivity of the graphitic carbon encapsulating layers.Moreover,the encapsulation of graphitic carbon layers provided superb stability without noticeable oxidation or depletion of Ni3S2 NPs within the nanocomposite.Therefore,the strategy introduced in this work can benefit the development of highly stable metal sulfide electrocatalysts for energy conversion and storage applications,without sacrificing electrocatalytic activity.     

Synthesis and electrocatalytic oxygen reduction properties of truncated octahedral Pt3Ni nanoparticles

Pt₃Ni nanoparticles have been obtained by shape-controlled synthesis and employed as oxygen reduction electrocatalysts for proton exchange membrane fuel cells (PEMFC). The effects of varying the synthesis parameters such as the types of the capping agent and the reducing agent, and the reaction time have been systematically studied. The as-prepared Pt₃Ni nanoparticles were subjected to a butylamine-based surface treatment in order to prepare carbon-supported electrocatalysts. The Pt₃Ni electrocatalysts show an areaspecific activity of 0.76 mA/cm²(Pt) at 0.9 V in an alkaline electrolyte, which is 4.5 times that of a commercial Pt/C catalyst (0.17 mA/cm² (Pt)). The mass activity reached 0.30 A/mg(Pt) at 0.9 V, which is about twice that of the commercial Pt/C catalyst. Our results also show that the area-specific activities of these carbon-supported Pt₃Ni electrocatalysts depend strongly on the (111) surface fraction, which is consistent with the results of a study based on Pt₃Ni extended single-crystal surfaces.     

Preparation of carbon-supported PtCo nanoparticle catalysts for the oxygen reduction reaction in polymer electrolyte fuel cells by an electron-beam irradiation reduction method

We prepared carbon-supported PtCo bimetallic nanoparticles (PtCo/C) as electrode catalysts for the oxygen reduction reaction (ORR) at the cathodes in polymer electrolyte membrane fuel cells (PEFCs) by an electron-beam irradiation reduction method (EBIRM). An EBIRM allows nanoparticles to be easily prepared by the reduction of precursor ions in an aqueous solution irradiated with a high-energy electron beam. The structures of PtCo/C were characterized by transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, and the techniques of X-ray diffraction and X-ray absorption near edge structure. It found for the first time that both PtCo alloy and Co oxide were prepared simultaneously on the carbon support by an EBIRM. The catalytic activity and durability of PtCo/C were evaluated by linear-sweep voltammetry and cyclic voltammetry, respectively. The addition of Co to Pt/C not only enhanced the catalytic activity for the ORR but also improved the catalytic durability. As the Co concentration increased, both behaviors became pronounced. These improvements are explained by the effects of both PtCo alloy and Co oxide. We demonstrated that an EBIRM can not only synthesize the alloy and oxide simultaneously on the carbon support but also mass-produce the electrode catalysts for PEFC cathodes.     

N- and S-doped high surface area carbon derived from soya chunks as scalable and efficient electrocatalysts for oxygen reduction

Abstract

Highly stable, cost-effective electrocatalysts facilitating oxygen reduction are crucial for the commercialization of membrane-based fuel cell and battery technologies. Herein, we demonstrate that protein-rich soya chunks with a high content of N, S and P atoms are an excellent precursor for heteroatom-doped highly graphitized carbon materials. The materials are nanoporous, with a surface area exceeding 1000 m² g^?1, and they are tunable in doping quantities. These materials exhibit highly efficient catalytic performance toward oxygen reduction reaction (ORR) with an onset potential of ?0.045 V and a half-wave potential of ?0.211 V (versus a saturated calomel electrode) in a basic medium, which is comparable to commercial Pt catalysts and is better than other recently developed metal-free carbon-based catalysts. These exhibit complete methanol tolerance and a performance degradation of merely ～5% as compared to ～14% for a commercial Pt/C catalyst after continuous use for 3000 s at the highest reduction current. We found that the fraction of graphitic N increases at a higher graphitization temperature, leading to the near complete reduction of oxygen. It is believed that due to the easy availability of the precursor and the possibility of genetic engineering to homogeneously control the heteroatom distribution, the synthetic strategy is easily scalable, with further improvement in performance.     

N- and S-doped high surface area carbon derived from soya chunks as scalable and efficient electrocatalysts for oxygen reduction

Highly stable, cost-effective electrocatalysts facilitating oxygen reduction are crucial for the commercialization of membrane-based fuel cell and battery technologies. Herein, we demonstrate that protein-rich soya chunks with a high content of N, S and P atoms are an excellent precursor for heteroatom-doped highly graphitized carbon materials. The materials are nanoporous, with a surface area exceeding 1000 m² g⁻¹, and they are tunable in doping quantities. These materials exhibit highly efficient catalytic performance toward oxygen reduction reaction (ORR) with an onset potential of −0.045 V and a half-wave potential of −0.211 V (versus a saturated calomel electrode) in a basic medium, which is comparable to commercial Pt catalysts and is better than other recently developed metal-free carbon-based catalysts. These exhibit complete methanol tolerance and a performance degradation of merely ∼5% as compared to ∼14% for a commercial Pt/C catalyst after continuous use for 3000 s at the highest reduction current. We found that the fraction of graphitic N increases at a higher graphitization temperature, leading to the near complete reduction of oxygen. It is believed that due to the easy availability of the precursor and the possibility of genetic engineering to homogeneously control the heteroatom distribution, the synthetic strategy is easily scalable, with further improvement in performance.     

Shape-controlled synthesis of porous AuPt nanoparticles and their superior electrocatalytic activity for oxygen reduction reaction

Control of structure and morphology of Pt-based nanomaterials is of great importance for electrochemical energy conversions. In this work, we report an efficient one-step synthesis of bimetallic porous AuPt nanoparticles (PAuPt NPs) in an aqueous solution. The proposed synthesis is performed by a simple stirring treatment of an aqueous reactive mixture including K₂PtCl₄, HAuCl₄, Pluronic F127 and ascorbic acid at a pH value of 1 without organic solvent or high temperature. Due to their porous structure and bimetallic composition, as-made PAuPt NPs exhibit excellent electrocatalytic activity for oxygen reduction reaction.     

Rapid synthesis of cubic Pt nanoparticles and their use for the preparation of Pt nanoagglomerates

We report the synthesis of hexadecyltrimethylammonium bromide (CTAB)-stabilized cubic Pt nanoparticles by NaBH4 reduction of H2PtCl6 in aqueous CTAB solution. These Pt nanoparticles (average size of 7 nm) were well dispersed in aqueous solution and stable at least for 2 months. Addition of a trace amount of AgNO3 can alter the morphology of these Pt nanoparticles. More interestingly, the as-prepared uniform Pt nanoparticles were further developed into bigger Pt nanoagglomerates (approximately 20 to 47 nm) by a seed-mediate growth process. Dentritic and spherical Pt nanoagglomerates can be synthesized by altering the incubation time and their size can be tuned by controlling the amount of the seeds added.     

Controllable self-assembly of Pd nanowire networks as highly active electrocatalysts for direct formic acid fuel cells

Highly dispersed and uniform palladium nanowire networks (NWNs) are synthesized by a controllable, templateless and polyelectrolyte-mediated self-assembly process. In this method, anisotropic Pd(2+)-polysodium-p-styrenesulfonate (PSS) networks are assembled between Pd(2+) ions and SO(3)(-) attached to the pendent aromatic ring of PSS in solution by an electrostatic attraction. Reduction of Pd(II) cations to metallic Pd(0) leads to the formation of Pd nanostructures from cubic nanoparticles to highly dispersed NWNs. The Pd nanostructure formation depends on the rate of nucleation and crystallization of Pd(0) which in turn is controlled by the solution pH and reducing agent. The results demonstrate that highly dispersed and uniform Pd NWNs have a very high aspect ratio and are highly active and stable for the formic acid electrooxidation in acid media, demonstrating the promising potential of Pd NWNs as effective electrocatalysts for direct formic acid fuel cells.     

Rational design of Fe-N-C electrocatalysts for oxygen reduction reaction:From nanoparticles to single atoms

As an alternative energy,hydrogen can be converted into electrical energy via direct electrochemical conversion in fuel cells.One important drawback of full cel...     

Facile preparation of nitrogen-doped reduced graphene oxide as a metal-free catalyst for oxygen reduction reaction

The electronic and chemical properties of reduced graphene oxide (RGO) can be modulated by chemical doping foreign atoms and functional moieties. Nitrogen-doped reduced graphene oxide (N-RGO) is a promising candidate for oxygen reduction reaction (ORR) in fuel cells. However, there are still some challenges in further preparation and modification of N-RGO. In this work, a low-cost industrial material, urea, was chosen to modify RGO by a facile, catalyst-free thermal annealing approach in large scale. The obtained N-RGO, as a metal-free catalyst for oxygen reduction was characterized by XRD, XPS, Raman, SEM, TEM, and electrochemical measurements. It was found that the optimum synthesis conditions were a mass ratio of graphene oxide and urea equal to 1:10 and an annealing temperature of 800 °C. Detailed X-ray photoelectron spectrum analysis of the optimum product shows that the atomic percentage of N-RGO samples can be adjusted up to 2.6 %, and the resultant product can act as an efficient metal-free catalyst, exhibiting enhanced electrocatalytic properties for ORR in alkaline electrolytes. This simple, cost-effective, and scalable approach opens up the possibility for the synthesis of other nitrogen doping materials in gram-scale. It can be applied to various carbon materials for the development of other metal-free efficient ORR catalysts for fuel cell applications, and even new catalytic materials for applications beyond fuel cells.     

Rational design of hierarchically porous Fe-N-doped carbon as efficient electrocatalyst for oxygen reduction reaction and Zn-air batteries

The rational design and construction of hierarchically porous nanostructure for oxygen reduction reaction (ORR) electrocatalysts is crucial to facilitate the exposure of accessible active sites and promote the mass/electron transfer under the gas-solid-liquid triple-phase condition. Herein, an ingenious method through the pyrolysis of creative polyvinylimidazole coordination with Zn/Fe salt precursors is developed to fabricate hierarchically porous Fe-N-doped carbon framework as efficient ORR electrocatalyst. The volatilization of Zn species combined with the nanoscale Kirkendall effect of Fe dopants during the pyrolysis build the hierarchical micro-, meso-, and macroporous nanostructure with a high specific surface area (1,586 m²·g⁻¹), which provide sufficient exposed active sites and multiscale mass/charge transport channels. The optimized electrocatalyst exhibits superior ORR activity and robust stability in both alkaline and acidic electrolytes. The Zn-air battery fabricated by such attractive electrocatalyst as air cathode displays a higher peak power density than that of Pt/C-based Zn-air battery, suggesting the great potential of this electrocatalyst for Zn-air batteries.