Synthesis and electrochemical performances of LiNiCuZn oxides as anode and cathode catalyst for low temperature solid oxide fuel cell

Low temperature solid oxide fuel cell (LTSOFC, 300-600 degrees C) is developed with advantages compared to conventional SOFC (800-1000 degrees C). The electrodes with good catalytic activity, high electronic and ionic conductivity are required to achieve high power output. In this work, a LiNiCuZn oxides as anode and cathode catalyst is prepared by slurry method. The structure and morphology of the prepared LiNiCuZn oxides are characterized by X-ray diffraction and field emission scanning electron microscopy. The LiNiCuZn oxides prepared by slurry method are nano Li0.28Ni0.72O, ZnO and CuO compound. The nano-crystallites are congregated to form ball-shape particles with diameter of 800-1000 nm. The LiNiCuZn oxides electrodes exhibits high ion conductivity and low polarization resistance to hydrogen oxidation reaction and oxygen reduction reaction at low temperature. The LTSOFC using the LiNiCuZn oxides electrodes demonstrates good cell performance of 1000 mW cm(-2) when it operates at 470 degrees C. It is considered that nano-composite would be an effective way to develop catalyst for LTSOFC.     

Fe-PPy-TsOH/C用作质子交换膜燃料电池氧电极催化剂的研究

氧电极催化剂是制约质子交换膜燃料电池(PEMFCs)发展和应用的一个重要因素, 开发低价高效的非贵金属催化剂对PEMFCs来说已成为当务之急。本研究选择氮掺杂的碳载过渡金属(M-N/C)类催化剂为研究对象, 以铁盐作为金属前驱体, BP2000为碳源, 聚吡咯(PPy)为氮源, 对甲基苯磺酸(TsOH)为掺杂剂, 合成了非贵金属催化剂Fe-PPy-TsOH/C, 探究了不同的热处理温度及钴原子的掺杂对其氧还原催化性能的影响。研究结果表明: 800℃制备的Fe-PPy-TsOH/C催化剂因结晶度高、颗粒大小适中且分布均匀而具有最佳的氧还原催化性能; 一定量的钴原子取代可以改善Fe-PPy-TsOH/C的氧还原催化性能, 当钴的掺杂量为33.33%时(铁钴原子比为2︰1), 催化剂的性能达到最优。     

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.     

Growth of phthalocyanine doped and undoped nanotubes using mild synthesis conditions for development of novel oxygen reduction catalysts

Precious metal alloys have been the predominant electrocatalyst used for oxygen reduction in fuel cells since the 1960s. Although performance of these catalysts is high, they do have drawbacks. The two main problems with precious metal alloys are catalyst passivation and cost. This is why new novel catalysts are being developed and employed for oxygen reduction. This paper details the low temperature solvothermal synthesis and characterization of carbon nanotubes that have been doped with both iron and cobalt centered phthalocyanine. The synthesis is a novel low-temperature, supercritical solvent synthesis that reduces halocarbons to form a metal chloride byproduct and carbon nanotubes. Perchlorinated phthalocyanine was added to the nanotube synthesis to incorporate the phthalocyanine structure into the graphene sheets of the nanotubes to produce doped nanotubes that have the catalytic oxygen reduction capabilities of the metallo-phthalocyanine and the advantageous material qualities of carbon nanotubes. The cobalt phthalocyanine doped carbon nanotubes showed a half wave oxygen reduction potential of -0.050 ± 0.005 V vs Hg\HgO, in comparison to platinum's half wave oxygen reduction potential of -0.197 ± 0.002 V vs Hg\HgO.     

质子交换膜燃料电池中Pt/C及Pt合金/C催化剂的衰退机制研究综述

成本和耐久性依然是制约质子交换膜燃料电池商业化发展的两大瓶颈。首先综述了质子交换膜燃料电池阴极Pt/C催化剂在实际工作条件下的降解情况,并给出了可能的降解机制。结果表明,Pt/C催化剂在实际工作条件下,尤其是在汽车应用中是不稳定的,通常无法用作燃料电池阴极催化剂。而Pt合金催化剂因具有优异的氧还原催化性能和相对较好的耐久性,被认为有望解决成本和耐久性这两大难题,因此在质子交换膜燃料电池中日益得到重视和应用。但如何改善合金催化剂的耐久性依然是一个棘手的问题,文章最后详细综述了PtxCoy合金催化剂可能的衰退机理,以及可在一定程度上提高Pt合金催化剂耐久性的Pt单层结构和Pt核壳结构,这对催化剂的合成和设计具有一定的指导意义。     

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.     

Formation, microstructural characteristics and stability of carbon supported platinum catalysts for low temperature fuel cells

Supported platinum electrocatalysts are generally used in low temperature fuel cells to enhance the rates of the hydrogen oxidation and oxygen reduction reactions. In such catalysts, the high surface to volume ratios of the platinum particles maximize the area of the surfaces available for reaction. It is the structure and proper dispersal of these platinum particles that make low-loading catalysts feasible for fuel cell operation, lowering the cost of the system. If the platinum particles cannot maintain their structure over the lifetime of the fuel cell, change in the morphology of the catalyst layer from the initial state will result in a loss of electrochemical activity. This loss of activity in the platinum/carbon catalysts due to the agglomeration of platinum particles is considered to be a major cause of the decrease in cell performance, especially in the case of the cathode. In the light of the latest advances on this field, this paper reviews the preparation methods of these catalysts, their microstructural characteristic and their effect on both thermal and in cell conditions stability.     

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.     

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.     

微生物燃料电池Fe-N掺杂炭黑阴极催化剂性能研究

炭黑是一种廉价且具有高导电性的氧还原催化剂, 可应用于微生物燃料电池(MFCs)的阴极。然而, 纯炭黑的催化性能较差, 不能满足实际应用需求。为了提高炭黑的催化性能, 以氯化铁(FeCl₃)和三聚氰胺作为Fe源和N源按一定比例与炭黑混合共炭化, 对炭黑进行改性处理。结果表明, 当Fe-N与炭黑的质量比例为2.6∶1时, MFCs的输出功率密度达到最高值, 为1395 mW/m², 比Pt/C催化剂(876 mW/m²)提高了59%。SEM观察到炭黑基体上形成了椭圆形或柱状晶体, XRD和XPS测试结果显示是在共炭化过程中生成的Fe₃C晶体, 引入了吡啶氮和石墨氮, 在催化剂表面形成更多的活性位点, 这是复合催化剂性能提升的关键因素。随着Fe-N比例的提高, 复合催化剂的导电性和比表面积逐渐下降, 从另一方面又限制了其性能的提升。综上所述, 氯化铁、三聚氰胺和炭黑共炭化制备的复合催化剂是一种具有良好性价比的MFCs阴极催化剂, 可在规模化应用中发挥更大作用。     

酸处理对FeN/ZIF-8催化剂氧还原反应催化性能的影响

研发高性能、低成本的非贵金属阴极氧还原反应催化剂是目前质子交换膜燃料电池的主要研究方向之一。以1, 10-菲啰啉为氮源, FeSO₄·7H₂O为铁源, 考察以ZIF-8为载体制备的FeN/ZIF-8催化剂的氧还原反应催化性能, 并探究酸处理对FeN/ZIF-8催化剂结构及性能的影响。通过X射线衍射、比表面积和孔径分布测试、透射电子显微镜等物理表征手段对催化材料进行结构表征, 使用旋转圆盘电极对催化剂氧还原反应催化活性和稳定性进行测试。结果表明: 以ZIF-8为载体制备的催化剂含有Fe₃C, 以及具有较大的比表面积, 这可能是催化剂具有较高氧还原反应初始催化活性的原因。酸处理可去除催化剂中部分不稳定的含铁碳化物和无序碳结构, 使催化剂具有更大的比表面积、更丰富的介孔结构和更高的孔体积; 同时, 酸处理可提高碳基体的耐腐蚀性, 在老化测试中维持催化剂所具有的较高比表面积和丰富的介孔结构, 从而使FeN/ZIF-8-A催化剂表现出更好的氧还原反应活性和稳定性。     

直接硼氢化物燃料电池(DBFC)阳极催化剂的研究进展

直接硼氢化物燃料电池(DBFC)具有理论电池电压高和能量密度大等特点, 而其阳极催化剂是决定电池性能的关键因素之一。因此, 研究者们在提高阳极催化剂催化活性和降低催化剂成本方面开展了大量的研究工作。本文在简要介绍DBFC工作原理和阳极反应机理的基础上, 从催化剂种类和性能角度综述了近年来DBFC中贵金属、过渡金属以及储氢合金阳极催化剂的主要研究进展, 指出了阳极催化剂研究所面临的问题, 同时提出了今后的发展方向。     

Effect of the nanosized TiO2 particles in Pd/C catalysts as cathode materials in direct methanol fuel cells

Pd-TiO2/C catalysts were prepared by impregnating titanium dioxide (TiO2) on carbon-supported Pd (Pd/C) for use as the catalyst for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFCs). Transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were carried to confirm the distribution, morphology and structure of Pd and TiO2 on the carbon support. In fuel cell test, we confirmed that the addition of TiO2 nanoparticles make the improved catalytic activity of oxygen reduction. The electrochemical characterization of the Pd-TiO2/C catalyst for the ORR was carried out by cyclic voltammetry (CV) in the voltage window of 0.04 V to 1.2 V with scan rate of 25 mV/s. With the increase in the crystallite size of TiO2, the peak potential for OH(ads) desorption on the surface of Pd particle shifted to higher potential. This implies that TiO2 might affect the adsorption and desorption of oxygen molecules on Pd catalyst. The performance of Pd-TiO2/C as a cathode material was found to be similar to or better performance than that of Pt/C.     

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.     

Oxygen reduction activity of carbon nitride supported on carbon nanotubes

Fuel cells offer an alternative to burning fossil fuels, but use platinum as a catalyst which is expensive and scarce. Cheap, alternative catalysts could enable fuel cells to become serious contenders in the green energy sector. One promising class of catalyst for electrochemical oxygen reduction is iron-containing, nanostructured, nitrogen-doped carbon. The catalytic activity of such N-doped carbons has improved vastly over the years bringing industrial applications ever closer. Stoichiometric carbon nitride powder has only been observed in recent years. It has nitrogen content up to 57% and as such is an extremely interesting material to work with. The electrochemical activity of carbon nitride has already been explored, confirming that iron is not a necessary ingredient for 4-electron oxygen reduction. Here, we synthesize carbon nitride on a carbon nanotube support and subject it to high temperature treatment in an effort to increase the surface area and conductivity. The results lend insight into the mechanism of oxygen reduction and show the potential for carbon nanotube-supported carbon nitride to be used as a catalyst to replace platinum in fuel cells.     

碳载体预处理对燃料电池Co-N/C非铂催化剂氧还原性能的影响EI北大核心CSCD

钴(Co)基氧还原催化剂以价格低、储量高、易获得等优势成为代替铂基氧还原催化剂重要选择之一。本工作先对科琴黑进行硝酸酸化预处理,与四水合乙酸钴混合后在氨气气氛下800℃热解制备出Co-N/C氧还原催化剂。由红外光谱测试、联碱中和滴定与比表面积测定可知,经硝酸酸化预处理后,科琴黑表面含氧官能团数量增多,科琴黑孔径不变,中孔比例增加。XRD和TEM测试表明科琴黑和四水合乙酸钴经氨气热处理后,生成了分散均匀无团聚的Co_(5.47)-N/C催化剂。电化学测试表明载体经预处理后,制备的Co-N/C催化剂的氧还原反应(ORR)的电催化性能更好,在碱性条件下电流密度达到了预处理前的4.2倍,在催化动力学中属于四电子转移。     

铂钴合金纳米电催化剂的制备及性能研究

研制高活性的电催化剂是实现质子交换膜燃料电池的商业化应用必须解决的关键技术之一。本研究以三乙胺为碱性络合剂、硼氢化钠为还原剂, 采用液相合成法制备PtCo纳米合金电催化剂, 再通过高温热处理实现最佳电化学性能。采用各种表征方法对催化剂的微观结构及电化学性能进行测定, 探究硼氢化钠、三乙胺的添加量及高温热处理对催化剂电化学性能的影响。结果显示, 适量的硼氢化钠可提升催化剂的电化学活性面积, 三乙胺可以改变催化剂的质量活性, 高温热处理能有效提升催化剂的质量活性, 极大提升催化剂的氧还原反应(ORR)能力; 在同一测试体系下, 添加100 mg硼氢化钠及100 μL三乙胺在500 ℃高温热处理条件下制备的PtCo纳米合金电催化剂的质量活性达到133 mA/mg_Pt, 是田中贵金属工业株式会社(TKK)商用PtCo合金催化剂的3倍。     

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.     

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.     

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。