碳纳米管基非贵金属催化剂在电催化氧化还原中的应用研究进展

燃料电池和金属-空气电池是将化学能直接转化成电能的绿色电池,具有能量密度高、安全和环保等优点,相比传统能源具有独特优势。然而,目前阴极氧还原反应(oxygen reduction reaction,ORR)使用的贵金属铂(Pt)储量低,成本高,易中毒失活,严重限制了燃料电池的大规模应用。因此,开发廉价、高效、稳定的非贵金属催化剂成为研究热点。碳纳米管具有本征sp~2杂化结构、优异的导电性、高比表面积、良好的化学稳定性等突出优点,受到广泛关注。本文综述了碳纳米管基非贵金属ORR催化剂的最新进展,主要包括非金属掺杂、过渡金属-氮-碳纳米管、负载过渡金属及其衍生物(氧化物、碳化物、氮化物、硫化物等)、负载单原子、与其他碳材料(石墨烯、多孔碳、碳纳米纤维)复合以及碳纳米管基自支撑电极。最后,对碳纳米管基非贵金属ORR催化剂的研究前景和下一步研究方向进行了展望。     

氮掺杂碳纳米管高负载金属催化剂在铝空气电池中的应用

在铁基催化剂(Fe-N-C)中引入金属铈,采用高温热解法合成了氮掺杂碳纳米管(NCNTs)高负载金属催化剂(Fe/Ce-NCNTs)。金属铈的引入能更好地促进碳纳米管(CNTs)的生长,锚定更多的铁原子,增加 Fe—N_X活性位点的数量。Fe/Ce-NCNTs催化剂在碱性介质中表现出良好的催化活性和稳定性,半波电位为 0.86 V(vs RHE)。将 Fe/Ce-NCNTs催化剂应用于铝空气电池(AABs),其峰值功率密度可达142 mW·cm^-2,在50 mA·cm^-2电流密度下放电比容量达到865 mAh·g^-1,在高电流密度负载下具有较高的电压。     

α-Ti(HPO4)2微球负载型催化剂的合成及其烯烃聚合催化性能

2种茂金属催化剂及1种后过渡金属催化剂分别被固载于经过甲基铝氧烷处理后的α-Ti（HPO₄）₂微球表面,制备得到3种微球负载型催化剂。在烯烃聚合反应过程中,3种负载型催化剂均表现出比硅胶负载型催化剂更高的催化活性。2种茂金属负载型催化剂在乙烯、丙烯聚合反应中的活性分别高达6.8×10⁷ g_PE·（mol_Zr·h）^-1和5.0×10⁷ g_PP·（mol_Zr·h）^-1,所产生的烯烃聚合产物分子量分布较窄（M_w/M_n<2.3）,表现出良好的单中心催化特性,而且丙烯聚合产物的等规度高达96.5%。负载型后过渡金属催化剂在乙烯聚合反应中的活性稍低,但也能够达到8.3×10⁶ g_PE·（mol_Fe·h）^-1。3种负载型催化剂催化烯烃聚合产物均成微球型,能够很好地复制载体的形貌。     

α-Ti(HPO4)2微球负载型催化剂的合成及其烯烃聚合催化性能

2种茂金属催化剂及1种后过渡金属催化剂分别被固载于经过甲基铝氧烷处理后的α-Ti（HPO₄）₂微球表面,制备得到3种微球负载型催化剂。在烯烃聚合反应过程中,3种负载型催化剂均表现出比硅胶负载型催化剂更高的催化活性。2种茂金属负载型催化剂在乙烯、丙烯聚合反应中的活性分别高达6.8×10⁷ g_PE·（mol_Zr·h）^-1和5.0×10⁷ g_PP·（mol_Zr·h）^-1,所产生的烯烃聚合产物分子量分布较窄（M_w/M_n<2.3）,表现出良好的单中心催化特性,而且丙烯聚合产物的等规度高达96.5%。负载型后过渡金属催化剂在乙烯聚合反应中的活性稍低,但也能够达到8.3×10⁶ g_PE·（mol_Fe·h）^-1。3种负载型催化剂催化烯烃聚合产物均成微球型,能够很好地复制载体的形貌。     

Co2+/Cd2+复合材料的合成及其催化性质

在相同的反应条件下,基于配体（Hpypymba=4-（（3-（吡嗪-2-基）-1H-吡唑-1-基）甲基）苯甲酸）和过渡金属离子（Co（Ⅱ）、Cd（Ⅱ））合成同构金属掺杂材料[Co_xCd_1-x（pypymba）₂]_n（0 ≤ x ≤ 1）（配合物1~5）,运用粉末X射线衍射（PXRD）、紫外等分析手段对其结构与形貌进行表征。将得到的MOFs作为催化剂载体负载Ag离子进行4-硝基苯酚的还原反应。研究表明含Co²⁺的化合物1是良好的催化剂载体,随着配合物中Cd²⁺比例的增加,反应速率下降,甚至对反应有一定的抑制效果。该MOFs对于Ag的最大负载量为47%（w/w）,Ag@compound 1经4次循环后依然有96%的催化效率。     

非共价键功能化石墨烯/碳纳米管负载型金属配合物催化剂及催化反应中的应用

碳材料（石墨烯、碳纳米管）具有超大的比表面积、高机械强度、化学稳定性、环境友好等特点，使得其作为一类新型非均相催化剂的优良载体，固载的金属配合物催化剂在许多催化反应中得到了广泛的应用.由于弱相互作用（π-π键、氢键、静电）功能化可以有效的保护碳材料的完整性，从而更好地发挥碳材料本身的优异性能.通过改变温度、溶液极性、外场力来调控非共价键功能化碳材料催化剂在催化反应中载体与催化剂的吸附与分离，使其具有均相催化剂优良的催化活性和多相催化剂的可回收性.综述了近些年来非共价键功能化石墨烯和碳纳米管固载的金属配合物催化剂在催化反应中的研究进展.     

碳基无金属电催化剂的本征缺陷研究进展

自首次报道氮掺杂碳纳米管具有优良的氧还原催化性能以来,碳基无金属材料作为贵金属基电催化剂的潜在替代品而被寄予厚望。碳骨架中普遍存在的本征缺陷位点是影响碳材料物理化学性质的重要因素。特定碳缺陷的引入可以打破原本完整的sp²碳骨架而形成局部畸变,改变邻近碳原子的电荷或自旋密度分布,进而优化催化过程反应物和中间产物的吸附/脱附,提升活性位点的催化活性。因此,在碳基材料中设计创造特定的缺陷结构成为了制备高活性电催化剂的重要研究方向。本文对近年来碳基无金属电催化剂中本征缺陷的研究进展进行了综述,归纳了碳材料中常见的3类本征缺陷（边界、空位或孔洞、拓扑畸变）的制备策略和表征手段,并深入讨论了不同类型碳缺陷的构型和电子结构与其电催化活性的内在关系。最后,我们对目前本征碳缺陷在电催化领域的研究挑战和未来前景进行了总结和展望。     

基于非贵金属氧还原催化剂的质子交换膜燃料电池性能

质子交换膜燃料电池的成本和寿命问题是制约其商业化的主要瓶颈. 开发高效稳定的新型非铂氧还原催化剂是降低电池成本的重要途径. 过渡金属-氮-碳型非贵金属催化剂具有较高催化活性、资源丰富、价格低廉等优点, 被认为是未来最有希望替代铂的氧还原催化剂. 本综述从催化剂的设计构筑、催化层结构优化以及电池测试等方面, 对过渡金属-氮-碳型非贵金属催化剂的国内外最新研究进展进行了重点讨论, 并对未来其发展趋势提出展望.     

基于碳纳米管负载的电催化剂高效检测还原型谷胱甘肽

通过两步法合成了10-甲基吩噻嗪/2-羟丙基-β-环糊精主客体化合物修饰的多壁碳纳米管复合材料MPT-HP-β-CD/MWNT,并用FT-IR、UV-Vis、荧光光谱、拉曼光谱、TEM等对其组成进行表征。通过CV曲线、i-t曲线对谷胱甘肽（GSH）的催化性能以及对催化剂阻抗的研究,证明了MWNT可以提高导电能力,提高对GSH的催化活性。此外,还研究了pH值、温度、扫速等对催化剂催化活性的影响,表明该复合材料可用于GSH的电化学检测,并具有良好的稳定性、重现性以及很高的灵敏度。最优检测浓度范围为5×10^-7~4.95×10^-5 mol·L^-1,检测限为3.96×10^-8 mol·L^-1（S/N=3）。     

分级孔结构的Fe-N-C催化剂用于高效电催化氧还原

氧还原反应（ORR）是金属空气电池以及质子交换膜燃料电池（PEMFCs）系统重要的阴极反应,研究具有高活性与高稳定性的非贵金属催化剂具有重要意义。本研究使用了一种具有分级孔结构的MIL-101-(Al-Fe)作为金属前驱体模板,成功制备出具有分级多孔结构的Fe-N-C催化剂。电化学测试结果表明,在0.1 mol/L KOH电解液中,Fe-N-C-MIL-900催化剂表现出最优的氧还原性能（半波电位0.905 V以及5000圈CV测试后半波电位仅下降5 mV）,远高于纯碳基N-C-MIL-900催化剂（0.845 V）。通过旋转环盘电极测试发现,Fe-N-C-MIL-900催化剂ORR电子转移数为3.98,H2O2产率低于3%,表现出明显的4电子ORR路径。这一工作为制备具有高ORR活性的Fe-N-C催化剂提供了一种新的途径。     

Mn-N-P doped carbon spheres as an efficient oxygen reduction catalyst for high performance Zn-Air batteries

Low-cost and efficient oxygen reduction reaction (ORR) electrocatalysts are the key to developing Zn-air batteries for renewable energy storage. Herein, the Mn-N-P doped carbon sphere was prepared through polymerization of hexachlorotripolyphosphazene (HCCP) and phloroglucinol, and then followed the calcination at 900 °C. Theory calculations demonstrated the introduction of Mn in N-P doped carbon could lower the dissociation barrier of O₂ into O* and promote the ORR through a 4e^? pathway. The as-prepared catalysts exhibited a half-wave potential of 0.82 V vs. RHE and limiting current density of 5.2 mA/cm² toward ORR, which was comparable to those of the commercial Pt/C catalysts. In addition, Zn-air batteries with 0.05 Mn-N-P-C catalysts showed a high specific capacity of 830 mAh/g_Zn and excellent cycle stability. This facile approach demonstrated herein could be a solution to develop optimum non-precious metal catalysts for the application in cathodes of proton exchange membrane fuel cells. This study also provides new insight to design the catalysts of multi-heteroatom coordinated metal in the carbon matrix for both fundamental researches and practical applications.     

MnO/N-Doped Mesoporous Carbon as Advanced Oxygen Reduction Reaction Electrocatalyst for Zinc–Air Batteries

The development of alternative electrocatalysts exhibiting high activity in the oxygen reduction reaction (ORR) is vital for the deployment of large-scale clean energy devices, such as fuel cells and zinc–air batteries. N-doped carbon materials offer a promising platform for the design and synthesis of electrocatalysts due to their high ORR activity, high surface area, and tunable porosity. In this study, materials in which MnO nanoparticles are entrapped in N-doped mesoporous carbon (MnO/NC) were developed as electrocatalysts for the ORR, and their performances were evaluated in zinc–air batteries. The obtained carbon materials had large surface area and high electrocatalytic activity toward the ORR. The carbon compounds were fabricated by using NaCl as template in a one-pot process, which significantly simplifies the procedure for preparing mesoporous carbon materials and in turn reduces the total cost. A primary zinc–air battery based on this material exhibits an open-circuit voltage of 1.49 V, which is higher than that of conventional zinc–air batteries with Pt/C (Pt/C cell) as ORR catalyst (1.41 V). The assembled zinc–air battery delivered a peak power density of 168 mW cm⁻² at a current density of about 200 mA cm⁻², which is higher than that of an equivalent Pt/C cell (151 mW cm⁻² at a current density of ca. 200 mA cm⁻²). The electrocatalytic data revealed that MnO/NC is a promising nonprecious-metal ORR catalyst for practical applications in metal–air batteries.     

Sulfur-Induced Growth of Coordination Polymer Derived-Straight Carbon Nanotubes on Carbon Nanofiber Network for Zn-Air Batteries

Low-cost heteroatom-doped carbon nanomaterials have been widely studied for efficient oxygen reduction reaction and energy storage and conversion in metal-air batteries. A Masson pine twigs-like 3-dimensional network construction of carbon nanofibers (CNFs) with abundant straight long Co, N, and S-doped carbon nanotubes (CNTs) is developed by thermal treatment of Co-based polymer coated onto polyacrylonitrile nanofiber network together with thiourea at 900 °C, denoted as CNFT-Co₉S₈-900. It is interesting to note that the introduction of a high concentration of sulfur does not lead to the complete toxicity of catalysts, but promotes the axial growth to selectively form straight CNTs instead of curly bamboo-like CNTs. The highly graphitized in-situ grown Co, N, S-doped CNTs and the 3-dimensional N-doped CNF network provide both active catalytic sites and highly conductive paths, which are beneficial for oxygen reduction reaction (ORR). Thus, the optimal CNFT-Co₉S₈-900 performs the excellent ORR catalytic activity with a half-wave potential of 0.84 V and a diffusion-limited current density of 5.49 mA cm⁻². Furthermore, the CNFT-Co₉S₈-900-based Zn-air devices also possess a high power density of 136.9 mW cm⁻² better than commercial Pt/C.     

Pomegranate‐Inspired Design of Highly Active and Durable Bifunctional Electrocatalysts for Rechargeable Metal–Air Batteries

Rational design of highly active and durable electrocatalysts for oxygen reactions is critical for rechargeable metal–air batteries. Herein, we report the design and development of composite electrocatalysts based on transition metal oxide nanocrystals embedded in a nitrogen‐doped, partially graphitized carbon framework. Benefiting from the unique pomegranate‐like architecture, the composite catalysts possess abundant active sites, strong synergetic coupling, enhanced electron transfer, and high efficiencies in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The Co₃O₄‐based composite electrocatalyst exhibited a high half‐wave potential of 0.842 V for ORR, and a low overpotential of only 450 mV at the current density of 10 mA cm^?2 for OER. A single‐cell zinc–air battery was also fabricated with superior durability, holding great promise in the practical implementation of rechargeable metal–air batteries.     

Recent advances in carbon-based electrocatalysts for oxygen reduction reaction

Fuel cells are one of the most promising clean energy devices to substitute for fossil fuel in the future to alleviate energy crisis and environmental pollution.As the key reaction on the cathode in the fuel cells,oxygen reduction reaction(ORR)still requires efficient noble metal catalysts such as the comme rcial Pt/C to boost the reaction for its sluggish kinetics.Therefore,it is critical to design earth-abundant carbonbased catalysts with high efficiency and long-term stability to replace the noble metal-based catalysts.This review focuses on the recent progress about carbon-based ORR catalysts including non-metal doped carbon materials,transition metal-nitrogen-carbon species,transition metal carbides/carbon,single atom catalysts,and other carbon hybrids.And we further infer that the excellent ORR performances can be achieved by the balance of geometric and electronic structures of catalysts such as conductivity,surface area,hierarchical porous structure,defect and doping effect.Additionally,the perspective development trend is also proposed to guide the rational designation of carbon-based catalysts for ORR and even extend to other energy storage and conversion fields in the future.     

Polyaniline/Pure Carbon Assemblies as Efficient Self‐standing Metal‐free Oxygen Electrodes in Alkaline Media for Zn‐Air Batteries

A facile design and fabrication of self‐standing metal‐free polyaniline (PANI)@carbon nanotubes (CNTs) composite membrane was initially proposed by straightforward noncovalent wrapping the polymer around pure CNTs. Without introduction of extra heteroatoms into CNTs, the optimized PANI@CNTs composite exhibits a much better electrocatalytic performance for oxygen evolution reaction (OER) than pure CNTs via favorable interfacial modification with PANI to largely expose the active sites of on the surface of pure CNTs. Besides, it displays good oxygen reduction reaction (ORR) performance. When directly utilized as bifunctional air electrode without extra additive agents, the composite membrane‐enabled rechargeable Zn‐air batteries not only deliver a high peak power density (201.9 W g^?1) and a large energy density (850.3 Wh kg_Zn^?1), but also present robust cycling performance for 216 cycles with a high energy efficiency of 57.8%.     

Construction of a sp3/sp2 Carbon Interface in 3D N‐Doped Nanocarbons for the Oxygen Reduction Reaction

The development of highly efficient metal‐free carbon electrocatalysts for the oxygen reduction reaction (ORR) is one very promising strategy for the exploitation and commercialization of renewable and clean energy, but this still remains a significant challenge. Herein, we demonstrate a facile approach to prepare three‐dimensional (3D) N‐doped carbon with a sp³/sp² carbon interface derived from ionic liquids via a simple pyrolysis process. The tunable hybrid sp³ and sp² carbon composition and pore structures stem from the transformation of ionic liquids to polymerized organics and introduction of a Co metal salt. Through tuning both composition and pores, the 3D N‐doped nanocarbon with a high sp³/sp² carbon ratio on the surface exhibits a superior electrocatalytic performance for the ORR compared to that of the commercial Pt/C in Zn–air batteries. Density functional theory calculations suggest that the improved ORR performance can be ascribed to the existence of N dopants at the sp³/sp² carbon interface, which can lower the theoretical overpotential of the ORR.     

DNA‐Directed Growth of Pd Nanocrystals on Carbon Nanotubes towards Efficient Oxygen Reduction Reactions

Unique DNA‐promoted Pd nanocrystals on carbon nanotubes (Pd/DNA–CNTs) are synthesized for the first time, in which through its regularly arranged PO₄^3? groups on the sugar–phosphate backbone, DNA directs the growth of ultrasmall Pd nanocrytals with an average size of 3.4 nm uniformly distributed on CNTs. The Pd/DNA–CNT catalyst shows much more efficient electrocatalytic activity towards oxygen reduction reaction (ORR) with a much more positive onset potential, higher catalytic current density and better stability than other Pd‐based catalysts including Pd nanocrystals on carbon nanotubes (Pd/CNTs) without the use of DNA and commercial Pd/C catalyst. In addition, the Pd/DNA–CNTs catalyst provides high methanol tolerance. The high electrocatalytic performance is mainly contributed by the ultrasmall Pd nanocrystal particles grown directed by DNA to enhance the mass transport rate and to improve the utilization of the Pd catalyst. This work may demonstrate a universal approach to fabricate other superior metal nanocrystal catalysts with DNA promotion for broad applications in energy systems and sensing devices.     

Understanding the Catalytic Sites of Metal–Nitrogen–Carbon Oxygen Reduction Electrocatalysts

The development of low-cost catalysts containing earth-abundant elements as alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR) is crucial for the large-scale commercial application of proton exchange membrane fuel cells (PEMFCs). Nonprecious metal–nitrogen–carbon (M-N-C) materials represent the most promising candidates to replace Pt-based catalysts for PEMFCs applications. However, the high-temperature pyrolysis process for the preparation of M-N-C catalysts frequently leads to high structural heterogeneity, that is, the coexistence of various metal-containing sites and N-doped carbon structures. Unfortunately, this impedes the identification of the predominant catalytic active structure, and thus, the further development of highly efficient M-N-C catalysts for the ORR. This Minireview, after a brief introduction to the development of M-N-C ORR catalysts, focuses on the commonly accepted views of predominant catalytic active structures in M-N-C catalysts, including atomically dispersed metal–N_x sites, metal nanoparticles encapsulated with nitrogen-doped carbon structures, synergistic action between metal–N_x sites and encapsulated metal nanoparticles, and metal-free nitrogen-doped carbon structures.