氧还原反应(ORR)和氧析出反应(OER)是质子交换膜燃料电池和可充放锌空电池能量转换系统的核心反应，决定着电池的转化效率和性能。然而，它们的过电位高，动力学过程缓慢，使用的贵金属催化剂(Pt、Ir、Ru)价格昂贵和稳定性较差，阻碍了电池的商业化进程。因此，开发和设计高效、稳定、价格低廉的催化剂对推动燃料电池和锌空电池的大规模应用和商业化具有重大的意义。碳基材料在电催化中的应用已经被广泛地研究，本文立足于碳材料的杂化或复合，设计并开发出了一系列杂化碳材料，将其作为贵金属载体，或结合过渡金属，研究它们作为ORR催化剂或是同时作为ORR和OER双功能催化剂的性能。主要可以分为三类：一是将石墨烯与多孔碳纳米纤维或多壁碳纳米管进行杂化以及杂元素掺杂处理，将其负载贵金属Pt纳米颗粒或一维的PtPd合金纳米棒催化剂，应用在质子交换膜燃料电池的阴极ORR催化剂领域；二是通过几种简单原料的热解制备Co、 N双掺杂碳纳米管／类石墨烯碳纳米片氧还原催化剂，作为一次锌空电池的空气电极催化剂；三是采用静电纺丝以及CVD技术在嵌入过渡金属FeCo合金的碳纳米纤维上嫁接碳纳米管，作为一种具有ORR和OER双功能的催化剂，应用于可充放锌空电池的空气电极催化剂。具体研究内容和结论如下： (1)以“一步改性Hummers法”及后期碳化工艺，成功将多孔碳纳米纤维(PCNF)或碳纳米纤维(CNF)掺入到石墨烯(G)纳米片层中间，形成了一种三维贯穿网络结构的石墨烯-多孔碳纳米纤维(G-PCNF)或石墨烯-碳纳米纤维(G-CNF)杂化载体。G-PCNF和G-CNF的比表面积均高于纯石墨烯，负载Pt后，Pt纳米颗粒不但分散得更加均匀而且尺寸进一步减小。通过循环伏安法(CV)和线性扫描伏安法(LSV)测试了催化剂的ORR催化活性和稳定性，研究结果表明Pt／G-PCNF和Pt／G-CNF催化剂的起始电位和半波电位明显高于Pt／G，证实了PCNF和CNF作为空间阻隔剂对G的有效掺杂作用，它们不但有利于减少石墨烯的堆积，提高Pt纳米颗粒的利用率，还能够作为石墨烯片层的桥梁，加快电子转移。与商业JM20(20 wt％ Pt／C)催化剂相比，Pt／G-PCNF和Pt／G-CNF表现出优越性，它们的半波电位分别为0.766V和0.762V，比JM20分别高29 mV和25 mV。在电极电位为0.8V(vs.RHE)时，Pt／G-PCNF和Pt／G-CNF的质量比活性分别是JM20催化剂的2倍和1.7倍。在0.5 M H₂SO₄溶液中，对Pt／PCNF和JM20催化剂进行2000次的电极电位循环扫描后，Pt／GPCNF的ECSA保留率为83.0％，半波电位仅损失9 mV，而JM20的ECSA保留率只有50.4％，半波电位损失154 mV，说明G-PCNF载体负载Pt具有优良的耐久性。 (2)采用“一步改性Hummers法”，将直径更细的多壁碳纳米管掺入到石墨烯片层中间得到了石墨烯-多壁碳纳米管杂化载体(GM)，碳纳米管的掺入使得G-M相比于G的比表面积提高了约25％。以双氰胺为氮源前驱体与G-M共热处理得到N-G-M，杂原子氮不仅增加了G-M载体的缺陷程度，而且能与Pt纳米颗粒之间发生相互作用，有利于Pt纳米颗粒的均匀沉积，改善Pt的电子结构。ORR半电池测试结果表明Pt／N-G-M比Pt／M、Pt／G、Pt／G-M具有更好的ORR催化活性，这归因于N-G-M杂化载体高的表面积和多级孔的三维结构以及其与Pt的协调作用。相比于商业JM20催化剂，Pt／N-G-M表现出更优的ORR催化活性和稳定性，证明了其在燃料电池阴极催化剂的潜在应用价值。 (3)通过一种简单、无模板的甲酸还原法将PtPd合金纳米棒成功负载在G-M杂化载体上。在温和的甲酸溶液体系下，PtPd合金在G-M表面主要为沿着<111>方向异相成核的生长方式，并逐渐长成棒状结构，直径分布在2.5-4 nm之间，长度约为十几纳米。电化学测试结果表明：PtPd NRs／G-M的半波电位为0.810 V，比商业JM40(40 wt％Pt／C)催化剂高出30 mV；在电极电位为0.85 V时，它的质量比活性约为JM40的2.1倍；经过2000次的电极电位循环扫描后，它的ECSA只损失了22.4％，同样好于JM40的36.4％。PtPd NRs／G-M良好的ORR催化活性和稳定性来源于G-M载体和一维PtPd合金纳米棒的协调作用，G-M载体为合金纳米棒提供高的比面积，而一维结构的PtPd合金纳米棒能够促进氧的有效还原，并且表面能低，在循环过程中更加稳定，提高了催化剂的寿命。 (4)以价格低廉、来源广泛的六水合氯化钴、葡萄糖、二氰二胺在高温下进行热解成功制备了Co、N双掺杂碳纳米管／类石墨烯碳纳米片催化剂(Co-NCNT／Ng)。它表现出三维贯穿的网络结构，具有高表面积和多级孔结构。电化学测试结果表明：在900℃碳化时， Co-NCNT／Ng-900的ORR催化活性最好，优于Co-NCNT-900和Ng900催化剂。由于具有独特的三维结构和多级孔结构以及大量的活性位点(吡啶氮、石墨氮和Co-N〓活性点)，Co-NCNT／Ng-900表现出与商业20 wt％Pt／C相当的ORR活性以及更好的稳定性。此外，基于Co-NCNT／Ng-900催化剂的一次锌空电池的功率密度高达174.4 mW ㎝⁻²，在10 mA ㎝⁻²电流密度下比容量为795 mAh g⁻¹，能够在不同的电流密度下稳定运行较长的时间，具有较好的动态响应，有望满足生活中小型电子产品的供电需求。 (5)采用静电纺丝法结合CVD技术成功在FeCo合金嵌入的CNF骨架上嫁接了CNT得到FeCo-NSCNF@NCNT催化剂。以FeCo为催化剂，实现了CNT在CNF骨架上的原位生长，并且相互贯穿，形成一种三维的网络结构。电化学结果测试表明：FeCo-NSCNF@NCNT是一种优良的双功能催化剂，在半电池测试中半波电位为0.792V，j=10mA㎝⁻²的过电位为360mV，两者的电压差(△E =E〓-E〓)仅为0.8 V，优于商业的Pt／C+IrO₂催化剂。三维贯穿的网络结构增加了催化剂的导电性，有利于活性物质传输；N、 S双掺杂能够进一步提高催化剂的缺陷，增加催化剂对氧还原的活性； FeCo合金分散嵌入在纤维中，不仅促使碳管的原位生长，而且Fe、 Co的协调作用以及周围的石墨碳层促进了催化剂的ORR和OER性能，同时碳层能保护合金颗粒，进一步增加催化剂的稳定性。将FeCo-NSCNF@NCNT催化剂喷涂于碳纸上得到锌空电池的空气电极，进行测试后发现FeCo-NSCNF@NCNT表现出较高的充放电效率，较低的充放电电压差以及长达100 h的充放电循环稳定性。 关键词：质子交换膜燃料电池；锌空电池；碳基材料；杂元素掺杂；贵金属催化剂；过渡金属化合物

 Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the core electrode reactions of fuel cells or metal-air batteries, which determine the energy conversion efficiency and performance. However, they suffer from high overpotentials and sluggish kinetic processes. Up to now, precious catalysts (Pt, Ir, Ru etc) still serve as the most efficient oxygen electrocatalysts, the commercial application of which is significantly plagued by the high price, terrestrial scarcity and unsatisfactory stability. Therefore, it is highly desirable to develop high-performance, earth-abundant and durable catalysts to promote the large-scale application and commercialization of fuel cells and Zinc-air batteries. The past decades have witnessed considerable achievements for the rational design of carbon-based materials as the efficient oxygen efficient electrocatalysts. In this work, one series of carbon hybrids are developed, which are employed as the supports of precious catalysts or combine with the transition metals as the oxygen electrocatalysts. They all show high electrochemical activities towards ORR or OER. Three kinds of electrocatalysts are included. The first one is that PCNF, CNF or MWCNT are incorporated into the graphene nanosheets as nanospacers to form G-PCNF, G-CNF and G-M hybrid supports, which are used to deposit Pt nanoparticles or PtPd nanorods as the ORR electrocatalysts in proton exchange membrane fuel cells (PEMFC). The second one is non-precious metal catalysts (Co-NCNT/Ng) synthesized by a feasible annealing as the ORR electrocatalysts in primary Zinc-air battery. The third one is FeCo alloy nanoparticles embedded in the nitrogen-doped carbon nanotube-grafted nitrogen and sulfur co-doped carbon nanofibers (FeCo-NSCNF@NCNT) synthesized by the electrospinning and chemical vapor deposition (CVD) as the bifunctional electrocatalysts in rechargeable Zinc-air battery. The main research contents and conclusions in the work are as following aspects: (1)Graphene-porous carbon nanofiber (G-PCNF) and Graphene-carbon nanofiber (G-CNF) hybrid materials were prepared by the one-pot modified Hummers method followed by thermal annealing as the Pt supports. Particularly, 1D PCNF and CNF can be nanospacers for 2D graphene (G) to make full utilization of the high specific intrinsic surface area of graphene and the Pt nanoparticles can be deposited uniformly with smaller Pt size on the hybrid supports compared with G. The newly developed Pt/G-PCNF and Pt/G-CNF exhibit higher ORR activites compared to Pt/G, demonstrating the effective incorporation of PCNF or CNF nanospacers into graphene nanosheets. The nanospacers not only decrease the aggregation of graphene, but also work as the spacing bridges of graphene nanosheets, accelerating the electronic transfer. The electrochemical results show that the half-wave potentials of Pt/G-PCNF and Pt/G-CNF are 0.766 V and 0.762 V, 29 mV and 25 mV higher than JM20 (20 wt% Pt/C). The mass activities (at 0.8 V) of Pt/G-PCNF and Pt/G-CNF are 2 and 1.7 times as high as JM20. Pt/G-PCNF also demonstrates better stability, maintaining 50.4% of its electrochemical active surface area (ECSA) after the accelerated durability testing (ADT) whereas JM20 only retains 17.0%. Furthermore, the half-wave potential of Pt/G-PCNF loses about only 9 mV, significantly superior to the 154 mV half-wave potential loss for JM20. (2)The potential of graphene-multiwalled carbon nanotube (G-M) hybrid prepared by the same one-pot modified Hummers method followed by thermal annealing has been demonstrated by employing one as the electrocatalyst support for oxygen reduction reaction (ORR). The specific surface area of G-M increases by 25% compared with G. N-modification of the G-M (N-G-M) was performed by grinding G-M and dicyandiamide (DCDA) followed by subsequent calcination, which effectively modifies the electronic structure of the G-M hybrid support, beneficial for the uniform distribution and more exposure of Pt nanoparticles. The half-cell tests reveal that Pt/N-G-M shows the most excellent electrochemical performance compared with Pt/G-M, Pt/G and Pt/M, which is attributed to synergistic effect between N-G-M support and Pt nanoparticles. Even compared with commercial JM20, Pt/N-G-M demonstrates its advantages in terms of ORR performance and durability. The highly efficient and durable Pt/N-G-M electrocatalyst paves the way for the potential application in PEMFC. (3)One-dimensional (1D) anisotropic platinum-based nanorods are particularly attractive electrocatalysts for oxygen reduction reaction (ORR) owing to the inherent structural advantages. In this research part, ultrathin PtPd alloy nanorods supported on Graphene-Multiwalled carbon nanotube (G-M) hybrid were fabricated via a facile surfactant-free and template-free HCOOH reduction method. In the mild HCOOH solution, PtPd nanorods preferred the anisotropic growth along with <111> direction, which is promoted by the very slow reduction rate at room temperature and the lowest energy principle. The electrochemical results show that the halfwave potential of PtPd NRs/G-M is 30 mV higher than JM40 (40 wt% Pt/C) and the mass activity (at 0.85 V) is 2.1 times higher than JM40. After the accelerated durability tests, it also maintains superior stability than JM40. The superior performance is attributed to the combination of the advantageous 1D morphological motif and the synergistic effect with G-M support. Firstly, the high specific surface area, porous and defect structure of G-M hybrid support not provides active sites for the loading of PtPd NRs but also benefits the mass transfer. Secondly, 1D nanorods possess higher percentage of high-coordinated surface atoms exposed for the active species in comparison with nanoparticles, so they not only have less structure-sensitive inhibiting effect of OH〓 species, benefiting the ORR performance, but also subject less to dissolution, Ostawald ripening, and aggregation in acid condition. Lastly, the modified surface electronic structure of the PtPd alloy resulting from the interactions between Pt and Pd may also promote the electrocatalytic activities. (4)Co,N encapsulated nanocarbon hybrid of carbon nanotubes in situ grown between the graphene-like carbon nanosheets (Co-NCNT/Ng) are fabricated via a one-pot pyrolysis of the mixture of Co precursor, dicyandiamide and glucose. The Co-NCNT/Ng catalysts with a three-dimensional (3D) interconnected framework possess a high specific surface area, hierarchical porous structure and effective doping of Co and N. The optimized Co-NCNT/Ng pyrolyzed at 900 ℃ manifests the highest ORR performance, which also outperforms Ng-900 and Co-NCNT-900. Due to the synergistic utilization of active sites and effective mass transfer, the 3D hybrid delivers comparable ORR catalytic activity to commercial 20 wt% Pt/C catalyst as evidenced by the half-cell potential of 0.825 V, long-term stability as well as strong methanol tolerance in alkaline medium. Notably, the real validations for the Co-NCNT/Ng-900 as the cathode catalyst can be carried out by an assembled primary Zinc-air battery, which has a maximum peak power density of 174.4 mW ㎝⁻², surpassing the Pt/C catalyst. Moreover, the specific capacity is calculated to be 795.0 mAh g⁻¹ at the discharge density of 10 mA ㎝⁻². Most remarkably, the Zinc-air battery catalyzed by Co-NCNT/Ng-900 exhibits excellent dynamic responses in broad discharge current densities ranging from 5 mA ㎝⁻² to 50 mA ㎝⁻². (5)Research on extremely efficient bifunctional electrocatalysts to promote both the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics is of paramount importance for the advanced rechargeable Zinc-air battery. Herein, a cost-effective and scalable strategy is proposed for the synthesis of FeCo alloy nanoparticles embedded in the nitrogen-doped carbon nanotube-grafted nitrogen and sulfur co-doped carbon nanofibers (FeCo-NSCNF@NCNT). These frizzlelike NCNTs possess diameters of ca. 20-40 nm and lengths in the range of several hundred nanometers with quite uniform and dense posture grafted on the nanofiber scaffolds. The newly obtained catalyst with three-dimensional interconnected network architecture demonstrates high ORR and OER catalytic activities as evidenced by the high half-wave potential (0.792 V) for the ORR and a low overpotential (360 mV) for the OER. The potential gap (ΔE) between OER and ORR (ΔE = E〓- E〓) of FeCo-NSCNF@NCNT is 0.80 V, superior than Pt/C + IrO₂ catalyst. The prominent bifunctionality is attributed to the unique structure, hierarchical porous channels together with large amounts of active sites in the as-synthesized FeCo-NSCNF@NCNT hybrid, which strikingly provide fast reaction kinetics and increased catalytic performance. With the novel catalyst employed as the air electrode of an assembled Zinc-air battery, narrow charge-discharge voltage gap and superb cycling stability (over 100 h) at the current density of 10 mA ㎝⁻² can be obtained, signifying the promising application in the next generation of rechargeable metal-air batteries. KEY WORDS: Proton exchange membrane fuel cells; Zinc-air battery; Carbon-based materials; Heteroatom doping; Precious metal catalysts; Transtation metal.