BCN Graphene as Efficient Metal-Free Electrocatalyst for the Oxygen Reduction Reaction
BCN Graphene as Efficient Metal-Free Electrocatalyst for the Oxygen Reduction Reaction
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DOI：
10.1002/anie.201109257
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Dai, Liming
中科院分区：
文献类型：
--
作者：
Wang, Shuangyin;Zhang, Lipeng;Dai, Liming
阴极氧还原反应（ORR）是燃料电池和金属-空气电池中的重要过程。[1-3]尽管Pt基电催化剂由于其相对低的过电位和高电流密度而通常用于商业燃料电池中，但它们仍然遭受严重的中间耐受性、阳极交叉、缓慢的动力学和在电化学环境中的差的稳定性。这一点，加上铂的高成本及其有限的自然保护区，促使人们广泛寻找替代的低成本和高性能的ORR电催化剂。在这种情况下，碳基无金属ORR电催化剂由于其低成本、高电催化活性和选择性以及优异的耐久性而引起了极大的兴趣。[4-9]特别感兴趣的是，我们以前已经制备了垂直排列的氮掺杂碳纳米管（VA-NCNT）作为ORR电催化剂，它是免费的阳极交叉和CO中毒，并显示出三倍更高的催化活性和更好的耐久性比商业Pt/C催化剂。[4]量子力学计算[4]表明，VA-NCNT对ORR的增强的催化活性可归因于氮物质的电子接受能力，其在CNT表面上产生净正电荷以增强氧吸附并容易从阳极吸引电子以促进ORR。在氮掺杂的碳纳米管电极中揭示这种新的ORR机制是重要的，因为相同的原理可以应用于开发用于燃料电池应用甚至超越燃料电池的各种其他无金属的高效ORR催化剂。实际上，最近在开发无金属ORR电催化剂方面的密集研究努力已经产生了大量种类的基于碳的无金属ORR电催化剂，包括杂原子（N、B或P）掺杂的碳纳米管、石墨烯和石墨。[4-14]最近，我们已经成功地合成了N和B共掺杂的垂直排列的碳纳米管（VA-BCN），并且相对于掺杂有N或B的CNT，仅由于N和B共掺杂产生的协同效应，证明了对ORR的显著改善的电催化活性。[15]然而，大多数报道的碳基ORR电催化剂（特别是杂原子掺杂的纳米管和石墨烯）是通过化学气相沉积（CVD）工艺生产的，该工艺涉及基于真空的精细和仔细的制造，这对于大规模生产来说通常太繁琐和太昂贵。因此，如本研究所示，开发一种简便的方法将BCN石墨烯作为低成本和有效的ORR电催化剂是非常重要的。溶液剥离的氧化石墨（GO）[16]的最近可用性允许通过GO的常规物理化学处理来大规模生产石墨烯和衍生物。在此，我们已经开发了一种简单的方法，通过在硼酸和氨的存在下简单地对GO进行热退火，将具有可调B/N共掺杂水平的无金属BCN石墨烯作为有效的ORR电催化剂。所得BCN石墨烯显示出具有上级商业Pt/C电催化剂（C2-20，20%铂在Vulcan XC-72 R上; E-TEK）的电催化活性。第一性原理计算解释了BCN石墨烯的高催化能力。因此，这种新开发的方法可以提供简单但有效和通用的方法，以低成本大规模生产BCN石墨烯，作为燃料电池和其他应用的高效无金属ORR电催化剂。图1显示了三种不同BCN石墨烯样品的XPS测量光谱。
The cathodic oxygen reduction reaction (ORR) is an important process in fuel cells and metal–air batteries.[1–3] Although Pt-based electrocatalysts have been commonly used in commercial fuel cells owing to their relatively low overpotential and high current density, they still suffer from serious intermediate tolerance, anode crossover, sluggish kinetics, and poor stability in an electrochemical environment. This, together with the high cost of Pt and its limited nature reserves, has prompted the extensive search for alternative low-cost and high-performance ORR electrocatalysts. In this context, carbon-based metal-free ORR electrocatalysts have generated a great deal of interest owing to their low-cost, high electrocatalytic activity and selectivity, and excellent durability.[4–9] Of particular interest, we have previously prepared vertically aligned nitrogendoped carbon nanotubes (VA-NCNTs) as ORR electrocatalysts, which are free from anode crossover and CO poisoning and show a threefold higher catalytic activity and better durability than the commercial Pt/C catalyst.[4] Quantum mechanics calculations [4] indicate that the enhanced catalytic activity of VA-NCNTs toward ORR can be attributed to the electron-accepting ability of the nitrogen species, which creates net positive charges on the CNT surface to enhance oxygen adsorption and to readily attract electrons from the anode for facilitating the ORR. Uncovering this new ORR mechanism in nitrogen-doped carbon nanotube electrodes is significant as the same principle could be applied to the development of various other metal-free efficient ORR catalysts for fuel-cell applications and even beyond fuel cells. Indeed, recent intensive research efforts in developing metal-free ORR electrocatalysts have led to a large variety of carbon-based metal-free ORR electrocatalysts, including heteroatom (N, B, or P)-doped carbon nanotubes, graphene, and graphite.[4–14] More recently, we have successfully synthesized vertically aligned carbon nanotubes co-doped with N and B (VA-BCN) and demonstrated a significantly improved electrocatalytic activity toward the ORR, with respect to CNTs doped with either N or B, only due to a synergetic effect arising from the N and B co-doping.[15] However, most of the reported carbon-based ORR electrocatalysts (particularly, heteroatom-doped nanotubes and graphene) were produced by chemical vapor-deposition (CVD) processes involving vacuum-based elaborate and careful fabrication, which are often too tedious and too expensive for mass production. As demonstrated in this study, therefore, it is of great importance to develop a facile approach to BCN graphene as low-cost and efficient ORR electrocatalysts. The recent availability of solution-exfoliated graphite oxide (GO)[16] allows the mass production of graphene and derivatives by conventional physicochemical treatments of GO. Herein, we have developed a facile approach to metalfree BCN graphene of tunable B/N co-doping levels as efficient ORR electrocatalysts simply by thermal annealing GO in the presence of boric acid and ammonia. The resultant BCN graphene was shown to have superior electrocatalytic activities to the commercial Pt/C electrocatalyst (C2-20, 20% platinum on Vulcan XC-72R; E-TEK). First-principles calculations were performed to explain the high catalytic capability of the BCN graphene. This newly developed method can thus provide simple but efficient and versatile approaches to low-cost mass production of BCN graphene as efficient metal-free ORR electrocatalysts for fuel cells and other applications.Figure1 shows XPS survey spectra for three BCN graphene samples of different …