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日益严重的能源和全球变暖问题引发的先进能源设备的新型电极材料的设计与开发研究。直接甲醇燃料电池（DMFC）已经吸引了相当大的兴趣，近年来由于其能量转换效率高，操作和低污染排放的缓解。1–3认为直接甲醇燃料电池的性能是由它的电极材料和离子/电子传递速率的电极和在电极–电解质界面的电催化活性。

其能量转换效率高，操作和低污染排放的缓解

它的电极材料和离子/电子传递速率的电极和在电极–电解质界面的电催化活性

为了提高DMFC性能的一个有效方法是研究具有高活性和稳定性的催化剂。在以前的报告中，一些贵金属如铂，钯，钌和铂基合金已被证明具有高的电催化活性。但利用率低，这些材料的成本高和腐烂的活动限制在商业上的应用。因此，一个新兴的概念，探讨了低成本、高活性的过渡金属氧化物催化剂如氧化镍，镍磷，四氧化三钴和锰。特别是，NiO是最广泛研究的非铂催化剂由于其相对较低的成本和高的活性。但这些金属氧化物的导电率低，阻碍了他们的应用。因此，新型金属氧化物催化剂具有高导电性和高的催化活性，探索在这方面是一个关键的挑战。

NiCo2O4是一种很有前途的二元材料被广泛应用于锂离子电池，电容器，电催化，光电器件和磁性器件。这可能是由于该材料的耐人寻味的优势，如成本低具有，相对丰度和环境友好。更重要的是，据报道，NiCo2O4具有更好的导电性，至少两个数量高于氧化镍和氧化钴的大小。高电子电导率在电极的快速电子转移是有益的。最近，已经有在NiCo2O4在电容器中的应用合成许多报道，但据我们所知，有了这种材料在甲醇氧化中的应用未见报道。在这份报告中，NiCo2O4提出作为一个潜在的高性能催化剂的甲醇氧化。

另一个有趣的策略来提高电池性能的电活性物种的直接合成的离子/电子传递速率对电极加速。在传统的电极的制备过程中，为了避免电活性物质的损失，粘合剂是必要的。但粘合剂的存在将大大降低电化学性能。一方面，粘合剂会阻碍动力学的离子和电子的电极和在电极-电解质界面的运输。另一方面，丰富了粘合剂的活性表面很大一部分阻止电极与电解液接触。为了解决这个问题的一个有效的方法是电活性物质在电极上的直接生长。虽然有在纳米Co3O4电极上原位生长的许多报告，据我们所知，有对NiCo2O4纳米结构的导电性基板的制造很少的报道。考虑到这一点，根据以前的报告中，电沉积和随后的退火工艺用于

NiCo2O4在不锈钢电极直接合成。然后，NiCo2O4 / SS电极可直接作为无粘结剂的电极材料在直接甲醇燃料电池中的应用。

这无粘结剂的电极有几个明显的优点。由于每个活性纳米结构直接连接到电极，电子电阻和离子扩散阻力是不是一个大问题，和电解质可以很容易地渗透到电极材料。在没有粘合剂，几乎所有的电活性的表面暴露，因而能够参与电化学反应，最大限度地利用作为电活性材料。

在这份报告中，NiCo2O4纳米结构是一个由一个浅显的过程涉及的沉积和随后的热处理不锈钢电极直接生长。的无粘结剂NiCo2O4 / SS电极直接用于甲醇氧化，显示高的电催化活性和良好的稳定性。

以上

Direct growth of NiCo2O4 nanostructures on conductive substrates with enhanced electrocatalytic activity and stability for methanol oxidation†

Lei Qian,a Li Gu,a Li Yang,a Hongyan Yuanb and Dan Xiao*ab

In this report, NiCo2O4 nanostructures with different morphologies were directly grown on conductive substrates (stainless steel and ITO) by a facile electrodeposition method in addition to a post-annealing process. The morphology changes on different conductive substrates are discussed in detail. The NiCo2O4 on stainless steel (SS) had a high surface area (119 m2 g 1) and was successfully used in the electrocatalytic oxidation of methanol. The electrocatalytic performance was investigated by cyclic

voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy (EIS) measurements. Impressively, the NiCo2O4 showed much higher electrocatalytic activity, lower overpotential and greater stability compared to that of only NiO or Co3O4 synthesized by the same

method. The higher electrocatalytic activity is due to the high electron conductivity, large surface area of NiCo2O4 and the fast ion/electron transport in the electrode and at the electrolyte–electrode interface.

This is important for further development of high performance non-platinum electrocatalysts for application in direct methanol fuel cells.

Introduction

Ever-worsening energy and global warming issues have triggered significant research efforts in the design and development of novel electrode materials for advanced energy devices. Direct methanol fuel cells (DMFCs) have attracted considerable interest in recent years due to their high energy conversion efficiency, ease of operation and low pollutant emission.1–3 It is accepted that the performance of a DMFC is governed by the electrocatalytic activity of its electrode materials and the ion/electron transport rate in the electrode and at the electrode–electrolyte interface. One effective way to improve the performance of DMFCs is to explore electrocatalysts with high activity and stability. In previous reports, some noble metals such as Pt, Pd, Ru and Pt based alloys have been demonstrated to possess high electrocatalytic activity. But the low utilization, high cost and decaying activity of these materials limit their commercial application. Hence, an emerging new concept is to explore low cost and high activity transitional metal oxide catalysts such as NiO, nickel phosphate, Co3O4 and MnOx. Particularly, NiO and Co3O4 are the most widely investigated non-platinum catalysts because of their relative low cost and high activity. But the low conductivity of these metal oxides hampers their application. Therefore, the exploration of novel metal oxide catalysts exhibiting both high conductivity and high catalytic activity is a key challenge in this field.

NiCo2O4 is a promising binary material which is widely used in Li-ion batteries, capacitors, electrocatalysts, optoelectronic Devices and magnetic devices. This may be due to the intriguing advantages possessed by this material such as low cost, relative abundance and environmental friendliness. More significantly, it has been reported that NiCo2O4 possesses much better

electronic conductivity, at least two orders of

magnitude higher than nickel oxide and cobalt oxide.26,31 The high electronic conductivity is of benefit to the fast electron transfer in an electrode. Recently, there have been many reports on the synthesis of NiCo2O4 and its application in capacitors, but as far as we know, there have been no reports on the application of this material in the oxidation of methanol. In this report, NiCo2O4 is proposed as a potential high performance catalyst for methanol oxidation. Another fascinating strategy to improve the performance of the DMFC is acceleration of the ion/electron transport rate by direct synthesis of electroactive species on the electrode. In traditional electrode preparation processes, binders are necessary in order to avoid the loss of the electroactive species. But the presence of the binder will greatly decrease the electrochemical performance. On one hand, the binder may hinder the kinetics of ion and electron transport in the electrodes and at the electrode-electrolyte interface. On the other hand, a large portion of the electroactive surface of the binder-enriched electrode is blocked from contact with the electrolyte. An efficient method to address this problem is the direct growth of electroactive species on the electrode. Although there are many reports on the in situ growth of Co3O4 nanostructures on electrodes, to the best of our knowledge, there are very few reports on the fabrication of NiCo2O4

nanostructures on conductive substrates. Bearing this in mind, according to the previous report, electrodeposition and a subsequent annealing process were used for the direct synthesis of NiCo2O4 on a SS electrode. The NiCo2O4/SS electrode can then be directly used as a binder free electrode material for application in a DMFC. This binder-free electrode

has several apparent advantages. Since every electroactive nanostructure is directly attached to the electrode, the electronic resistance and ion diffusion resistance are not a big concern, and the electrolyte can easily penetrate into the electrode material. In the absence of binder, almost all electroactive surfaces are exposed, and are thus able to participate in the electrochemical reaction, maximizing their utilization as electroactive materials. In this report, NiCo2O4 nanostructures were directly grown

on a SS electrode by a facile process involving electrodeposition and subsequent heat treatment. The binder-free NiCo2O4/SS electrode was directly used for methanol oxidation, displaying both high electrocatalytic activity and excellent stability.