Graphene Nanoplatelets Doped with N at its Edges as Metal-Free Cathodes for Organic Dye-Sensitized Solar Cells
Graphene Nanoplatelets Doped with N at its Edges as Metal-Free Cathodes for Organic Dye-Sensitized Solar Cells
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DOI：
10.1002/adma.201304986
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发表时间：
2014-05-01
影响因子：
29.4
通讯作者：
Baek, Jong-Beom
中科院分区：
文献类型：
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作者：
Ju, Myung Jong;Jeon, In-Yup;Baek, Jong-Beom
然而，Pt CEs对于Co络合物的电化学稳定性差，并且Pt/电解质界面处的电荷转移电阻（RCT）相对较高。[11此外，通过改善DSSC内的其它组分的性能，例如CE的电化学稳定性和CE/电解质界面处的低RCT，DSSC的效率存在进一步改善的空间。[13]与Pt相比，碳基材料可以以低成本以可扩展的数量生产，并且它们在DSSC中具有更好的腐蚀稳定性。因此，炭黑，[14]碳纳米颗粒，[15]碳纳米管，[16，17]和石墨烯纳米片[18-22]已被广泛研究，希望找到有前途的替代品铂基材料。它们的电催化活性对于传统的I-/I 3-氧化还原对来说与Pt不可比较，但是石墨烯基CE在已经报道的Co基介体中优于传统的Pt CE。[11此外，氮掺杂的碳纳米材料由于碳（χ= 2.55）和氮（χ= 3.04）之间的电负性差异引起的高电荷极化而表现出高的电催化性能，导致增强的催化活性和电荷转移性质。[11我们能够证明通过繁琐的湿化学方法制备的氮掺杂的石墨烯纳米片[32]在DSSC中显示出高性能。[11]尽管通过电荷极化富集的催化活性位点对于高效催化剂是极其重要的，但是使用化学气相沉积（CVD）将杂原子（例如氮）结合到石墨框架中限于约4%的最大浓度。[33]我们还设计了一种简便的合成方案，用于制备“NGNPs”，石墨烯纳米片，其中氮掺杂发生在片边缘;石墨在氮气存在下经历简单的机械化学球磨。[26]通过合并我们最近对DSSC [11]和氮掺杂的基本发现的见解，[32]我们开发了一种高性能DSSC，其中新合成的NGNPs作为CE。此外，NGNPs在许多极性溶剂中分散良好，包括N-甲基-2-吡咯烷酮（NMP）和醇，允许生态友好的电喷雾（e-spray）沉积到F掺杂的SnO 2（FTO）/玻璃上。在将NGnPs作为CE引入实际DSSC器件之前，采用循环伏安法（CV）、电化学阻抗谱（EIS）和计时电流法（CA）系统研究了沉积在FTO基底上的NGnPs对Co（bpy）3 2+/3+氧化还原对（bpy= 2，2′-bipyridine）的电催化活性.染料敏化太阳能电池（Dye-sensitized solar cells，DSSC）是20年前发展起来的一种新型太阳能电池，由于其成本低、染料易得、易于制造和高功率转换效率（power conversion efficiency，PCE），被认为是目前硅基太阳能电池的潜在替代品。[1，2]典型的DSSC由透明导电氧化物（TCO）、涂覆有染料的TiO 2、电解质和对电极（CE）组成。CEs在DSSC中的关键作用是将电子从外部电路转移到电解质并催化氧化还原对的还原。高效CE的要求包括1）通过氧化还原对的电荷极化实现高效的还原催化活性，以及2）由于低薄层电阻而具有良好的电荷转移性能。[3-5]为了满足这些要求，迄今为止已知铂...
However, the electrochemical stability of Pt CEs for Co complexes is poor, and charge-transfer resistance (RCT) at the Pt/electrolyte interface is relatively high.[11, 12] Moreover, there is room for further improvement in the efficiency of DSSCs by improving the performance of the other components within a DSSC, such as the electrochemical stability of the CE and the low RCT at the CE/electrolyte interface.[13] In contrast to Pt, carbon-based materials can be produced in scalable quantity at low cost, and they have better corrosion stability in DSSCs. As a result, carbon blacks,[14] carbon nanoparticles,[15] carbon nanotubes,[16, 17] and graphene nanosheets [18–22] have been widely studied in hopes of finding promising alternatives to Pt-based materials. Their electrocatalytic activities are not comparable to Pt for the conventional I−/I 3− redox couple, but graphene-based CEs outperformed the conventional Pt CEs in the Co-based mediators that have been reported.[11, 12, 23–25] Moreover, nitrogen-doped carbon nanomaterials have demonstrated high electrocatalytic performance due to the high charge polarization stemming from the difference in electronegativity between carbon (χ= 2.55) and nitrogen (χ= 3.04), leading to enhanced catalytic activity and charge-transfer properties.[11, 26–34] We were able to demonstrate that nitrogen-doped graphene nanoplatelets that were prepared via a tedious wetchemical process [32] displayed high-performance in DSSCs.[11] Although catalytic active sites enriched by charge polarization are extremely important for efficient catalysts, the incorporation of hetero-atoms such as nitrogen into graphitic frameworks using chemical vapor deposition (CVD) is limited to a maximum concentration of~ 4%.[33] We also devised a facile synthetic protocol for preparing “NGnPs,” graphene nanoplatelets where nitrogen-doping has occurred at the platelet edges; graphite undergoes simple mechanochemical ball-milling in the presence of nitrogen gas.[26] By merging insights from our recent fundamental findings for DSSCs [11] and for nitrogen-doping,[32] we developed a highperformance DSSC with the newly synthesized NGnPs as the CEs. In addition, the NGnPs disperse well in many polar solvents, including N-methyl-2-pyrrolidone (NMP) and alcohols, allowing an ecologically friendly electrospray (e-spray) deposition onto F-doped SnO 2 (FTO)/glass. Prior to the incorporation of NGnPs as CEs in actual DSSC devices, the electrocatalytic activities of the NGnP deposited on FTO substrates for the Co (bpy) 3 2+/3+ redox couple (bpy= 2, 2′-bipyridine) were systematically studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chrono-amperometry (CA). The NGnP/FTOs were then used as the CEs in organic DSSCs in conjunction with the Co (bpy) 3 2+/3+ redox couple, which wasDye-sensitized solar cells (DSSCs), which were developed two decades ago, are considered to be potential alternatives to current silicon-based solar cells because of their low cost, the dye availability, their easy fabrication, and their high power conversion efficiency (PCE).[1, 2] Typical DSSCs are composed of a transparent conducting oxide (TCO), TiO 2 coated with a dye, an electrolyte, and a counter electrode (CE). The key roles of CEs in DSSCs are to transfer electrons from the external circuit to the electrolyte and to catalyze the reduction of the redox couple. The requirements for efficient CEs include 1) efficient reduction catalytic activity by charge polarization for the redox couple and 2) good charge-transfer properties due to low sheet resistance.[3–5] To meet these requirements, platinum is known thus far to …