离子液体/MOF-808复合材料优化质子交换膜燃料电池铂/离聚物界面

doi:10.1016/S1872-2067(25)64662-6

摘要/Abstract

摘要：

作为氢能领域的关键技术之一, 质子交换膜燃料电池(PEMFC)在未来清洁能源体系中占据重要地位, 但其大规模商业化需要大幅降低对铂(Pt)的使用. 近期研究表明, 当前普遍采用的全氟磺酸(PFSA)离聚物电解质的侧链在阴极催化层(CCL)中的Pt催化剂表面会发生强的吸附. 这不仅会毒化催化活性位点, 同时诱导离聚物主链在Pt表面结晶形成致密薄层, 显著提高了界面的局域氧传输阻抗(R_local), 限制了大电流密度下性能的提升, 降低催化剂的利用率. 因此, 优化CCL中Pt/PFSA离聚物界面的结构以改善离聚物分布并减弱Pt表面的磺酸基吸附, 对提升PEMFC在低Pt用量下的性能、推动其商业化至关重要. 为此, 本文发展离子液体(IL)与金属有机框架(MOF)的复合材料作为CCL添加组分, 突破限制低Pt CCL性能提升的瓶颈. 具体而言, 利用1-丁基-3-甲基咪唑硫酸氢盐离子液体(BMImHSO₄)修饰MOF-808, 获得多孔复合材料BMImHSO₄@MOF-808, 显著降低PFSA侧链磺酸根在Pt表面的吸附覆盖度、R_local和质子传导电阻. 通过对IL在MOF中的修饰量以及BMImHSO₄@MOF-808在CCL中的添加量进行优化, 使PEMFC表现出良好的性能, 在氢氧条件下峰值功率密度达到约1.9 W cm^-2, 与常规无添加的CCL相比在氢空条件下将PEMFC功率密度提升约20%.

X射线衍射、红外光谱、热重分析、X射线光电子能谱(XPS)、扫描电镜和高分辨透射电镜测试结果表明, BMImHSO₄通过与MOF-808中未饱和配位的Zr结合而成功插入孔道之中, 且不破坏MOF的框架结构. 进一步结合系统的结构、谱学和电化学技术表征结果表明, BMImHSO₄@MOF-808作为添加组分能从三方面改善Pt/离聚物界面. 首先, 低过电位区的电化学阻抗、电化学活性面积和XPS等测试结果表明, 其分子结构中不饱和的金属中心可以与磺酸根配位, 从而减弱磺酸根在Pt表面的吸附. CO吸附置换和电化学剥离测试结果表明, 磺酸根的吸附率由~13.4%下降至~10.4%. 其次, 通过系统分析不同氧气分压下的单电池极限电流, 发现BMImHSO₄@MOF-808添加使催化层中的R_local降低了约19%. 对比研究发现, 如果添加没有IL修饰的MOF-808, R_local降低得更多, 但质子传导阻抗则会上升. 这可能是由于MOF本身的质子导电率低的缘故, 修饰IL后, 质子传导阻抗则恢复正常. 说明IL修饰可以通过形成氢键网络改善质子传导.

综上, 本文展示的IL修饰MOF复合材料不仅结合了两者的优势, 同时有效克服了各自的局限. 比如, 缓解了MOF对质子传导的抑制作用, 同时又解决了IL因水溶性导致的在催化层流失的问题, 为发展低Pt PEMFC提供了新思路.

关键词: 质子交换膜燃料电池, Pt/离聚物界面, 局域氧传输, MOF-808, 离子液体, 磺酸根吸附

Abstract:

The large-scale commercialization of proton exchange membrane fuel cells (PEMFCs) has been hindered by the high demand of platinum (Pt) in the cathode due to the sluggish kinetics of the oxygen reduction reaction. Reducing the amount of Pt would worsen the problems caused by the adsorption of perfluorinated sulfonic acid (PFSA) ionomers to Pt via the side chains, namely, blocking the active sites of Pt and inducing densely packed layers of fluorocarbon backbones on Pt surface to obstruct local O₂ transport at the Pt/PFSA interfaces. This work aims at optimizing the Pt/ionomer interface to mitigate the sulfonate adsorption and in the meantime to reduce the local O₂ transport resistance (R_local), by using a porous composite of 1-butyl-3-methylimidazolium hydrogen sulfate ionic liquid (IL) modified MOF-808 (BMImHSO₄@MOF-808) as additive in cathodic catalyst layer (CCL). Through detailed physical, spectroscopic and electrochemical characterizations, we demonstrate a three-fold optimization mechanism of Pt/ionomer interface structure by BMImHSO₄@MOF-808: the unsaturated metal sites in MOF-808 effectively inhibit the sulfonate adsorption on Pt through coordination with the sulfonates of PFSA, thereby improving catalyst utilization; the pores in MOF-808 establish efficient transport channels for gaseous oxygen, significantly reducing R_local; the IL modification layers facilitate the formation of continuous proton transport networks, increasing proton conductivity. The incorporation of BMImHSO₄@MOF-808 in a low-Pt CCL (0.1 mg_Pt cm^-2) yields a peak power density of 1.9 W cm^-2 for PEMFC under H₂-O₂ condition, and ca. 20% increase of power density under H₂-air condition as compared with conventional CCL, indicating the prospect of IL-MOF composites as an efficient additive to enhance the performance of PEMFCs.

Key words: Proton exchange membrane fuel cells, Pt/ionomer interface, Local oxygen transport, MOF-808, Ionic liquid, Sulfonate adsorption

严黄丽, 余成文, 张贤明, 唐美华, 陈胜利. 离子液体/MOF-808复合材料优化质子交换膜燃料电池铂/离聚物界面[J]. 催化学报, 2025, 75: 84-94.

Yan Huangli, Yu Chengwen, Zhang Xianming, Tang Meihua, Chen Shengli. Three-fold optimization of Pt/ionomer interface by ionic liquid-modified MOF-808 in cathode of proton exchange membrane fuel cells[J]. Chinese Journal of Catalysis, 2025, 75: 84-94.

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链接本文: https://www.cjcatal.com/CN/10.1016/S1872-2067(25)64662-6

https://www.cjcatal.com/CN/Y2025/V75/I8/84

图/表 7

Scheme 1. The synthesis route of MOF-808, BMImHSO4@MOF-808 and BSO3HMImHSO4@MOF-808.

Fig. 1. XRD patterns (a) and FT-IR (b) and TGA (c) of MOF-808, BSO?HMImHSO4@MOF-808 and BMImHSO4@MOF-808.

Fig. 2. (a) H2-air fuel cell performance of MOF-808 free, MOF-808, BSO3HMImHSO4@MOF-808 and BMImHSO4@MOF-808. The cell temperature, feeding gas pressure, RH are 80 °C, 250 kPaabs, and 100%, respectively; Nyquist plots corresponding to polarisation curves at 0.5 A cm-2 (b) and 3 A cm-2 (c).

Fig. 3. H2-air fuel cell performance for different MEAs: (a) MOF-808 free and BMImHSO4@MOF-808 with different BMImHSO4 loadings and (b) different BMImHSO4@MOF-808 addition amount in CCL. The cell temperature, feeding gas pressure, RH are 80 °C, 250 kPaabs, and 100%, respectively.

Fig. 4. (a) H2-O2 cell performance of MOF-808 free, MOF-808 and BMImHSO4@MOF-808. The temperature, operating pressure, RH are 80 °C, 250 kPaabs, and 100%, respectively. (b) EIS analysis corresponding to polarisation curves at 0.5 A cm-2. CV curves (c) and ECSA (d) of the cells.

Fig. 5. (a) Pt 4f XPS spectra of BMImHSO4@MOF-808-Nafion-Pt/C, MOF-808-Nafion-Pt/C, Nafion-Pt/C and JM Pt/C in the catalyst layer. (b) CO displacement results at 0.45 V. CO stripping curves (c) and the sulfonate group coverage on Pt (in percent) (d) for BMImHSO4@MOF-808-Nafion-Pt/C, MOF-808-Nafion-Pt/C and Nafion-Pt/C.

Fig. 6. (a) Rtotal of MEA with MOF-808 free, MOF-808 and BMImHSO4@MOF-808 plotted versus the absolute gas pressure. RH+ at different humidity: 100% RH (b); 40% RH (c); dry proton accessibility analysis (d).

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