摘要
开发经济高效的析氧反应电催化剂对于推进可充电金属-空气电池和电解水技术的发展至关重要.一般来说,具有完整蜂窝结构的石墨碳基面是电化学惰性的,需要依赖缺陷或者掺杂结构诱导的电荷极化效应来提升催化活性.相比于基面,边缘位点具有特殊的局域电子态,为提升石墨碳电极的本征催化活性开辟了新的思路,然而其结构精准构筑目前仍面临极大挑战.本文以"人字形"多壁碳纳米管(H-MWCNTs)作为研究切入点,利用高温熔盐介质主导的插层剥离和截断效应,实现"边缘-平面位点"结构可控构筑,为实现高效电解水析氧反应(OER)提供了重要的结构基础.通过熔盐辅助热解方法可控制备了具有完全暴露的内外边缘平面的目标催化剂H-MWCNTs-MS,并研究其OER催化性能.在碱性介质中10 mA cm 2电流密度所需过电位仅为236 mV,是目前报道的较好的非金属电催化剂.同时,H-MWCNTs-MS在10,50和100 mA cm 2电流密度下均表现出较好的电化学稳定性.利用原位衰减全反射-表面增强红外吸收光谱(ATR-SEIRAS)技术研究了"边缘-平面位点"在OER过程中的结构重构过程,与理论计算分析的高能"边缘态"结果一致,并确定酮氧官能化位点为真实催化活性中心.理论计算结果表明,氧官能团修饰结构能够显著促进电荷的再分配,增强层间耦合作用,降低关键含氧中间体*OOH的形成能垒,加速OER反应动力学.此外,H-MWCNTs-MS的开放式结构极大程度提高了"边缘-平面位点"的利用率,减小的纳米管壁厚促进了层间电荷迁移,也是增强OER活性的关键要素.综上,精准构筑"边缘-平面位点"为开发高效石墨碳电极开辟了新的思路,通过原位谱学技术揭示边缘位点催化结构重构,能够进一步丰富研究者对于电催化协同效应的科学认识.
Abstract
Endowing metal-free graphitic carbon electrodes with high electrocatalytic reactivity is a field of intense research,but remains elusive.Here,we introduce a prototypical edge-plane-site-specific engineering strategy on"herringbone"multi-walled carbon nanotubes by performing an intercala-tion-exfoliation and truncation process in molten inorganic salts.Controllable synthesis of the target H-MWCNTs-MS with fully exposed edge-plane sites on both the outer surface and inner channels was demonstrated.in-situ infrared spectroscopic study supports the theoretically energetic"edge-state"and identifies the reconstructed ketone/carboxyl-terminated edge sites under oxygen evolution reaction(OER)conditions.These oxygenated edge-plane sites boost charge redistribution and interlayer coupling,which essentially govern the synergistic catalysis,as evidenced by com-bined theoretical,electrokinetic,and H/D isotopic studies.Benefiting from the dense reactive sites and efficient electron tunneling,the H-MWCNTs-MS demonstrated impressive OER activity with an overpotential of 236 mV at a current density of 10 mA cm-2 in alkaline media,outperforming most state-of-the-art metal-free electrocatalysts reported to date.Furthermore,the catalyst displayed no noticeable degradation during 100 h of operation,indicating its potential for practical applications.
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