Exploring the chemical and structural change of copper porphyrins upon charging by means of synchrotron X-ray absorption spectroscopy

Abstract In response to the growing demand for battery materials, researchers explore alternative resources with a focus on sustainability. Among these, organic electrode materials—including porphyrins—have emerged as promising candidates due to their advantageous properties, such as rapid charging capabilities and high energy densities. However, despite their potential, the precise charging mechanism of these alternatives remains elusive. To address this gap, our study delved into copper porphyrins, with a primary focus on [5,15-bis(ethynyl)-10,20-diphenylporphinato] copper(II) (CuDEPP). Employing synchrotron X-ray absorption spectroscopy in operando mode, we probed the evolution in chemical and electronic structure of Cu in CuDEPP. Our findings unequivocally demonstrate the participation of copper as a redox center during reversible charge storage, shedding light on its superior electrochemical performance. Furthermore, a combined approach involving extended X-ray absorption fine structure (EXAFS) studies and theoretical calculations provided deeper insights into the observed structural distortion during the charge storage process. Notably, our results support the hypothesis that redox processes, specifically those involving the aromatic porphyrin ring, drive the electrochemical activity of CuDEPP. In summary, our investigation offers important insights into the charging mechanism of copper porphyrins—an essential step toward advancing sustainable organic materials for batteries.摘要 针对电池材料日益增长的需求，研究人员正聚焦可持续性方向探索替代资源。其中，有机电极材料——包括卟啉（porphyrins）——因具备快速充电能力、高能量密度等优良特性，已成为颇具前景的候选材料。尽管这类材料拥有应用潜力，但其精确的充电机制仍尚不明确。 为填补这一研究空白，本研究以铜卟啉为对象，重点探讨[5,15-双(乙炔基)-10,20-二苯基卟啉合]铜(II)（CuDEPP）。本研究采用原位同步辐射X射线吸收光谱技术，对CuDEPP中铜元素的化学与电子结构演化过程进行了探究。研究结果明确证实，铜在可逆储电过程中作为氧化还原中心参与反应，阐明了其优异的电化学性能来源。 此外，通过结合扩展X射线吸收精细结构（extended X-ray absorption fine structure, EXAFS）实验与理论计算的联合分析方法，我们对储电过程中观测到的结构畸变现象获得了更深入的认知。值得注意的是，本研究结果验证了如下假说：氧化还原过程——尤其是涉及芳香族卟啉环的过程——主导了CuDEPP的电化学活性。 综上，本研究对铜卟啉的充电机制提供了重要见解，这是推动可持续有机电池材料发展的关键一步。