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.