Cross-Investigation on Copper Nitroprusside: Combining XRD and XAS for In-Depth Structural Insights

Angelo Mullaliu,Marco Giorgetti,Jasper Rikkert Plaisier,Giuliana Aquilanti

doi:10.3390/condmat6030027

Angelo Mullaliu, Marco Giorgetti + Show 2 more

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https://doi.org/10.3390/condmat6030027

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Abstract

The emerging energy demand and need to develop sustainable energy storage systems have drawn extensive attention to fundamental and applied research. Anion redox processes were proposed in cathodic materials in addition to traditional transition metal redox to boost the specific capacity and the electrochemical performance. Alternatively, copper nitroprusside (CuNP) features an electroactive nitrosyl ligand alongside the two structural metals (Fe, Cu), representing an alternative to anion redox in layered oxides. Here, a deep structural investigation is carried out on CuNP by complementing the long-range order sensitivity of X-ray diffraction (XRD) and the local atomic probe of X-ray absorption (XAS). Two different CuNP materials are studied, the hydrated and dehydrated forms. A new phase for hydrated CuNP not reported in the literature is solved, and Rietveld refined. The XAS spectra of the two materials at the Cu and Fe K-edges show a similar yet different atomic environment. The extended XAS spectra (EXAFS) analysis is accomplished by considering three- and four-body terms due to the high collinearity of the atomic chains and gives accurate insight into the first-, second-, and third-shell interatomic distances. Both materials are mounted in Li-ion and Na-ion cells to explore the link between structure and electrochemical performance. As revealed by the charge/discharge cycles, the cyclability in Na-ion cells is negatively affected by interstitial water. The similarity in the local environment and the electrochemical differences suggest a long-range structural dependence on the electrochemical performance.

Highlights

In this growing age of clean energy demand and efficient use of resources to circumvent the use of traditional fossil fuel technologies, batteries of greater capacity, storage capability, and efficiency are becoming increasingly indispensable [1]
By considering the reference structure reported by Gómez et al [15], a Pawley refinement was performed on the X-ray diffraction (XRD) pattern of the hydrated compound by using the Amm2 orthorhombic space group
By taking a closer look at some reflections, it is discernable that the adopted reference model has a higher symmetry than the actual one

Summary

Introduction

In this growing age of clean energy demand and efficient use of resources to circumvent the use of traditional fossil fuel technologies, batteries of greater capacity, storage capability, and efficiency are becoming increasingly indispensable [1]. There is currently widespread attention being paid to them at both the fundamental and applied levels, as demonstrated by the indispensable use of LIB in electric vehicles nowadays [3]. The reason for this resides in the low reduction potential, as Li has −3.045 V vs SHE Li is the third lightest element and has one of the smallest ionic radii of any single charged ion These factors allow Li-based batteries to have high gravimetric and volumetric capacity and power density [3,4]. Sodium (SIB) and potassium ion (KIB) battery technology has recently been paid increasing attention inside the scientific community, representing a valid alternative to Li-ions, with such ions being

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