Development of High-Throughput Methods for Sodium-Ion Battery Cathodes.

Combinatorial synthesis of Li-ion batteries has proven extremely powerful in screening complex compositional spaces for next-generation materials. To date, no Na-ion counterpart exists wherein Na-ion cathodes can be synthesized in such a way to be comparable to that obtained in bulk synthesis. Herein, we develop a synthesis route wherein hundreds of milligram-scale powder samples can be made in a total time of 3 days. We focus on materials in the Na-Fe-Mn-O pseudoternary system of high immediate interest. Using a sol-gel method, developed herein, yields both phase-pure combinatorial samples of Na2/3Fe1/2Mn1/2O2 and NaFe1/2Mn1/2O2, consistent with previous reports on bulk samples of interest commercially. By contrast, the synthesis route used for Li-ion cathodes (namely coprecipitations) does not yield phase pure materials, suggesting that the sol-gel method is more effective in mixing the Na, Fe, and Mn than coprecipitation. This has important consequences for all attempts to make these materials, even in bulk. Finally, we demonstrate that these milligram-scale powder samples can be tested electrochemically in a combinatorial cell. The resulting cyclic voltammograms are in excellent agreement with those found on bulk samples in the literature. This demonstrates that the methodology developed here will be effective in characterizing the hundreds of samples needed to understand the complex ternary systems of interest and that such results will scale-up well to the gram and kilogram scale.

Simultaneous Electrochemical and Emission Monitoring of Electrogenerated Chemiluminescence through Instrument Hyphenation.

One of the long-standing challenges to performing electrogenerated chemiluminescence (ECL) research is the need for dedicated instrumentation or highly customized cells to achieve reproducibility. This manuscript describes an approach to designing ECL systems through the hyphenation of existing laboratory instruments, which provide innate time correlation of electrochemical and emission data. This design methodology lowers the entry barrier required to obtaining reproducible ECL measurements and provides flexibility in the scope of applications. Uniquely, the simplicity of this system's experimental interface, a spectrochemical quartz cuvette, readily enables collaboration with finite element modeling that simulates ECL occurring in the cuvette-based cell. This combination of empirical and simulation data allowed for the investigation of the intertwined kinetics behind the coreactant ECL mechanism of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+) and tripropylamine (TPA). The complexity of the system measurable via the hyphenation methodology was further scaled though the addition of tris[2-(4,6-difluorophenyl)pyridinato-C2, N] iridium(III) (Ir(dFppy)3) and the observation of real time multiplexing.

Combined Spectroelectrochemical and Simulated Insights into the Electrogenerated Chemiluminescence Coreactant Mechanism.

Electrogenerated chemiluminescence (ECL) based sensors have the intrinsic advantage of having zero theoretical background signal, derived from the electrochemical initiation of the luminescence process. Since the limit of detection (LOD) for sensors is defined as three times the noise of the background over the sensitivity of the system, further improvement to an ECL based detection limit is tied to improving sensitivity. Enhancing ECL sensitivity can be achieved through optimizing the mechanistic or kinetic performance of the reagents. While the mechanism for many luminophore-coreactant pairs have been established, the kinetics for the competing homogeneous reactions responsible for photon emission have not been directly resolved. This is due to the difficulty in experimentally probing and isolating a single homogeneous reaction while multiple simultaneous heterogeneous and homogeneous reactions are occurring. Combining the techniques of spectroelectrochemistry and finite element modeling, we monitor the homogeneous reactions for the coreactant pair, tris(2,2'-bipyridine)ruthenium(II) (Ru(BPY)32+) and tripropylamine (TPA). Corresponding trends found in the experimental absorbance and theoretical concentration profiles demonstrated that the reaction between Ru(BPY)33+ and TPA• intermediates proceeds significantly faster than the other available pathways. The identification of the oxidized intermediates as the dominant electron transfer pathway implies that the screening of luminophore and coreactant pairs that increase the stability of these kinetically labile intermediates would increase ECL sensitivity and ultimately performance.

Assembly and dichroism of a four-component halogen-bonded metal-organic cocrystal salt solvate involving dicyanoaurate(I) acceptors.

We describe the use of dicyanoaurate ions as linear ditopic metal-organic acceptors for the halogen bond-driven assembly of a dichroic metal-organic cocrystal based on azobenzene chromophores. Structural analysis by single crystal X-ray diffraction revealed that the material is a four-component solid, consisting of anticipated anionic metal-organic halogen-bonded chains based on dicyanoaurate ions, as well as complex potassium-based cations and discrete molecules of the crown ether 15-crown-5. Importantly, the structural analysis revealed the parallel alignment of the halogen-bonded chains required for dichroic behaviour, confirming that crystal engineering principles developed for the design of halogen-bonded dichroic organic cocrystals are also applicable to metal-based structures. In the broader context of crystal engineering, the structure of the herein reported dichroic material is additionally interesting as the presence of an ion pair, a neutral azobenzene and a molecule of a room-temperature liquid make it an example of a solid that simultaneously conforms to definitions of a salt, a cocrystal, and a solvate.