MSE Seminar: Ying Chen

About this event

Title: A Tale of Two Organic Cathodes and Nonclassical Nucleation Pathways: Magnetic Resonance Insights into Materials Science

Abstract: Organic electrode materials offer a sustainable alternative to inorganic cathodes but typically suffer from low intrinsic electronic conductivity. The material historically reported as bis-tetraaminobenzoquinone (TAQ) exhibits bulk conductivity two orders of magnitude higher than its close analogue tetraaminophenazine-tetraone (TAPT), despite their common precursor and nearly identical short-range structure. This disparity has previously been attributed to distinct molecular skeletons, with TAQ proposed to adopt a piperazine-type linkage and TAPT a pyrazine ring. Here, combining synchrotron X-ray scattering, solid-state 15N and 13C nuclear magnetic resonance (NMR), microcrystal electron diffraction (MicroED), continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopy, we show that “TAQ” has the same pyrazine-based molecular structure as TAPT, with no evidence for piperazine core or keto–enol tautomerization. Their key difference lies in synthesis-dependent degree of crystallinity: “TAQ” exhibits greater long-range structural coherence and a crystallographically resolved intermolecular hydrogen-bonding network, whereas TAPT is more disordered. EPR further shows that the higher structural order in “TAQ” is associated with a strongly delocalized π-spin manifold, while TAPT favors localized or weakly delocalized radicals and stronger local spin coupling. These findings identify degree of crystallinity and hydrogen-bonding order as key structural features associated with radical delocalization and enhanced conductivity in organic electrodes.

Beyond energy-storage materials, NMR also offers unique opportunities to capture intermediates along nonclassical nucleation pathways. Using operando 1H and 13C solution- and solid-state NMR, we observed the transformation of Ca·HCO3 ion pairs into a Ca·HCO3 dense liquid phase (DLP), followed by the decomposition reaction of the DLP to hydrated ACC. In a second example, combined in situ and ex situ solid-state 27Al multiple quantum magic angle spinning (MQMAS) NMR demonstrates that a large, purely six-coordinated aluminum cluster forms directly from amorphous aluminum hydroxide gel and converts to gibbsite via the release of Al-O monomers, whereas tetra-coordinated clusters serve as intermediates that do not transform into the crystalline phase. Together, these studies highlight the power of NMR and EPR to resolve local structure, radical speciation, and transient intermediates, providing molecular-level insight into both functional energy materials and non-classical nucleation pathways.

Bio: Dr. Ying Chen is a Materials Scientist at Pacific Northwest National Laboratory. Her research uses solution- and solid-state nuclear magnetic resonance together with electron paramagnetic resonance to probe molecular structure, dynamics, and radical speciation in emerging materials and connect these microscopic insights to bulk properties. She also applies operando magnetic resonance methods to track nucleation, crystal growth, and chemical transformations in real time.