Beyzanur Erdivan

X-ray photoelectron spectroscopy (XPS) has revealed many possible Li-induced interfacial reactions in solid-state electrolytes (SSEs), but most in situ studies form Li|electrolyte interfaces through non-electrochemical Li deposition, including evaporation, sputtering, or electron-beam-induced deposition. These routes may introduce additional energy that activates reaction pathways not accessed during electrochemical Li plating. Here, we use lab-based operando XPS to directly evaluate oxide solid-state electrolyte stability during electrochemical Li formation. Using this approach, we find sharply different responses for two representative oxide SSEs: NASICON-type Li1+xAlxTi2–x(PO4)3 (LATP) is reduced upon Li plating, forming a Li+/Ti3+-rich mixed-conducting interphase that partially relaxes through coupled ionic–electronic redistribution, whereas garnet-type Li7La3Zr2O12 (LLZO) shows no spectroscopically resolvable Zr or La reduction. This work represents the first direct operando XPS evaluation of SSE stability against electrochemically plated Li metal.

Unveiling interfacial dynamics in solid‐state batteries under operando conditions remains a major challenge in solid‐state battery research, largely due to the limited temporal resolution of conventional analytical techniques. Here, we introduce a laboratory‐based operando x‐ray photoelectron spectroscopy (XPS) methodology employing a snapshot spectral acquisition mode that enables real‐time tracking of interfacial chemistry in solid‐state battery systems. The approach is demonstrated by monitoring electrochemical lithiation occurring in Sb and Cu films deposited on the surface of the Li _6.25 Al _0.25 La ₃ Zr ₂ O ₁₂ solid‐state electrolyte (SSE). Understanding these processes is critical for developing effective SSE/Li interfacial layers that improve the cycling stability of lithium metal anodes and for advancing anode‐free solid‐state battery architectures. When combined with the static in‐situ non‐destructive depth‐profiling capabilities of hard x‐ray photoelectron spectroscopy (HAXPES), this methodology has strong potential to become a key analytical approach for probing buried interfaces in solid‐state batteries under operando conditions.

A precious metal-free bimetallic Fe_xMn_1-x(OH)_y hydroxide catalyst was developed that is capable of catalyzing aerobic C-H oxidation reactions at low temperatures, without the need for an initiator, relying sustainably on molecular oxygen. Through a systematic synthetic effort, we scanned a wide nanoparticle synthesis parameter space to lay out a detailed set of catalyst design principles unraveling how the Fe/Mn cation ratio, NaOH(aq) concentration used in the synthesis, catalyst washing procedures, extent of residual Na⁺ promoters on the catalyst surface, reaction temperature, and catalyst loading influence catalytic C-H activation performance as a function of the electronic, surface chemical, and crystal structure of Fe_xMn_1-x(OH)_y bimetallic hydroxide nanostructures. Our comprehensive XRD, XPS, BET, ICP-MS, ¹H NMR, and XANES structural/product characterization results as well as mechanistic kinetic isotope effect (KIE) studies provided the following valuable insights into the molecular level origins of the catalytic performance of the bimetallic Fe_xMn_1-x(OH)_y hydroxide nanostructures: (i) catalytic reactivity is due to the coexistence and synergistic operation of Fe³⁺ and Mn³⁺ cationic sites (with minor contributions from Fe²⁺ and Mn²⁺ sites) on the catalyst surface, where in the absence of one of these synergistic sites (i.e., in the presence of monometallic hydroxides), catalytic activity almost entirely vanishes, (ii) residual Na⁺ species on the catalyst surface act as efficient electronic promoters by increasing the electron density on the Fe³⁺ and Mn³⁺ cationic sites, which in turn, presumably enhance the electrophilic adsorption of organic reactants and strengthen the interaction between molecular oxygen and the catalyst surface, (iii) in the fluorene oxidation reaction the step dictating the reaction rate likely involved the breaking of a C-H bond (k_H/k_D = 2.4), (iv) reactivity patterns of a variety of alkylarene substrates indicate that the C-H bond cleavage follows a stepwise PT-ET (proton transfer-electron transfer) pathway.