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The manipulation of ions in complex oxide materials can be used to mimic brain-like plasticity through changes to the resistivity of a neuromorphic device. Advances in the design of more energy efficient devices require improved understanding of how ions migrate within a material and across its interface. We investigate the exchange of oxygen and hydrogen in a model SrCoOx epitaxial film—a material that transitions between a ferromagnetic metal and antiferromagnetic insulator depending on the oxygen concentration. Changes to the film during ionic liquid gating were measured by in situ synchrotron x-ray techniques as a function of time and gate voltage, examining the reversibility of the oxide over one complete gating cycle. We find that the out-of-plane lattice constant and oxygen vacancy concentration of SrCoOx are largely reversible although changes were observed in the ordered vacancy structure. Our results provide much needed insight into electrolyte-gated phase behavior in the transition metal oxides. 

ArticleCathodic Corrosion-Induced Structural Evolution of CuNi Electrocatalysts for Enhanced CO2 ReductionWenjin Sun 1,†, Bokki Min 2,†, Maoyu Wang 3, Xue Han 4, Qiang Gao 1, Sooyeon Hwang 5, Hua Zhou 3, and Huiyuan Zhu 1,2,*1 Department of Chemistry, University of Virginia, Charlottesville, VA 22904, USA2 Department of Chemical Engineering, University of Virginia, Charlottesville, VA 22904, USA3 Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439, USA4 Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA5 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA* Correspondence: kkx8js@virginia.com† These authors contributed equally to this work.Received: 22 October 2024; Revised: 25 November 2024; Accepted: 27 November 2024; Published: 4 December 2024 Abstract: The electrochemical CO2 reduction reaction (CO2RR) has attracted significant attention as a promising strategy for storing intermittent energy in chemical bonds while sustainably producing value-added chemicals and fuels. Copper-based bimetallic catalysts are particularly appealing for CO2RR due to their unique ability to generate multi-carbon products. While substantial effort has been devoted to developing new catalysts, the evolution of bimetallic systems under operational conditions remains underexplored. In this work, we synthesized a series of CuxNi1−x nanoparticles and investigated their structural evolution during CO2RR. Due to the higher oxophilicity of Ni compared to Cu, the particles tend to become Ni-enriched at the surface upon air exposure, promoting the competing hydrogen evolution reaction (HER). At negative activation potentials, cathodic corrosion has been observed in CuxNi1−x nanoparticles, leading to the significant Ni loss and the formation of irregularly shaped Cu nanoparticles with increased defects. This structural evolution, driven by cathodic corrosion, shifts the electrolysis from HER toward CO2 reduction, significantly enhancing the Faradaic efficiency of multi-carbon products (C2+). 

Abstract Mixed‐conducting perovskites are workhorse electrochemically active materials, but typical high‐temperature processing compromises their catalytic activity and chemo‐mechanical integrity. Low‐temperature pulsed laser deposition of amorphous films plus mild thermal annealing is an emerging route to form homogeneous mixed conductors with exceptional catalytic activity, but little is known about the evolution of the oxide‐ion transport and transference numbers during crystallization. Here the coupled evolution of ionic and electronic transport behavior and structure in room‐temperature‐grown amorphous (La,Sr)(Ga,Fe)O_3‐xfilms as they crystallize is explored.In situ ac‐impedance spectroscopy with and without blocking electrodes, simultaneous capturingsynchrotron‐grazing‐incidence X‐ray diffraction, dc polarization, transmission electron microscopy, and molecular dynamics simulations are combined to evaluate isothermal and non‐isothermal crystallization effects and the role of grain boundaries on transference numbers. Ionic conductivity increases by ≈2 orders of magnitude during crystallization, with even larger increases in electronic conductivity. Consequently, as crystallinity increases, LSGF transitions from a predominantly ionic conductor to a predominantly electronic conductor. The roles of evolving lattice structural order, microstructure, and defect chemistry are examined. Grain boundaries appear relatively nonblocking electronically but significantly blocking ionically. The results demonstrate that ionic transference numbers can be tailored over a wide range by tuning crystallinity and microstructure without having to change the cation composition. 

Crossover designs play an increasingly important role in precision medicine. We show the search of an optimal crossover design can be formulated as a convex optimization problem and convex optimization tools, such as CVX, can be directly used to search for an optimal crossover design.  We first demonstrate how to transform crossover design problems into convex optimization problems and show CVX can effortlessly find optimal crossover designs that coincide with a few theoretical crossover optimal designs in the literature. The proposed approach is especially useful when it becomes problematic to construct optimal designs analytically for complicated models. We then apply CVX to find crossover designs for models with auto-correlated error structures or when the information matrices may be singular and analytical answers are unavailable. We also construct N-of-1 trials frequently used in precision medicine to estimate treatment effects on the individuals or to estimate average treatment effects, including finding dual-objective optimal crossover designs.