Yong Lak Joo

Electrochemical CO2 reduction (CO2RR) offers a promising strategy to convert CO2 into high-value chemicals and fuels. However, probing the mechanism of dynamic catalyst reconstruction remains a longstanding challenge, which calls for operando time-resolved and quantitative spectroscopic methods. Here, we employed operando high-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) to monitor real-time structural evolution of bimetallic FeCu single-atom catalysts (SACs) on nitrogen-doped carbon (FeCu–N–C) as a model single-atom catalyst for the CO2RR. FeCu–N–C exhibits a 2-fold increase in Faradaic efficiency for CO formation and an order-of-magnitude enhancement in the CO partial current density at the same applied potential, when compared to monometallic Fe SAC (Fe–N–C). To elucidate the origin of this performance enhancement, operando HERFD-XAS was used to directly probe the dynamic evolution of metal oxidation states and coordination environments under operating conditions, revealing a dynamic reconstruction of isolated Fe and Cu single atoms into catalytically active metallic clusters. In contrast, the Fe SAC control remains atomically dispersed over the course of CO2RR. The atomic-scale structural insights are further corroborated by aberration-corrected scanning transmission electron microscopy. These findings shed light on the synergistic role of Cu in modulating the dynamic reconstruction of single-atom Fe sites and provide fundamental insights for the rational design of high-performance single-atom catalysts for CO2 electroreduction.

Ammonia (NH₃) synthesis via electrochemical nitric oxide reduction (NORR) has emerged as a promising alternative to the Haber-Bosch process, which requires high temperatures and pressures. However, NORR still faces critical challenges, including side reactions, limited mass transfer, and high overpotential requirements. Transition metals have been widely employed to address these issues owing to their favorable NO adsorption properties; however, they suffer from intermediate overbinding and require high overpotentials to achieve meaningful catalytic activity. To overcome these limitations, we introduce a noble-metal alloying strategy that combines the high electron-transfer kinetics of noble metals with the tunable NO adsorption properties of transition metals, thereby synergistically enhancing catalytic activity for selective NH₃ production. We designed Ru-Cu alloy nanoparticles supported on nitrogen-doped carbon nanorods (Ru_xCu_100-x@NCNR), and the optimized Ru₅Cu₉₅@NCNR catalyst exhibited an ammonia yield of 32.66 ± 4.38 μmol cm^-2 h^-1 and a Faradaic efficiency of 94 ± 1.25% (FE_NH3) at -0.2 V vs RHE, notably lower overpotential than that reported for conventional NORR catalysts, demonstrating energy-efficient ammonia production. Long-term stability tests confirmed the sustained catalytic performance, and its practical applicability was further validated through integration into a Zn-NO battery system, highlighting its potential for next-generation energy conversion devices. Mechanistic investigations revealed that precise control of Ru content induces structural modulation of the RuCu alloy, thereby regulating the strength of NO adsorption and facilitating efficient protonation, ultimately governing high NH₃ selectivity.

Scalable synthesis of electrochemically inert nanofilms with precise spatial and compositional control enables rational design of solid-electrolyte interphases (SEIs) in rechargeable batteries. Ion and molecule transport through SEIs largely determines the cycling stability of high-energy rechargeable metal and metal-ion batteries, where electroreduction during charging often occurs beyond electrolyte stability limits. We report nanometer-thick gradient zwitterionic polymer (G-ZWP) interphases, synthesized via a scalable solvent-free method, to regulate transport and electroreduction kinetics at Li-metal anodes, achieving stable cycling. The synthesis combines initiated chemical vapor deposition and diffusion-limited vapor derivatization to form a zwitterionic top layer with high ionic conductivity and an inner covalently cross-linked layer blocking solvent access while remaining stable at reducing potentials. Cu substrates with G-ZWP interphases show >2000-hour cycling at 1 milliampere per square centimeter [6 milliampere hours per square centimeter (mA·hour/cm ² )]. The interphases also enable long-term cycling of Li batteries (N/P = 0 to 2.5) and Li–dry-air batteries (10 mA·hour/cm ² ) and stabilize Na/Zn electrodeposition.

The batteries that power untethered underwater vehicles (UUVs) serve a single purpose: to provide energy to electronics and motors; the more energy required, the bigger the robot must be to accommodate space for more energy storage. By choosing batteries composed primarily of liquid media [e.g., redox flow batteries (RFBs)], the increased weight can be better distributed for improved capacity with reduced inertial moment. Here, we formed an RFB into the shape of a jellyfish, using two redox chemistries and architectures: (i) a secondary ZnBr ₂ battery and (ii) a hybrid primary/secondary ZnI ₂ battery. A UUV was able to be powered solely by RFBs with increased volumetric ( Q ~ 11 ampere-hours per liter) and areal (108 milliampere-hours per square centimeter) energy density, resulting in a long operational lifetime ( T ~ 1.5 hours) for UUVs composed of primarily electrochemically energy-dense liquid (~90% of the robot’s weight).

While chemically doped graphene has shown great promise, the lack of cost-effective manufacturing has hindered its use. This study utilizes a facile fabrication approach for modality-tunable N-doped graphene via thermal annealing of aqueous-phase-exfoliated few-layered graphene from a Taylor-Couette reactor. This method demonstrates a high level of N-doping (27 atom % N) and offers modality tunability of the C-N bond without foregoing scalability and green chemistry principles. The resulting N-doped graphene, with varying N content and doping modality, is utilized in the lithium-sulfur battery electrolyte to address low ionic conductivity, lithium polysulfide (LiPS) shuttling, and Li anode instability. The study reveals that higher N content and pyridinic N modality graphene in the electrolyte positively influence battery performance. The results are 2-fold: higher overall N content improves capacity retention (73%) after 225 cycles at 0.2 C, and pyridinic-type nitrogen demonstrates the best performance at high C rates, exhibiting a 4-fold capacity increase relative to the reference cell at 2 C. Further, the computational study validates the adsorption affinity of LiPS to pyridinic nitrogen and improved Li⁺ mobility on the graphene backbone observed experimentally. This first experimental study on the impact of N-dopant concentration and modality on electrochemical performance provokes insights into tailoring N functionalization to achieve superior electrochemical performance.

Solid-state electrolytes (SSEs) are challenged by complex interfacial chemistry and poor ion transport through the interfaces they form with battery electrodes. Here, we investigate a class of SSE composed of micrometer-sized lithium oxide (Li ₂ O) particles dispersed in a polymerizable 1,3-dioxolane (DOL) liquid. Ring-opening polymerization (ROP) of the DOL by Lewis acid salts inside a battery cell produces polymer-inorganic hybrid electrolytes with gradient properties on both the particle and battery cell length scales. These electrolytes sustain stable charge-discharge behavior in Li||NCM811 and anode-free Cu||NCM811 electrochemical cells. On the particle length scale, Li ₂ O retards ROP, facilitating efficient ion transport in a fluid-like region near the particle surface. On battery cell length scales, gravity-assisted settling creates physical and electrochemical gradients in the hybrid electrolytes. By means of electrochemical and spectroscopic analyses, we find that Li ₂ O particles participate in a reversible redox reaction that increases the effective CE in anode-free cells to values approaching 100%, enhancing battery cycle life.

In this study, a fused deposition modeling 3D printer is modified into a motionless printer, which has the potential to print patterns in a noiseless manner possibly with improved resolution and in less delay time by eliminating the movement of nozzle or collector. In this motionless 3D printer, both nozzle and collector are fixed, whereas the extruded polymer melt is driven by high-voltage switching points on the collector. By this approach, simple 3D patterns such as multilayer circles, squares, and walls have been printed using two polymer melts with different rheological properties, high-temperature polylactic acid and acrylonitrile butadiene styrene. Furthermore, a discretized, nonisothermal bead and spring model is developed to probe printing patterns. The effect of parameters, such as number of conducting points, switching time, voltage and material properties on the accuracy of the printed simple 3D patterns, are thoroughly studied, and we demonstrated that various fiber collection patterns obtained from the experiments are favorably compared with the simulation results.

Aqueous Zn batteries have recently emerged as promising candidates for large-scale energy storage, driven by the need for a safe and cost-effective technology with sufficient energy density and readily accessible electrode materials. However, the energy density and cycle life of Zn batteries have been limited by inherent chemical, morphological, and mechanical instabilities at the electrode-electrolyte interface where uncontrolled reactions occur. To suppress the uncontrolled reactions, we designed a crystalline polymer interphase for both electrodes, which simultaneously promotes electrode reversibility via fast and selective Zn transport through the adaptive formation of ion channels. The interphase comprises an ultrathin layer of crystalline poly(1H,1H,2H,2H-perfluorodecyl acrylate), synthesized and applied as a conformal coating in a single step using initiated chemical vapor deposition (iCVD). Crystallinity is optimized to improve interphase stability and Zn-ion transport. The optimized interphase enables a cycle life of 9500 for Zn symmetric cells and over 11,000 for Zn-MnO₂ full-cell batteries. We further demonstrate the generalizability of this interphase design using Cu and Li as examples, improving their stability and achieving reversible cycling in both. The iCVD method and molecular design unlock the potential of highly reversible and cost-effective aqueous batteries using earth-abundant Zn anode materials, pointing to grid-scale energy storage.

A comprehensive understanding of the physicochemical properties of organic-inorganic hybrids is essential for their solid-state lighting applications. Therefore, a single crystal of [NH2(CH3)(2)](2)CdBr4 was grown; the crystal structure was monoclinic, and the phase transition temperatures for the four phases IV, III, II, and I were 383 K (T-C1), 417 K (T-C2), and 427 K (TC3). Furthermore, the chemical shifts caused by the local field around H-1, C-13, N-14, and Cd-113 changed continuously with temperature, especially near TC1, indicating that the local environment changes with temperature. Owing to the large change in Cd-113 chemical shifts, the coordination geometry of Br around Cd in the CdBr4 tetrahedra changes near T-C1. Therefore, it is proposed that Br plays a significant role in the N-H center dot center dot center dot Br hydrogen bond. Finally, the spin-lattice relaxation time T-1 rho, representing the energy transfer around the H-1 and C-13 atoms of the cation, changed significantly with temperature. The activation energies obtained from the T-1 rho results were two times larger at high temperatures than at low temperatures. This study provides an understanding of the fundamental properties of organic-inorganic hybrid compounds to broaden their applications.

Rechargeable metal–air batteries operated in ambient air fail as a result of complex anode surface reactions. Interphases composed of metallic In protect Li anodes, enabling Li–air batteries to operate in ambient air.