Cooperative Atomically Dispersed Fe-N and Sn-N Moieties for Durable and More Active Oxygen Electroreduction in Fuel Cells.

One grand challenge for deploying porous carbons with embedded metal-nitrogen-carbon (M-N-C) moieties as platinum group metal (PGM)-free electrocatalysts in proton-exchange membrane fuel cells is their fast degradation and inferior activity. Here, we report the modulation of the local environment at Fe-N sites via the application of atomic Sn-N sites for simultaneously improved durability and activity. We discovered that Sn-N sites not only promote the formation of the more stable D2 FeNC sites but also invoke a unique D3 SnN-FeN site that is characterized by having atomically dispersed bridged Sn-N and Fe-N.

Proton Relay for the Rate Enhancement of Electrochemical Hydrogen Reactions at Heterogeneous Interfaces.

Proton transfer is critically important to many electrocatalytic reactions, and directed proton delivery could open new avenues for the design of electrocatalysts. However, although this approach has been successful in molecular electrocatalysis, proton transfer has not received the same attention in heterogeneous electrocatalyst design. Here, we report that a metal oxide proton relay can be built within heterogeneous electrocatalyst architectures and improves the kinetics of electrochemical hydrogen evolution and oxidation reactions.

Dual functions of epigallocatechin gallate surface-modified Au nanorods@selenium composites for near-infrared-II light-responsive synergistic antibacterial therapy.

Diseases caused by bacterial infections pose ever-increasing threats to human health, making it important to explore alternative antibacterial strategies. Herein, epigallocatechin gallate (EGCG) surface-modified Au nanorods@selenium composites (ASE NPs) were developed for synergistic NIR-II light-responsive antibacterial therapy. antibacterial experiments demonstrated the improved antibacterial effect of ASE NPs against () compared with EGCG alone.

Role of Polysulfide Anions in Solid-Electrolyte Interphase Formation at the Lithium Metal Surface in Li-S Batteries.

Delineating intricate interactions between highly reactive Li-metal electrodes and the diverse constituents of battery electrolytes has been a long-standing scientific challenge in materials design for advanced energy storage devices. Here, we isolated lithium polysulfide anions (LiS) from an electrolyte solution based on their mass-to-charge ratio and deposited them on Li-metal electrodes under clean vacuum conditions using ion soft landing (ISL), a highly controlled interface preparation technique. The molecular level precision in the construction of these model interfaces with ISL, coupled with X-ray photoelectron spectroscopy and theoretical calculations, allowed us to obtain unprecedented insight into the parasitic reactions of well-defined polysulfides on Li-metal electrodes.

Continuous Fly-Through High-Temperature Synthesis of Nanocatalysts.

The conventional thermal treatment systems typically feature low ramping/cooling rates, which lead to steep thermal gradients that generate inefficient, nonuniform reaction conditions and result in nanoparticle aggregation. Herein, we demonstrate a continuous fly-through material synthesis approach using a novel high-temperature reactor design based on the emerging thermal-shock technology. By facing two sheets of carbon paper with a small distance apart (1-3 mm), uniform and ultrahigh temperatures can be reached up to 3200 K within 50 ms by simply applying a voltage of 15 V.

Reversible ketone hydrogenation and dehydrogenation for aqueous organic redox flow batteries.

Aqueous redox flow batteries with organic active materials offer an environmentally benign, tunable, and safe route to large-scale energy storage. Development has been limited to a small palette of organics that are aqueous soluble and tend to display the necessary redox reversibility within the water stability window. We show how molecular engineering of fluorenone enables the alcohol electro-oxidation needed for reversible ketone hydrogenation and dehydrogenation at room temperature without the use of a catalyst.

Mapping Localized Peroxyl Radical Generation on a PEM Fuel Cell Catalyst Using Integrated Scanning Electrochemical Cell Microspectroscopy.

Understanding molecular-level transformations resulting from electrochemical reactions is important in designing efficient and reliable energy technologies. In this work, a novel integrated scanning electrochemical cell microspectroscopy (iSECCMS) capability is developed by combining a high spatial resolution electrochemical scanning probe with fluorescence spectroscopy. Using 6-carboxyfluorescein as a fluorescent probe, the iSECCMS platform is employed to measure the effect of the detrimental generation of reactive oxygen species (ROS) formed at the active sites of oxygen reduction reaction (ORR) catalysts.

Low-PGM and PGM-Free Catalysts for Proton Exchange Membrane Fuel Cells: Stability Challenges and Material Solutions.

Fuel cells as an attractive clean energy technology have recently regained popularity in academia, government, and industry. In a mainstream proton exchange membrane (PEM) fuel cell, platinum-group-metal (PGM)-based catalysts account for ≈50% of the projected total cost for large-scale production. To lower the cost, two materials-based strategies have been pursued: 1) to decrease PGM catalyst usage (so-called low-PGM catalysts), and 2) to develop alternative PGM-free catalysts.

LiNiO/Ni Heterostructure with Strong Basic Lattice Oxygen Enables Electrocatalytic Hydrogen Evolution with Pt-like Activity.

The low-cost hydrogen production from water electrolysis is crucial to the deployment of sustainable hydrogen economy but is currently constrained by the lack of active and robust electrocatalysts from earth-abundant materials. We describe here an unconventional heterostructure composed of strongly coupled Ni-deficient LiNiO nanoclusters and polycrystalline Ni nanocrystals and its exceptional activities toward the hydrogen evolution reaction (HER) in aqueous electrolytes. The presence of lattice oxygen species with strong Brønsted basicity is a significant feature in such heterostructure, which spontaneously split water molecules for accelerated Volmer H-OH dissociation in neutral and alkaline HER.

A Highly Reversible Zn Anode with Intrinsically Safe Organic Electrolyte for Long-Cycle-Life Batteries.

Dendrite and interfacial reactions have affected zinc (Zn) metal anodes for rechargeable batteries many years. Here, these obstacles are bypassed via adopting an intrinsically safe trimethyl phosphate (TMP)-based electrolyte to build a stable Zn anode. Along with cycling, pristine Zn foil is gradually converted to a graphene-analogous deposit via TMP surfactant and a Zn phosphate molecular template.

Joint Charge Storage for High-Rate Aqueous Zinc-Manganese Dioxide Batteries.

Aqueous rechargeable zinc-manganese dioxide batteries show great promise for large-scale energy storage due to their use of environmentally friendly, abundant, and rechargeable Zn metal anodes and MnO cathodes. In the literature various intercalation and conversion reaction mechanisms in MnO have been reported, but it is not clear how these mechanisms can be simultaneously manipulated to improve the charge storage and transport properties. A systematical study to understand the charge storage mechanisms in a layered δ-MnO cathode is reported.

PGM-Free Cathode Catalysts for PEM Fuel Cells: A Mini-Review on Stability Challenges.

In recent years, significant progress has been achieved in the development of platinum group metal-free (PGM-free) oxygen reduction reaction (ORR) catalysts for proton exchange membrane (PEM) fuel cells. At the same time the limited durability of these catalysts remains a great challenge that needs to be addressed. This mini-review summarizes the recent progress in understanding the main causes of instability of PGM-free ORR catalysts in acidic environments, focusing on transition metal/nitrogen codoped systems (M-N-C catalysts, M: Fe, Co, Mn), particularly MN moiety active sites.

Iron-Free Cathode Catalysts for Proton-Exchange-Membrane Fuel Cells: Cobalt Catalysts and the Peroxide Mitigation Approach.

High-performance and inexpensive platinum-group-metal (PGM)-free catalysts for the oxygen reduction reaction (ORR) in challenging acidic media are crucial for proton-exchange-membrane fuel cells (PEMFCs). Catalysts based on Fe and N codoped carbon (Fe-N-C) have demonstrated promising activity and stability. However, a serious concern is the Fenton reactions between Fe and H O generating active free radicals, which likely cause degradation of the catalysts, organic ionomers within electrodes, and polymer membranes used in PEMFCs.

Carbon-Based Metal-Free ORR Electrocatalysts for Fuel Cells: Past, Present, and Future.

Replacing precious platinum with earth-abundant materials for the oxygen reduction reaction (ORR) in fuel cells has been the objective worldwide for several decades. In the last 10 years, the fastest-growing branch in this area has been carbon-based metal-free ORR electrocatalysts. Great progress has been made in promoting the performance and understanding the underlying fundamentals.

Minimizing Polysulfide Shuttle Effect in Lithium-Ion Sulfur Batteries by Anode Surface Passivation.

Lithium-ion sulfur batteries use nonlithium materials as the anode for extended cycle life. However, polysulfide shuttle reactions still occur on the nonmetal anodes (such as graphite and Si), and result in undesirable low Coulombic efficiency. In this work, we used AlO layers coated by atomic layer deposition (ALD) technique to suppress the shuttle reactions.

Nitrogen-Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells.

Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt-free and Fe-free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). Herein, a high-performance nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks (MOFs) through a one-step thermal activation.

Water-Lubricated Intercalation in V O ·nH O for High-Capacity and High-Rate Aqueous Rechargeable Zinc Batteries.

Low-cost, environment-friendly aqueous Zn batteries have great potential for large-scale energy storage, but the intercalation of zinc ions in the cathode materials is challenging and complex. Herein, the critical role of structural H O on Zn intercalation into bilayer V O ·nH O is demonstrated. The results suggest that the H O-solvated Zn possesses largely reduced effective charge and thus reduced electrostatic interactions with the V O framework, effectively promoting its diffusion.

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation.

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). Here, we report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates.

Improving Lithium-Sulfur Battery Performance under Lean Electrolyte through Nanoscale Confinement in Soft Swellable Gels.

Li-S batteries have been extensively studied using rigid carbon as the host for sulfur encapsulation, but improving the properties with a reduced electrolyte amount remains a significant challenge. This is critical for achieving high energy density. Here, we developed a soft PEOLiTFSI polymer swellable gel as a nanoscale reservoir to trap the polysulfides under lean electrolyte conditions.

Formation of Reversible Solid Electrolyte Interface on Graphite Surface from Concentrated Electrolytes.

Li-ion batteries (LIB) have been successfully commercialized after the identification of ethylene-carbonate (EC)-containing electrolyte that can form a stable solid electrolyte interphase (SEI) on carbon anode surface to passivate further side reactions but still enable the transportation of the Li cation. These electrolytes are still utilized, with only minor changes, after three decades. However, the long-term cycling of LIB leads to continuous consumption of electrolyte and growth of SEI layer on the electrode surface, which limits the battery's life and performance.

Ammonium Additives to Dissolve Lithium Sulfide through Hydrogen Binding for High-Energy Lithium-Sulfur Batteries.

In rechargeable Li-S batteries, the uncontrollable passivation of electrodes by highly insulating LiS limits sulfur utilization, increases polarization, and decreases cycling stability. Dissolving LiS in organic electrolyte is a facile solution to maintain the active reaction interface between electrolyte and sulfur cathode, and thus address the above issues. Herein, ammonium salts are demonstrated as effective additives to promote the dissolution of LiS to 1.

Role of Manganese Deposition on Graphite in the Capacity Fading of Lithium Ion Batteries.

Lithium ion batteries utilizing manganese-based cathodes have received considerable interest in recent years for their lower cost and more favorable environmental friendliness relative to their cobalt counterparts. However, Li ion batteries using these cathodes combined with graphite anodes suffer from severe capacity fading at high operating temperatures. In this paper, we report on how the dissolution of manganese impacts the capacity fading within the Li ion batteries.

Atomistic Conversion Reaction Mechanism of WO3 in Secondary Ion Batteries of Li, Na, and Ca.

Intercalation and conversion are two fundamental chemical processes for battery materials in response to ion insertion. The interplay between these two chemical processes has never been directly seen and understood at atomic scale. Here, using in situ HRTEM, we captured the atomistic conversion reaction processes during Li, Na, Ca insertion into a WO3 single crystal model electrode.

Interface Promoted Reversible Mg Insertion in Nanostructured Tin-Antimony Alloys.

An interface promoted approach is developed for guiding the design of stable and high capacity materials for Mg batteries using SnSb alloys as model materials. Experimental and theoretical studies reveal that the SnSb alloy has exceptionally high reversible capacity (420 mA h g(-1)), excellent rate capability, and good cyclic stability for hosting Mg ions due to the stabilization/promotion effects of the interfaces between the multicomponent phases generated during repeated magnesiation-demagnesiation.