Flash heating process for efficient meat preservation.

Maintaining food safety and quality is critical for public health and food security. Conventional food preservation methods, such as pasteurization and dehydration, often change the overall organoleptic quality of the food products. Herein, we demonstrate a method that affects only a thin surface layer of the food, using beef as a model. In this method, Joule heating is generated by applying high electric power to a carbon substrate in <1 s, which causes a transient increase of the substrate temperature to > ~2000 K. The beef surface in direct contact with the heating substrate is subjected to ultra-high temperature flash heating, leading to the formation of a microbe-inactivated, dehydrated layer of ~100 µm in thickness. Aerobic mesophilic bacteria, Enterobacteriaceae, yeast and mold on the treated samples are inactivated to a level below the detection limit and remained low during room temperature storage of 5 days. Meanwhile, the product quality, including visual appearance, texture, and nutrient level of the beef, remains mostly unchanged. In contrast, microorganisms grow rapidly on the untreated control samples, along with a rapid deterioration of the meat quality. This method might serve as a promising preservation technology for securing food safety and quality.

Tailoring Local Chemical Ordering via Elemental Tuning in High-Entropy Alloys.

Due to the large multi-elemental space desired for property screening and optimization, high-entropy alloys (HEAs) hold greater potential over conventional alloys for a range of applications, such as structural materials, energy conversion, and catalysis. However, the relationship between the HEA composition and its local structural/elemental configuration is not well understood, particularly in noble-metal-based HEA nanomaterials, hindering the design and development of nano-HEAs in energy conversion and catalysis applications. Herein, we determined precise atomic-level structural and elemental arrangements in model HEAs composed of RhPtPdFeCo and RuPtPdFeCo to unveil their local characteristics. Notably, by changing just one constituent element in the HEA (Rh to Ru), we found dramatic changes in the elemental arrangement from complete random mixing to a local single elemental ordering feature. Additionally, we demonstrate that the local ordering in RuPtPdFeCo can be further controlled by varying the Ru concentration, allowing us to toggle between local Ru clustering and distinct heterostructures in multicomponent systems. Overall, our study presents a practical approach for manipulating local atomic structures and elemental arrangements in noble-metal-based HEA systems, which could provide in-depth knowledge to mechanistically understand the functionality of noble-metal-based HEA nanomaterials in practical applications.

A solution-processed radiative cooling glass.

Passive daytime radiative cooling materials could reduce the energy needed for building cooling up to 60% by reflecting sunlight and emitting long-wave infrared (LWIR) radiation into the cold Universe (~3 kelvin). However, developing passive cooling structures that are both practical to manufacture and apply while also displaying long-term environmental stability is challenging. We developed a randomized photonic composite consisting of a microporous glass framework that features selective LWIR emission along with relatively high solar reflectance and aluminum oxide particles that strongly scatter sunlight and prevent densification of the porous structure during manufacturing. This microporous glass coating enables a temperature drop of ~3.5° and 4°C even under high-humidity conditions (up to 80%) during midday and nighttime, respectively. This radiative "cooling glass" coating maintains high solar reflectance even when exposed to harsh conditions, including water, ultraviolet radiation, soiling, and high temperatures.

Stability of high-entropy alloys under electrocatalytic conditions.

High-entropy alloys are claimed to possess superior stability due to thermodynamic contributions. However, this statement mostly lies on a hypothetical basis. In this study, we use on-line inductively coupled plasma mass spectrometer to investigate the dissolution of five representative electrocatalysts in acidic and alkaline media and a wide potential window targeting the most important applications. To address both model and applied systems, we synthesized thin films and carbon-supported nanoparticles ranging from an elemental (Pt) sample to binary (PtRu), ternary (PtRuIr), quaternary (PtRuIrRh), and quinary (PtRuIrRhPd) alloy samples. For certain metals in the high-entropy alloy under alkaline conditions, lower dissolution was observed. Still, the improvement was not striking and can be rather explained by the lowered concentration of elements in the multinary alloys instead of the synergistic effects of thermodynamics. We postulate that this is because of dissolution kinetic effects, which are always present under electrocatalytic conditions, overcompensating thermodynamic contributions.

Highly Selective Electrochemical Nitrate to Ammonia Conversion by Dispersed Ru in a Multielement Alloy Catalyst.

Electrochemical reduction of nitrate to ammonia (NH3) converts an environmental pollutant to a critical nutrient. However, current electrochemical nitrate reduction operations based on monometallic and bimetallic catalysts are limited in NH3 selectivity and catalyst stability, especially in acidic environments. Meanwhile, catalysts with dispersed active sites generally exhibit a higher atomic utilization and distinct activity. Herein, we report a multielement alloy nanoparticle catalyst with dispersed Ru (Ru-MEA) with other synergistic components (Cu, Pd, Pt). Density functional theory elucidated the synergy effect of Ru-MEA than Ru, where a better reactivity (NH3 partial current density of -50.8 mA cm-2) and high NH3 faradaic efficiency (93.5%) is achieved in industrially relevant acidic wastewater. In addition, the Ru-MEA catalyst showed good stability (e.g., 19.0% decay in FENH3 in three hours). This work provides a potential systematic and efficient catalyst discovery process that integrates a data-guided catalyst design and novel catalyst synthesis for a range of applications.

Depolymerization of plastics by means of electrified spatiotemporal heating.

Depolymerization is a promising strategy for recycling waste plastic into constituent monomers for subsequent repolymerization1. However, many commodity plastics cannot be selectively depolymerized using conventional thermochemical approaches, as it is difficult to control the reaction progress and pathway. Although catalysts can improve the selectivity, they are susceptible to performance degradation2. Here we present a catalyst-free, far-from-equilibrium thermochemical depolymerization method that can generate monomers from commodity plastics (polypropylene (PP) and poly(ethylene terephthalate) (PET)) by means of pyrolysis. This selective depolymerization process is realized by two features: (1) a spatial temperature gradient and (2) a temporal heating profile. The spatial temperature gradient is achieved using a bilayer structure of porous carbon felt, in which the top electrically heated layer generates and conducts heat down to the underlying reactor layer and plastic. The resulting temperature gradient promotes continuous melting, wicking, vaporization and reaction of the plastic as it encounters the increasing temperature traversing the bilayer, enabling a high degree of depolymerization. Meanwhile, pulsing the electrical current through the top heater layer generates a temporal heating profile that features periodic high peak temperatures (for example, about 600 °C) to enable depolymerization, yet the transient heating duration (for example, 0.11 s) can suppress unwanted side reactions. Using this approach, we depolymerized PP and PET to their monomers with yields of about 36% and about 43%, respectively. Overall, this electrified spatiotemporal heating (STH) approach potentially offers a solution to the global plastic waste problem.

Rapid Synthesis of High-Entropy Oxide Microparticles.

High-entropy nanoparticles have received notable attention due to their tunable properties and broad material space. However, these nanoparticles are not suitable for certain applications (e.g., battery electrodes), where their microparticle (submicron to micron) counterparts are more preferred. Conventional methods used for synthesizing high-entropy nanoparticles often involve various ultrafast shock processes. To increase the size thereby achieving high-entropy microparticles, longer reaction time (e.g., heating duration) is usually used, which may also lead to undesired particle overgrowth or even densified microstructures. In this work, an approach based on Joule heating for synthesizing high-entropy oxide (HEO) microparticles with uniform elemental distribution is reported. In particular, two key synthesis conditions are identified to achieve high-quality HEO microparticles: 1) the precursors need to be loosely packed to avoid densification; 2) the heating time needs to be accurately controlled to tens of seconds instead of using milliseconds (thermal shock) that leads to nanoparticles or longer heating duration that forms bulk structures. The utility of the synthesized HEO microparticles for a range of applications, including high-performance Li-ion battery anode and water oxidation catalyst. This study opens up a new door toward synthesizing high-entropy microparticles with high quality and broad material space.

Interface Engineering Between Multi-Elemental Alloy Nanoparticles and a Carbon Support Toward Stable Catalysts.

Multi-elemental alloy (MEA) nanoparticles have recently received notable attention owing to their high activity and superior phase stability. Previous syntheses of MEA nanoparticles mainly used carbon as the support, owing to its high surface area, good electrical conductivity, and tunable defective sites. However, the interfacial stability issue, such as nanoparticle agglomeration, remains outstanding due to poor interfacial binding between MEA and carbon. Such a problem often causes performance decay when MEA nanoparticles are used as catalysts, hindering their practical applications. Herein, an interface engineering strategy is developed to synthesize MEA-oxide-carbon hierarchical catalysts, where the oxide on carbon helps disperse and stabilize the MEA nanoparticles toward superior thermal and electrochemical stability. Using several MEA compositions (PdRuRh, PtPdIrRuRh, and PdRuRhFeCoNi) and oxides (TiO2 and Cr2 O3 ) as model systems, it is shown that adding the oxide renders superior interfacial stability and therefore excellent catalytic performance. Excellent thermal stability is demonstrated under transmission electron microscopy with in situ heating up to 1023 K, as well as via long-term cycling (>370 hours) of a Li-O2 battery as a harsh electrochemical condition to challenge the catalyst stability. This work offers a new route toward constructing efficient and stable catalysts for various applications.

Tailoring the Local Environment of Platinum in Single-Atom Pt1 /CeO2 Catalysts for Robust Low-Temperature CO Oxidation.

A single-atom Pt1 /CeO2 catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over-stabilization of Pt2+ in a highly symmetric square-planar Pt1 O4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt2+ by thermal-shock (TS) synthesis leads to a highly active and thermally stable Pt1 /CeO2 catalyst. Ultrafast shockwaves (>1200 °C) in an inert atmosphere induced surface reconstruction of CeO2 to generate Pt single atoms in an asymmetric Pt1 O4 configuration. Owing to this unique coordination, Pt1 δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low-temperature performance. CO oxidation reactivity on the Pt1 /CeO2 _TS catalyst was retained under oxidizing conditions.

Stamping Flexible Li Alloy Anodes.

Li metal holds great promise to be the ultimate anode choice owing to its high specific capacity and low redox potential. However, processing Li metal into thin-film anode with high electrochemical performance and good safety to match commercial cathodes remains challenging. Herein, a new method is reported to prepare ultrathin, flexible, and high-performance Li-Sn alloy anodes with various shapes on a number of substrates by directly stamping a molten metal solution. The printed anode is as thin as 15 µm, corresponding to an areal capacity of ≈3 mAh cm-2 that matches most commercial cathode materials. The incorporation of Sn provides the nucleation center for Li, thereby mitigating Li dendrites as well as decreasing the overpotential during Li stripping/plating (e.g., <10 mV at 0.25 mA cm-2 ). As a proof-of-concept, a flexible Li-ion battery using the ultrathin Li-Sn alloy anode and a commercial NMC cathode demonstrates good electrochemical performance and reliable cell operation even after repetitive deformation. The approach can be extended to other metal/alloy anodes such as Na, K, and Mg. This study opens a new door toward the future development of high-performance ultrathin alloy-based anodes for next-generation batteries.

Direct observation of the formation and stabilization of metallic nanoparticles on carbon supports.

Direct formation of ultra-small nanoparticles on carbon supports by rapid high temperature synthesis method offers new opportunities for scalable nanomanufacturing and the synthesis of stable multi-elemental nanoparticles. However, the underlying mechanisms affecting the dispersion and stability of nanoparticles on the supports during high temperature processing remain enigmatic. In this work, we report the observation of metallic nanoparticles formation and stabilization on carbon supports through in situ Joule heating method. We find that the formation of metallic nanoparticles is associated with the simultaneous phase transition of amorphous carbon to a highly defective turbostratic graphite (T-graphite). Molecular dynamic (MD) simulations suggest that the defective T-graphite provide numerous nucleation sites for the nanoparticles to form. Furthermore, the nanoparticles partially intercalate and take root on edge planes, leading to high binding energy on support. This interaction between nanoparticles and T-graphite substrate strengthens the anchoring and provides excellent thermal stability to the nanoparticles. These findings provide mechanistic understanding of rapid high temperature synthesis of metal nanoparticles on carbon supports and the origin of their stability.

Overcoming immiscibility toward bimetallic catalyst library.

Bimetallics are emerging as important materials that often exhibit distinct chemical properties from monometallics. However, there is limited access to homogeneously alloyed bimetallics because of the thermodynamic immiscibility of the constituent elements. Overcoming the inherent immiscibility in bimetallic systems would create a bimetallic library with unique properties. Here, we present a nonequilibrium synthesis strategy to address the immiscibility challenge in bimetallics. As a proof of concept, we synthesize a broad range of homogeneously alloyed Cu-based bimetallic nanoparticles regardless of the thermodynamic immiscibility. The nonequilibrated bimetallic nanoparticles are further investigated as electrocatalysts for carbon monoxide reduction at commercially relevant current densities (>100 mA cm-2), in which Cu0.9Ni0.1 shows the highest multicarbon product Faradaic efficiency of ~76% with a current density of ~93 mA cm-2. The ability to overcome thermodynamic immiscibility in multimetallic synthesis offers freedom to design and synthesize new functional nanomaterials with desired chemical compositions and catalytic properties.

Computationally aided, entropy-driven synthesis of highly efficient and durable multi-elemental alloy catalysts.

Multi-elemental alloy nanoparticles (MEA-NPs) hold great promise for catalyst discovery in a virtually unlimited compositional space. However, rational and controllable synthesize of these intrinsically complex structures remains a challenge. Here, we report the computationally aided, entropy-driven design and synthesis of highly efficient and durable catalyst MEA-NPs. The computational strategy includes prescreening of millions of compositions, prediction of alloy formation by density functional theory calculations, and examination of structural stability by a hybrid Monte Carlo and molecular dynamics method. Selected compositions can be efficiently and rapidly synthesized at high temperature (e.g., 1500 K, 0.5 s) with excellent thermal stability. We applied these MEA-NPs for catalytic NH3 decomposition and observed outstanding performance due to the synergistic effect of multi-elemental mixing, their small size, and the alloy phase. We anticipate that the computationally aided rational design and rapid synthesis of MEA-NPs are broadly applicable for various catalytic reactions and will accelerate material discovery.

High-throughput, combinatorial synthesis of multimetallic nanoclusters.

Multimetallic nanoclusters (MMNCs) offer unique and tailorable surface chemistries that hold great potential for numerous catalytic applications. The efficient exploration of this vast chemical space necessitates an accelerated discovery pipeline that supersedes traditional "trial-and-error" experimentation while guaranteeing uniform microstructures despite compositional complexity. Herein, we report the high-throughput synthesis of an extensive series of ultrafine and homogeneous alloy MMNCs, achieved by 1) a flexible compositional design by formulation in the precursor solution phase and 2) the ultrafast synthesis of alloy MMNCs using thermal shock heating (i.e., ∼1,650 K, ∼500 ms). This approach is remarkably facile and easily accessible compared to conventional vapor-phase deposition, and the particle size and structural uniformity enable comparative studies across compositionally different MMNCs. Rapid electrochemical screening is demonstrated by using a scanning droplet cell, enabling us to discover two promising electrocatalysts, which we subsequently validated using a rotating disk setup. This demonstrated high-throughput material discovery pipeline presents a paradigm for facile and accelerated exploration of MMNCs for a broad range of applications.

General, Vertical, Three-Dimensional Printing of Two-Dimensional Materials with Multiscale Alignment.

Two-dimensional (2D) materials (e.g., boron nitride (BN), graphene, and MoS2) have great potential in emerging energy, environmental, and electronics applications. Assembly of 2D materials into vertically aligned structures is highly desirable (e.g., low tortuosity for rapid ion transport in fast charging-discharging batteries, guiding thermal transport for efficient thermal management), yet extremely challenging due to the energetically unfavorable in processing. Herein, we reported a general three-dimensional (3D) printing method to fabricate vertically aligned 2D materials in multiscale, using BN nanosheet as the proof-of-concept. The 3D-printed macroscale rods are composed of vertically aligned BN nanosheets at the nanoscale. The formation of the hierarchical aligned structure is enabled by the optimized ink that holds a significant shear-thinning behavior and an ultrahigh storage modulus, as identified at a narrow region in the printability diagram. The resulting vertically aligned multiscale structure with 2D nanosheets demonstrated an outstanding through-plane thermal conductivity, up to 5.65 W m-1 K-1, significantly higher than the value of conventional BN based structures where the sheets are horizontally aligned. The vertical 3D printing of 2D BN nanosheets can be expanded to other 2D materials in constructing hierarchically aligned structures for a range of emerging technologies such as batteries, membranes, and structural materials.

Highly efficient decomposition of ammonia using high-entropy alloy catalysts.

Ammonia represents a promising liquid fuel for hydrogen storage, but its large-scale application is limited by the need for precious metal ruthenium (Ru) as catalyst. Here we report on highly efficient ammonia decomposition using novel high-entropy alloy (HEA) catalysts made of earth abundant elements. Quinary CoMoFeNiCu nanoparticles are synthesized in a single solid-solution phase with robust control over the Co/Mo atomic ratio, including those ratios considered to be immiscible according to the Co-Mo bimetallic phase diagram. These HEA nanoparticles demonstrate substantially enhanced catalytic activity and stability for ammonia decomposition, with improvement factors achieving >20 versus Ru catalysts. Catalytic activity of HEA nanoparticles is robustly tunable by varying the Co/Mo ratio, allowing for the optimization of surface property to maximize the reactivity under different reaction conditions. Our work highlights the great potential of HEAs for catalyzing chemical transformation and energy conversion reactions.

High temperature shockwave stabilized single atoms.

The stability of single-atom catalysts is critical for their practical applications. Although a high temperature can promote the bond formation between metal atoms and the substrate with an enhanced stability, it often causes atom agglomeration and is incompatible with many temperature-sensitive substrates. Here, we report using controllable high-temperature shockwaves to synthesize and stabilize single atoms at very high temperatures (1,500-2,000 K), achieved by a periodic on-off heating that features a short on state (55 ms) and a ten-times longer off state. The high temperature provides the activation energy for atom dispersion by forming thermodynamically favourable metal-defect bonds and the off-state critically ensures the overall stability, especially for the substrate. The resultant high-temperature single atoms exhibit a superior thermal stability as durable catalysts. The reported shockwave method is facile, ultrafast and universal (for example, Pt, Ru and Co single atoms, and carbon, C3N4 and TiO2 substrates), which opens a general route for single-atom manufacturing that is conventionally challenging.

Ultrafast, Controllable Synthesis of Sub-Nano Metallic Clusters through Defect Engineering.

Supported metallic nanoclusters (NCs, < 2 nm) are of great interests in various catalytic reactions with enhanced activities and selectivities, yet it is still challenging to efficiently and controllably synthesize ultrasmall NCs with a high-dispersal density. Here we report the in situ synthesis of surfactant-free, ultrasmall, and uniform NCs via a rapid thermal shock on defective substrates. This is achieved by using high-temperature synthesis with extremely fast kinetics while limiting the synthesis time down to milliseconds (e.g., ∼1800 K for 55 ms) to avoid aggregation. Through defect engineering and optimized loading, the particle size can be robustly tuned from >50 nm nanoparticles to <1 nm uniform NCs with a high-dispersal density. We demonstrate that the ultrasmall NCs exhibit drastically improved activities for catalytic CO oxidation as compared to their nanoparticulated counterparts. In addition, the reported method shows generality in synthesizing most metallic NCs (e.g., Pt, Ru, Ir, Ni) in an extremely facile and efficient manner. The ultrafast and controllable synthesis of uniform, high-density, and size-controllable NCs paves the way for the utilization and nanomanufacturing of NCs for a range of catalytic reactions.

Fly-through synthesis of nanoparticles on textile and paper substrates.

The fast and efficient synthesis of nanoparticles on flexible and lightweight substrates is increasingly critical for various medical and wearable applications. However, conventional high temperature (high-T) processes for nanoparticle synthesis are intrinsically incompatible with temperature-sensitive substrates, including textiles and paper (i.e. low-T substrates). In this work, we report a non-contact, 'fly-through' method to synthesize nanoparticles on low-T substrates by rapid radiative heating under short timescales. As a demonstration, textile substrates loaded with platinum (Pt) salt precursor are rapidly heated and quenched as they move across a 2000 K heating source at a continuous production speed of 0.5 cm s-1. The rapid radiative heating method induces the thermal decomposition of various precursor salts and nanoparticle formation, while the short duration ensures negligible change to the respective low-T substrate along with greatly improved production efficiency. The reported method can be generally applied to the synthesis of metal nanoparticles (e.g. gold and ruthenium) on various low-T substrates (e.g. paper). The non-contact and continuous 'fly-through' synthesis offers a robust and efficient way to synthesize supported nanoparticles on flexible and lightweight substrates. It is also promising for ultrafast and roll-to-roll manufacturing to enable viable applications.