Showing papers on "Amorphous solid published in 2022"

Crystalline‐Amorphous Interfaces Coupling of CoSe2/CoP with Optimized d‐Band Center and Boosted Electrocatalytic Hydrogen Evolution

Abstract: Amorphous and heterojunction materials have been widely used in the field of electrocatalytic hydrogen evolution due to their unique physicochemical properties. However, the current used individual strategy still has limited effects. Hence efficient tailoring tactics with synergistic effect are highly desired. Herein, the authors have realized the deep optimization of catalytic activity by a constructing crystalline–amorphous CoSe2/CoP heterojunction. Benefiting from the strong electronic coupling at the interfaces, the d‐band center of the material moves further down compared to its crystalline–crystalline counterpart, optimizing the valence state and the H adsorption of Co and lowering the kinetic barrier of hydrogen evolution reaction (HER). The heterojunction shows an overpotential of 65 mV to drive a current density of 10 mA cm−2 in the acidic medium. Besides, it also shows competitive properties in both neutral and basic media. This work provides inspiration for optimizing the catalytic activity through combining a crystalline and amorphous heterojunction, which can be implemented for other transition metal compound electrocatalysts.

Amorphization engineered VSe2-x nanosheets with abundant Se-vacancies for enhanced N2 electroreduction

Abstract: Electrochemical N2 fixation through nitrogen reduction reaction (NRR) is a promising way for sustainable NH3 synthesis, while exploring high-performing NRR catalysts lies at the heart of attaining high-efficiency NRR electrocatalysis....

Recent Development and Future Perspectives of Amorphous Transition Metal‐Based Electrocatalysts for Oxygen Evolution Reaction

Abstract: Oxygen evolution reaction (OER), as a relevant half reaction for water splitting to address the energy crisis, has captured a great deal of attention. However, this technology has always been impeded by the lack of a highly efficient and stable electrocatalyst. Amorphous materials, which possess long‐range disorder and only short‐range order over a few atoms, are often superior to their crystalline counterparts in electrocatalysis owing to their more active sites, broader chemical composition range, and more structural flexibility. This review first introduces some assessment criteria for the OER and then presents theoretical modeling of the OER mechanisms and the state‐of‐the‐art amorphous transition metal‐based OER electrocatalysts, involving oxides, hydroxides, sulfides, phosphides, borides, and their composites, as well as their practical applications in the OER. Finally, recent development, existing challenges, and future perspectives for amorphous transition metal‐based OER electrocatalysts are discussed. This paper offers valuable guidance in designing highly efficient and stable amorphous OER electrocatalysts for future energy applications.

Metal–Organic Network-Forming Glasses

Abstract: The crystal-liquid-glass phase transition of coordination polymers (CPs) and metal-organic frameworks (MOFs) offers attractive opportunities as a new class of amorphous materials. Unlike conventional glasses, coordination chemistry allows the utilization of rational design concepts to fine-tune the desired properties. Although the glassy state has been rare in CPs/MOFs, it exhibits diverse advantages complementary to their crystalline counterparts, including improved mass transport, optical properties, mechanical properties, and the ability to form grain-boundary-free monoliths. This Review discusses the current achievements in improving the understanding of anomalous phase transitions in CPs/MOFs. We elaborate on the criteria for classifying CP/MOF glasses and comprehensively discuss the three common strategies employed to obtain a glassy state. We include all CP/MOF glass research progress since its inception, discuss the current challenges, and express our perspective on future research directions.

Achievement of giant cryogenic refrigerant capacity in quinary rare-earths based high-entropy amorphous alloy

Abstract: Magnetic refrigeration (MR) by utilizing the magnetocaloric (MC) effect is recognized as one of the most potential promising solid state environmentally friendly and high efficiency alternative method to the well-used state-of-the-art gas compression cooling technique. In this work, a systematic investigation of quinary equi-atomic rare-earths (RE) based Er20Ho20Gd20Ni20Co20 high-entropy (HE) amorphous alloy in terms of the microstructure, magnetic and magnetocaloric (MC) properties have been reported. The Er20Ho20Gd20Ni20Co20 exhibits promising glass forming ability with an undercooled liquid region of 72 K. Excellent cryogenic MC performances can be found in wide temperature from ∼25 and ∼75 K, close to H2 and N2 liquefaction, respectively. Apart from the largest magnetic entropy change (-ΔSM) reaches 17.84 J/(kg K) with 0-7 T magnetic field change, corresponding refrigerant capacity (RC) attains a giant value of 1030 J/kg. The promising cryogenic MC performances together with the unique HE amorphous characterizations make the quinary Er20Ho20Gd20Ni20Co20 HE amorphous alloy attractive for cryogenic MR applications.

Understanding, quantifying, and controlling the molecular ordering of semiconducting polymers: from novices to experts and amorphous to perfect crystals

Abstract: Molecular packing and texture of semiconducting polymers are often critical to the performance of devices using these materials. Although frameworks exist to quantify the ordering, interpretations are often just qualitative, resulting in imprecise use of terminology. Here, we reemphasize the significance of quantifying molecular ordering in terms of degree of crystallinity (volume fractions that are ordered) and quality of ordering and their relation to the size scale of an ordered region. We are motivated in part by our own imprecise and inconsistent use of terminology in the past, as well as the need to have a primer or tutorial reference to teach new group members. We strive to develop and use consistent terminology with regards to crystallinity, semicrystallinity, paracrystallinity, and related characteristics. To account for vastly different quality of ordering along different directions, we classify paracrystals into 2D and 3D paracrystals and use paracrystallite to describe the spatial extent of molecular ordering in 1-10 nm. We show that a deeper understanding of molecular ordering can be achieved by combining grazing-incidence wide-angle X-ray scattering and differential scanning calorimetry, even though not all aspects of these measurements are consistent, and some classification appears to be method dependent. We classify a broad range of representative polymers under common processing conditions into five categories based on the quantitative analysis of the paracrystalline disorder parameter (g) and thermal transitions. A small database is presented for 13 representative conjugated and insulating polymers ranging from amorphous to semi-paracrystalline. Finally, we outline the challenges to rationally design more perfect polymer crystals and propose a new molecular design approach that envisions conceptual molecular grafting that is akin to strained and unstrained hetero-epitaxy in classic (compound) semiconductors thin film growth.

Amorphizing noble metal chalcogenide catalysts at the single-layer limit towards hydrogen production

Abstract: Rational design of noble metal catalysts with the potential to leverage efficiency is vital for industrial applications. Such an ultimate atom-utilization efficiency can be achieved when all noble metal atoms exclusively contribute to catalysis. Here, we demonstrate the fabrication of a wafer-size amorphous PtSex film on a SiO2 substate via a low-temperature amorphization strategy, which offers single-atom-layer Pt catalysts with high atom-utilization efficiency (~26 wt%). This amorphous PtSex (1.2 < x < 1.3) behaves as a fully activated surface, accessible to catalytic reactions, and features a nearly 100% current density relative to a pure Pt surface and reliable production of sustained high-flux hydrogen over a 2 inch wafer as a proof-of-concept. Furthermore, an electrolyser is demonstrated to generate a high current density of 1,000 mA cm−2. Such an amorphization strategy is potentially extendable to other noble metals, including the Pd, Ir, Os, Rh and Ru elements, demonstrating the universality of single-atom-layer catalysts. The scarcity and high price of noble metal catalysts pose critical challenges for the chemical industry, and finding strategies that ensure complete atom efficiency has become a pivotal endeavour. This work introduces the fabrication of amorphous single-layer PtSex catalysts for the hydrogen evolution reaction with high atom-utilization efficiency.

Amorphous Boron Carbide on Titanium Dioxide Nanobelt Arrays for High-Efficiency Electrocatalytic NO Reduction to NH3.

Abstract: Electrocatalytic NO reduction is regarded as an attractive strategy to degrade NO contaminant into useful NH3, but the lack of efficient and stable electrocatalysts to facilitate such multiple proton-coupled electron-transfer processes impedes its applications. Here, we report on developing amorphous B2.6C supported on a TiO2 nanoarray on a Ti plate (a-B2.6C@TiO2/Ti) as an NH3-producing nanocatalyst with appreciable activity and durability toward the NO electroreduction. It shows a yield of 3678.6 μg h-1 cm-2 and a FE of 87.6%, superior to TiO2/Ti (563.5 μg h-1 cm-2, 42.6%) and a-B2.6C/Ti (2499.2 μg h-1 cm-2, 85.6%). An a-B2.6C@TiO2/Ti-based Zn-NO battery achieves a power density of 1.7 mW cm-2 with an NH3 yield of 1125 μg h-1 cm-2. An in-depth understanding of catalytic mechanisms is gained by theoretical calculations.

In situ unraveling surface reconstruction of Ni5P4@FeP nanosheet array for superior alkaline oxygen evolution reaction

Abstract: Oxygen evolution reaction (OER) is a key step for electrochemical water splitting and understanding the surface reconstruction of OER pre-catalysts is of vital importance. Herein, hybrid Ni 5 P 4 @FeP nanosheet arrays were evaluated as promising OER pre-catalysts. The dynamic surface evolution was probed by in situ Raman spectroscopy, which revealed that Ni 5 P 4 @FeP was rapidly reconstructed to NiFe 2 O 4 during the anodic scan. The structural instability of amorphous NiFe 2 O 4 led to partial reconstitution to Ni/FeOOH at high oxidation potentials. As-formed Ni/FeOOH@NiFe 2 O 4 hybrid with high structural reversibility was established as a truly active species, which exhibited excellent alkaline OER performance with a low overpotential of 205 and 242 mV under current densities of 10 and 100 mA cm −2 , respectively. This work provides a facile strategy to in situ construct an amorphous spinel/oxyhydroxide hybrid structure using electrochemical activation that holds strong promise for potential application in electrochemical water splitting and related energy devices. • Surface reconstruction of Ni 5 P 4 @FeP was probed by in situ Raman spectroscopy. • Ni 5 P 4 @FeP was oxidized to NiFe 2 O 4 and further to Ni/FeOOH at high potentials. • The real active intermediate was identified as Ni/FeOOH and NiFe 2 O 4 hybrid. • High structural reversibility between NiFe 2 O 4 and Ni/FeOOH was found. • As-formed amorphous NiOOH and NiFe 2 O 4 hybrid showed superior OER activity.

Breaking the scaling relations of oxygen evolution reaction on amorphous NiFeP nanostructures with enhanced activity for overall seawater splitting

Abstract: The instinct scaling relations between the adsorption energies of key intermediates during OER lead to large overpotential for water/seawater splitting. Herein, we develop a new strategy to fabricate amorphous nickel-iron phosphides (NiFeP) with controllable morphologies as high-performance catalysts for overall seawater splitting. The ligand effect of P tunes the electronic states of the oxidized NiFe sites, thus breaks the scaling relations for OER and reduce the adsorption energy gap between HO* and HOO* from 3.08 eV to 2.62 eV. The NiFeP nanostructures exhibit extraordinarily low overpotentials of 129 mV for OER and 126 mV for HER at 100 mA cm−2 in simulated alkaline seawater, which outperform the best reported electrocatalysts. They could also be operated at 1.57 V with 100 mA cm−2 in a two-electrode electrolyzer and work for more than 500 h. Our work may provide a universal guidance for the design of highly active seawater splitting electrocatalysts.

Breaking the scaling relations of oxygen evolution reaction on amorphous NiFeP nanostructures with enhanced activity for overall seawater splitting

Abstract: The instinct scaling relations between the adsorption energies of key intermediates during OER lead to large overpotential for water/seawater splitting. Herein, we develop a new strategy to fabricate amorphous nickel-iron phosphides (NiFeP) with controllable morphologies as high-performance catalysts for overall seawater splitting. The ligand effect of P tunes the electronic states of the oxidized NiFe sites, thus breaks the scaling relations for OER and reduce the adsorption energy gap between HO* and HOO* from 3.08 eV to 2.62 eV. The NiFeP nanostructures exhibit extraordinarily low overpotentials of 129 mV for OER and 126 mV for HER at 100 mA cm −2 in simulated alkaline seawater, which outperform the best reported electrocatalysts. They could also be operated at 1.57 V with 100 mA cm −2 in a two-electrode electrolyzer and work for more than 500 h. Our work may provide a universal guidance for the design of highly active seawater splitting electrocatalysts. Amorphous NiFeP catalysts with extremely high activity for overall seawater splitting are developed. Theoretical calculations suggest that the P atom on the oxidized NiFe surface can significantly reduce the adsorption free energy gap between HO* and HOO*, thus breaks the scaling relations for oxygen evolution significantly and enhances the activity. The NiFeP catalysts can be operated for more than 500 h, demonstrating exceptional durability. • Amorphous NiFeP with controllable morphologies were prepared as bifunctional catalysts for overall seawater splitting. • P on the oxidized NiFe surface can break the scaling relations for OER and reduce the energy barrier between HO* and HOO*. • P can optimize the adsorption/desorption of H* on the amorphous NiFe structure and facilitate the evolution of hydrogen. • The catalysts can operate at 1.57 V with a current density of 100 mA cm -2 in a two-electrode electrolyzer and work for 500 h.

Crystalline-amorphous interface of mesoporous Ni2P@FePOxHy for oxygen evolution at high current density in alkaline-anion-exchange-membrane water-electrolyzer

Abstract: For industrial high-purity hydrogen production, it is essential to develop low-cost, earth-abundant, highly-efficient, and stable electrocatalysts which deliver high current density (j) at low overpotential (η) for oxygen evolution reaction (OER). Herein, we report an active mesoporous Ni 2 P @ FePO x H y pre-electrocatalyst, which delivers high j = 1 A cm −2 at η = 360 mV in 1 M KOH with long-term durability (12 days), fulfilling all the desirable commercial criteria for OER. The electrocatalyst shows abundant interfaces between crystalline metal phosphide and amorphous phosphorus-doped metal-oxide, improving charge transfer capability and providing access to rich electroactive sites. Combined with an excellent non-noble metal-based HER catalyst, we achieve commercially required j = 500/1000 mA cm −2 at 1.65/1.715 V for full water-splitting with excellent stability in highly corrosive alkaline environment (30% KOH). The alkaline-anion-exchange-membrane water-electrolyzer (AAEMWE) fabricated for commercial viability exhibits high j of 1 A cm −2 at 1.84 V with long-term durability as an economical hydrogen production method, outperforming the state-of-the-art Pt/C – IrO 2 catalyst. • Noble-metal free catalysts for oxygen evolution reactions are investigated. • Crystalline (Ni 2 P) and amorphous (FePO x H y ) phases in Ni 2 P @ FePO x H y catalyst provide more electrocatalytic active sites. • The Ni 2 P @ FePO x H y catalyst shows excellent AAEMWE cell performance with a low overpotential and good stability. • The Ni 2 P @ FePO x H y catalyst exhibits a low overpotential of 360 mV for OER to deliver a high current density of 1 A cm −2 .

Oxygen Vacancies and Interface Engineering on Amorphous/Crystalline CrOx -Ni3 N Heterostructures toward High-Durability and Kinetically Accelerated Water Splitting.

Abstract: Manipulating catalytic active sites and reaction kinetics in alkaline media is crucial for rationally designing mighty water-splitting electrocatalysts with high efficiency. Herein, the coupling between oxygen vacancies and interface engineering is highlighted to fabricate a novel amorphous/crystalline CrOx -Ni3 N heterostructure grown on Ni foam for accelerating the alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory (DFT) calculations reveal that the electron transfer from amorphous CrOx to Ni3 N at the interfaces, and the optimized Gibbs free energies of H2 O dissociation (ΔGH-OH ) and H adsorption (ΔGH ) in the amorphous/crystalline CrOx -Ni3 N heterostructure are conducive to the superior and stable HER activity. Experimental data confirm that numerous oxygen vacancies and amorphous/crystalline interfaces in the CrOx -Ni3 N catalysts are favorable for abundant accessible active sites and enhanced intrinsic activity, resulting in excellent catalytic performances for HER and OER. Additionally, the in situ reconstruction of CrOx -Ni3 N into highly active Ni3 N/Ni(OH)2 is responsible for the optimized OER performance in a long-term stability test. Eventually, an alkaline electrolyzer using CrOx -Ni3 N as both cathode and anode has a low cell voltage of 1.53 V at 10 mA cm-2 , together with extraordinary durability for 500 h, revealing its potential in industrial applications.

A Multifunctional Artificial Interphase with Fluorine‐Doped Amorphous Carbon layer for Ultra‐Stable Zn Anode

Abstract: Building an artificial interphase layer for tackling uncontrollable Zn dendrites and serious side reactions is a highly desirable strategy, but it is often hampered by the limited Zn2+ transport. Here, a stable fluorine‐doped amorphous carbon (CF) artificial layer is constructed on a Cu current collector (CF‐Cu) via facile carbonization treatment of a fluoropolymer coating to realize underlying Zn deposition. As evidenced experimentally and theoretically, this inorganic CF layer with ionic conductivity and electronic insulation successfully triggers dendrite‐free Zn deposition at the CF‐Cu interface with preferred Zn(002) crystal plane stacking parallel to the substrate surface, thus greatly promoting the inhibition of Zn‐dendrites and blocking of interfacial side reactions. The introduced fluorine atoms as abundant zincophilic sites play an important role in driving fast zinc‐ion transfer kinetics, which can partly convert into ZnF2 as an artificial solid Zn2+ conductor to further guide uniform Zn deposition. Consequently, the CF‐Cu electrode enables high reversibility with 99% coulombic efficiency and a long cycling stability of 1900 cycles at 2 mA cm–2. The integrated CF‐Cu@Zn anode achieves up to 2200 h cycles with a low voltage polarization. This study provides inspiration for the design of artificial interphase layers for stable nondendritic metal batteries.

Amorphous-to-Crystalline Transformation: General Synthesis of Hollow Structured Covalent Organic Frameworks with High Crystallinity.

Abstract: Morphological control of covalent organic frameworks (COFs) is particularly interesting to boost their applications; however, it remains a grand challenge to prepare hollow structured COFs (HCOFs) with high crystallinity and uniform morphology. Herein, we report a versatile and efficient strategy of amorphous-to-crystalline transformation for the general and controllable fabrication of highly crystalline HCOFs. These HCOFs exhibited ultrahigh surface areas, radially oriented nanopore channels, quite uniform morphologies, and tunable particle sizes. Mechanistic studies revealed that H2O, acetic acid, and solvent played a crucial role in manipulating the hollowing process and crystallization process by regulating the dynamic imine exchange reaction. Our approach was demonstrated to be applicable to various amines and aldehydes, producing up to 10 kinds of HCOFs. Importantly, based on this methodology, we even constructed a library of unprecedented HCOFs including HCOFs with different pore structures, bowl-like HCOFs, cross-wrinkled COF nanocapsules, grain-assembled HCOFs, and hydrangea-like HCOFs. This strategy was also successfully applied to the fabrication of COF-based yolk-shell nanostructures with various functional interior cores. Furthermore, catalytically active metal nanoparticles were implanted into the hollow cavities of HCOFs with tunable pore diameters, forming attractive size-selective nanoreactors. The obtained metal@HCOFs catalysts showed enhanced catalytic activity and outstanding size-selectivity in hydrogenation of nitroarenes. This work highlights the significance of nucleation-growth kinetics of COFs in tuning their morphologies, structures, and applications.

Achieving Highly Efficient pH-Universal Hydrogen Evolution by Superhydrophilic Amorphous/Crystalline Rh(OH)3/NiTe Coaxial Nanorod Array Electrode

Abstract: Design of high-performance pH-universal electrocatalysts is critical to practical large-scale hydrogen generation as a carbon-neutral fuel, yet challenging. Herein, we report an unique motif with crystalline nickel tellurium nanorods enclosed by amorphous rhodium hydroxide (a-Rh(OH)3/NiTe), formed through a hydrothermal synthesis and a subsequent chemical etching process, to address this challenge. The as-prepared a-Rh(OH)3/NiTe cathode enables a current density of 100 mA cm−2 with low overpotentials of 51, 109, and 64 mV for HER in alkaline, neutral and acidic media, respectively. As revealed by density functional theory (DFT) calculations, the electronic interactions between a-Rh(OH)3 and NiTe enhance the performance of Rh active sites. More importantly, the motif possesses superhydrophilicity and aerophobicity features, which not only facilitates the access to electrolytes but also ensures the fast release of hydrogen bubbles, endowing the electrocatalyst with advanced pH-universal HER activity. This work provides insights for the design of highly efficient electrocatalysts for hydrogen evolution at both molecular and mesoscopic levels.

Metal‐Organic Framework Glass Anode with an Exceptional Cycling‐Induced Capacity Enhancement for Lithium‐Ion Batteries

Abstract: Metal-organic frameworks (MOFs) hold great promise as high-energy anode materials for next-generation lithium-ion batteries (LIBs) due to their tunable chemistry, pore structure and abundant reaction sites. However, the pore structure of crystalline MOFs tends to collapse during lithium-ion insertion and extraction, and hence, their electrochemical performances are rather limited. As a critical breakthrough, a MOF glass anode for LIBs has been developed in the present work. In detail, it is fabricated by melt-quenching Cobalt-ZIF-62 (Co(Im)1.75 (bIm)0.25 ) to glass, and then by combining glass with carbon black and binder. The derived anode exhibits high lithium storage capacity (306 mAh g-1 after 1000 cycles at of 2 A g-1 ), outstanding cycling stability, and superior rate performance compared with the crystalline Cobalt-ZIF-62 and the amorphous one prepared by high-energy ball-milling. Importantly, it is found that the Li-ion storage capacity of the MOF glass anode continuously rises with charge-discharge cycling and even tripled after 1000 cycles. Combined spectroscopic and structural analyses, along with density functional theory calculations, reveal the origin of the cycling-induced enhancement of the performances of the MOF glass anode, that is, the increased distortion and local breakage of the CoN coordination bonds making the Li-ion intercalation sites more accessible.