Disordered solid‐solution high‐entropy alloys have attracted wide research attention as robust electrocatalysts. In comparison, ordered high‐entropy intermetallics have been hardly explored and the ...effects of the degree of chemical ordering on catalytic activity remain unknown. In this study, a series of multicomponent intermetallic Pt4FeCoCuNi nanoparticles with tunable ordering degrees is fabricated. The transformation mechanism of the multicomponent nanoparticles from disordered structure into ordered structure is revealed at the single‐particle level, and it agrees with macroscopic analysis by selected‐area electron diffraction and X‐ray diffraction. The electrocatalytic performance of Pt4FeCoCuNi nanoparticles correlates well with their crystal structure and electronic structure. It is found that increasing the degree of ordering promotes electrocatalytic performance. The highly ordered Pt4FeCoCuNi achieves the highest mass activities toward both acidic oxygen reduction reaction (ORR) and alkaline hydrogen evolution reaction (HER) which are 18.9‐fold and 5.6‐fold higher than those of commercial Pt/C, respectively. The experiment also shows that this catalyst demonstrates better long‐term stability than both partially ordered and disordered Pt4FeCoCuNi as well as Pt/C when subject to both HER and ORR. This ordering‐dependent structure–property relationship provides insight into the rational design of catalysts and stimulates the exploration of many other multicomponent intermetallic alloys.
An ordering transformation of high‐entropy Pt4FeCoNiCu nanoparticles from disordered solid‐solution alloy to ordered intermetallic structure is demonstrated across multiple scales. The electrocatalytic hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) activities are revealed to be ordering‐dependent, and the highly ordered Pt4FeCoNiCu outperforms most other Pt‐based catalysts for HER and ORR with robust durability.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
2.
Organic materials as photocatalysts for water splitting Bai, Yang; Hippalgaonkar, Kedar; Sprick, Reiner Sebastian
Journal of materials chemistry. A, Materials for energy and sustainability,
08/2021, Volume:
9, Issue:
3
Journal Article
Peer reviewed
Open access
Solar water splitting offers a potential avenue for the production of clean and storable energy in the form of hydrogen. Semiconductors can be used as photocatalysts that enable the simultaneous ...production of hydrogen and oxygen from water
via
water splitting and in recent years inorganic semiconductor photocatalysts have been significantly improved in terms of their performance with organic semiconductors emerging as a potential alternative, though mostly studied for sacrificial half-reactions. Herein, we present recent developments in using organic semiconductors as photocatalysts highlighting their potential due to their synthetic tunability. We will particularly focus on their application in overall water splitting without using sacrificial reagents and suggest future directions in using these materials in large scale applications before concluding with suggestions for a wider community to focus research efforts on particular challenges in the field and opportunities that organic materials offer.
Solar water splitting offers a potential avenue for the production of clean and storable energy in the form of hydrogen. Conjugated polymer photocatalysts offer new opportunities which are discussed in this highlight.
Atomically thin Bi2O2Se has emerged as a new member in 2D materials with ultrahigh carrier mobility and excellent air‐stability, showing great potential for electronics and optoelectronics. In ...addition, its ferroelectric nature renders an ultralow thermal conductivity, making it a perfect candidate for thermoelectrics. In this work, the thermoelectric performance of 2D Bi2O2Se is investigated over a wide temperature range (20–300 K). A gate‐tunable transition from polar optical phonon (POP) scattering to piezoelectric scattering is observed, which facilitates the capacity of drastic mobility engineering in 2D Bi2O2Se. Consequently, a high power factor of more than 400 µW m−1 K−2 over an unprecedented temperature range (80–200 K) is achieved, corresponding to the persistently high mobility arising from the highly gate‐tunable scattering mechanism. This finding provides a new avenue for maximizing thermoelectric performance by changing the scattering mechanism and carrier mobility over a wide temperature range.
The thermoelectric (TE) transport in few‐layer Bi2O2Se is probed, where gating can effectively modulate its scattering mechanism from polar optical phonon to piezoelectric scattering. This facilitates the capacity of drastic mobility engineering, and high TE performance over a wide range of temperature can be achieved due to the persistently high mobility arising from the highly gate‐tunable scattering mechanism.
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Abstract
Thermoelectrics enable waste heat recovery, holding promises in relieving energy and environmental crisis. Lillianite materials have been long-term ignored due to low thermoelectric ...efficiency. Herein we report the discovery of superior thermoelectric performance in Pb
7
Bi
4
Se
13
based lillianites, with a peak figure of merit,
zT
of 1.35 at 800 K and a high average
zT
of 0.92 (450–800 K). A unique quality factor is established to predict and evaluate thermoelectric performances. It considers both band nonparabolicity and band gaps, commonly negligible in conventional quality factors. Such appealing performance is attributed to the convergence of effectively nested conduction bands, providing a high number of valley degeneracy, and a low thermal conductivity, stemming from large lattice anharmonicity, low-frequency localized Einstein modes and the coexistence of high-density moiré fringes and nanoscale defects. This work rekindles the vision that Pb
7
Bi
4
Se
13
based lillianites are promising candidates for highly efficient thermoelectric energy conversion.
Abstract
Thermal rectification is an exotic thermal transport phenomenon which allows heat to transfer in one direction but block the other. We demonstrate an unusual dual-mode solid-state thermal ...rectification effect using a heterogeneous “irradiated-pristine” polyethylene nanofiber junction as a nanoscale thermal diode, in which heat flow can be rectified in both directions by changing the working temperature. For the nanofiber samples measured here, we observe a maximum thermal rectification factor as large as ~50%, which only requires a small temperature bias of <10 K. The tunable nanoscale thermal diodes with large rectification and narrow temperature bias open up new possibilities for developing advanced thermal management, energy conversion and, potentially thermophononic technologies.
Although it has been qualitatively demonstrated that surface roughness can reduce the thermal conductivity of crystalline Si nanowires (SiNWs), the underlying reasons remain unknown and warrant ...quantitative studies and analysis. In this work, vapor–liquid–solid (VLS) grown SiNWs were controllably roughened and then thoroughly characterized with transmission electron microscopy to obtain detailed surface profiles. Once the roughness information (root-mean-square, σ, correlation length, L, and power spectra) was extracted from the surface profile of a specific SiNW, the thermal conductivity of the same SiNW was measured. The thermal conductivity correlated well with the power spectra of surface roughness, which varies as a power law in the 1–100 nm length scale range. These results suggest a new realm of phonon scattering from rough interfaces, which restricts phonon transport below the Casimir limit. Insights gained from this study can help develop a more concrete theoretical understanding of phonon–surface roughness interactions as well as aid the design of next generation thermoelectric devices.
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The conceptual understanding of charge transport in conducting polymers is still ambiguous due to a wide range of paracrystallinity (disorder). Here, we advance this understanding by presenting the ...relationship between transport, electronic density of states and scattering parameter in conducting polymers. We show that the tail of the density of states possesses a Gaussian form confirmed by two-dimensional tight-binding model supported by Density Functional Theory and Molecular Dynamics simulations. Furthermore, by using the Boltzmann Transport Equation, we find that transport can be understood by the scattering parameter and the effective density of states. Our model aligns well with the experimental transport properties of a variety of conducting polymers; the scattering parameter affects electrical conductivity, carrier mobility, and Seebeck coefficient, while the effective density of states only affects the electrical conductivity. We hope our results advance the fundamental understanding of charge transport in conducting polymers to further enhance their performance in electronic applications.
Since the advent of transformation optics and scattering cancelling technology, a plethora of unprecedented metamaterials, especially invisibility cloaks, have been successfully demonstrated in ...various communities, e.g., optics, acoustics, elastic mechanics, dc electric field, dc magnetic field, and thermotics. A long‐held captivation is that transformation‐optic metamaterials of anisotropic or noncentrosymmetric geometry (e.g., ellipsoids) commonly come along with parameter approximation/simplification or directional functions. Here, a synthetic paradigm with strictly full parameters and omnidirectionality is reported simultaneously to address this long‐held issue for molding heat flow and experimentally demonstrate a series of noncentrosymmetric thermal metadevices. It changes the usual perception that transformation thermotic/dc/acoustic metamaterials are just a direct and simplified derivatives of the transformation‐optic counterpart. Instead, the proposed methodology solves an intriguingly important and challenging problem that is not possibly achievable for transformation‐optic metamaterials. The approach is rigorous, exact, robust, and yet elegantly facile, which may open a new avenue to manipulating the Laplacian and wave‐dynamic fields in ways previously inconceivable.
A long‐held captivation is that transformation‐optic metamaterials of anisotropic or noncentrosymmetric geometry (e.g., ellipsoids) commonly come along with parameter approximation/simplification or directional functions. A synthetic paradigm with strictly full parameters and omnidirectionality is reported simultaneously to address this long‐held issue for molding heat flow, and a series of noncentrosymmetric thermal metadevices is experimentally demonstrated.
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In electrically conductive solids, the Wiedemann-Franz law requires the electronic contribution to thermal conductivity to be proportional to electrical conductivity. Violations of the ...Wiedemann-Franz law are typically an indication of unconventional quasiparticle dynamics, such as inelastic scattering, or hydrodynamic collective motion of charge carriers, typically pronounced only at cryogenic temperatures. We report an order-of-magnitude breakdown of the Wiedemann-Franz law at high temperatures ranging from 240 to 340 kelvin in metallic vanadium dioxide in the vicinity of its metal-insulator transition. Different from previously established mechanisms, the unusually low electronic thermal conductivity is a signature of the absence of quasiparticles in a strongly correlated electron fluid where heat and charge diffuse independently.
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