Energy Material Advances: From Fundamental Discoveries to Practical ApplicationsRead the full article
The Open Access journal Energy Material Advances, published in association with BIT, is an interdisciplinary platform for research in multiple fields from cutting-edge material to energy science.
Energy Material Advances’ editorial board is led by Feng Wu (Beijing Institute of Technology) and Jun Liu (University of Washington) and is comprised of experts who have made significant and well recognized contributions to the field.
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Intrinsic and Extrinsic Exciton Recombination Pathways in AgInS2 Colloidal Nanocrystals
Ternary I-III-VI2 nanocrystals (NCs), such as AgInS2 and CuInS2, are garnering interest as heavy-metal-free materials for photovoltaics, luminescent solar concentrators, LEDs, and bioimaging. The origin of the emission and absorption properties in this class of NCs is still a subject of debate. Recent theoretical and experimental studies revealed that the characteristic Stokes-shifted and long-lived luminescence of stoichiometric CuInS2 NCs arises from the detailed structure of the valence band featuring two sublevels with different parity. The same valence band substructure is predicted to occur in AgInS2 NCs, yet no experimental confirmation is available to date. Here, we use complementary spectroscopic, spectro-electrochemical, and magneto-optical investigations as a function of temperature to investigate the band structure and the excitonic recombination mechanisms in stoichiometric AgInS2 NCs. Transient transmission measurements reveal the signatures of two subbands with opposite parity, and photoluminescence studies at cryogenic temperatures evidence a dark state emission due to enhanced exchange interaction, consistent with the behavior of stoichiometric CuInS2 NCs. Lowering the temperature as well as applying reducing electrochemical potentials further suppress electron trapping, which represents the main nonradiative channel for exciton decay, leading to nearly 100% emission efficiency.
Porous Mixed Ionic Electronic Conductor Interlayers for Solid-State Batteries
Rechargeable solid-state batteries (SSBs) have emerged as the next-generation energy storage device based on lowered fire hazard and the potential of realizing advanced battery chemistries, such as alkali metal anodes. However, ceramic solid electrolytes (SEs) generally have limited capability in relieving mechanical stress and are not chemically stable against body-centered cubic alkali metals or their alloys with minor solute elements (β-phase). Swelling-then-retreating of β-phase often causes instabilities such as SE fracture and corrosion as well as the loss of electronic/ionic contact, which leads to high charge-transfer resistance, short-circuiting, etc. These challenges have called for the cooperation from other classes of materials and novel nanocomposite architectures in relieving stress and preserving essential contacts while minimizing detrimental disruptions. In this review, we summarize recent progress in addressing these issues by incorporating other classes of materials such as mixed ion-electron conductor (MIEC) porous interlayers and ion-electron insulator (IEI) binders, in addition to SE and metals (e.g., β-phase and current collectors) that are the traditional SSB components. In particular, we focus on providing theoretical interpretations on how open nanoporous MIEC interlayers manipulate β-phase deposition and stripping behavior and thereby suppress such instabilities, referring to the fundamental thermodynamics and kinetics governing the nucleation and growth of the β-phase. The review concludes by describing avenues for the future design of porous MIEC interlayers for SSBs.
3-D Edge-Oriented Electrocatalytic NiCo2S4 Nanoflakes on Vertical Graphene for Li-S Batteries
Polysulfide shuttle effect, causing extremely low Coulombic efficiency and cycling stability, is one of the toughest challenges hindering the development of practical lithium sulfur batteries (LSBs). Introducing catalytic nanostructures to stabilize the otherwise soluble polysulfides and promote their conversion to solids has been proved to be an effective strategy in attacking this problem, but the heavy mass of catalysts often results in a low specific energy of the whole electrode. Herein, by designing and synthesizing a free-standing edge-oriented NiCo2S4/vertical graphene functionalized carbon nanofiber (NCS/EOG/CNF) thin film as a catalytic overlayer incorporated in the sulfur cathode, the polysulfide shuttle effect is largely alleviated, revealed by the enhanced electrochemical performance measurements and the catalytic function demonstration. Different from other reports, the NiCo2S4 nanosheets synthesized here have a 3-D edge-oriented structure with fully exposed edges and easily accessible in-plane surfaces, thus providing a high density of active sites even with a small mass. The EOG/CNF scaffold further renders the high conductivity in the catalytic structure. Combined, this novel structure, with high sulfur loading and high sulfur fraction, leads to high-performance sulfur cathodes toward a practical LSB technology.
Rare-Earth Nd Inducing Record-High Thermoelectric Performance of (GeTe)85(AgSbTe2)15
As a promising midtemperature thermoelectric material with both higher thermoelectric performance and mechanical property, Tellurium Antimony Germanium Silver (TAGS-x), written as (GeTe)x(AgSbTe2)1-x, especially (GeTe)0.85(AgSbTe2)0.15 (TAGS-85), has attracted wide attention. Herein, we innovatively use Nd doping to synergistically decrease the carrier concentration to the optimal level leading to enhanced dimensionless figure of merit, zT. Our density-functional theory calculation results indicate that Nd-doping reduced carrier concentration should be attributed to the enlargement of band gap. The optimized carrier concentration results in an ultrahigh power factor of ~32 μW cm-1 K-2 at 727 K in Ge0.74Ag0.13Sb0.11Nd0.02Te. Simultaneously, the lattice thermal conductivity of Ge0.74Ag0.13Sb0.11Nd0.02Te retained as low as ~0.5 at 727 K. Ultimately, a record-high zT of 1.65 at 727 K is observed in the Ge0.74Ag0.13Sb0.11Nd0.02Te. This study indicates rare-earth Nd doping is effective in boosting the thermoelectric performance of TAGS-85 and approached a record-high level via synergistic effect.
Lattice Doping of Lanthanide Ions in Cs2AgInCl6 Nanocrystals Enabling Tunable Photoluminescence
Lead-free halide double perovskite Cs2AgInCl6 has become the research hotspot in the optoelectronic fields. It is a challenge to utilize the lattice doping by different lanthanide ions with rich and unique photoluminescence (PL) emissions for emerging photonic applications. Here, we successfully incorporated Dy3+, Sm3+, and Tb3+ ions into Cs2AgInCl6 nanocrystals (NCs) by the hot-injection method, bringing diverse PL emissions of yellowish, orange, and green light in Cs2AgInCl6:Ln3+ (Ln3+ = Dy3+, Sm3+, Tb3+). Moreover, benefiting from the energy transfer process, Sm3+ and Tb3+ ion-codoped Cs2AgInCl6 NCs achieved tunable emission from green to yellow orange and a fluorescent pattern from the as-prepared NC-hexane inks by spray coating was made to show its potential application in fluorescent signs and anticounterfeiting technology. This work indicates that lanthanide ions could endow Cs2AgInCl6 NCs the unique and tunable PL properties and stimulate the development of lead-free halide perovskite materials for new optoelectronic applications.
Graphene-Based Coronal Hybrids for Enhanced Energy Storage
Functional materials with designer morphologies are anticipated to be the next generation materials for energy storage applications. In this manuscript, we have developed a holistic approach to enhance the surface area and hence the properties of nanostructures by synthesizing coronal nanohybrids of graphene. These nanohybrids provide distinctive advantages in terms of performance and stability over vertically stacked nanocomposites reported in literature. Various double hydroxide materials self-assembled as coronal lamellae on graphene shells have been synthesized and systematically studied. These coronal nanohybrids result in about a threefold increase in energy storage capacity as compared to their traditionally synthesized nanocomposite counterparts. The 3D graphene-based nanofibrils in the synthesized coronal nanohybrids provide mechanical support and connect the nodes of the double hydroxide lattices to inhibit restacking. Complex morphologies such as coronal nanostructures increase the interaction surface of the nanostructure significantly. Such an approach is also expected to bring a paradigm shift in development of functional materials for various applications such as sensors, energy storage, and catalysis.