Tailoring Defects in Hard Carbon Anode towards Enhanced Na Storage Performance

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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.

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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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Expediting H2 Evolution over MAPbI3 with a Nonnoble Metal Cocatalyst Mo2C under Visible Light

Halide perovskites have been emerging as promising photocatalytic materials for H2 evolution from water due to their outstanding photoelectric properties. However, the lack of proper surface reactive sites greatly hinders the photocatalytic potential of these fascinating compounds. Here, Mo2C nanoparticles have been anchored onto methylammonium lead iodide (MAPbI3) as a nonnoble metal cocatalyst to promote H2 evolution reactions. The Mo2C nanoparticles have opposite zeta potential with MAPbI3 thereby electrostatically assembled onto the MAPbI3 surface, i.e., Mo2C@MAPbI3. Our results show that the anchored Mo2C nanoparticles have a strong interplay with MAPbI3 substrate so that photogenerated electrons of MAPbI3 can be rapidly separated and transferred into Mo2C for further H2 evolution reactions. Under optimal conditions, Mo2C@MAPbI3 delivers exceptionally high photocatalytic performance for visible light-driven H2 evolution that clearly outperforms pristine MAPbI3 and Pt-deposited MAPbI3. An apparent quantum efficiency as high as 12.65% at has been attained for H2 evolution, surpassing most of the MAPbI3-based photocatalyst reported. These results signify the usefulness and applicability of Mo2C as a new nonnoble metal-based cocatalyst in solar water splitting.

Research Article

Solvent Effects on Kinetics and Electrochemical Performances of Rechargeable Aluminum Batteries

The rechargeable aluminum batteries (RAB) have shown great potential for energy storage applications due to their low-cost and superior volumetric capacity. However, the battery performances are far from satisfactory owing to the poor kinetics of electrode reactions, including the solid-state ionic diffusion and interfacial charge transfer. The charge transfer reaction, typically the cation desolvation at the interface (Helmholtz plane), is crucial for determining the interfacial charge transfer, which induces the solvent effect in batteries but has not been explored in RABs. Herein, we provide a comprehensive understanding of solvent effects on interface kinetics and electrochemical performance of RAB by analyzing the desolvation process and charge transfer energy barrier. The pivotal role of solvent effects is confirmed by the successful application of Al(OTF)3-H2O electrolyte, which displays easy desolvation, low charge transfer resistance, and thus superior Al-ion storage performance over other electrolytes in our studies. In addition, based on the strong correlation between the calculated desolvation energy and charge transfer energy barrier, the calculation of dissociation energy of ion-solvent complex is demonstrated as an efficient index for designing electrolytes. The in-depth understanding of solvent effects provides rational guidance for new electrolyte and RAB design.

Research Article

Tuning Exciton Recombination Pathways in Inorganic Bismuth-Based Perovskite for Broadband Emission

Single-component emitters with broadband emission are attractive but challenging for illumination and display applications. The two-dimensional organic-inorganic hybrid perovskites have exhibited outstanding broad emission property due to low electronic dimensionality and strong exciton-phonon coupling. However, few layered all-inorganic lead-free perovskites with broadband emission have been explored, and the explicit mechanism of exciton recombination in them also needs in-depth understanding. Herein, the inorganic bismuth-based perovskite Cs3Bi2Br9 achieves the stable broadband emission under ambient temperature and pressure by tuning the exciton recombination pathways via antimony (Sb) doping, and the photoluminescence quantum yield (PLQY) realizes an enhancement from 2.9% to 15.9%. The photoluminescence excitation (PLE) spectra indicate that the doped Sb introduces newly extrinsic self-trapped states. The incorporation of Sb promotes the transfer of free excitons (FEs) to extrinsic self-trapped excitons (STEs) observed from Sb content-dependent steady-state PL spectra and, meanwhile, reduces the nonradiative recombination of the generated extrinsic STEs, which are primarily responsible for the remarkably enhanced broad emission. Furthermore, femtosecond transient absorption results elucidate a clear exciton dynamics, in which the transition from FEs to STEs might arise through the gradient energy levels, and finally extrinsic STEs at various energy states contribute to the broadband emission.

Research Article

Tailoring Defects in Hard Carbon Anode towards Enhanced Na Storage Performance

Hard carbon (HC) anodes show conspicuously commercialized potential for sodium-ion batteries (SIBs) due to their cost-effectiveness and satisfactory performance. However, the development of hard carbon anodes in SIBs is still hindered by low initial Coulombic efficiency (ICE) and insufficient cyclic stability, which are induced by inappropriate defects in the structure. Herein, we introduce a simple but effective method to tailor the defects in HC by the chemically preadsorbed K+. The soft X-ray absorption spectroscopy at the C K-edges reveals that K+ can anchor on the hard carbon via C-O-K bonds, occupying the irreversible reactive sites of Na+. Therefore, the irreversible capacity caused by some C-O bonds can be reduced. Moreover, the preadsorbed K+ can induce the rearrangement of carbon layers and lead to a high graphitization structure with fewer defects and large interlayer spacing, which not only improves the structural stability and electrical conductivity of the HC anode but also facilitates fast Na+ diffusion. Therefore, the as-obtained optimized anode demonstrates a higher ICE with better cyclic stability and superior rate capacities compared with the anode without preadsorbed K+. This work indicates that K+ preadsorbed into hard carbon is a practicable alternative to enhance the Na storage performances of HC anodes for SIBs.


Perovskite Semiconductor Nanocrystals

Review Article

Progress and Perspective of the Cathode Materials towards Bromine-Based Flow Batteries

Bromine-based flow batteries (Br-FBs) have been one of the most promising energy storage technologies with attracting advantages of low price, wide potential window, and long cycle life, such as zinc-bromine flow battery, hydrogen-bromine flow battery, and sodium polysulfide-bromine flow battery. The research and development of aqueous Br-FBs are very fast and many achievements have been realized. However, Br-FBs suffer from the sluggish kinetics of Br2/Br- redox couple and serious self-discharge caused by the diffusion of bromine, which hinder the further commercialization and industrialization of the aqueous Br-FBs. A series of mitigation strategies have been developed to figure out these challenges, especially the modifications on electrode materials. Electrode, one of the critical components in a Br-FB, provides the reactions sites for redox couples, upon which its properties exert a significant effect on the performance of Br-FBs. Up to now, extensive research has been carried out on electrode modifications to solve the aforementioned notorious issues of Br-FBs, including surface treatment and surface modification. In this review, various electrode materials and relevant modification approaches used for Br-FBs are overviewed and summarized. Moreover, the relevant mechanisms are illustrated deeply, providing comprehensive and available instruction to pursue and develop high-performance cathodes for Br-FBs with high power density and long lifespan.