Rechargeable aqueous Zn-ion energy
storage devices are promising
candidates for next-generation energy storage technologies. However,
the lack of highly reversible Zn2+-storage anode materials
with low potential windows remains a primary concern. Here, we report
a two-dimensional polyarylimide covalent organic framework (PI-COF)
anode with high-kinetics Zn2+-storage capability. The well-organized
pore channels of PI-COF allow the high accessibility of the build-in
redox-active carbonyl groups and efficient ion diffusion with a low
energy barrier. The constructed PI-COF anode exhibits a specific capacity
(332 C g–1 or 92 mAh g–1 at 0.7
A g–1), a high rate capability (79.8% at 7 A g–1), and a long cycle life (85% over 4000 cycles). In situ Raman investigation and first-principle calculations
clarify the two-step Zn2+-storage mechanism, in which imide
carbonyl groups reversibly form negatively charged enolates. Dendrite-free
full Zn-ion devices are fabricated by coupling PI-COF anodes with
MnO2 cathodes, delivering excellent energy densities (23.9
∼ 66.5 Wh kg–1) and supercapacitor-level
power densities (133 ∼ 4782 W kg–1). This
study demonstrates the feasibility of covalent organic framework as
Zn2+-storage anodes and shows a promising prospect for
constructing reliable aqueous energy storage devices.
Developing resource‐abundant and sustainable metal‐free bifunctional oxygen electrocatalysts is essential for the practical application of zinc–air batteries (ZABs). 2D black phosphorus (BP) with fully exposed atoms and active lone pair electrons can be promising for oxygen electrocatalysts, which, however, suffers from low catalytic activity and poor electrochemical stability. Herein, guided by density functional theory (DFT) calculations, an efficient metal‐free electrocatalyst is demonstrated via covalently bonding BP nanosheets with graphitic carbon nitride (denoted BP‐CN‐c). The polarized PN covalent bonds in BP‐CN‐c can efficiently regulate the electron transfer from BP to graphitic carbon nitride and significantly promote the OOH* adsorption on phosphorus atoms. Impressively, the oxygen evolution reaction performance of BP‐CN‐c (overpotential of 350 mV at 10 mA cm−2, 90% retention after 10 h operation) represents the state‐of‐the‐art among the reported BP‐based metal‐free catalysts. Additionally, BP‐CN‐c exhibits a small half‐wave overpotential of 390 mV for oxygen reduction reaction, representing the first bifunctional BP‐based metal‐free oxygen catalyst. Moreover, ZABs are assembled incorporating BP‐CN‐c cathodes, delivering a substantially higher peak power density (168.3 mW cm−2) than the Pt/C+RuO2‐based ZABs (101.3 mW cm−2). The acquired insights into interfacial covalent bonds pave the way for the rational design of new and affordable metal‐free catalysts.
In this work, high-throughput ab initio calculations are employed to identify the most promising chalcogenide-based semiconductors for p-type transparent conducting materials (TCMs).
In this work, we investigated ternary chalcogenide semiconductors to identify promising p-type transparent conducting materials (TCMs). Highthroughput calculations were employed to find the compounds that satisfies our screening criteria. Our screening strategy was based on the size of band gaps, the values of hole effective masses, and p-type dopability. Our search led to the identification of seven promising compounds (IrSbS, Ba 2 GeSe 4 , Ba 2 SiSe 4 , Ba(BSe 3 ) 2 , VCu 3 S 4 , NbCu 3 Se 4 , and CuBS 2 ) as potential TCM candidates. In addition, branch point energy and optical absorption spectra calculations support our findings. Our results open a new direction for the design and development of ptype TCMs.
The formation of an Rb‐containing In‐Se compound at the surface of Cu(In,Ga)Se2 (CIGS) thin films is assumed to be part of the mechanism of RbF post‐deposition treatments (PDTs) performed on these absorber layers. Alkali‐PDTs have acquired attention lately as they significantly enhance the efficiency of CIGS solar cells. In this contribution the formation of various phases during the RbF‐PDT has been investigated. The results indicate that RbInSe2 is the most probable phase to form. Combining theoretical and experimental investigations, fundamental properties of a thermally co‐evaporated RbInSe2 thin film are reported in order to serve as reference values in further studies.
Adaptive kinetic Monte Carlo simulation (aKMC) is employed to study the dynamics and the diffusion of point defects in the CuInSe 2 lattice. The aKMC results show that lighter alkali atoms can diffuse into the CuInSe 2 grains, whereas the diffusion of heavier alkali atoms is limited to the Cu-poor region of the absorber. The key difference between the diffusion of lighter and heavier alkali elements is the energy barrier of the ion exchange between alkali interstitial atoms and Cu. For lighter alkali atoms like Na, the interstitial diffusion and the ion-exchange mechanism have comparable energy barriers. Therefore, Na interstitial atoms can diffuse into the grains and replace Cu atoms in the CuInSe 2 lattice. In contrast to Na, the ion-exchange mechanism occurs spontaneously for heavier alkali atoms like Rb and the further diffusion of these atoms depends on the availability of Cu vacancies. The outdiffusion of alkali substitutional atoms from the grains results in the formation of Cu vacancies which in turn increases the hole concentration in the absorber. In this respect, Na is more efficient than Rb due to the higher concentration of Na substitutional defects in the CuInSe 2 grains.
In this work, a high-throughput screening of binary and ternary pnictide- and halide-based compounds is performed to identify promising p-type transparent conductors. Our investigation profits from the emergence of open-access databases based on ab-initio results. The band gap, stability, hole effective mass, and p-type dopability are employed for the materials screening and the validity of these descriptors is discussed. Among the final candidates, BaSiN2 is the most promising compound.
We performed ab initio calculations to study oxygen and hydrogen point defects in the CuInSe 2 (CISe) solar-cell material. We found that H interstitial defects (when one H atom is surrounded by four Se atoms) and H Cu (when a H atom is replacing a Cu atom) are the most stable defects. Whereas these H substitutional defects remain neutral, H interstitial defects act as donor defects and are detrimental to the cell performance. The incorporation of H 2 into the CISe lattice, on the other hand, is harmless to the p-type conductivity. Oxygen atoms tend to either substitute Se atoms in the CISe lattice or form interstitial defects, though the formation of substitutional defects is more favorable. All oxygen point defects have high formation energies, which results in a low concentration of these defects in CISe. However, the presence of oxygen in the system leads to the formation of secondary phases such as In 2 O 3 and InCuO 2 . In addition to the point defects, we studied the adsorption of H 2 O molecules on a defect-free surface and a surface with a (2V Cu + In Cu ) defect using the ab initio thermodynamics technique. Our results indicate that the dissociative water adsorption on the CISe surface is energetically unfavorable. Furthermore, in order to obtain a water-free surface, the surface with defects has to be calcined at a higher temperature compared to the defect-free surface.
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