Passivation of electronic defects at the surface and grain boundaries of perovskite materials has become one of the most important strategies to suppress charge recombination in both polycrystalline ...and single-crystalline perovskite solar cells. Although many passivation molecules have been reported, it remains very unclear regarding the passivation mechanisms of various functional groups. Here, we systematically engineer the structures of passivation molecular functional groups, including carboxyl, amine, isopropyl, phenethyl, and tert-butylphenethyl groups, and study their passivation capability to perovskites. It reveals the carboxyl and amine groups would heal charged defects via electrostatic interactions, and the neutral iodine related defects can be reduced by the aromatic structures. The judicious control of the interaction between perovskite and molecules can further realize grain boundary passivation, including those that are deep toward substrates. Understanding of the underlining mechanisms allows us to design a new passivation molecule, D-4-tert-butylphenylalanine, yielding high-performance p-i-structure solar cells with a stabilized efficiency of 21.4%. The open-circuit voltage (V OC) of a device with an optical bandgap of 1.57 eV for the perovskite layer reaches 1.23 V, corresponding to a record small V OC deficit of 0.34 V. Our findings provide a guidance for future design of new passivation molecules to realize multiple facets applications in perovskite electronics.
Phosphorene, a monolayer of black phosphorus, is promising for nanoelectronic applications not only because it is a natural p-type semiconductor but also because it possesses a layer-number-dependent ...direct bandgap (in the range of 0.3 to 1.5 eV). On basis of the density functional theory calculations, we investigate electronic properties of the bilayer phosphorene with different stacking orders. We find that the direct bandgap of the bilayers can vary from 0.78 to 1.04 eV with three different stacking orders. In addition, a vertical electric field can further reduce the bandgap to 0.56 eV (at the field strength 0.5 V/Å). More importantly, we find that when a monolayer of MoS2 is superimposed with the p-type AA- or AB-stacked bilayer phosphorene, the combined trilayer can be an effective solar-cell material with type-II heterojunction alignment. The power conversion efficiency is predicted to be ∼18 or 16% with AA- or AB-stacked bilayer phosphorene, higher than reported efficiencies of the state-of-the-art trilayer graphene/transition metal dichalcogenide solar cells.
A new two‐dimensional (2D) layered material, namely, titanium trisulfide (TiS3) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS3 ...monolayer is a direct‐gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in‐plane electron mobility of the 2D TiS3 is highly anisotropic, amounting to about 10 000 cm2 V−1 s−1 in the b direction, which is higher than that of the MoS2 monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS3 possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS3. Both dynamical and thermal stability of the TiS3 monolayer is examined by phonon‐spectrum calculation and Born–Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS3 monolayer a promising 2D atomic‐layer material for applications in future nanoelectronics.
New semiconductor: A titanium trisulfide monolayer is predicted to be a direct‐gap semiconductor with ultrahigh electron mobility (≈104 cm2 V−1 s−1), which is higher than that of MoS2 and phosphorene. The monolayer can be exfoliated from its bulk phase due to the lower exfoliation energy compared to graphite.
The oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are three critical reactions for energy-related applications, such as water electrolyzers ...and metal-air batteries. Graphene-supported single-atom catalysts (SACs) have been widely explored; however, either experiments or density functional theory (DFT) computations cannot screen catalysts at high speed. Herein, based on DFT computations of 104 graphene-supported SACs (M@C
3
, M@C
4
, M@pyridine-N
4
, and M@pyrrole-N
4
), we built machine learning (ML) models to describe the underlying pattern of easily obtainable physical properties and limiting potentials (mean square errors = 0.027/0.021/0.035 V for the ORR/OER/HER, respectively) and employed these models to predict the catalytic performance of 260 other graphene-supported SACs containing metal-N
x
C
y
active sites (M@N
x
C
y
). We recomputed the top catalysts recommended by ML towards the ORR/OER/HER by DFT, which confirmed the reliability of our ML model, and identified two OER catalysts (Ir@pyridine-N
3
C
1
and Ir@pyridine-N
2
C
2
) outperforming noble metal oxides, RuO
2
and IrO
2
. The ML models quantitatively unveiled the significance of various descriptors and quickly narrowed down the candidate list of graphene-supported single-atom catalysts. This approach can be easily used to screen and design other SACs and significantly accelerate the catalyst design for many other important reactions.
The oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are three critical reactions for energy-related applications, such as water electrolyzers and metal-air batteries.
Abstract
Ag/γ-Al
2
O
3
is widely used for catalyzing various reactions, and its performance depends on the valence state, morphology and dispersion of Ag species. However, detailed anchoring ...mechanism of Ag species on γ-Al
2
O
3
remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al
2
O
3
are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al
2
O
3
can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al
2
O
3
. Density-functional-theory calculations confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al
2
O
3
, but not on microsized γ-Al
2
O
3
. The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts.
Atomically thin two-dimensional (2D) materials have received intense research interest due to their novel properties and promising applications in nanodevices. By using density functional theory ...(DFT) calculations, we investigate catalytic activities of several newly predicted two-dimensional (2D) triphosphides GeP3, SnP3 and InP3 monolayers for hydrogen evolution reaction (HER). The calculation results show that GeP3 and SnP3 monolayers are active catalysts for HER with suitable free energy of hydrogen adsorption in the basal plane. In particular, the Gibbs free energy of hydrogen adsorption (ΔGH*) of GeP3 is 0.024 eV, a value even more favorable compared to the precious-group-metal (PGM) catalyst Pt. Moreover, the 2D GeP3 and SnP3 are intrinsically compatible with the graphene substrate so that the HER performance can be improved via building a hybrid multilayer with graphene sheet. The charge transfer from GeP3 or SnP3 to graphene, estimated to be 0.1278e or 0.2157e, can significantly enhance the electric conductivity and promote the electrocatalytic activity. Although the electronic band structure of GeP3 and SnP3 can be tuned by external strain, we find that the HER performance of GeP3 and SnP3 monolayer is actually insensitive to the external strain, a feature desirable for the catalytic application. The desirable properties for HER with nearly zero Gibbs free energy render 2D GeP3 and SnP3 promising candidates for future application in electrocatalysis.
Conspectus Understanding special stability of numerous ligand-protected gold nanoclusters has always been an active area of research. In the past few decades, several theoretical models, including ...the polyhedral skeletal electron pair theory (PSEPT), superatom complex (SAC), and superatom network (SAN), among others, have been developed for better understanding the stabilities and structures of selected ligand-protected gold nanoclusters. This Account overviews the recently proposed grand unified model (GUM) to offer some new insights into the structures and growth mechanism of nearly all crystallized and predicted ligand-protected gold nanoclusters. The main conceptual advancement of the GUM is identification of the duet and octet rules on the basis of the “big data” of 70+ reported ligand-protected gold nanoclusters. According to the two empirical rules, the cores of the gold nanoclusters can be regarded as being composed of two kinds of elementary blocks (namely, triangle Au3 and tetrahedron Au4), each having 2e closed-shell valence electrons (referred as Au3(2e) and Au4(2e)), as well as the secondary block (icosahedron Au13) with 8e closed-shell valence electrons (referred as Au13(8e)). The two elementary blocks (Au3(2e) and Au4(2e)) and the secondary block (Au13(8e)), from electron counting point of view, can be regarded as an analogy of the highly stable noble-gas atoms of He and Ne, respectively. In each elementary block, the Au atoms exhibit three different valence-electron states (i.e., 1e, 0.5e, and 0e), depending on the type of ligands bonded with these Au atoms. Such three valence-electron states are coined as three “flavors” of gold (namely, bottom, middle, and top “flavor”), a term borrowed from the quark model in the particle physics. Upon application of the duet and octet rules with accounting the three valence states of gold atoms, the Au3(2e), Au4(2e), and Au13(8e) blocks can exhibit 10 (denoted as Δ1–Δ10), 15 (denoted as T1–T15), and 91 (denoted as I1–I91) variants of valence states, respectively. When packing these blocks (with distinct electronic states) together, it forms the gold core of ligand-protected gold nanocluster. As such, the special stabilities of the ligand-protected gold nanoclusters are explained based on the local stability of each block. With GUM, rich and complex structures of ligand-protected gold nanoclusters have been analyzed through structure anatomy. Moreover, the growth of these clusters can be simply viewed as sequential addition of the blocks, rather than as addition of the gold atoms. Another useful application of the GUM is to analyze the structural isomerism. The three types of isomerism for the gold nanoclusters, i.e., core, staple, and complex isomerism, can be considered as an analogy of chain, point, and functional isomerism (known in organic chemistry), respectively. GUM can be applied to predict new clusters, thereby guiding experimental synthesis. Indeed, a number of ligand-protected gold nanoclusters with high stabilities were rationally designed based on the GUM.
A critical challenge in the commercialization of layer‐structured Ni‐rich materials is the fast capacity drop and voltage fading due to the interfacial instability and bulk structural degradation of ...the cathodes during battery operation. Herein, with the guidance of theoretical calculations of migration energy difference between La and Ti from the surface to the inside of LiNi0.8Co0.1Mn0.1O2, for the first time, Ti‐doped and La4NiLiO8‐coated LiNi0.8Co0.1Mn0.1O2 cathodes are rationally designed and prepared, via a simple and convenient dual‐modification strategy of synchronous synthesis and in situ modification. Impressively, the dual modified materials show remarkably improved electrochemical performance and largely suppressed voltage fading, even under exertive operational conditions at elevated temperature and under extended cutoff voltage. Further studies reveal that the nanoscale structural degradation on material surfaces and the appearance of intergranular cracks associated with the inconsistent evolution of structural degradation at the particle level can be effectively suppressed by the synergetic effect of the conductive La4NiLiO8 coating layer and the strong TiO bond. The present work demonstrates that our strategy can simultaneously address the two issues with respect to interfacial instability and bulk structural degradation, and it represents a significant progress in the development of advanced cathode materials for high‐performance lithium‐ion batteries.
Ti‐doped and La4NiLiO8‐coated Ni‐rich layered oxide cathodes are synchronously and in situ synthesized with the guidance of theoretical calculations, which exhibit good surficial stability, fast interfacial kinetic behaviors, suppressed inconsistent structural degradation in combination with markedly improved electrochemical performance. This work opens a new avenue of designing simple modification approaches and advanced cathodes for high‐energy lithium‐ion batteries.
The direct urea fuel cell (DUFC) is an important but challenging renewable energy production technology, it offers great promise for energy‐sustainable developments and mitigating water ...contamination. However, DUFCs still suffer from the sluggish kinetics of the urea oxidation reaction (UOR) owing to a 6 e− transfer process, which poses a severe hindrance to their practical use. Herein, taking β‐Ni(OH)2 nanosheets as the proof‐of‐concept study, we demonstrated a surface‐chemistry strategy to achieve metallic Ni(OH)2 nanosheets by engineering their electronic structure, representing a first metallic configuration of transition‐metal hydroxides. Surface sulfur incorporation successfully brings synergetic effects of more exposed active sites, good wetting behavior, and effective electron transport, giving rise to greatly enhanced performance for UOR. Metallic nanosheets exhibited a much higher current density, smaller onset potential and stronger durability.
Metal as anything: Surface sulfur incorporation into β‐Ni(OH)2 nanosheets gives the first metallic configuration of a transition‐metal hydroxide. The resulting metallic Ni(OH)2 nanosheets have more exposed active sites and metallic electrical conductivity, giving rise to greatly enhanced performance for the urea oxidation reaction (UOR) for direct urea fuel cells.
Abstract
The spectroscopic features of protonated water species in dilute acid solutions have been long sought after for understanding the microscopic behavior of the proton in water with gas-phase ...water clusters H
+
(H
2
O)
n
extensively studied as bottom-up model systems. We present a new protocol for the calculation of the infrared (IR) spectra of complex systems, which combines the fragment-based Coupled Cluster method and anharmonic vibrational quasi-degenerate perturbation theory, and demonstrate its accuracy towards the complete and accurate assignment of the IR spectrum of the H
+
(H
2
O)
21
cluster. The site-specific IR spectral signatures reveal two distinct structures for the internal and surface four-coordinated water molecules, which are ice-like and liquid-like, respectively. The effect of inter-molecular interaction between water molecules is addressed, and the vibrational resonance is found between the O-H stretching fundamental and the bending overtone of the nearest neighboring water molecule. The revelation of the spectral signature of the excess proton offers deeper insight into the nature of charge accommodation in the extended hydrogen-bonding network underpinning this aqueous cluster.
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