Yongqing Cai

• PhD
• Professor (Assistant) at University of Macau

Nitrate reduction to ammonia has attracted much attention for nitrate (NO3‐) removal and ammonia (NH3) production. Identifying promising catalyst for active nitrate electroreduction reaction (NO3RR) is critical to realize efficient upscaling synthesis of NH3 under low‐temperature condition. For this purpose, by means of spin‐polarized first‐princip...

The mixture of different A-site cations in lead halide perovskites is an effective method to stabilize the phase and improve reproducibility together with a promoted efficiency of power conversion. However,...

Ferroelasticity is a phenomenon in which a material exhibits two or more equally stable orientation variants and can be switched from one form to another under an applied stress. Recent works have demonstrated that two-dimensional layered organic–inorganic hybrid Ruddlesden–Popper perovskites can serve as ideal platforms for realizing ferroelastici...

As a prototype of the Weyl superconductor, layered molybdenum ditelluride (MoTe2) encompasses two semimetallic phases (1T' and Td) which differentiate from each other via a slight tilting of the out-of-plane lattice. Both phases are subjected to serious phase mixing, which complicates the analysis of its origin of superconductivity. Herein, we expl...

Shrinking the size of a bulk metal into nanoscale leads to the discreteness of electronic energy levels, the so-called Kubo gap. Renormalization of the electronic properties with a tunable and size-dependent Kubo gap renders fascinating photon emission and electron tunneling. In contrast with usual three-dimensional (3D) metal clusters, here we dem...

Two-dimensional organic-inorganic perovskites have garnered extensive interest due to their unique structure and optoelectronic performance. However, their loose structures complicate mechanism illustration and tend to cause uncertainty and diversity of...

This study proves the existence of bromine vacancies cluster in pairs and the ease formation of Cl and I substituted dopants in CsPbBr 3 , which provides critical insight into complex defects in all-inorganic metal halide perovskites.

Solid‐state sodium‐metal batteries (SSSBs) have emerged as a potential next‐generation energy storage technology due to their abundant resource, high energy density, and safety. However, the uncontrolled Na dendrite growth and low charging/discharging rate pose a severe constraint on their practical applications. Herein, high interfacial sodium‐ion...

The technique of conventional ferromagnet/heavy-metal spin-orbit torque (SOT) offers significant potential for enhancing the efficiency of magnetic memories. However, it faces fundamental physical limitations, including shunting effects from the metallic layer, broken symmetry for enabling antidamping switching, spin scattering caused by interfacia...

The Supporting Information contains the formulation adopted for elastic constants characterization and DFT simulation results (electronic band structures, density of states, and electron density contour plots) accessory to the main article; ACS Nano 16, 261 (2022).

The Supporting Information contains first-principles simulation results, schematics of the crystal structure of monolayer (BA)2PbI4, and molecular dynamics simulation results accessory to the main article; ACS Nano 18, 14187 (2024).

Ferroelasticity describes a phenomenon in which a material exhibits two or more equally stable orientation variants and can be switched from one form to another under an applied stress. Recent works have demonstrated that two-dimensional layered organic–inorganic hybrid Ruddlesden–Popper perovskites can serve as ideal platforms for realizing ferroe...

Hysteresis window observed in ferroelectric negative capacitance field-effect transistors (NCFETs) have been a persistent challenge in the development of reliable logic circuits, often leading to abnormal operational conditions. Despite its significance, the underlying factors driving this hysteresis phenomenon remain elusive. In this study, we emp...

Topological semimetals with protected surface states mark a new paradigm of research beyond the early landmarks of band-structure engineering, allowing fabrication of efficient catalyst to harness the rich metallic surface states to activate specific chemical processes. Herein, we demonstrate a facile solid-phase method for in-situ doping of Ir at...

Aqueous Zinc-Ion Batteries The dendrite growth issue which stems from chaotic zinc deposition/dissolution significantly hinders the cycling stability of zinc ion batteries. In article number 2400572, Hou Ian, Junpeng Xie, Guo Hong, and co-workers utilized adsorptive additives to manipulate zinc dissolution and achieved smooth morphological evolutio...

We examine the electronic and transport properties of a new phase PdSe monolayer with a puckered structure calculated by first-principles and Boltzmann transport equation. The spin–orbit coupling is found to play a negligible effect on the electronic properties of PdSe monolayer. The lattice thermal conductivity of PdSe monolayer exhibits remarkabl...

The commercialization of aqueous Zn‐ion batteries (AZIBs) for power‐grid energy storage systems is hindered by the safety concerns arising from the Zn dendrite growth. The primary approach in addressing this issue is to induce planar depositions. However, modulating the Zn dissolution process which directly reshapes surface morphology and reserves...

Heterogeneous structures and doping strategies have been intensively used to manipulate the catalytic conversion of polysulfides to enhance reaction kinetics and suppress the shuttle effect in lithium‐sulfur (Li‐S) batteries. However, understanding how to select suitable strategies for engineering the electronic structure of polar catalysts is lack...

Tungsten oxides (WO3) are widely recognized as multifunctional systems owing to the existence of rich polymorphs. These diverse phases exhibit distinct octahedra-tilting patterns, generating substantial tunnels that are ideally suited for iontronics. However, a quantitative comprehension regarding the impact of distinct phases on the kinetics of in...

Water is often viewed as detrimental to organic halide perovskite stability. However, evidence highlights its efficacy as a solvent during organic perovskite liquid synthesis. This paradox prompts an investigation into water's influence on perovskite nanoclusters. Employing first principle calculations and \textit{ab initio} molecular dynamics simu...

MoS2 and related transition metal dichalcogenides (TMDs) have recently been reported to exhibit extensive applications in nanoelectronics and catalysis due to their unique physical and chemical properties. However, one practical...

The technique of conventional ferromagnet/heavy-metal spin-orbit torque (SOT) offers significant potential for enhancing the efficiency of magnetic memories. However, it faces fundamental physical limitations, including hunting effects from the metallic layer, broken symmetry for enabling antidamping switching, spin scattering caused by interfacial...

Patterning antidots, which are regions of potential hills that repel electrons, into well-defined antidot lattices creates fascinating artificial periodic structures, leading to anomalous transport properties and exotic quantum phenomena in two-dimensional systems. Although nanolithography has brought conventional antidots from the semiclassical re...

Nitrate reduction to ammonia has attracted much attention for nitrate (NO3-) removal and ammonia (NH3) production. Identifying promising catalyst for active nitrate electroreduction reaction (NO3RR) is critical to realize efficient upscaling synthesis of NH3 under low-temperature condition. For this purpose, by means of spin-polarized first-princip...

Two-dimensional (2D) materials tend to have the preferably formation of vacancies at the outer surface. Here, contrary to the normal notion, we reveal a type of vacancy that thermodynamically initiates from the interior part of the 2D backbone of germanium selenide ({\gamma}-GeSe). Interestingly, the Ge-vacancy (VGe) in the interior part of {\gamma...

Hydrogen as the cleanest energy carrier is a promising alternative renewable resource to fossil fuels. There is an ever-increasing interest in exploring efficient and cost-effective approaches of hydrogen production. Recent experiments have shown that single platinum atom immobilized on the metal vacancies of MXenes allows a high-efficient hydrogen...

Recently synthesized novel phase of germanium selenide ({\gamma}-GeSe) adopts a hexagonal lattice and a surprisingly high conductivity than graphite. This triggers great interests in exploring its potential for thermoelectric applications. Herein, we explored the thermoelectric performance of monolayer {\gamma}-GeSe and other isostructural {\gamma}...

Molybdenum ditelluride (MoTe2) is an unique transition metal dichalcogenide owing to its energetically comparable 1H and 1T prime phases. This implies a high chance of coexistence of 1H-1T prime heterostructures which poses great complexity in the measurement of the intrinsic lattice thermal conductivities (kappa). In this work, via first-principle...

Solvent engineering is highly essential for the upscaling synthesis of high-quality metal halide perovskite materials for solar cells. The complexity in the colloidal containing various residual species poses great difficulty in the design of the formula of the solvent. Knowledge of the energetics of the solvent-lead iodide (PbI2) adduct allows a q...

Formamidinium lead triiodide (FAPbI3) with an ideal bandgap and good thermal stability has received wide attention and achieved a record efficiency of 26% in n–i–p (regular) perovskite solar cells (PSCs). However, imperfect FAPbI3 formation on the typical hole transport layer (HTL), high interfacial trap‐state density, and unfavorable energy alignm...

As a prototype of the Weyl superconductor, layered molybdenum telluride (MoTe2) encompasses two semimetallic phases (1T_prime and Td) which differentiate from each other via a slight tilting of the out-of-plane lattice. Both phases are subjected to serious phase mixing which complicates the analysis of its origin of superconductivity. Herein, we ex...

Patterning antidots ("voids") into well-defined antidot lattices creates an intriguing class of artificial structures for the periodic modulation of 2D electron systems, leading to anomalous transport properties and exotic quantum phenomena as well as enabling the precise bandgap engineering of 2D materials to address technological bottleneck issue...

The power conversion efficiency (PCE) of the state-of-the-art large area slot die-coated perovskite solar cells (PSCs) is now over 19%, but issues with their stability persist owing to significant intrinsic point defects and a mass of surface imperfections introduced during fabrication process. We report the utilization of a hydrophobic all-organic...

Recent successful growth of asymmetric transition metal dichalcogenides via accurate manipulation of different chalcogen atoms in top and bottom surfaces demonstrates exotic electronic and chemical properties in such Janus systems. Within the framework of density functional perturbation theory, anharmonic phonon properties of monolayer Janus MoSSe...

Hydrogen as the cleanest energy carrier is a promising alternative renewable resource to fossil fuels. There is an ever-increasing interest in exploring efficient and cost-effective approaches of hydrogen production. Recent experiments have shown that single platinum atom immobilized on the metal vacancies of MXenes allows a high-efficient hydrogen...

The flexomagnetic effect involves the coupling of inhomogeneous mechanical and magnetic excitations to generate exotic spin orders. The intrinsic edge stress associated with lifting of periodic degeneracy at surfaces or edges in nanostructures facilitates the flexocoupling effects. Here, we combine first-principles calculation and Maximum Informati...

The observation of room temperature sub-60 mV/dec subthreshold slope in MOSFET with ferroelectric layers in the gate stacks has attracted much attention. However, little consideration is given to reliability, which affects the long-term stability of the device. In this work, we investigate the reliability of the oxide layer in the negative capacita...

Two-dimensional (2D) materials tend to have the preferable formation of vacancies at the outer surface. Here, contrary to the normal notion, we reveal a type of vacancy that thermodynamically initiates from the interior part of the 2D backbone of germanium selenide (γ-GeSe). Interestingly, the Ge-vacancy (VGe) in the interior part of γ-GeSe possess...

Multilayers consisting of alternating soft and hard layers offer enhanced toughness compared to all-hard structures. However, shear instability usually exists in physically sputtered multilayers because of deformation incompatibility among hard and soft layers. Here, we demonstrate that 2D hybrid organic-inorganic perovskites (HOIP) provide an inte...

Magnetic Heterostructures In article number 2208528, Cai, Han, Lin and co‐workers report that multi‐configurational 2D CrxTey magnetic heterojunctions are visualized by transmission electron microscopy diffraction and atomic scanning transmission electron microscopy imaging. The lateral heterojunction of Cr2Te3‐Cr5Te8 shares the layered CrTe2 as th...

Understanding the hydration kinetics and interactions of hydration products of cement components with chlorides is crucial for designing durable cement-based materials. The most reactive component of ordinary Portland cement (OPC), tricalcium aluminate (C3A), was investigated on its hydration kinetics, chloride binding behaviors and hydrated phase...

Molybdenum ditelluride (MoTe2) is an unique transition metal dichalcogenide owing to its energetically comparable 1H and 1T′ phases. This implies a high chance of coexistence of 1H/1T′ heterostructures which poses great complexity in the measurement of the intrinsic lattice thermal conductivities (κL). In this work, via first-principles calculation...

Correction for ‘Low-energy interlayer phonon assisted carrier recombination in Z-scheme van der Waals heterostructures for photocatalysis’ by Hejin Yan et al. , J. Mater. Chem. A , 2022, 10 , 23744–23750, https://doi.org/10.1039/D2TA04935J.

Two-dimensional layered materials have attracted tremendous attention as photodetectors due to their fascinating features, including comprehensive coverage of band gaps, high potential in new-generation electronic devices, mechanical flexibility, and sensitive light–mass interaction. Currently, graphene and transition-metal dichalcogenides (TMDCs)...

While caesium lead bromide (CsPbBr 3) is promising for highly stable perovskite solar cells (PSCs), the usual solution-based methods require tedious multistep spin coating processes, which imposes a practical barrier against scaling up to large areas for industrial exploitation. Although sequential vapour deposition (SVD) can meet commercial requir...

Recently synthesized novel phase of germanium selenide (γ-GeSe) adopts a hexagonal lattice and a surprisingly high conductivity than graphite. This triggers great interests in exploring its potential for thermoelectric applications. Herein, we explored the thermoelectric performance of monolayer γ-GeSe and other isostructural γ-phase of group-IV mo...

Emerging 2D magnetic heterojunctions attract substantial interest due to their potential applications in spintronics. Achieving magnetic phase engineering with structural integrity in 2D heterojunctions is of paramount importance for their magnetism manipulation. Herein, starting with chromium ditelluride (CrTe2) as the backbone framework, various...

Recent discovery of a novel hexagonal phase of GeSe (Gamma-GeSe) has triggered great interests in nanoelectronics applications owing to its electrical conductivity of bulk phase even higher than graphite while its monolayer is a semiconductor. For potential applications, construction of functional two-dimensional (2D) contacts is indispensable. Her...

Two-dimensional (2D) van der Waals (vdW) materials have extraordinary thermal properties due to the effect of quantum confinement, making them promising for thermoelectric energy conversion and thermal management in microelectronic devices. In this review, the mechanism of phonon anharmonicity originating from three- and four-phonon interactions is...

As emerging atomically ultrathin metal compounds, MXenes show great promise for catalysts and nanoelectronics applications due to the abundant surface terminations and high metallic conductivity. However, the tendency of the interlayer adhesion and suffering from environmental disturbances significantly limit their endurance and efficiency. Herein...

Germanium selenide (GeSe) is a unique two-dimensional (2D) material showing various polymorphs stable at ambient condition. Recently, a new phase with a layered hexagonal lattice ({\gamma}-GeSe) was synthesized with ambient stability and extraordinary electronic conductivity even higher than graphite while its monolayer is semiconducting. In this w...

Layered hexagonal Gamma--GeSe, a new polymorph of GeSe synthesized recently, shows strikingly high electronic conductivity in its bulk form (even higher than graphite) while semiconducting in the case of monolayer (1L). In this work, by using first-principles calculations, we demonstrate that, different from its orthorhombic phases of GeSe, the Gam...

Germanium selenide (GeSe) is a unique two-dimensional (2D) material showing various polymorphs stable at ambient conditions. Recently, a new phase with a layered hexagonal lattice (GeSe) was synthesized with ambient stability and extraordinary electronic conductivity, even higher than that of graphite, while its monolayer is semiconducting. In this...

Establishing the coupling mechanism of hot carriers and phonons is at the heart of nanoelectronics and photocatalysis of vdW heterostructures. Herein, via ab initio simulations, we endeavor to examine the intralayer phononic assisted recombination in a designed Z-scheme vdW heterostructure based on an emerging WSi2N4 material and transition metal d...

Metal halide perovskites have become a research highlight in the optoelectronic field due to their excellent properties. The perovskite light-emitting diodes (PeLEDs) have achieved great improvement in performance in recent years, and the construction of quasi-2D perovskites by incorporating large-size organic cations is an effective strategy for f...

Chloride (Cl) induced steel corrosion is a major cause of durability issues of reinforced concrete (RC) structures and causes a large economic loss every year. Understanding the mechanisms of Cl induced steel corrosion in concrete is of great importance to develop anti-corrosion methods and further lowers down the repair and strengthening frequency...

Understanding the energetics and kinetics of chloride in cement-based materials is critical to identify effective ways to control chloride diffusion. Here, we performed an ab-initio molecular dynamics (AIMD) simulation on interfacial activities to reveal the reaction mechanism and dynamic nature of chloride. Chloride ions mainly distributed in the...

Two-dimensional (2D) van der Waals (vdW) materials have extraordinary thermal properties due to the effect of quantum confinement, making them promising for thermoelectric energy conversion and thermal management in microelectronic devices. In this review, the mechanism of phonon anharmonicity originating from three- and four-phonon interactions is...

Layered hexagonal γ-GeSe, a new polymorph of GeSe synthesized recently, shows strikingly high electronic conductivity in its bulk form (even higher than graphite) while semiconducting in the case of monolayer (1L). In this work, by using first-principles calculations, we demonstrate that, different from its orthorhombic phases of GeSe, the γ-GeSe s...

Aqueous zinc ion batteries (AZIBs) with high theoretical capacity, low cost and highly safety that have been considered as one of the most promising candidates for the next generation of electrochemical energy storage applications. However, the hydrated zinc ions have strong electrostatic force with the host material, causing the low output voltage...

2D Oxides for Electronics and Optoelectronics 2D oxides can be synthesized in a simple environment and show good stability, which has broad application prospect in electronics and optoelectronics. In article number 2200008, Xiaozong Hu, Shuang‐Quan Zang, Tianyou Zhai, and co‐workers review the advances in the synthesis, basic properties and applica...

Near-infrared (NIR) light-emitting materials are crucial for night vision, in vivo-imaging, and secret codes. However, issues such as thermal quenching and chemical stability tend to significantly suppress the efficiency. In this work, we modify NIR-emitting phosphor Y3(Al,Mg)2(Al,Si)3O12:Cr³⁺ (YMAS:Cr³⁺) by substitution via 2[Al³⁺]→[Mg²⁺]+[Si⁴⁺] b...

In recent years, 2D oxides have attracted considerable attention due to their novel physical properties and excellent stability. With the efforts of researchers, significant progress has been made in the synthesis and electronics and optoelectronics application of 2D oxides. Herein, a systematic review focusing on the preparation of 2D oxides and t...

The thermal conductivities of pristine and defective tungsten diselenide (WSe2) are investigated by using equilibrium molecular dynamics method. The thermal conductivity of WSe2 increases dramatically with size below a characteristic with of ~ 5 nm and levels off for broader samples and reaches a constant value of ~2 W/mK. By introducing atomic vac...

The thermal conductivities k of wurtzite InxGa1-xN are investigated using equilibrium molecular dynamics (MD) method. The k of InxGa1-xN rapidly declines from InN (k_InN = 141 W/mK) or GaN (k_GaN = 500 W/mK) to InxGa1-xN, and reaches a minimum (k_min = 19 W/mK) when x is around 0.5 at 300 K. The mean free path (MFP) of InxGa1-xN, ranging from 2 to...

Existence of van der Waals gaps renders two-dimensional (2D) materials ideal passages of lithium for being used as anode materials. However, the requirement of good conductivity significantly limits the choice of 2D candidates. So far only graphite is satisfying due to its relatively high conductivity. Recently, a new polymorph of layered germanium...

Lead-free tin-based perovskites are highly appealing for the next generation of solar cells due to their intriguing optoelectronic properties. However, the tendency of Sn2+ oxidation to Sn4+ in the tin-based perovskites induces serious film degradation and performance deterioration. Herein, we demonstrate, through the density functional theory base...

Existence of van der Waals gaps renders two‐dimensional (2D) materials ideal passages of lithium for being used as anode materials. However, the requirement of good conductivity significantly limits the choice of 2D candidates. So far, only graphite is satisfying due to its relatively high conductivity. Recently, a new polymorph of layered germaniu...

In this paper, we use multiscale modeling to explore the coupling of the atomic orbital and magnetic moment and their evolutions under the excitations of external stress and magnetic fields. Our results of density functional theory (DFT) calculations show that strain-induced spin reorientation and redistribution of orbital coupling are the fundamen...

The optical selection rules obeyed by two-dimensional materials with spin-valley coupling enable the selective excitation of carriers. We show that several members of the monolayer MA2Z4 (M=Mo and W;A=C, Si, and Ge; Z=N, P, and As) family are direct band-gap semiconductors with protected valley states and that circularly polarized infrared light ca...

Transition metal dichalcogenides (TMDs), two-dimensional (2D) layered Ruddlesden-Popper perovskite material, and their heterojunctions have attracted a great deal of interest in optoelectronic applications. Although various approaches for modulating their properties and applications have been demonstrated, knowledge of the interface band alignment...

Motivated by the recently synthesized layered material MoSi2N4, we investigate excitonic response of quasiparticle of monolayer MoSi2N4 by using G0W0 and Bethe-Salpeter equation calculations. With a dually sandwiched structure consisting of a central MoN2 layer analog of 2H−MoS2 capped with silicon-nitrogen (SiN) honeycomb outer layers, MoSi2N4 pos...

The thermal conductivities κ of wurtzite InxGa1-xN are investigated using equilibrium molecular dynamics (MD) method. The κ of InxGa1-xN rapidly declines from InN (κ InN = 141 W/mK) or GaN (κ GaN = 500 W/mK) to InxGa1-xN (x ≠ or 1), and reaches a minimum (κ min = 19 W/mK) when × is around 0.5 at 300 K. The mean free path (MFP) of InxGa1-xN, ra...

Lead-free tin-based perovskites are highly appealing for the next generation of solar cells due to their intriguing optoelectronic properties. However, the tendency of Sn²⁺ oxidation to Sn⁴⁺ in the tin-based perovskites induces serious film degradation and performance deterioration. Herein, we demonstrate, through the density functional theory base...