Wangyu Hu

Stacking fault energy dictates phase stability and deformation behavior in Co alloys and WC-Co cemented carbides, yet a quantitative assessment of alloying effects at finite temperatures remains poorly established. By integrating first-principles thermodynamics with microstructural characterization, we provide a rigorous evaluation of these influences across atomic and macroscopic scales. We show that stacking fault energetics at 0K for transition metal solutes are primarily governed by atomic misfit volume. While 4d and 5d elements follow a consistent linear trend, specific 3d solutes exhibit significant deviations due to non-negligible magnetic contributions. By incorporating phonon, electronic, longitudinal spin-fluctuation, and magnetic free-energy contributions, the model accurately captures the fcc-hcp transformation and quantifies how diverse solutes modulate the phase landscape. We demonstrate that V, Ni, Fe, Mo, and W lower the transformation temperature by stabilizing fcc phase, while Cr and C exhibit the opposite effect, consistent with experimental phase diagrams. Furthermore, microscopic analysis confirms that higher W content dissolved in the Co suppresses stacking-fault formation by elevating the stacking fault energy at finite temperatures. This work clarifies the physical mechanisms by which alloying regulates stacking fault energy and phase stability in Co-based systems, providing guidance for the design of Co-based alloys and WC-Co cemented carbides.

This paper presents an automated strategy for constructing machine-learning potential (MLP) datasets through a physics-strengthened point-sampling scheme called physics-strengthened machine-learning potential (PhyMLP). By integrating heterogeneous data sources - including the Rose equation of state, experimental pressure-volume (P-V) measurements, traditional empirical potentials, and first-principles calculations - this method effectively circumvents computational bottlenecks and reduces the reliance on the exhaustive density functional theory (DFT) computations inherent in conventional training-set construction. The PhyMLP employs an adaptive, physics-guided sampling strategy that leverages intrinsic material responses and requires only a limited number of critical DFT calculations to efficiently characterize the potential energy surface. Using body-centered cubic tungsten as a benchmark system, the moment tensor potential trained on the PhyMLP-generated dataset exhibited exceptional predictive accuracy across a wide spectrum of material properties, ranging from fundamental physical constants to complex defect energetics and kinetic behavior. Ultimately, this study established a systematic and computationally efficient paradigm for developing accurate transferable MLPs, thereby offering a robust framework for large-scale atomistic simulations and advanced material modeling.

Ferroelectric (FE) switching offers a pathway to bypass the Sabatier limit by toggling binding states, yet the computational cost for screening such dynamic materials remains prohibitive. Here, we present a machine learning-accelerated approach to discover two-dimensional FE metal–organic frameworks for switchable hydrogen evolution. We establish a geometric-electronic descriptor that enables quantitative cross-state prediction of adsorption energies, effectively halving the computational cost by forecasting the switched state solely from the initial-state features. Using this model, we identify candidate materials where polarization reversal drives the hydrogen adsorption free energy (ΔGH) from negative to positive, facilitating a direct transition from strong adsorption to spontaneous desorption. Microscopically, polarization-driven coordination field reconfiguration serves as a geometric switch to tune the energy level and occupation of the metal dz2 orbitals, while the magnitude of spin-polarization splitting ultimately governs the thermodynamic stability. This work provides a systematic framework for discovering intrinsic switchable catalysts via efficient cross-state prediction.

Grain boundary (GB) migration accompanied by Cr depletion is widely observed in Alloy 690 and is closely linked to intergranular degradation and stress corrosion cracking. However, the fundamental driving force for GB migration and its link with Cr depletion remains unclear. In this work, hybrid molecular dynamics and semi-grand canonical Monte Carlo simulations were employed to investigate GB migration in Alloy 690 under coupled solute diffusion and segregation effects across a range of GB characters. The results show that Cr segregation at GBs, while generally considered favorable for GB stability, can facilitate diffusion-induced GB migration and Cr depletion. Cr diffusion along GBs produces localized Cr depletion zones that are energetically incompatible with positively segregating GBs, generating a chemical driving force that drives GB migration toward the Cr-rich matrix, which ultimately results in persistent GB migration accompanied by a Cr depletion. By quantifying solute–GB interaction energetics, we demonstrate that GB migration is quantitively controlled by the coupled effects of solute diffusivity and segregation strength. These mechanistic insights provide a unified framework that rationalizes experimentally observed correlations between GB character, Cr depletion, and GB migration in Cr-containing alloys.

The Sabatier principle establishes a fundamental trade-off in heterogeneous electrocatalysis. In the hydrogen evolution reaction (HER), this trade-off is manifested by the coupling of the Volmer step, which requires strong hydrogen adsorption, with the Heyrovsky/Tafel step, which favors facile desorption—thus giving rise to the classical volcano relationship and limiting activity even at ΔGH*≈ 0. Here, we demonstrate a ferroelectric platform with dynamic tunability—monolayer GeS2 decorated with transition-metal atoms as a proof-of-concept—where polarization-driven surface electronic reconstruction enables real-time modulation of intermediate binding strength, thereby breaking the Sabatier constraint. Reversible control of hydrogen adsorption allows strong H* binding to accelerate the Volmer step, followed by weakened adsorption to promote the Heyrovsky/Tafel step. This dynamic adsorption–desorption decoupling not only surpasses the volcano limit to achieve unprecedented HER activity but also establishes a general paradigm for designing adaptive electrocatalysts capable of reconfiguring under operating conditions.

Spin states are pivotal in modulating the electrocatalytic activity of transition metal (TM)-based compounds, yet quantitatively evaluating the activity-spin state correlation remains a formidable challenge. Here, we propose an “activity index (η)” as a descriptor, to assess the activity of the spin states for the hydrogen evolution reaction (HER). η descriptor integrates three key electronic parameters: the proportion (P), broadening range (R), and center (εact) of the active spin state, which collectively account for the electronic structure modulation induced by both the intrinsic active site and its local coordination environment. Using 1T-phase ZrSe2-anchored TM atoms (TM = Sc to Ni) as prototypes, we reveal that the correlation between Gibbs free energy (ΔGH) and the η value follows a linear relation—ΔGH reduces as η decreases. Notably, ZrSe2-Mn exhibits the optimal η value (−0.56), corresponding to the best HER activity with a ΔGH of −0.04 eV—closer to the thermoneutral ideal value (0 eV) than even Pt (ΔGH = −0.09 eV). This relationship suggests that η is an effective descriptor of the active spin state for HER of TM-based catalysts. Our study establishes a quantitative correlation between HER activity and spin polarization, enabling performance prediction through spin-resolved physical descriptor.

Harnessing intrinsic properties to modulate the electronic structure of two-dimensional (2D) materials is essential for clean energy conversion, but challenging. Herein, we demonstrate that tuning intrinsic dipole is an effective strategy to enhance hydrogen evolution reaction (HER) activity of 2D Janus MXenes, which is exemplified by Mo2C_XY (X/Y = O, F, S, H, OH), using density functional theory calculations. Particularly, Mo2C_OF exhibits four intrinsic dipoles (μS↑, μM↑, μL↑, and μ↓), each characterized by distinct magnitudes and/or directions originated from the Mo3+ displacement and its phase change. We propose a single-atom dipole moment to elucidate the underlying mechanism controlling the variation of intrinsic dipole moments in Janus monolayer MXenes. It is found that intrinsic dipole significantly influences the HER activity. Specifically, the adsorption energy of H is reduced when the dipole direction points toward the adsorbed intermediate. Among them, Mo2C_OOH has the Gibbs free energy of −0.04 eV, surpassing the catalytic performance of commercial Pt. Furthermore, we demonstrate that intrinsic dipoles can be tuned via external strain or electronic doping, providing a pathway for optimizing catalytic performance.

Photocatalytic water splitting is a promising route for clean energy production, yet remains constrained by poor carrier utilization and low solar-to-hydrogen (STH) efficiency. Here, we demonstrate the role of out-of-plane polarization in addressing these limitations by using 1H phase Cr-based Janus monolayers. The out-of-plane polarization optimizes band edges to match water redox potentials at pH = 0, and the out-of-plane piezoelectric electron redistribution via the Poisson effect extends photocatalytic activity to full pH levels. The Janus homojunction constructed from these monolayers inherits the optimized overpotential and naturally forms a type-II band alignment, and dipole-induced electric field further drives the segregated carriers to opposite sides participating in the respective half-reactions, facilitating exciton dissociation. Remarkably, out-of-plane polarization can break traditional bandgap lower limits of 1.23 eV, which enhances light absorption and boosts STH efficiency to 38.1% for the CrSSe homojunction at pH = 0 and 37% for the −2.5% CrSeTe homojunction in the pH range of 7–11. This work highlights the out-of-plane polarization as a powerful strategy to enhance photocatalytic water splitting performance, offering insight for designing high-efficiency photocatalysts.

Structural materials exposed to supercritical carbon dioxide (S-CO2) environment will face serious corrosion failure that presents significant challenges to the durability and safety of materials in critical industrial applications, such as nuclear reactors and energy storage systems. Based on density functional theory calculations, a new and highly accurate Fe/C/O reactive force field parameter set has been developed to reveal the corrosion mechanisms of iron (Fe) under S-CO2 environment via molecular dynamics simulation. The influence of temperature, oxygen atoms, and carbon atoms on the corrosion process is also discussed in this work. We demonstrate that high temperature significantly accelerates the corrosion rate without altering the corrosion mechanism. After exposure to the S-CO2 environment, a multilayered corrosion structure (including a porous outer oxide layer with a carbide layer, a dense inner oxide layer, and an innermost carburized layer) was observed on the surface. The dense inner oxide layer hinders the penetration of carbon atoms into deeper regions. However, the presence of carbon disrupts the oxide layer, hastening substrate degradation. Additionally, pre-oxidation treatment effectively suppresses Fe–C bond formation and substantially enhances substrate corrosion resistance. These findings offer crucial insights for guiding the design of corrosion-resistant materials and the development of effective surface treatments for high-temperature and high-pressure industrial applications.

Photovoltaic solar cell is one of the main renewable energy sources, and its power conversion efficiency (PCE) is improved by employing doping or heterojunction to reduce the photogenerated carrier recombination. Here, we propose a straightforward strategy for constructing high-PCE homojunction solar cells, where intrinsic driving forces can simultaneously enhance the efficiency of carrier separation and transport. Thanks to the intrinsic dipole of Janus structure, doping-free Janus homojunction has naturally not only a type-II band alignment to promote the photoexciton dissociation, but also a reduced effective bandgap to enhance light absorption. More importantly, the interfacial dipole can facilitate the separation of carriers into different layers, thereby promoting carrier separation; and the intrinsic dipole across the Janus structure can drive photoinduced electron and hole transfer to opposite layers, enhancing carrier transport. We illustrate the concept in titanium-based Janus monolayer homojunction, where the theoretically observed PCE reaches 23.22% of TiSSe homojunction. In contrast to the previous cell architectures that require complex processing procedures and often result in defects, the doping-free homojunction configuration promises both high PCE and significantly lower manufacturing costs. Our work opens an avenue to design low-cost, high-efficiency solar cells.