Wei Wei

The electrochemical CO2 reduction reaction (CO2RR) on Cu surfaces is constrained by the scaling relations among intermediate adsorption energies. We demonstrate that Cu-terminated Ti3CuC2, featuring an atomically thin Cu monolayer, is an efficient CO2RR catalyst. Charge transfer from Ti3C2 to Cu enriches the reaction sites with electrons and thus reconstructs their local electronic environment, downshifting the Cu d-band center. This regulation selectively enhances CO2 adsorption while it attenuates CO binding. The potential-determining step is hence diverted from *CO + H+ + e– → *CHO to alternative steps (ΔG = 0.02 eV). Such a mechanistic shift leads to low limiting potentials of −0.20 V for CH3OH and −0.30 V for CH4, simultaneously transforming the formidable C–C coupling into an exothermic process (ΔG = −0.10 eV) and enabling favorable pathways toward C2H4 and C2H5OH. These findings establish the selective regulation of CO2/CO adsorption as a promising design principle for efficient CO2RR catalysts.

In condensed matter physics, the excitonic insulator (EI) state has always been the key for macroscopic quantum coherence, the experimental detection of which, however, remains elusive. In this work, we propose a new mechanism for realizing the EI phase in quantum spin Hall insulators (QSHIs), in which the synergy between exciton binding energy (E_b) and quasi-particle (QP) band gap (E_g) can be broken. In GeCH₃ and SnCH₃, we verify that E_b > E_g, signaling spontaneous exciton formation and condensation to a reconstructed many-body ground state. In accordance with the Pauli exclusion, the exchange interaction of the Fermion constituents of the composite bosonic excitons causes bright-dark conversion, and these "indirectly photo-excited" dark excitons turn into the ground state due to the interband Coulomb interaction. In the case where bright and dark excitons coexist, the "gray condensate" forms, which will provide feasible solutions to the challenges in the experimental detection of EI.

In many-particle physics, excitonic Bose-Einstein condensation (BEC) reveals a long-sought macroscopic quantum coherent phase, which is scarce. In single-phase multilayer Ga₂Ge₂X₂ (X = S, Se), we prove that a new kind of spatially indirect exciton, the quadrupolar exciton, can be optically generated, which is in stark contrast to the previous findings based exclusively on the artificial van der Waals layers of transition metal dichalcogenides (TMDCs). In particular, we verify the bright-dark exciton transition due to the fermion exchange interaction, indicative of excitonic BEC constituted by quadrupolar dark excitons with ultralong lifetimes. In light of long lifetimes, small effective mass, and large binding energy, theoretical critical temperature for the BEC in Ga₂Ge₂S₂/Ga₂Ge₂Se₂ achieves as high as 395.3/386.7 K and 98.8/96.7 K for the Berezinskii-Kosterlitz-Thouless (BKT) superfluid phase. In this work, results open new possibilities for the study of excitonic physics and correlated quantum phase.

Efficient control of valley index is of great importance for both fundamental research and device applications, yet it remains a challenging problem. Here, through symmetry analysis and an effective k·p model, we propose a novel mechanism for coupling valley index with ferroelectricity in two-dimensional (2D) multiferroic lattice. The physics lies in that inequivalent potential arising from ferroelectricity can reverse and annihilate nonsymmetric trigons. Owning to the intimate connection between nonsymmetric trigons and valley physics, the valley index is locked to ferroelectric polarization. This enables the efficient electrical reversal of valley index for carriers, and electrical creation/annihilation of valley polarization. Moreover, based on first-principles calculations, we validate this mechanism in 2D multiferroic semiconductor TiCr₂O₄, which favors paraelectric as metastable state. Our work establishes a new paradigm for the design and optimization of valleytronic devices.

Excitonic insulator (EI), a long-sought yet exceptionally scarce macroscopic quantum phase of matter, has remained elusive. We propose that quantum spin Hall insulators (QSHIs) can be promising candidates for realizing excitonic instability. This is enabled by the atypical inverse quasiparticle (QP) correction to the inverted bands of QSHIs, which decouples the synergy of the QP band gap (E_g) and exciton binding energy (E_b). Combining first-principles calculations with many-body perturbation theory, we verify our proposal in the QSHIs TlX (X = As, Sb, Bi) with E_b exceeding the QP E_g. In stark contrast to the previously proposed EI dominated by dark excitons, the EI state in this study is constituted by bright excitons with negative formation energy and large oscillator strength, providing an optically accessible signature for detecting the EI. In particular, the emergence of correlated EI accompanied by nontrivial band topology unveils a novel paradigm of (bright) topological EI.

By exploring 161 distinct MN₄X–C SACs, optimal HER, OER, and ORR catalysts were identified. The axial ligand-induced d–p orbital hybridization (Δ_d–p) could govern the activity via orbital passivation and electron redistribution.

氨(NH3)是一种重要的工业原料. 传统的Haber−Bosch制氨工艺是能源密集型的，且释放大量二氧化碳(CO2)造成严重污染. 以一氧化氮(NO)为前驱体的电化学合成氨方法是在环境条件下可操作的，并且能够同时实现大气污染物NO的去除和利用，因此被认为是一种可持续、清洁和环保的新能源技术. 本文综述了电催化NO还原反应(NORR)生成NH3的机理，重点介绍了单原子配位，表、界面和缺陷工程等对电催化过程的影响及对电催化活性的优化和调控，总结了NORR催化还原体系的最新进展，最后讨论了NORR合成NH3的研究前景和面临的挑战.

In conjunction with the first-principles calculations, we confirm the fascinating valley-selective linear dichroism and the possibility of excitonic condensation in multiatomic-layer LaOBiS₂ of a tetragonal lattice by the effective tight-binding model and many-body perturbation theory. In LaOBiS₂, which indicates a spontaneous valley polarization due to crystalline symmetry reduction rather than conventional time-reversal symmetry breaking, we unravel that the excitons in X and X' valleys exclusively coupled to x- and y-linearly polarized lights, respectively. In sharp contrast to coupled quantum wells and van der Waals architectures, a new type of spatially indirect exciton is identified in single-crystal LaOBiS₂, manifesting itself as an engaging platform for investigating the excitonic Bose-Einstein condensation (BEC) and superfluidity. In light of large binding energy, large radius, and small effective mass of the exciton, the transition temperature for BEC and superfluidity achieves record-high values of 325.1 and 81.3 K, respectively.

Electrochemical nitrogen conversion for ammonia (NH3) synthesis, driven by renewable electricity, offers a sustainable alternative to the traditional Haber–Bosch process. However, this conversion process remains limited by a low Faradaic efficiency (FE) and NH3 yield. Although transition metals have been widely studied as catalysts for NH3 synthesis through effective electron donation/back-donation mechanisms, there are challenges in electrochemical environments, including competitive hydrogen evolution reaction (HER) and catalyst stability issues. In contrast, p-block elements show unique advantages in light of higher selectivity for nitrogen activation and chemical stability. The present article explores the potential of p-block element-based catalysts as active sites for NH3 synthesis, discussing their activation mechanisms, performance modulation strategies, and future research directions from a theoretical perspective.

In van der Waals (vdW) architectures of transition metal dichalcogenides (TMDCs), the coupling between interlayer exciton and quantum degrees of freedom opens unprecedented opportunities for excitonic physics. Taking the MoSe₂ homobilayer as representative, we identify that the interlayer registry defines the nature and dynamics of the lowest-energy interlayer exciton. The large layer polarization (P_n) is proved, which ensures the formation of layer-resolved interlayer excitons. In particular, sliding ferroelectric polarization couples to the dipole orientation of the interlayer exciton, thus achieving the long-sought electric control of excitonic states. In line with the phase winding of the Bloch states under C₃ rotational symmetry, we clarify the valley optical circular dichroism, enriching the exciton valleytronics. We also elucidate the Hall effect of the layer- and valley-polarized interlayer excitons, which advances our understanding of the spatial transport properties of the composite particles and provides new insights into the exciton-based applications.