Boron-based 2D materials are of current interest. However, graphene-like geometry is unstable for B due to the electron deficiency, which can be stabilized by introducing H, F and Cl. Here, using density functional theory combined with phonon Boltzmann transport equation, we perform systematic studies on how the functionalization changes the lattice thermal conductivity (LTC). We find that when going from hydrogenation to fluorination and chlorination, the LTC along zigzag direction changes from 367.6 to 211.3 and 43.0 W/(m·K), while the corresponding values in armchair direction are 279.6, 198.9, and 41.6 W/(m·K), respectively. These huge differences imply the sensitivity of LTC to functionalization, which can be attributed to the enhanced anharmonicity as revealed by analyzing group velocity, Gruneisen parameter, anharmonic scattering rates, and three-phonon scattering space.

Inspired by the recent experimental synthesis of graphene nanoribbons (GNRs) and theoretical research on their edge-decoration, we comprehensively studied the electrocatalytic performance of GNRs edge-decorated with Cu for CO₂ reduction. Compared to zigzag GNRs, the Cu-terminated armchair GNRs with a width of n = 3p + 2 were more efficient catalysts for producing methanol from CO₂ with a free energy barrier of less than 0.5 eV, offering the advantages of a lower overpotential and higher selectivity than bulk Cu and other graphene-supported Cu structures. On the other hand, the competing hydrogen evolution reaction could be effectively suppressed by Cu-terminated armchair GNRs. Hence, the edge-decorated GNRs offer great flexibility for tuning the catalytic efficiency and selectivity for CO₂ electroreduction.

C₂ is a well-known pseudo-oxygen unit with an electron affinity of 3.4 eV. We show that it can exhibit metal-ion like behavior when embedded in a porphyrin sheet and form a metal-free two-dimensional material with superior oxygen reduction performance. Here, the positively charged C=C units are highly active for oxygen reduction reaction (ORR) via dissociation pathways with a small energy barrier of 0.09 eV, much smaller than that of other non-platinum group metal (non-PGM) ORR catalysts. Using a microkinetics-based model, we calculated the partial current density to be 3.0 mA/cm² at 0.65 V vs. a standard hydrogen electrode (SHE), which is comparable to that of the state-of-the-art Pt/C catalyst. We further confirm that the C=C embedded porphyrin sheet is dynamically and thermally stable with a quasi-direct band gap of 1.14 eV. The superior catalytic performance and geometric stability make the metal-free C=C porphyrin sheet ideal for fuel cell applications.

We report a density functional theory study of a phase transition of a VS₂ monolayer that can be tuned by the in-plane biaxial strain. This results in both a metal-insulator transition and a low spin-high spin magnetic transition. At low temperature, the semiconducting H-phase is stable and large strain (> 3%) is required to provoke the transition. On the other hand, at room temperature (300 K), only a small tensile strain of 2% is needed to induce the phase transition from the semiconducting H-phase to the metallic T-phase together with the magnetic transition from high spin to low spin. The phase diagram dependence on both strain and temperature is also discussed in order to provide a better understanding of the phase stability of VS₂ monolayers.