Developing alternatives to precious Pt for hydrogen production from water splitting is central to the area of renewable energy. This work predicts extremely high catalytic activity of transition metal (Fe, Co, and Ni) promoted two‐dimensional MXenes, fully oxidized vanadium carbides (V2CO2), for hydrogen evolution reaction (HER). The first‐principle calculations show that the introduction of transition metal can greatly weaken the strong binding between hydrogen and oxygen and engineer the hydrogen adsorption free energy to the optimal value ≈0 eV by choosing the suitable type and coverage of the promoters as well as the active sites. Strain engineering on the performance of transition metal promoted V2CO2 further reveals that the excellent HER activities can maintain well while those poor ones can be modulated to be highly active. This study provides new possibilities for cost‐effective alternatives to Pt in HER and for the application of 2D MXenes.
The environmental instability of single-or few-layer black phosphorus (BP) has become am ajor hurdle for BPbased devices.T he degradation mechanism remains unclear and finding ways to protect BP from degradation is still highly challenging.Based on ab initio electronic structure calculations and molecular dynamics simulations,athree-step picture on the ambient degradation of BP is provided:g eneration of superoxide under light, dissociation of the superoxide,a nd eventual breakdown under the action of water.T he wellmatched band gap and band-edge positions for the redox potential accelerates the degradation of thinner BP.F urthermore,i tw as found that the formation of P-O-P bonds can greatly stabilizet he BP framework. Ap ossible protection strategy using afully oxidized BP layer as the native capping is thus proposed. Suchafully oxidization layer can resist corrosion from water and leave the BP underneath intact with simultaneous high hole mobility.
A new three-step photo-oxidative degradation mechanism of MAPbI3 is proposed. A strategy for protecting MAPbI3 by 2-(4-fluorophenyl)propan-2-amine modification is designed.
Sulfur vacancies (SVs) inherent in MoS are generally detrimental for carrier mobility and optical properties. Thiol chemistry has been explored for SV repair and surface functionalization. However, the resultant products and reaction mechanisms are still controversial. Herein, a comprehensive understanding on the reactions is provided by tracking potential energy surfaces and kinetic studies. The reactions are dominated by two competitive mechanisms that lead to either functionalization products or repair SVs, and the polarization effect from decorating thiol molecules and thermal effect are two determining factors. Electron-donating groups are conducive to the repairing reaction whereas electron-withdrawing groups facilitate the functionalization process. Moreover, the predominant reaction mechanism can be switched by increasing the temperature. This study fosters a way of precisely tailoring the electronic and optical properties of MoS by means of thiol chemistry approaches.
Molybdenum disulfide (MoS2) is considered to be one
of the most promising low-cost catalysts for the hydrogen evolution
reaction (HER). So far, the limited active sites and high kinetic
barriers for H2 evolution still impede its practical application
in electrochemical water splitting. In this work, on the basis of
comprehensive first-principles calculations, we predict that the recently
produced template-grown MoS2 nanowires (NWs) on Au(755)
surfaces have both ultralow kinetic barriers for H2 evolution
and ultrahigh active site density simultaneously. The calculated kinetic
barrier of H2 evolution through the Tafel mechanism is
only 0.49 eV on the Mo edges, making the Volmer–Tafel mechanism
operative, and the Tafel slope can be as low as 30 mV/dec. Through
substitution of the Au(755) substrate with non-noble metals, such
as Ni(755) and Cu(755), the activity can be maintained. This work
provides a possible way to achieve the ultrahigh HER activity of MoS2-based catalysts.
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