Although the electrochemical N 2 reduction reaction (NRR) to NH 3 provides a promising avenue for artificial N 2 fixation, building of efficient NRR electrocatalysts with high activity and stability remains a tremendous challenge. The combined experimental results and theoretical calculation reveal that MoS 2 with sulfur-vacancy defect (V S -MoS 2 ) is an admirable NRR catalyst. Electrochemical results demonstrate that V S -MoS 2 (5:2) possesses outstanding NRR performances, including a superior NH 3 average yield rate (46.1 × 10 −11 mol s −1 cm −2 at -0.5 V vs reversible hydrogen electrode (RHE)), an excellent faraday efficiency (FE: 4.58% at -0.4 V vs RHE), good electrochemical stability (at least 24 h), and high selectivity (no by-product of N 2 H 4 ). Density functional theory (DFT) calculations demonstrate that the rate determining steps (RDSs) of all V S -MoS 2 (010)-2, V S -MoS 2 (010)-1, and MoS 2 (010) are the first hydrogenation step to form *NNH intermediate, as reflected by the energy barriers of 0.06 eV, 0.20 eV, and 0.93 eV, the significantly charge transfer (1.02 e , 0.45 e vs. 0.41 e ) from two Mo atoms to N 2 , as well as the stretching of N N bond (1.200 Å, 1.140 Å vs. 0.970 Å), respectively. These results reveal that V S -MoS 2 (010)-2 can effectively activate inert N 2 molecule and have the potential application in nitrogen fixation under mild conditions.
Electrocatalytic selective hydrogenation of α,β-unsaturated aldehydes with water as the hydrogen donor is of great significance to produce fine chemicals. Here, we propose a facile vapor-phase hydrothermal (VPH) method to directly grow defective MoS2 nanoparticles on commercial carbon fiber cloth (MoS2/CFC) for electrocatalytic selective hydrogenation of cinnamaldehyde (CAL). The as-prepared MoS2/CFC exhibited the highest CAL conversion of 88.8% with a maximum TOF value of 12.8 mmol mmolMoS2−1 h−1 at −0.7 V vs. RHE. The high selectivity of CAL hydrogenation could be realized by adjusting the applied potentials, CO hydrogenation product cinnamyl alcohol (COL) was easier to form under lower applied potentials, whereas CC hydrogenation product hydrocinnamaldehyde (HCAL) was easier to achieve under higher applied potentials. Density functional theory (DFT) calculation findings demonstrated that the Mo vacancies in the defective MoS2/CFC facilitated the adsorption of hydrogen atoms, which benefited the generation of Hads and the proceeding of electrocatalytic hydrogenation. Additionally, the existence of Mo vacancies made the CO group more active than the CC group, and reduced the reaction energy of CAL hydrogenation toward COL. Combined with the experimental results and calculation data, we speculate that the real catalytic active center of the defective MoS2/CFC is the defective configuration of Mo vacancies. Furthermore, the high conversion and selectivity of furfural and benzaldehyde hydrogenation confirmed the universality of the defective MoS2/CFC catalyst in electrocatalytic hydrogenation reduction of unsaturated and saturated aldehydes.
Defect-rich MoS 2 /r-GO hybrids are successfully synthesized via microwave-assisted solvothermal process, and their electrocatalytic properties for hydrogen evolution reaction (HER) are evaluated. The hybrids exhibit low overpotential of 86 mV at 10 mA cm −2 , with a Tafel slope of 44 mV dec −1 as well as promising long-term stability. The activation energy required by HER is 25.4 kJ/mol, and the faraday efficiency reaches 86.3% at −0.16 V (vs. RHE). The attractive performance can be attributed to the abundant defects generated in highly disordered MoS 2 phase, which help to expose a large number of active sites. In addition, the interaction between r-GO and MoS 2 particles promotes the charge transfer process. This work provides a simple strategy for the rational design and mass fabrication of defect-rich MoS 2 -based electrocatalysts for hydrogen evolution reaction.
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