RESUMO
Risley-prism-based image sensors can expand the imaging field of view through beam control. The larger the top angle of the prism, the higher the magnification of the field of view, but at the same time, it aggravates the problem of imaging aberrations, which also puts higher requirements on the aberration correction method for the Risley-prism-based image sensor. To improve the speed, accuracy, and stability of the aberration correction process, an automatic calibration method for the Risley-prism-based image sensor is proposed based on a two-axis turntable. The image datasets of the calibration plate with different prism rotation angles and object distances are acquired using a two-axis turntable. Then, the images of the calibration plate are pre-processed using the bicubic interpolation algorithm. The calibration parameters are finally calculated, and parameter optimization is performed. The experimental results verify the feasibility of this automated calibration method. The reprojection error of the calibration is within 0.26 pixels when the distance of the imaging sensor is 3.6 m from the object, and the fine aberration correction results are observed.
RESUMO
Vacancy engineering is proposed to effectively modulate the hydrogen evolution reaction (HER) activity of M2CO2 MXene. A single C vacancy slightly weakens the H adsorption, while the introduction of a M vacancy or coupled M+C vacancies can greatly enhance the H binding. For a MXene with intrinsic too-strong H adsorption, double C vacancies are effective in weakening the binding and promoting the activity. The activity tuning is closely correlated to the electronic structures of the defected MXene, where the highest occupied peak position of the surface O electronic states shows an apparent linear trend with ΔGH and can be used to qualitatively predict the activity. The weakened or strengthened H adsorption by a C or M vacancy is attributed to the upshifted or downshifted Fermi level of surface O, respectively. Our results indicate the potential of defect chemistry to tune the catalytic activity of MXene and provide new possibilities to enhance the applications of MXene.
RESUMO
The 2D MXenes have attracted great recent attention as the electrocatalytic materials for hydrogen evolution reaction (HER). However, the activity and the modification strategy of the catalytic properties have not been firmly established yet. In this study, we performed density functional theory (DFT) calculations to investigate the stability and HER performance of functionalized Mo2 C MXene. The Pourbaix diagram indicates the fully oxidized surface is the most stable state. The oxidized Mo2 CO2 is electrically conductive, yet the surface HER activity is unsatisfactory owing to the strong first H adsorption. The doping of transition metals (TM) into the Mo lattice, however, leads to much more enhanced H adsorption and deteriorates the activity. Alternatively, the H binding can be effectively weakened and flexibly tuned by anchoring the TM atoms over the surface with appropriate coverage, and Mn/Fe decoration at 12.5 % ML (monolayer) coverage is identified as the promising candidates with close to zero Gibbs free energy of H adsorption (ΔGH* ) for the first H adsorption. The weakening effect arises from charge transfer from TM to surface O, resulting in increased occupancy and weakened O-H bonds. Furthermore, contrary to the weakening effect, the tensile strain leads to enhanced O-H binding by the up-shifted Op electronic states, which can further modulate the HER performance of TM-modified Mo2 CO2 . The synergistic effect between TM modification and strain engineering offers beneficial advantages for the realization of efficient electrochemical HER, which can be applied to other MXenes for electronic and catalytic applications.
