Unraveling the atomistic structures of electric double layers (EDL) at electrified interfaces is of paramount importance for understanding the mechanisms of electrocatalytic reactions and rationally designing electrode materials with better performance. Despite numerous efforts dedicated in the past, a molecular level understanding of the EDL is still lacking. Combining the state-of-the-art ab initio molecular dynamics (AIMD) and recently developed computational standard hydrogen electrode (cSHE) method, it is possible to realistically simulate the EDL under well-defined electrochemical conditions. In this work, we report extensive AIMD calculation of the electrified Pt(111)-H ad /water interfaces at the saturation coverage of adsorbed hydrogen (H ad ) corresponding to the typical hydrogen evolution reaction conditions. We calculate the electrode potentials of a series of EDL models with various surface charge densities using the cSHE method and further obtain the Helmholtz capacitance that agrees with experiment. Furthermore, the AIMD simulations allow for detailed structural analyses of the electrified interfaces, such as the distribution of adsorbate H ad and the structures of interface water and counterions, which can in turn explain the computed dielectric property of interface water. Our calculation provides valuable molecular insight into the electrified interfaces and a solid basis for understanding a variety of electrochemical processes occurring inside the EDL.
The structural reconstruction dynamics and the real HER/OER active species of cobalt phosphides/chalcogenides were revealed through operando XAS/Raman spectroscopy.
Single atom catalysts (SACs) are ideal model systems in catalysis research. Here we employ SACs to address the fundamental catalytic challenge of generating well-defined active metal centers to elucidate their interactions with coordinating atoms, which define their catalytic performance. We introduce a soft-landing molecular strategy for tailored SACs based on metal phthalocyanines (MPcs, M = Ni, Co, Fe) on graphene oxide (GO) layers to generate well-defined model targets for mechanistic studies. The formation of electronic channels through -conjugation with the graphene sheets enhances the MPc-GO performance in both oxygen evolution and reduction reactions (OER and ORR). Density functional theory (DFT) calculations unravel that the outstanding ORR activity of FePc-GO among the series is due to the high affinity of Fe atoms toward O2 species. Operando X-ray absorption spectroscopy and DFT studies demonstrate that the OER performance of the catalysts relates to thermodynamic or kinetic control at low-or high-potential ranges, respectively. We furthermore provide evidence that the participation of ligating N and C atoms around the metal centers provides a wider selection of active OER sites for both NiPc-GO and CoPc-GO. Our strategy promotes the understanding of coordination-activity relationships of high-performance SACs and their optimization for different processes through tailored combinations of metal centers and suitable ligand environments.
A complete catalytic cycle for methane combustion on the Co3O4(110) surface was investigated and compared with that on the Co3O4(100) surface on the basis of first-principles calculations. It is found that the 2-fold coordinated lattice oxygen (O2c) would be of vital importance for methane combustion over Co3O4 surfaces, especially for the first two C–H bond activations and the C–O bond coupling. It could explain the reason the Co3O4(110) surface significantly outperforms the Co3O4(100) surface without exposed O2c for methane combustion. More importantly, it is found that the cooperation of homogeneous multiple sites for multiple elementary steps would be indispensable. It not only facilitates the hydrogen transfer between different sites for the swift formation of H2O to effectively avoid the passivation of the active low-coordinated O2c site but also stabilizes surface intermediates during the methane oxidation, optimizing the reaction channel. An understanding of this cooperation of multiple active sites not only might be beneficial in developing improved catalysts for methane combustion but also might shed light on one advantage of heterogeneous catalysts with multiple sites in comparison to single-site catalysts for catalytic activity.
As the most active new frontier, a single-atom catalyst (SAC) combining the merits of heterogeneous and homogeneous catalysts would have a significant effect on the 100 year history of ammonia synthesis research. Here, the Ru SAC has been demonstrated to be active and efficient for ammonia synthesis. To this end, an ideal model catalyst, pure siliceous zeolite-supported Ru SAC (Ru SAs/S-1), which shows surprising catalytic ammonia synthesis activity compared to that of a conventional Ru catalyst, was designed. Both atomic-resolution scanning transmission electron microscopy, X-ray absorption spectrometric analysis, and in situ diffuse reflectance infrared Fourier transform spectroscopy identify the single-Ru-atom nature of Ru SAs/S-1 before and after the reaction. Further DFT calculations reveal that the reaction mechanism is different from traditional mechanisms. Therefore, this paper provides an alternative SAC strategy to design high-performance Ru catalysts for ammonia synthesis.
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