RESUMEN
Defects have been found to enhance the electrocatalytic performance of NiFe-LDH for oxygen evolution reaction (OER). Nevertheless, their specific configuration and the role played in regulating the surface reconstruction of electrocatalysts remain ambiguous. Herein, cationic vacancy defects are generated via aprotic-solvent-solvation-induced leaking of metal cations from NiFe-LDH nanosheets. DFT calculation and in situ Raman spectroscopic observation both reveal that the as-generated cationic vacancy defects tend to exist as VM (M=Ni/Fe); under increasing applied voltage, they tend to assume the configuration VMOH , and eventually transform into VMOH-H which is the most active yet most difficult to form thermodynamically. Meanwhile, with increasing voltage the surface crystalline Ni(OH)x in the NiFe-LDH is gradually converted into disordered status; under sufficiently high voltage when oxygen bubbles start to evolve, local NiOOH species become appearing, which is the residual product from the formation of vacancy VMOH-H . Thus, we demonstrate that the cationic defects evolve along with increasing applied voltage (VM â VMOH â VMOH-H ), and reveal the essential motif for the surface restructuration process of NiFe-LDH (crystalline Ni(OH)x â disordered Ni(OH)x â NiOOH). Our work provides insight into defect-induced surface restructuration behaviors of NiFe-LDH as a typical precatalyst for efficient OER electrocatalysis.
RESUMEN
It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel-cell catalysts. Surface enhanced Raman spectroscopy (SERS) is a powerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range, however, using it to probe practical nanocatalysts remains extremely challenging. Herein, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt3 Co nanocatalyst structures. Direct spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt3 Co in both acidic and basic environments. Density functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt3 Co surface accounts for enhanced ORR activity. This work shows SHINERS is a promising technique for the real-time observation of catalytic processes.
RESUMEN
The single molecular conductance of amino acids was measured by a scanning tunneling microscope (STM) break junction. Conductance measurement of alanine gives out two conductance values at 10-1.85 G0 (1095 nS) and 10-3.7 G0 (15.5 nS), while similar conductance values are also observed for aspartic acid and glutamic acid, which have one more carboxylic acid group compared with alanine. This may show that the backbone of NH2-C-COOH is the primary means of electron transport in the molecular junction of aspartic acid and glutamic acid. However, NH2-C-COOH is not the primary means of electron transport in the methionine junction, which may be caused by the strong interaction of the Au-SMe (methyl sulfide) bond for the methionine junction. The current work reveals the important role of the anchoring group in the electron transport in different amino acids junctions.
