Catalytic Activity of Defect-Engineered Transition Me tal Dichalcogenides Mapped with Atomic-Scale Precision by Electrochemical Scanning Tunneling Microscopy

Abstract

Unraveling structure–activity relationships is a key objective of catalysis. Unfortunately, the intrinsic complexity and structural heterogeneity of materials stand in the way of this goal, mainly because the activity measurements are area-averaged and therefore contain information coming from different surface sites. This limitation can be surpassed by the analysis of the noise in the current of electrochemical scanning tunneling microscopy (EC-STM). Herein, we apply this strategy to investigate the catalytic activity toward the hydrogen evolution reaction of monolayer films of MoSe2. Thanks to atomically resolved potentiodynamic experiments, we can evaluate individually the catalytic activity of the MoSe2 basal plane, selenium vacancies, and different point defects produced by the intersections of metallic twin boundaries. The activity trend deduced by EC-STM is independently confirmed by density functional theory calculations, which also indicate that, on the metallic twin boundary crossings, the hydrogen adsorption energy is almost thermoneutral. The micro- and macroscopic measurements are combined to extract the turnover frequency of different sites, obtaining for the most active ones a value of 30 s–1 at −136 mV vs RHE.

Elucidating the Active Sites and Synergies in Water Splitting on Manganese Oxide Nanosheets on Graphite Support

“…Subsequently, we show the nanosheets' nature of active sites using electrochemical noise scanning tunneling microscopy (n‐EC‐STM), [ 32 ] which enables an in situ observation of the local activity [ 33–36 ] as recently demonstrated by different groups. [ 37–39 ] These observations are supported and systematically explained by the most probable reaction pathways using density functional theory (DFT) calculations. Herein, the MnO 2 NS were modeled as a sheet of birnissite‐type δ‐MnO 2, which has been shown to have similar features to the Mn 4 CaO 5 in PS II.…”

Recent advances in molybdenum diselenide-based electrocatalysts: preparation and application in the hydrogen evolution reaction

“…83,84 More recently, note that MoSe 2 monolayer (ML) grown by molecular beam epitaxy (MBE) on a bilayer of graphene (G) supported on a 6H-SiC single crystal (MoSe 2 /G/SiC) was used as a characteristic HER catalyst to individually detect the catalytic activity of the MoSe 2 basal plane, selenium vacancies, and different point defects produced by the intersections of metallic twin boundaries characterized using electrochemical scanning tunneling microscopy (EC-STM). 134 As is known, although MoSe 2 indicated a low electrical conductivity and a limited active site for HER performance, the conductivity of MoSe 2 is higher than that of MoS 2 owing to the substitution of highly conductive Se atoms (≈1 × 10 −3 S m −1 ) with low-conductive S atoms (≈5 × 10 −28 S m −1 ). Hence, MoSe 2 still showed relatively superior electrochemical catalytic activity and chemical stability.…”

“…83,84 More recently, note that MoSe 2 monolayer (ML) grown by molecular beam epitaxy (MBE) on a bilayer of graphene (G) supported on a 6H-SiC single crystal (MoSe 2 /G/SiC) was used as a characteristic HER catalyst to individually detect the catalytic activity of the MoSe 2 basal plane, selenium vacancies, and different point defects produced by the intersections of metallic twin boundaries characterized using electrochemical scanning tunneling microscopy (EC-STM). 134…”

“…Some advanced instruments such as EC-STM, SEM, and confocal laser scanning microscopy (CLSM) are necessary. 134,204 In situ monitoring the evolution of catalyst surface during the HER process can precisely reveal the origin of the improved catalytic performance through the quasi-operando XPS survey spectra and potential-dependent in situ Raman spectra recorded. 62,63 In all molybdenum dichalcogenides, MoS 2 was often used as an electrocatalyst in HER and was reported to be stable under acidic conditions.…”

Unveiling the Interplay between a Au(100) Electrode, Adsorbed TTMAPP Porphyrin Cations, and Iodide Anions: An EC-STM and CV Study

“…Furthermore, we extend the investigations into the negative potential regime below the iodine adsorption/desorption peaks, where the TTMAPP molecules adsorb directly on the I-free (1 × 1) Au(100) surface . The use of both STM and CV in EC investigations in liquids enables the simultaneous in situ and in operando characterization of both the clean and the adsorbate-covered electrode surfaces. − As specified above, by exploring the self-assembly of TTMAPP on an iodine-modified Au(100) electrode, this study aims to enhance our understanding of the potential-induced modification of noncovalent interactions, such as van der Waals and electrostatic forces, between the assembled molecules and the substrate. In this context, we also found that the adsorbed TTMAPP molecules not only hinder the readsorption of iodine on the surface but also hinder the desorption of iodine from the surface.…”