The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. Platinum-based materials are the most active electrocatalysts for catalyzing HER, but reducing the use of Pt is required because of the high price and scarcity of Pt. Here, we achieve pseudo-atomic-scale dispersion of Pt, i.e. individual atoms or subnanometer clusters, on the sidewalls of single-walled carbon nanotubes (SWNTs) with a simple and readily upscalable electroplating deposition method. These SWNTs activated with an ultralow amount of Pt exhibit activity similar to that of commercial Pt/C with a notably higher (∼66–333-fold) Pt loading for catalyzing the HER under the acidic conditions required in proton exchange membrane technology. These catalysts resemble pseudo-atomic-scale Pt systems which are mainly composed of a few to tens of Pt atoms dispersed on the sidewalls of the SWNTs. The Pt loading is only 0.19–0.75 atom % at the electrode surface, and characteristic peaks for Pt cyclic voltammograms are undetectable. The atomic dispersion increases the portion of the surface active-atom sites, and therefore, notably lower Pt loading is needed to attain a high catalytic activity. Density functional theory (DFT) calculations suggest higher ability for SWNTs, in comparison to graphene, as a catalyst support for immobilizing Pt atoms, thus providing an atomic dispersion. Moreover, a high HER activity for the SWNTs activated with Pt atoms, similar to that of bulk Pt, is predicted.
We report a comprehensive computational study of the intricate structure-property relationships governing the hydrogen adsorption trends on MoS 2 edges with varying S-and H-coverages, as well as provide insights into the role of individual adsorption sites. Additionally, the effect of singleand dual S-vacancies in the basal plane on the adsorption energetics is assessed, likewise with an emphasis on the H-coverage dependency. The employed edge/site-selective approach reveals significant variations in the adsorption free energies, ranging between ∼ ±1.0 eV for the different edges-types and S-saturations, including differences of even as much as ∼ 1.2 eV between sites on the same edge. The incrementally increasing hydrogen coverage is seen to mainly weaken the adsorption, but intriguingly for certain configurations a stabilizing effect is also observed. The strengthened binding is seen to be coupled with significant surface restructuring, most notably the splitting of terminal S 2 -dimers. Our work links the energetics of hydrogen adsorption on 2H-MoS 2 to both static and dynamic geometrical features and quantifies the observed trends as a function of H-coverage, thus illustrating the complex structure/activity relationships of the MoS 2 catalyst. The results of this systematical study aims to serve as guidance for experimentalists by suggesting feasible edge/S-coverage combinations, the synthesis of which would potentially yield the most optimally performing HER-catalysts.
The computational hydrogen evolution activity of Pt(111) remains controversial due to apparent discrepancies with experiments concerning rate-determining activation free energies and equilibrium hydrogen coverages. A fundamental source of error may lie within the static representations of the metal−water interface commonly employed in density functional theory (DFT)based kinetic models neglecting important entropic effects on reaction dynamics. In this work, we present a dynamic reassessment of the Volmer−Tafel hydrogen evolution pathway on Pt(111) through DFT-based constrained molecular dynamics simulations and thermodynamic integration. Hydrogen coverage effects are gauged at two distinct surface saturations, while the critical potential dependence and constant potential conditions are accounted for using a capacitive model of the electrified interface. The uncertainty in the highly nontrivial treatment of the electrode potential is carefully examined, and we provide a quantitative estimation of the error associated with dynamically simulated electrochemical barriers. The dynamic description of the electrochemical interface promotes a substantial decrease of the Tafel free energy barrier as the coverage is increased to a full monolayer. This follows from a decreased entropic barrier due to suppressed adlayer dynamics compared to the unsaturated surface, a detail easily missed by static calculations predicting notably higher barriers at the same coverage. Due to observed endergonic adsorption of active hydrogen intermediates, the Tafel step remains ratedetermining irrespective of the coverage as illustrated by composed Volmer−Tafel free energy landscapes. Importantly, our explicitly dynamic approach avoids the ambiguous choice of frozen solvent configuration, decreasing the reliance on error cancellation and paving the way for less biased electrochemical simulations.
Electrochemical devices for efficient production of hydrogen as energy carrier rely still largely on rare platinum group metal catalysts. Chemically and structurally modified metal dichalcogenide MoS2 is a promising substitute for these critical raw materials at the cathode side where the hydrogen evolution reaction takes place. For precise understanding of structure and hydrogen adsorption characteristics in chemically modified MoS2 nanostructures, we perform comprehensive density functional theory calculations on transition metal (Fe, Co, Ni, Cu) doping at the experimentally relevant MoS2 surfaces at substitutional Mo-sites. Clear benefits of doping the basal plane are found, whereas at the Mo- and S-edges complex modifications at the whole edge are observed. New insight into doping-enhanced activity is obtained and guidance is given for further experiments. We study a machine learning model to facilitate the screening of suitable structures and find a promising level of prediction accuracy with minimal structural input.
This study presents the first direct simulation of the hydrogen evolution reaction using a fully explicit, dynamic DFT approach and highlights the importance of incorporating solvent dynamics in the rigorous description of electrochemical reactions.
Atomically flat, single-crystal solid−liquid interfaces attract considerable interest through their electrochemical relevance and well-defined structure facilitating controlled atomistic characterization. Yet, crucial details especially regarding the nanoscale adlayer−water dynamics remain uncertain. Here, the influence of adsorbate coverage on the interfacial structure and solvent relaxation on hydrogenated Pt( 111) is examined by extensive density functional molecular dynamics simulations. Pronounced water dynamics is observed with increasing hydrogen coverage, for which an interpretation based on displacement of specifically co-adsorbed water and strong screening of the electrostatic interaction across the interface is proposed. However, the magnitude of the solvent fluctuations is argued to be partly overestimated by the employed RPBE-D3 exchange-correlation functional, which impedes water chemisorption and charge transfer to sparsely hydrogenated platinum. This manifests as overestimated equilibrium electrode potentials compared to experimental adsorption isotherms, which are conversely well reproduced by static calculations invoking the computational hydrogen electrode formalism. By coupling the interfacial structure with electrostatic properties, our work underscores the profound importance of functional choice as well as the persisting value and comparable precision of carefully employed static approximations in electrochemical simulations.
Designing earth‐abundant element based efficient and durable electrocatalysts for hydrogen evolution reaction (HER) is attracting growing attention as the renewable electricity supply sector urgently needs sustainable methods for storing energy. Nitrogen functionalized carbon nanomaterials are an interesting electrocatalysts option because of their attractive electrical properties, excellent chemical stability and catalytic activity. Hence, this study reports the HER mechanism on nitrogen functionalized few‐walled carbon nanotubes (N‐FWCNT). With this earth‐abundant element based catalyst 250 mV overpotential is required to reach 10 mA cm−2 current density and so its HER activity is comparable to other non‐noble metal catalysts, and clearly among the highest previously reported for N‐FWCNTs. To gain fundament insight on their functioning, computational analysis has been carried out to verify the effect of nitrogen and to analyze the reaction mechanism. The reaction mechanism has also been analyzed experimentally with a pH series, and both the methods suggest that the HER proceeds via the Volmer‐Heyrovský mechanism. Overall hydrogen surface coverage on N‐FWCNT is also suggested to affect the HER rate. Interestingly, in the studied structure, carbons in vicinity of nitrogen atoms, but not directly bound to nitrogen, appear to promote the HER most actively. Furthermore, durability of N‐FWCNTs has been demonstrated by operating a full electrolyzer cell for five weeks.
Combining precision cluster synthesis with atomistic modelling uncovers fundamental differences in the influence of transition metal dopants on the electrocatalytic activity of MoS2 towards the hydrogen evolution reaction.
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