Stabilizing Hydrogen Adsorption through Theory-Guided Chalcogen Substitution in Chevrel-Phase Mo₆X₈ (X=S, Se, Te) Electrocatalysts

Abstract

In this work, we implement a facile microwaveassisted synthesis method to yield three binary Chevrel-Phase chalcogenides (Mo 6 X 8 ; X = S, Se, Te) and investigate the effect of increasing chalcogen electronegativity on hydrogen evolution catalytic activity. Density functional theory predictions indicate that increasing chalcogen electronegativity in these materials will yield a favorable electronic structure for proton reduction. This is confirmed experimentally via X-ray absorption spectroscopy as well as traditional electrochemical analysis. We have identified that increasing the electronegativity of X in Mo 6 X 8 increases the hydrogen adsorption strength owing to a favorable shift in the pband position as well as an increase in the Lewis basicity of the chalcogen, thereby improving hydrogen evolution reaction energetics. We find that Mo 6 S 8 exhibits the highest hydrogen evolution activity of the Mo 6 X 8 series of catalysts, requiring an overpotential of 321 mV to achieve a current density of 10 mA cm −2 ECSA , a Tafel slope of 74 mV per decade, and an exchange current density of 6.01 × 10 −4 mA cm −2 ECSA . Agreement between theory and experiment in this work indicates that the compositionally tunable Chevrel-Phase chalcogenide family is a promising framework for which electronic structure can be predictably modified to improve catalytic small-molecule reduction reactivity.

A Synergistic Approach to Unraveling the Thermodynamic Stability of Binary and Ternary Chevrel Phase Sulfides

“…Although these materials have been extensively characterized as multivalent ion intercalation cathodes during reversible battery cycling, − ,,,− alternative applications for this chalcogenide family are abundant. Previous characterization suggests that these materials have promising applications as thermoelectrics, , as superconductors, − and as energy-conversion catalysts, ,,, where tunable electronic characteristics can be leveraged to induce favorable charge carrier propagation and adsorption kinetics . It has been observed that intercalation by metallic species leads to donation of electron density into Mo 6 X 8 clusters (Figure A), thereby both altering the electronic structure of the chalcogen site , andby modulation of intracluster Mo–Mo bond distancesaffording control over the d-band structure that is of critical importance for tuning electron-transfer kinetics. − The strongly composition- and structure-dependent properties of CP materials and of chalcogenides in general make them a rich space for discovering novel materials and motivated our application of a combination of experimental and computational approaches to understand and predict the thermodynamic stability of these compositionally flexible solid-state frameworks.…”

Multi-dimensional designer catalysts for negative emissions science (NES): bridging the gap between synthesis, simulations, and analysis

“…We have this potential testbed in 2D cross-dimensional heterostructures ( vide infra ). However, we must establish surface structure–reactivity relationships taking into account the surface and bulk composition which can help accelerate discovery and design ( Perryman et al., 2020a ; Ortiz-Rodríguez et al., 2020 ). Where 2D vdW structures are posited to afford bidentate coordination environments ( Figure 1 A) for catalytically important intermediate species in the CO2RR as an alternative to potentially less favorable monodentate structures ( Figure 1 B), it has been shown that the ternary composition of 3D chalcogenides like Chevrel phases affords a similar level of control over adsorbate binding ( Liu et al., 2010 ; Liu and Liu, 2015 ).…”

“…2D photocatalysts (aka 2-periodic) based on metal chalcogenides (e.g. MoS 2 , SnS 2 , WSe 2 , Bi 2 S 3 , Chevrel phases, to mention a few) ( Rahman et al., 2016 ; Degrauw et al., 2017 ; Ortiz-Rodríguez et al., 2020 ; Perryman et al., 2020a , 2020b ; Perryman and Velázquez, 2021 ; Hill and Hill, 2019 , 2021 ; Strange et al., 2020 ; Hill et al., 2020 ; Tolbert and Hill, 2021 ) and 2D metal halide perovskites ( Amerling et al., 2020 , 2021 ; Wu et al., 2021 ; Yuan et al., 2021 ; Pareja-Rivera et al., 2021 ) are well-suited materials for the reduction of CO 2 due to their strong light-matter interactions. Although many low-dimensional photocatalysts have a high density of electronically active sites for CO 2 binding, these same sites can act as recombination centers that detrimentally affect CO 2 conversion efficiencies.…”

“…Additionally, the 2D heterostructure arrangements should provide high current densities (>200 mA/cm 2 ) given the high electron mobility (200–1,500 S cm −1 ) of the individual building blocks ( Ogle et al., 2021 ; Ortiz-Rodríguez et al., 2020 ; Perryman et al., 2020a , 2020b ; Perryman and Velázquez, 2021 ). An important research direction will be to model the catalytic activity of 2DMOFs, Chevrel phases, and 2DMHPs, their active sites, and selectivity toward reducing CO 2 into high value-added molecules.…”

Modification of TiO2 with Metal Chalcogenide Nanoclusters for Hydrogen Evolution

“…[60] Through a combination of experiment and computation, the authors reported that H adsorption strength increased with the electronegativity of the chalcogen (S = 2.58; Se = 2.55) [61]. This result manifests in the electronic structure as a lower p-band centre.…”