scholarly journals Atoms vs. Ions: Intermediates in Reversible Electrochemical Hydrogen Evolution Reaction

Catalysts ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1135
Author(s):  
Jurga Juodkazytė ◽  
Kȩstutis Juodkazis ◽  
Saulius Juodkazis
Keyword(s):  
Electron Transfer ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Ionic Species ◽  
Absolute Temperature ◽  
Main Reaction ◽  
Adsorbed Hydrogen ◽  
H2 Evolution ◽  
Hydrogen Electrode ◽  
Reported Data

We present a critical analysis of the mechanism of reversible hydrogen evolution reaction based on thermodynamics of hydrogen processes considering atomic and ionic species as intermediates. Clear distinction between molecular hydrogen evolution/oxidation (H2ER and H2OR) and atomic hydrogen evolution/oxidation (HER and HOR) reactions is made. It is suggested that the main reaction describing reversible H2ER and H2OR in acidic and basic solutions is: H3O++2e−⇌(H2+)adH2+OH− and its standard potential is E0 = −0.413 V (vs. standard hydrogen electrode, SHE). We analyse experimentally reported data with models which provide a quantitative match (R.J.Kriek et al., Electrochem. Sci. Adv. e2100041 (2021)). Presented analysis implies that reversible H2 evolution is a two-electron transfer process which proceeds via the stage of adsorbed hydrogen molecular ion H2+ as intermediate, rather than Had as postulated in the Volmer-Heyrovsky-Tafel mechanism. We demonstrate that in theory, two slopes of potential vs. lg(current) plots are feasible in the discussed reversible region of H2 evolution: 2.3RT/F≈60 mV and 2.3RT/2F≈30 mV, which is corroborated by the results of electrocatalytic hydrogen evolution studies reported in the literature. Upon transition to irreversible H2ER, slowdown of H2+ formation in the first electron transfer stage manifests, and the slope increases to 2.3RT/0.5F≈120 mV; R,F,T are the universal gas, Faraday constants and absolute temperature, respectively.

scholarly journals Atoms vs. Ions: Intermediates in Reversible Electrochemical Hydrogen Evolution Reaction

2021 ◽  
Author(s):  
Jurga Juodkazyte ◽  
Kestutis Juodkazis ◽  
Saulius Juodkazis
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Atomic Hydrogen ◽  
Critical Analysis ◽  
Molecular Hydrogen ◽  
Ionic Species ◽  
Main Reaction ◽  
Hydrogen Electrode ◽  
Basic Solutions ◽  
Reported Data

We present a critical analysis of the mechanism of reversible hydrogen evolution reaction based on thermodynamics of hydrogen processes considering atomic and ionic species as intermediates. Clear distinction between molecular hydrogen evolution/oxidation (H$_2$ER and H$_2$OR) and atomic hydrogen evolution/oxidation (HER and HOR) reactions is made. It is suggested that the main reaction describing reversible H$_2$ER and H$_2$OR in acidic and basic solutions is: $\ce{H3O^+} + 2e^- \xrightleftharpoons{\mathrm{({H}_{2}^{+}})_{ad}} \ce{H2} + \ce{OH^-}$, which proceeds via the formation of hydrogen molecular ion as intermediate and its potential is $E^{0}$ = 0.414~V (at the standard Hydrogen electrode SHE scale). We analyse experimentally reported data with models which provide \emph{quantitative} match (R.J.Kriek et al., Electrochem. Sci. Adv. e2100041 (2021)). The experimentally observed slope of $\lg(Current)$ vs. $Potential$ equal to $\approx 30$~mV/dec corroborates the presented model of H$_2$ER/H$_2$ER based on \ce{H2$^+$} as intermediate.

PbTe quantum dots as electron transfer intermediates for the enhanced hydrogen evolution reaction of amorphous MoSx/TiO2 nanotube arrays

Nanoscale ◽  
2018 ◽  
Vol 10 (21) ◽  
pp. 10288-10295 ◽  
Author(s):  
Shiyuan Gao ◽  
Bin Wang ◽  
Xinyu Liu ◽  
Zhanhu Guo ◽  
Zhongqing Liu ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Electron Transfer ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Tio2 Nanotube Arrays ◽  
Tio2 Nanotube ◽  
Nanotube Arrays

PbTe quantum dots (QDs) function as electron transfer intermediates for higher electrocatalytic performances from MoSx/PbTe QDs/TNAs.

scholarly journals How Stable Are 2H-MoS2 Edges Under Hydrogen Evolution Reaction Conditions?

2021 ◽  
Author(s):  
Nawras Abidi ◽  
Audrey Bonduelle-Skrzypczak ◽  
Stephan Steinmann
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Active Sites ◽  
Density Functional ◽  
External Source ◽  
Operating Conditions ◽  
Adsorbed Hydrogen ◽  
Functional Theory ◽  
Acidic Conditions

MoS<sub>2</sub>, have emerged as a promising class of electrocatalysts for the production of H<sub>2</sub> via the hydrogen evolution reaction (HER) in acidic conditions.<div>The edges of MoS<sub>2</sub> are known for their HER activity, but their precise atomistic nature and stability under HER conditions is not yet known. In contrast to other typical uses of MoS<sub>2</sub> as a catalyst, under HER there is no external source of sulfur. Therefore, the sulfidation of the edges can only decrease under operating conditions and the thermodynamics of the process are somewhat ill-defined. Our results suggest that the 50%S S-edge may be active for HER via the Volmer-Tafel mechanism and is, despite a high H coverage, stable with respect to H<sub>2</sub>S release. </div><div>At the 50%S Mo-edge, the adsorbed hydrogen opens the way for H<sub>2</sub>S release, leading to the 0%S Mo-edge, which was previously investigated and found to be HER active. HER being a water-based process, we also considered the effect of the presence of H<sub>2</sub>O and the in-situ formation of OH. For the 50%S Mo-edge, H<sub>2</sub>O is only very weakly adsorbed and OH formation is unfavorable. Nevertheless, OH assists the loss of sulfur coverage, leading to OH-based HER active sites. In contrast, OH is strongly adsorbed on the 50%S S-edge. By explicitly considering the electrochemical potential using grand-canonical density functional theory, we unveil that the Volmer-Heyrovsky mechanism on sulfur sites is still accessible in the presence of surface OH at the 50%S S-edge. However, the 50%S S-edge is found to be mildly unstable with respect to H<sub>2</sub>S in the presence of water/OH. Hence, we suggest that the 50%S S-edge evolves over time towards a 0%S S-edge, covered by surface OH that will block permanently the active sites. </div>

scholarly journals Insights into Hydrogen Evolution Reaction on 2D Transition Metal Dichalcogenides

2021 ◽  
Author(s):  
Zhenbin Wang ◽  
Michael Tang ◽  
Ang Cao ◽  
Karen Chan ◽  
Jens Kehlet Nørskov
Keyword(s):  
Transition Metal ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Adsorption Energy ◽  
Density Functional ◽  
Hydrogen Adsorption ◽  
Activation Barrier ◽  
Transition Metal Dichalcogenides ◽  
Adsorbed Hydrogen ◽  
Metal Dichalcogenides

<p>Understanding the hydrogen evolution reaction (HER) behaviors over 2D transition metal dichalcogenides (2D-TMDs) is critical for the development of non-precious HER electrocatalysts with better activity. In this work, by combining density functional theory calculations with microkinetic modelling, we thoroughly investigated the HER mechanism on 2D-TMDs. We find there is an important dependence of simulated cell size on the calculated hydrogen adsorption energy and the activation barrier for MoS<sub>2</sub>. Distinct from previous “H migration” mechanisms proposed for the Heyrovsky reaction − the rate-determining step for MoS<sub>2</sub>, we propose the Mo site only serves as the stabilized transition state rather than H adsorption. In comparison to transition metal electrocatalysts, we find that the activation barrier of the Heyrovsky reaction on 2D-TMDs scales with the hydrogen adsorption energy exactly as for transition metals except that all activation energies are displaced upwards by <i>ca.</i> 0.4 eV. This higher Heyrovsky activation barrier is responsible for the substantially lower activity of 2D-TMDs. We further show that this higher activation barrier stems from the more positively charged adsorbed hydrogen on the chalcogenides interacting repulsively with the incoming proton. Based on these insights, we discuss potential strategies for the design of non-precious HER catalysts with activity comparable to Pt.</p>

Hierarchical nickel-vanadium nanohybrid with strong electron transfer for accelerated hydrogen evolution reaction

2020 ◽  
Vol 528 ◽  
pp. 146982
Author(s):  
Jiangnan Liu ◽  
Jingsong Cui ◽  
Jianhang Sun ◽  
Hui Liu ◽  
Wei Li ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Strong Electron

Influence of adsorption of organic compounds and surface heterogeneity on the hydrogen evolution reaction

1997 ◽  
Vol 75 (11) ◽  
pp. 1615-1623 ◽  
Author(s):  
Andrzej Lasia
Keyword(s):  
Kinetic Parameters ◽  
Hydrogen Evolution ◽  
Organic Compounds ◽  
Hydrogen Evolution Reaction ◽  
Surface Heterogeneity ◽  
Adsorbed Hydrogen ◽  
Heterogeneous Surfaces ◽  
Tafel Slopes ◽  
Adsorption Energies ◽  
Temkin Adsorption Isotherm

The hydrogen evolution reaction on rough or porous surfaces often leads to low Tafel slopes that cannot be explained in terms of the Volmer–Heyrovsky–Tafel mechanism. In addition, adsorption of organic compounds and ions causes an increase in the Tafel slopes. To explain such behavior, a concept of distribution of adsorption energies on heterogeneous surfaces, leading to a distributed kinetics, was studied. Simulations of the dependence of the current and the surface coverage by adsorbed hydrogen on overpotential are presented for different values of the kinetic parameters in the absence and presence of the adsorbed foreign substances. These results were compared with those obtained using the Frumkin/Temkin adsorption isotherm. It was found that for some kinetic parameters and a flat distribution of adsorption energies, low Tafel slopes, similar to those observed experimentally, are obtained. Keywords: hydrogen evolution, adsorption, heterogeneous surfaces, distributed kinetics, Frumkin/Temkin isotherm.

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