Kinetics of the hydrogen evolution reaction on gold electrode. A new case of the barrierless discharge

Khanova, L. A.; Krishtalik, L. I.

doi:10.1016/j.jelechem.2011.01.016

Cited by 33 publications

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References 30 publications

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“…6,8,[13][14][15][16][17][18][19][20][21] However, a literature survey shows no general agreement on the underlying mechanism of this reaction to date. [13][14][15]17,18,20,21 Besides, the majority of the proposed mechanisms have been developed based on experimental results obtained in highly acidic environments, 6,8,13-21 but were not examined over an extended pH range.The experimental polarization curves obtained on gold in acidic solutions repeatedly reported to have two distinct Tafel slopes with values in the range of 50-70 mV at lower current densities and 100-130 mV at higher current densities. 3,6,16,18,21,22 A number of different explanations for the underlying mechanism based on these observed Tafel slopes have been proposed in the literature.…”

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confidence: 99%

“…[13][14][15]17,18,20,21 Besides, the majority of the proposed mechanisms have been developed based on experimental results obtained in highly acidic environments, 6,8,13-21 but were not examined over an extended pH range.…”

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confidence: 99%

“…3,6,16,18,21,22 A number of different explanations for the underlying mechanism based on these observed Tafel slopes have been proposed in the literature. In a study by Ives 20 in 0.1 N HCl solutions, the author reported polarization curves with an uncharacterized region at low current densities preceding to the 120 mV Tafel slope range.…”

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“…13,21 * Electrochemical Society Student Member. z E-mail: ak702711@ohio.edu Khanova and Krishtalik 13 suggest that barrierless discharge is feasible on a gold surface at significantly low overpotentials.…”

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“…The transition to 120 mV Tafel slope was then associated with the change to ordinary discharge with β = 1/2. 13,21 Considering the rate determining Volmer reaction throughout the full range of cathodic currents, either as an ordinary charge transfer reaction or a barrierless reaction, the surface coverage of H ads is expected to be low (θ→0), as discussed in more detail in H + adsorption rate determining step section below. However, this was found to be in contrast with the findings from a study by Chun et al 6 where a significant coverage of H ads (θ→1) was reported in the 120 mV Tafel slope region.…”

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Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

Kahyarian

Brown

Nešić

2017

J. Electrochem. Soc.

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Despite numerous studies investigating the kinetics of the hydrogen evolution reaction (HER) on a gold surface in acidic solutions, the underlying mechanism of this reaction have remained controversial to date. In the present study, the existing mechanisms are reevaluated and found to be inadequate in explaining the steady state polarization behavior of the hydrogen evolution reaction in an extended cathodic potentials and mildly acidic pH range. It was shown that a mechanism including a surface diffusion step of H ads alongside the Volmer, Heyrovsky, and Tafel elementary steps, best describes the experimental data obtained in acidic perchlorate solutions up to pH 5, while the rate determining step changes both with pH and electrode potential. This overall HER mechanism was further verified using a comprehensive mathematical model based on the proposed elementary steps, where a satisfactory agreement with experimental results was obtained. The hydrogen evolution reaction (HER) has been the subject of numerous studies, either as a platform for investigating the theory of electrochemical processes, 1-9 or in terms of hydrogen production, energy storage, and energy conversion, 10-12 due to its significance in the alternative energy source framework. This trend had also include extensive investigations of the mechanism of the HER on gold in acidic solutions. 6,8,[13][14][15][16][17][18][19][20][21] However, a literature survey shows no general agreement on the underlying mechanism of this reaction to date. [13][14][15]17,18,20,21 Besides, the majority of the proposed mechanisms have been developed based on experimental results obtained in highly acidic environments, 6,8,13-21 but were not examined over an extended pH range.The experimental polarization curves obtained on gold in acidic solutions repeatedly reported to have two distinct Tafel slopes with values in the range of 50-70 mV at lower current densities and 100-130 mV at higher current densities. 3,6,16,18,21,22 A number of different explanations for the underlying mechanism based on these observed Tafel slopes have been proposed in the literature. In a study by Ives 20 in 0.1 N HCl solutions, the author reported polarization curves with an uncharacterized region at low current densities preceding to the 120 mV Tafel slope range. That uncharacterized section of the voltammograms had a significantly lower Tafel slope with values about 50-70 mV, which was extended to the cathodic currents up to about 1 A.m −2 and overpotentials up to about 150 mV. The author associated this lower Tafel slope with the interference of the hydrogen oxidation reaction. 20 However, considering the experimental conditions in that study, no significant interference of anodic currents due to hydrogen gas oxidation is expected, especially at the cathodic overpotentials as high as 150 mV.Bockris et al. 14,23 suggested that the apparent change of Tafel slope to ∼60 mV was caused by the change in potential drop across the diffusion double layer. This effect was believed to be most profoun...

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Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

Kahyarian

Brown

Nešić

2017

J. Electrochem. Soc.

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Electrocatalytic Conversion of CO ₂ to Syngas

Díaz‐Pérez

Lucas-Consuegra

Serrano‐Ruiz

2021

Engineering Solutions for CO2 Conversion

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Benchmarking the Activity, Stability, and Inherent Electrochemistry of Amorphous Molybdenum Sulfide for Hydrogen Production

Escalera‐López

Lou

Rees

2019

Advanced Energy Materials

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can be efficiently produced on demand and in a decentralized manner with (photo) electrochemical methods via the hydrogen evolution reaction (HER). [1][2][3][4] Despite of being the best performing HER catalysts, [5,6] noble metals such as Pt, Ir, and Pd are scarce and consequently hamper the viability of water electrolysis technologies. Hence earth-abundant materials, and notably transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS 2 ), have been extensively investigated as HER electrocatalysts. [7][8][9][10][11] The edge sites-driven hydrogen electroadsorption properties of TMDs [12,13] have prompted the fabrication of amorphous molybdenum sulfide materials (MoS x ) to minimize exposure of the electrocatalytically inert MoS 2 basal planes [14] for multiple applications. [15][16][17][18][19] A simple, yet scalable method to fabricate MoS x has been reported by substrate-insensitive electrodeposition from a [MoS 4 ] 2− precursor, [20,21] and critical properties in MoS x materials such as film thickness, [22] morphology, [23][24][25][26] Mo:S stoichiometry, [27] as well as incorporation of dopants [28][29][30] or nanocomposite formation, [31][32][33][34][35] have been easily tuned by experimental parameters.For long-term electrocatalytic applications, however, HER activity and stability of TMDs are paramount. In crystalline MoS 2 , basal plane activation, [36][37][38][39][40][41][42][43] edge site exposure, [44][45][46][47][48][49][50][51][52][53] and metal doping/incorporation/intercalation [54][55][56][57][58][59][60][61][62][63][64][65][66] are the most employed strategies.In contrast, the [Mo 3 S 13 ] 2− cluster-based polymeric structure of electrodeposited MoS x[67] requires alternative approaches to maximize activity. In addition, the detailed HER mechanism as well as the true catalytically active sites are still under debate. Whilst pioneering studies on ambient pressure X-ray photoelectron spectroscopy (XPS) indicated the MoS 2 edge-like sites formed after MoS 3 phase transformation under in operando conditions responsible for the HER performance, [68] in situ X-ray absorption spectroscopy experiments suggested terminal S 2 2− ligands (S 2 2− terminal ) to be the proton acceptor sites, [69] and more recently in situ Raman spectroscopy indicated these to be the electrochemically cleaved bridging S 2 2− ligands (S 2 2− bridging ). [70] Another study claimed that unsaturated Mo centers formed after cathodic dissolution of S 2 2− terminal to be the true HER Anodically electrodeposited amorphous molybdenum sulfide (AE-MoS x ) has attracted significant attention as a non-noble metal electrocatalyst for its high activity toward the hydrogen evolution reaction (HER). The [Mo 3 S 13 ] 2− polymerbased structure confers a high density of exposed sulfur moieties, widely regarded as the HER active sites. However, their intrinsic complexity conceals full understanding of their exact role in HER catalysis, hampering their full potential for water splitting applications. In this report, a unifying app...

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Kinetics of the hydrogen evolution reaction on gold electrode. A new case of the barrierless discharge

Cited by 33 publications

References 30 publications

Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

Electrocatalytic Conversion of CO ₂ to Syngas

Benchmarking the Activity, Stability, and Inherent Electrochemistry of Amorphous Molybdenum Sulfide for Hydrogen Production

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Kinetics of the hydrogen evolution reaction on gold electrode. A new case of the barrierless discharge

Cited by 33 publications

References 30 publications

Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

Mechanism of the Hydrogen Evolution Reaction in Mildly Acidic Environments on Gold

Electrocatalytic Conversion of CO 2 to Syngas

Benchmarking the Activity, Stability, and Inherent Electrochemistry of Amorphous Molybdenum Sulfide for Hydrogen Production

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Product

Resources

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Electrocatalytic Conversion of CO ₂ to Syngas