Innocent buffers reveal the intrinsic pH- and coverage-dependent kinetics of the hydrogen evolution reaction on noble metals

Jung, Onyu; Jackson, Megan N.; Bisbey, Ryan P.; Clemente, Leonardo; Surendranath, Yogesh

doi:10.1016/j.joule.2022.01.007

Cited by 51 publications

(42 citation statements)

References 40 publications

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“…[ 18,37,43 ] The extent to which the overpotential is reduced with the SRBW, can be observed from Figure 2c to be 0.52 and 1.37 V for current densities of −10 and −100 mA cm −2 , respectively. More specifically, with 20 dBm SRBW, the system requires a 0.2 V overpotential to reach a current density of −1 mA cm −2 (Figure 2b), which is lower than the 0.3–0.5 V [ 17 ] expected for neutral electrolytes with similar molarities. For −10 mA cm −2 , the requisite overpotential of 0.4 V is approximately half of that reported for platinum (Pt) in neutral electrolytes, [ 18,44 ] suggesting that SRBW‐energized Au electrodes have superior performance to even Pt electrodes under neutral conditions.…”

Section: Resultsmentioning

confidence: 87%

“…In addition to diffusion limitations, this is due to the rapid consumption of H 3 O + , which creates a bottleneck that limits the extent of reaction until higher overpotentials are able to drive H 2 O reduction. [10,[15][16][17] Even with the best electrodes (i.e., PGMs), H 2 production is several orders of magnitude lower under neutral conditions, [7] such that the overpotential required to reach a current density of −4 mA cm −2 exceeds 0.25 V in a 0.1 M KClO 4 electrolyte compared to as little as 30 mV in 0.5 M H 2 SO 4 . [18,19] Similarly poor performance is obtained with the use of nickel-based electrocatalysts, which are generally favored for alkaline conditions, given their affinity for OH − adsorption.…”

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confidence: 99%

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Acoustically‐Induced Water Frustration for Enhanced Hydrogen Evolution Reaction in Neutral Electrolytes

Ehrnst

Sherrell

Rezk

et al. 2022

Advanced Energy Materials

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Despite its appeal of green H 2 production using energy from renewable sources, water electrolysis currently only accounts for a small percentage of global H 2 production due to the need for expensive electrocatalysts to compensate for Ohmic losses associated with the kinetic overpotential of the system. [4][5][6] At present, H 2 production via electrolysis is predominantly carried out in strong acidic/alkaline electrolytes using state-of-the-art platinum group metal (PGM) electrocatalysts, which enables hydrogen evolution reactions (HER) to be conducted at the lowest onset potential, albeit at practically insurmountable industrial costs due to the metal's scarcity. [7,8] To attain industrially-relevant current densities (200-500 mA cm −2 ), an overpotential between 1.8 and 2.5 V is typically required. [9] At these levels though, acidic electrolytes-while providing an abundant source of protons (H + ) and hydronium (H 3 O + ) ions-produce acid fog under high temperatures that can corrode the electrolyzer and contaminate the product. [10] Alkaline electrolysis, on the other hand, is commonly plagued by unstable electrocatalysts and the need for expensive pH-tolerant membranes. [11][12][13] It is therefore desirable to carry out electrolysis in neutral or near-neutral electrolytes (pH 5-9) with non-PGM electrocatalysts. [14] The HER rate under these conditions is, nevertheless, significantly lower than those for electrolytes with extreme pH levels. In addition to diffusion limitations, this is due to the rapid consumption of H 3 O + , which creates a bottleneck that limits the extent of reaction until higher overpotentials are able to drive H 2 O reduction. [10,[15][16][17] Even with the best electrodes (i.e., PGMs), H 2 production is several orders of magnitude lower under neutral conditions, [7] such that the overpotential required to reach a current density of −4 mA cm −2 exceeds 0.25 V in a 0.1 M KClO 4 electrolyte compared to as little as 30 mV in 0.5 M H 2 SO 4 . [18,19] Similarly poor performance is obtained with the use of nickel-based electrocatalysts, which are generally favored for alkaline conditions, given their affinity for OH − adsorption. [20] To circumvent these limitations, novel electrocatalysts have been designed, in which the electrode is doped to tailor its catalytic sites for both H* and OH* adsorption to complement the electrolytic conditions, [21][22][23] or through the introduction of complex architectures that facilitate more favorable local pH environments, [24] although these strategies A novel strategy utilizing high-frequency (10 MHz) hybrid sound waves to dramatically enhance hydrogen evolution reactions (HER) in notoriously difficult neutral electrolytes by modifying their network coordination state is presented. Herein, the practical limitations associated with existing electrolyzer technology is addressed, including the need for highly corrosive electrolytes and expensive electrocatalysts, by redefining conceptually-poor hydrogen electrocatalysts in neutral electrolytes. The impro...

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Section: Resultsmentioning

confidence: 87%

mentioning

confidence: 99%

Acoustically‐Induced Water Frustration for Enhanced Hydrogen Evolution Reaction in Neutral Electrolytes

Ehrnst

Sherrell

Rezk

et al. 2022

Advanced Energy Materials

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“…The invariance of the chemical overpotential across the entire pH range combined with the large change in the charge transfer overpotential provides the clearest evidence to date that HER efficiency losses stem predominantly, if not exclusively, from changes in charge transfer kinetics. Numerous previous studies have examined the impact of electrolyte cations and buffering species on HER kinetics, 15,[17][18][19][20]22 and we posit that the methodology developed here can be readily extended to isolate the relative chemical and charge transfer overpotential contributions in each case.…”

Section: Comparing the Chemical And Charge Transfer Overpotential Par...mentioning

confidence: 97%

“…It is now widely appreciated that that the overall kinetics of HER are strongly dependent on reaction conditions: on noble metals, HER kinetics are attenuated by two orders of magnitude in base vs acid; [11][12][13][14][15][16] the presence of alkali cations and buffering anions in the electrolyte can promote HER kinetics; [17][18][19][20] and surface bound species are known to both promote 14,21,22 and inhibit [23][24][25][26] catalysis. In all these cases, it remains unclear whether these dramatic effects stem from changes in the thermokinetic profile of the charge transfer steps, the chemical reaction steps, or some combination of both.…”

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confidence: 99%

Reaction Environment Impacts Charge Transfer But Not Chemical Reaction Steps in Hydrogen Evolution Catalysis

Tang

Bisbey

Lodaya

et al. 2022

Preprint

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Heterogeneous electrocatalysis involves elementary chemical and charge transfer reaction steps, with the kinetics of each step contributing to the overpotential requirement at a given reaction rate. Typical experiments report on the aggregate rate-overpotential profile with no information about the relative contributions from charge transfer and chemical steps. For the hydrogen evolution reaction (HER), the applied overpotential can be partitioned into a charge transfer overpotential, the overpotential necessary to drive proton-coupled electron transfer (PCET) to and from the surface, and a chemical overpotential, corresponding to a change in surface H activity. Reaction conditions can affect either or both the charge transfer and chemical components. Herein, we employ a Pd membrane double cell to spatially separate the charge transfer and chemical reactions steps of HER catalysis, enabling quantification of the chemical and charge transfer overpotential. We further analyze how each depend on pH, and the introduction of HER poisons and promoters. We find that for a given rate of H2 release, the chemical overpotential is constant across diverse reaction environments whereas the charge transfer overpotential is strongly sensitive to reaction conditions. These findings suggest that reaction condition dependent-HER efficiencies are driven predominantly by changes to the kinetics of charge transfer rather than the chemical reactivity of surface H.

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“…Exposing the intrinsic thermodynamic and kinetic factors controlling interfacial hydride transfer requires the separation of this reaction step from other competing reactions. Owing to all these complexities, the hydride transfer reactivity of surface M−H has been primarily investigated by computational modeling, [26][27][28][29][30][33][34][35][36] rather than direct experiments.…”

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confidence: 99%

Metal surfaces catalyze polarization-dependent hydride transfer from H2

Wang

Toh

Tang

et al. 2022

Preprint

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Hydride transfer is a critical elementary reaction step that spans biological catalysis, organic synthesis, and energy conversion. Conventionally, hydride transfer reactions are carried out using (bio)molecular hydride reagents under homogeneous conditions. Herein, we report a conceptually distinct heterogeneous hydride transfer reaction via the net electrocatalytic hydrogen reduction reaction (HRR) which reduces H2 to hydrides. The reaction proceeds by H2 dissociative adsorption on a metal electrode to form surface M−H species, which are then negatively polarized to drive hydride transfer to molecular hydride acceptors with up to 95% Faradaic efficiency. We find that the hydride transfer reactivity of surface M−H species is highly tunable and its thermochemistry depends on the applied potential in a Nernstian fashion. Thus, depending on the electrode potential, we observe that the thermodynamic hydricity of Pt−H on the same Pt electrode can span a range of >40 kcal mol−1. This work highlights the critical role of electrical polarization on heterogeneous hydride transfer reactivity and establishes a strategy for accessing reactive hydrides directly from H2.

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Innocent buffers reveal the intrinsic pH- and coverage-dependent kinetics of the hydrogen evolution reaction on noble metals

Cited by 51 publications

References 40 publications

Acoustically‐Induced Water Frustration for Enhanced Hydrogen Evolution Reaction in Neutral Electrolytes

Acoustically‐Induced Water Frustration for Enhanced Hydrogen Evolution Reaction in Neutral Electrolytes

Reaction Environment Impacts Charge Transfer But Not Chemical Reaction Steps in Hydrogen Evolution Catalysis

Metal surfaces catalyze polarization-dependent hydride transfer from H2

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