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Abstract Despite the advantages of aqueous zinc (Zn) metal batteries (AZMB) like high specific capacity (820 mAh g−1and 5,854 mAh cm−3), low redox potential (−0.76 V vs. the standard hydrogen electrode), low cost, water compatibility, and safety, the development of practically relevant batteries is plagued by several issues like unwanted hydrogen evolution reaction (HER), corrosion of Zn substrate (insulating ZnO, Zn(OH)2, Zn(SO4)x(OH)y, Zn(ClO4)x(OH)yetc. passivation layer), and dendrite growth. Controlling and suppressing HER activity strongly correlates with the long‐term cyclability of AZMBs. Therefore, a precise quantitative technique is needed to monitor the real‐time dynamics of hydrogen evolution during Zn electrodeposition. In this study, we quantify hydrogen evolution using in situ electrochemical mass spectrometry (ECMS). This methodology enables us to determine a correction factor for the faradaic efficiency of this system with unmatched precision. For instance, during the electrodeposition of zinc on a copper substrate at a current density of 1.5 mA/cm2for 600 seconds, 0.3 % of the total charge is attributed to HER, while the rest contributes to zinc electrodeposition. At first glance, this may seem like a small fraction, but it can be detrimental to the long‐term cycling performance of AZMBs. Furthermore, our results provide insights into the correlation between HER and the porous morphology of the electrodeposited zinc, unravelling the presence of trapped H2and Zn corrosion during the charging process. Overall, this study sets a platform to accurately determine the faradaic efficiency of Zn electrodeposition and provides a powerful tool for evaluating electrolyte additives, salts, and electrode modifications aimed at enhancing long‐term stability and suppressing the HER in aqueous Zn batteries.
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Quaternary Ammonium Additives as Dual Inhibitors of Hydrogen Evolution and Cathodic Corrosion in Aqueous Electrosynthesis
In organic electrosynthesis, the hydrogen evolution reaction (HER) is a parasitic process that significantly diminishes the faradaic efficiency (FE) of aqueous electrochemical reductions and contributes to the cathodic corrosion of widely used metals such as lead and tin. Developing strategies that selectively suppress HER without hindering desired electrochemical transformations is therefore crucial. In this study, we demonstrate that various quaternary ammonium salts (QAS) suppress HER on lead cathodes even under acidic conditions (pH 1). These QAS electrostatically self-assemble at the negatively charged lead surface, forming a cationic barrier that hinders hydronium ion (H3O+) diffusion to the surface, thereby mitigating HER. Chronoamperometry (CA) at −1.8 V vs Ag/AgCl for 1 h revealed stark differences in QAS performance depending on molecular structure. H12MS (N,N,N,N′,N′,N′-hexamethyl-1,12-dodecanediammonium methyl sulfate) was the most effective salt, suppressing hydrogen evolution from ∼0.76 to ∼0.11 mmol cm–2 (an 85% decrease), even at concentrations as low as 1 μM. CA also showed that the monotonic increase in current over time for blank lead electrodes, which is due to corrosion and surface roughening, was also suppressed in the presence of QAS, underscoring their dual role as inhibitors of both HER and cathodic corrosion. Moreover, during the electrochemical hydrogenation of fumaric acid at −1.7 V vs Ag/AgCl, the addition of 1 mM H12MS enhanced the faradaic efficiency from 7.3% to 38.5% (a 5.3-fold increase) without affecting the yield of succinic acid. These findings highlight the effectiveness of QAS additives in tailoring the boundary layer to improve the efficiency and durability of electrochemical processes.
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- Award ID(s):
- 2140342
- PAR ID:
- 10661431
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- ACS Electrochemistry
- Volume:
- 2
- Issue:
- 1
- ISSN:
- 2997-0571
- Page Range / eLocation ID:
- 175 to 187
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/acselectrochem.5c00398
