Quantification of Interfacial pH Variation at Molecular Length Scales Using a Concurrent Non‐Faradaic Reaction

Ryu, Jaeyune; Wuttig, Anna; Surendranath, Yogesh

doi:10.1002/anie.201802756

Cited by 65 publications

(72 citation statements)

References 25 publications

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“…The interfacial pH changes have been assessed by coupling a redox reaction, which changes H + concentration near the electrode surface with a non-Faradaic reaction, which is dependent on the pH value. [49] In this approach a non-Faradaic reaction was coupled to electrochemical oxidation of H 2 Figure 1. Theoretical pH profiles for a 25-μm-diameter disk electrode with applied currents of A) 5 and B) 10 nA at a bulk solution pH of 4.36.…”

Section: Analysis Of the Local Interfacial Ph Changes Produced By Elementioning

confidence: 99%

Electrochemically Generated Interfacial pH Change: Application to Signal‐Triggered Molecule Release

2020

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Electron transfer processes during redox reactions are frequently accompanied with protonation/deprotonation processes, thus changing H+/OH− concentrations. When the redox reactions proceed at electrode surfaces, being electrochemically processed, changes in local interfacial pH are possible, particularly when the electrolyte solution is not strongly buffered. The pH gradient can be produced in the diffusion layer and its thickness depends on the rate of electrochemical process, which is measured as the current density, diffusion rates, and buffer capacity. While conventional techniques for measuring pH values are not applicable to a very thin diffusional layer, special methods have been developed for the interfacial pH measurements, including scanning electrochemical microscopy (SECM), rotating ring‐disk electrode (RRDE) measurements, various optical methods, particularly using confocal fluorescent microscopy, and others. Dramatic pH changes proceeding in a near‐electrode layer have been reported for H2O reduction/oxidation, O2 reduction, and some other electrochemical electron/proton transfer processes. These pH changes can be used to trigger some other physical processes, particularly (bio)molecule release processes from modified electrodes, which can be destabilized upon the electrochemically generated pH changes, thus releasing entrapped/loaded target molecules. This review‐type article overviews the formation and analysis of locally produced interfacial pH changes and their use for electrochemically triggered (bio)molecule release. The paper briefly reviews the research area, then concentrating on the systems designed recently by the authors.

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Section: Analysis Of the Local Interfacial Ph Changes Produced By Elementioning

confidence: 99%

Electrochemically Generated Interfacial pH Change: Application to Signal‐Triggered Molecule Release

2020

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“…27 When the reactions are carried out at a high current density or in electrolytes that have poor buffer action and/or mass transport, the pH near the cathode surface is well known to increase compared to the bulk value. [28][29] Although the impact of local conditions on the selectivity of metal electrodes is well recognized, simulated and reproduced, 25,[27][28]30 it is still a common practice to test high surface area electrodes in very low buffer capacity solutions which promotes a high selectivity towards carbon based products resulting from the suppression of hydrogen evolution. While the surface structure of a catalyst is very important to determine its selectivity and activity, the distinction between the effect of surface morphology and mass transport effects on the electrocatalytic activity is not explicitly clear and needs to be urgently clarified in order to improve fundamental understanding of reaction mechanisms and provide faster routes for optimization.…”

Section: Introductionmentioning

confidence: 99%

Tenacious Mass Transfer Limitations Drive Catalytic Selectivity during Electrochemical Carbon Dioxide Reduction

Yang¹,

Kaş²,

Smith³

2019

Preprint

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Over the past decade, electrochemical carbon dioxide reduction has become a thriving area of research with the aim of converting electricity to renewable chemicals and fuels. New life has been breathed into the field as nanostructured electrodes have been deployed as electrocatalysts, which have significantly improved the catalytic selectivity. However, evaluation of the performance of these electrocatalysts has been complicated, not only due to their intricate surface morphology and mesoscopic structure, but also by immense concentration gradients existing between the electrode surface and bulk solution. In this work, by using in-situ surface enhanced infrared absorption spectroscopy (SEIRAS) and computational modelling, we explicitly show that commonly used phosphate buffers cannot sustain the interfacial pH during CO 2 electroreduction on copper electrodes at relatively low current densities,<10 mA/cm 2 . The pH near the electrode surface was observed to be as much as 5 pH units higher compared to bulk solution in 0.2 M phosphate buffer at potentials relevant to the formation of hydrocarbons (-1 V vs RHE), even on smooth polycrystalline copper electrodes. Drastically increasing the buffer capacity did not stand out as a viable solution for the problem on polycrystalline and copper nanowire electrodes as the concurrent production of hydrogen increased dramatically, which resulted in a breakdown of the buffer in a narrow potential range. These unforeseen results imply that most of the aqueous CO 2 electroreduction studies in H-cells, if not all, were evaluated under mass transport limitations on smooth and rough copper electrodes. We underscore that the large concentration gradients on electrodes with high local current density (i.e. Nanostructured) have important implications on the selectivity, activity, and kinetic analysis, and any attempt to draw structure-activity relationships must rule out mass transport effects.

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“…But earth abundant metal compounds in this kind of catalysts can only work in a narrow pH window and thus always suffer stability issues . This is because the local pH of the electrolyte near the electrode surface changed significantly during prolonged electrolysis, due to insufficient mass transfer for compensating the fast consumption of H + (in acidic electrolytes) or H 2 O (in neutral or alkaline electrolytes) . This would become more serious under industrially high current density conditions in a membrane containing electrolyzer .…”

mentioning

confidence: 99%

“…This is because the local pH of the electrolyte near the electrode surface changed significantly during prolonged electrolysis, due to insufficient mass transfer for compensating the fast consumption of H + (in acidic electrolytes) or H 2 O (in neutral or alkaline electrolytes) . This would become more serious under industrially high current density conditions in a membrane containing electrolyzer . Therefore, the development of low‐cost catalysts with high stability and pH tolerance are still highly desirable for practical conditions in the large scale water splitting …”

mentioning

confidence: 99%

Amorphous Ruthenium‐Sulfide with Isolated Catalytic Sites for Pt‐Like Electrocatalytic Hydrogen Production Over Whole pH Range

Duan

Wang

et al. 2019

Small

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Electrocatalytic hydrogen evolution reaction (HER) is an efficient way to generate hydrogen fuel for the storage of renewable energy. Currently, the widely used Pt‐based catalysts suffer from high costs and limited electrochemical stability; therefore, developing an efficient alternative catalyst is very urgent. Herein, one pot hydrothermal synthesis is reported of amorphous ruthenium‐sulfide (RuSx) nanoparticles (NPs) supported on sulfur‐doped graphene oxide (GO). The as‐obtained composite serves as a Pt‐like HER electrocatalyst. Achieving a current density of −10 mA cm−2 only requires a small overpotential (−31, −46, and −58 mV in acidic, neutral, and alkaline electrolyte, respectively) with high durability. The isolated Ru active site inducing Volmer–Heyrovsky mechanism in the RuSx NPs is demonstrated by the Tafel analysis and X‐ray absorption spectroscopy characterization. Theoretical simulation indicates the isolated Ru site exhibits Pt‐like Gibbs free energy of hydrogen adsorption (−0.21 eV) therefore generating high intrinsic HER activity. Moreover, the strong bonding between the RuSx and S–GO, as well as pH tolerance of RuSx are believed to contribute to the high stability. This work shows a new insight for amorphous materials and provides alternative opportunities in designing advanced electrocatalysts with low‐cost for HER in the hydrogen economy.

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Quantification of Interfacial pH Variation at Molecular Length Scales Using a Concurrent Non‐Faradaic Reaction

Cited by 65 publications

References 25 publications

Electrochemically Generated Interfacial pH Change: Application to Signal‐Triggered Molecule Release

Electrochemically Generated Interfacial pH Change: Application to Signal‐Triggered Molecule Release

Tenacious Mass Transfer Limitations Drive Catalytic Selectivity during Electrochemical Carbon Dioxide Reduction

Amorphous Ruthenium‐Sulfide with Isolated Catalytic Sites for Pt‐Like Electrocatalytic Hydrogen Production Over Whole pH Range

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