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A Metal-Organic Framework derived Cu_x O_y C_z Catalyst for Electrochemical CO₂ Reduction and Impact of Local pH Change.

ABSTRACT: Developing highly efficient and selective electrocatalysts for the CO₂ reduction reaction to produce value-added chemicals has been intensively pursued. We report a series of Cu_x O_y C_z nanostructured electrocatalysts derived from a Cu-based MOF as porous self-sacrificial template. Blending catalysts with polytetrafluoroethylene (PTFE) on gas diffusion electrodes (GDEs) suppressed the competitive hydrogen evolution reaction. 25 to 50 wt % teflonized GDEs exhibited a Faradaic efficiency of ≈54 % for C₂₊ products at -80 mA cm^-2 . The local OH^- ions activity of PTFE-modified GDEs was assessed by means of closely positioning a Pt-nanoelectrode. A substantial increase in the OH^- /H₂ O activity ratio due to the locally generated OH^- ions at increasing current densities was determined irrespective of the PTFE amount.

SUBMITTER: Sikdar N

PROVIDER: S-EPMC8597168 | biostudies-literature | 2021 Oct

REPOSITORIES: biostudies-literature

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A Metal-Organic Framework derived Cux Oy Cz Catalyst for Electrochemical CO2 Reduction and Impact of Local pH Change.

Sikdar Nivedita N Junqueira João R C JRC Dieckhöfer Stefan S Quast Thomas T Braun Michael M Song Yanfang Y Aiyappa Harshitha B HB Seisel Sabine S Weidner Jonas J Öhl Denis D Andronescu Corina C Schuhmann Wolfgang W

Angewandte Chemie (International ed. in English) 20210923 43

Developing highly efficient and selective electrocatalysts for the CO2 reduction reaction to produce value-added chemicals has been intensively pursued. We report a series of Cux Oy Cz nanostructured electrocatalysts derived from a Cu-based MOF as porous self-sacrificial template. Blending catalysts with polytetrafluoroethylene (PTFE) on gas diffusion electrodes (GDEs) suppressed the competitive hydrogen evolution reaction. 25 to 50 wt % teflonized GDE ...[more]

PMID: 34355835

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Project description:The electrochemical reduction of CO2 is widely studied as a sustainable alternative for the production of fuels and chemicals. The electrolyte's bulk pH and composition play an important role in the reaction activity and selectivity and can affect the extent of the buildup of pH gradients between the electrode surface and the bulk of the electrolyte. Quantifying the local pH and how it is affected by the solution species is desirable to gain a better understanding of the CO2 reduction reaction. Local pH measurements can be realized using Scanning Electrochemical Microscopy (SECM); however, finding a pH probe that is stable and selective under CO2 reduction reaction conditions is challenging. Here, we have used our recently developed voltammetric pH sensor to perform pH measurements in the diffusion layer during CO2 reduction using SECM, with high time resolution. Using a 4-hydroxylaminothiophenol (4-HATP)/4-nitrosothiophenol (4-NSTP) functionalized gold ultramicroelectrode, we compare the local pH developed above a gold substrate in an argon atmosphere, when only hydrogen evolution is taking place, to the pH developed in a CO2 atmosphere. The pH is monitored at a fixed distance from the surface, and the sample potential is varied in time. In argon, we observe a gradual increase of pH, while a plateau region is present in CO2 atmosphere due to the formation of HCO3 - buffering the reaction interface. By analyzing the diffusion layer dynamics once the sample reaction is turned "off", we gain insightful information on the time scale of the homogeneous reactions happening in solution and on the time required for the diffusion layer to fully recover to the initial bulk concentration of species. In order to account for the effect of the presence of the SECM tip on the measured pH, we performed finite element method simulations of the fluid and reaction dynamics. The results show the significant localized diffusion hindrance caused by the tip, so that in its absence, the pH values are more acidic than when the tip is present. Nonetheless, through the simulation, we can account for this effect and estimate the real local pH values across the diffusion layer.

Dataset Information

A Metal-Organic Framework derived Cu_x O_y C_z Catalyst for Electrochemical CO₂ Reduction and Impact of Local pH Change.

Publications

A Metal-Organic Framework derived Cu<sub>x</sub> O<sub>y</sub> C<sub>z</sub> Catalyst for Electrochemical CO<sub>2</sub> Reduction and Impact of Local pH Change.

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