Role of ion-selective membranes in the carbon balance for CO2 electroreduction via gas diffusion electrode reactor designs

In this work, the effect of ion-selective membranes on the detailed carbon balance was systematically analyzed for high-rate CO2 reduction in flow electrolyzers. By using different ion-selective membranes, we show nearly identical catalytic selectivity for CO2 reduction, which is primarily due to a similar local reaction environment created at the cathode/electrolyte interface via the introduction of a catholyte layer. In addition, based on a systematic exploration of gases released from electrolytes and the dynamical change of electrolyte speciation, we demonstrate the explicit discrepancy in carbon balance paths for the captured CO2 at the cathode/catholyte interface via reaction with OH- when using different ion-selective membranes: (i) the captured CO2 could transport through an anion exchange membrane in the form of CO32-, subsequently releasing CO2 along with O2 in the anolyte, (ii) with a cation exchange membrane, the captured CO2 would be accumulated in the catholyte in the forms of CO32-, (iii) whereas under the operation of a BPM, the captured CO2 could be released at the catholyte/membrane interface in the form of gaseous CO2. The unique carbon balance path for each type of membrane is linked to ion species transported through membranes.

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Role of Ion-Selective Membranes in the Carbon Balance for CO2 Electroreduction via Gas Diffusion Electrode Reactor Designs

10.26434/chemrxiv.12213215 ◽

2020 ◽

Author(s):

Ming Ma ◽

Sangkuk Kim ◽

Ib Chorkendorff ◽

Brian Seger

Keyword(s):

Carbon Balance ◽

Gas Diffusion ◽

High Rate ◽

Membrane Interface ◽

Systematic Exploration ◽

Co2 Electroreduction ◽

Exchange Membrane ◽

Ion Species ◽

Selective Membranes

In this work, the effect of ion-selective membranes on the detailed carbon balance was systematically analyzed for high-rate CO2 reduction in flow electrolyzers. By using different ion-selective membranes, we show nearly identical catalytic selectivity for CO2 reduction, which is primarily due to a similar local reaction environment created at the cathode/electrolyte interface via the introduction of a catholyte layer. In addition, based on a systematic exploration of gases released from electrolytes and the dynamical change of electrolyte speciation, we demonstrate the explicit discrepancy in carbon balance paths for the captured CO2 at the cathode/catholyte interface via reaction with OH- when using different ion-selective membranes: (i) the captured CO2 could transport through an anion exchange membrane in the form of CO32-, subsequently releasing CO2 along with O2 in the anolyte, (ii) with a cation exchange membrane, the captured CO2 would be accumulated in the catholyte in the forms of CO32-, (iii) whereas under the operation of a BPM, the captured CO2 could be released at the catholyte/membrane interface in the form of gaseous CO2. The unique carbon balance path for each type of membrane is linked to ion species transported through membranes.

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Insights into the carbon balance for CO2 electroreduction on Cu using gas diffusion electrode reactor designs

Energy & Environmental Science ◽

10.1039/d0ee00047g ◽

2020 ◽

Vol 13 (3) ◽

pp. 977-985 ◽

Cited By ~ 28

Author(s):

Ming Ma ◽

Ezra L. Clark ◽

Kasper T. Therkildsen ◽

Sebastian Dalsgaard ◽

Ib Chorkendorff ◽

...

Keyword(s):

Carbon Balance ◽

Gas Diffusion ◽

Gas Diffusion Electrode ◽

High Rate ◽

Catalytic Selectivity ◽

Co2 Electroreduction ◽

Gas Products

The carbon balance during high-rate CO2 reduction in flow electrolyzers was rigorously analyzed, showing that CO2 consumption should be taken into account for evaluating catalytic selectivity of gas products.

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Insights into the Carbon Balance for CO2 Electroreduction on Cu using Gas Diffusion Electrode Reactor Designs

10.26434/chemrxiv.11365136.v1 ◽

2020 ◽

Author(s):

Ming Ma ◽

Ezra Lee Clark ◽

Kasper T. Therkildsen ◽

Sebastian Dalsgaard ◽

Ib Chorkendorff ◽

...

Keyword(s):

Carbon Balance ◽

Gas Flow ◽

High Current Density ◽

Substantial Reduction ◽

Co2 Reduction ◽

Gas Diffusion ◽

High Rate ◽

Co2 Consumption ◽

Electrolyte Interface ◽

Co2 Electroreduction

In this work, the carbon balance during high-rate CO2 reduction in flow electrolyzers is rigorously analyzed. The CO2 consumption at gas-diffusion electrodes due to electrochemical reduction and reaction with OH- at the electrode-electrolyte interface leads to a substantial reduction in the volumetric flowrate of gas flow out of the electrolyzer, especially when highly alkaline electrolytes and elevated current densities are utilized, mainly owing to elevated pH at cathode/electrolyte interface. Without considering the CO2 consumption, the Faradaic efficiencies for major gas products could be significantly overestimated during high current density CO2 reduction conditions, particularly in the case of high pH electrolyte. In addition, a detailed carbon balance path is elucidated via a two-step procedure of CO2 reaction with OH- at cathode/electrolyte interface and subsequent CO2 generation at anode/electrolyte interface caused by a relatively low pH in the vicinity of the anode. Based on the proposed two-step carbon balance path, a systemic exploration of gases released in anolyte reveals the transformation of a HCO3- or OH- catholyte to a CO32- catholyte, which was further confirmed by pH measurement.

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Insights into the Carbon Balance for CO2 Electroreduction on Cu using Gas Diffusion Electrode Reactor Designs

10.26434/chemrxiv.11365136 ◽

2020 ◽

Author(s):

Ming Ma ◽

Ezra Lee Clark ◽

Kasper T. Therkildsen ◽

Sebastian Dalsgaard ◽

Ib Chorkendorff ◽

...

Keyword(s):

Carbon Balance ◽

Gas Flow ◽

High Current Density ◽

Substantial Reduction ◽

Co2 Reduction ◽

Gas Diffusion ◽

High Rate ◽

Co2 Consumption ◽

Electrolyte Interface ◽

Co2 Electroreduction

In this work, the carbon balance during high-rate CO2 reduction in flow electrolyzers is rigorously analyzed. The CO2 consumption at gas-diffusion electrodes due to electrochemical reduction and reaction with OH- at the electrode-electrolyte interface leads to a substantial reduction in the volumetric flowrate of gas flow out of the electrolyzer, especially when highly alkaline electrolytes and elevated current densities are utilized, mainly owing to elevated pH at cathode/electrolyte interface. Without considering the CO2 consumption, the Faradaic efficiencies for major gas products could be significantly overestimated during high current density CO2 reduction conditions, particularly in the case of high pH electrolyte. In addition, a detailed carbon balance path is elucidated via a two-step procedure of CO2 reaction with OH- at cathode/electrolyte interface and subsequent CO2 generation at anode/electrolyte interface caused by a relatively low pH in the vicinity of the anode. Based on the proposed two-step carbon balance path, a systemic exploration of gases released in anolyte reveals the transformation of a HCO3- or OH- catholyte to a CO32- catholyte, which was further confirmed by pH measurement.

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