Tailoring acidic microenvironments for carbon-efficient CO₂electrolysis over a Ni–N–C catalyst in a membrane electrode assembly electrolyzer

Abstract

CO2 electrolysis converting CO2 into valuable fuels and chemicals powered by renewable electricity shows great promise for practical applications. However, it suffers from low energy efficiency and carbon efficiency due...

Carbonation in Low-Temperature CO2 Electrolyzers: Causes, Consequences, and Solutions

“…Region 6 is deficient in protons ((bi)­carbonate formation region), and region 7 is deficient in CO 2 (mass transport limitation). Therefore, the key for suppressing HER and (bi)­carbonate formation in acidic media is to find the operating conditions that comply with the requirements of region 1 in Figure . − Clearly, efficient CO2R in acidic media relies on a proper understanding of both the CO2RR and the HER as a function of the reaction conditions (e.g., pH, temperature, pressure, electrolyte type and concentrations, etc.). In choosing the reaction conditions for CO2R in (slightly) acidic media, it is important to know the relative contributions of H + reduction and water reduction to the HER for a specific catalyst as a function of process variables like the pH and temperature.…”

Why Membranes Matter: Ion Exchange Membranes in Holistic Process Optimization of Electrochemical CO2 Reduction

“…[32,33,[62][63][64][65] Yet, most of these studies are not on the level of buffered CEM and AEM characteristics in terms of Faradaic efficiency and cell voltage. Only most recently, Li et al [31] achieved up to 95% CO Faradaic efficiency and 3.6 V at a current density of 500 mA cm −2 using a Ni-N-C catalyst in a CEM zerogap electrolyzer design. Even though the work of Li et al shows a promising perspective for acidic CO 2 electrolysis, long-term stability of the process and the Ni-N-C catalyst was only shown for a few hours with a decrease in Faradaic efficiency, a loss of electrode hydrophobicity, and slight formation of carbonate salt visible after only 8 h of the experiment.…”

“…However, recent trends in acidic zero-gap CO 2 electrolysis can overcome the poor energetics and mass transport issues at elevated current densities in buffered CEM configurations by reducing ohmic voltage losses and suppressing detrimental carbonate formation. [31] In contrast, the AEM and BPM electrolysis processes are more susceptible to variations in the Faradaic efficiency. It must be noted that for the AEM and BPM electrolyzer, an increase of the Faradaic efficiency by ≈5% and ≈12% already lead to an of resulting in a nonlinear trend in the tornado charts.…”

“…[30] The major drawback of using CEMs in CO 2 electrolysis is the typically increased presence of H + ions at the membrane surface, which usually requires the implementation of a buffer layer between the membrane and the electrode. [12,13] However, recent studies report notable CO Faradaic efficiencies in acidic zero-gap electrolyzers when using single-atom catalysts such as nickel-nitrogen-doped carbon, [31] employing protective nanocages encapsulating the catalyst, [32] and tuning the ratio of H + and alkali cations crossing over from the anolyte. [33] Several experimental studies discuss the advantages and disadvantages of each membrane type on electrochemical CO 2 reduction.…”

Surface-Immobilized Cross-linked Cationic Polyelectrolyte Enables CO2 Reduction with Metal Cation-free Acidic Electrolyte

“…9 Recently, techniques of CO 2 reduction with acidic electrolyte were developed to circumvent the asmentioned issues. [9][10][11][12][13][14][15][16][17][18][19][20][21] Alkali cations play an important role to suppress hydrogen evolution reaction (HER) and promote CO 2 reduction in acidic condition. However, alkali cations induce bicarbonate precipitation on the cathode during CO 2 reduction in acidic electrolyte, which is still an issue that hinders the sustainability of CO 2 reduction.…”