Bubble Formation in the Electrolyte Triggers Voltage Instability in CO2 Electrolyzers

Abstract

The electrochemical reduction of CO 2 is promising for mitigating anthropogenic greenhouse gas emissions; however, voltage instabilities currently inhibit reaching high current densities that are prerequisite for commercialization. Here, for the first time, we elucidate that product gaseous bubble accumulation on the electrode/electrolyte interface is the direct cause of the voltage instability in CO 2 electrolyzers. Although bubble formation in water electrolyzers has been extensively studied, we identified that voltage instability caused by bubble formation is unique to CO 2 electrolyzers. The appearance of syngas bubbles within the electrolyte at the gas diffusion electrode (GDE)-electrolyte chamber interface (i.e. $10% bubble coverage of the GDE surface) was accompanied by voltage oscillations of 60 mV. The presence of syngas in the electrolyte chamber physically inhibited two-phase reaction interfaces, thereby resulting in unstable cell performance. The strategic incorporation of our insights on bubble growth behavior and voltage instability is vital for designing commercially relevant CO 2 electrolyzers.

Understanding the Effects of Anion Interactions with Ag Electrodes on Electrochemical CO2 Reduction in Choline Halide Electrolytes

“…However, FE CO in ChI remained lower than ChCl and ChBr. The subtle difference in FE CO between ChBr and ChCl could be due to uncertainty in the results attributed to various factors such as catalyst deposition on the GDE, [17] cations/anions in the catholyte, [17,67] hydrodynamic layer, [67] and the presence of gas bubbles [68–70] . The FE CO results observed in the flow‐cell (beyond 10 mA cm −2 ) are inconsistent with the H‐type cell results at more negative potentials (beyond −1.0 V vs. RHE).…”

The inchoate horizon of electrolyzer designs, membranes and catalysts towards highly efficient electrochemical reduction of CO2 to formic acid

“…However, under this circumstance, it is prone to show product crossow via the GDL due to the pressure difference and CO 2 bubbles in the catholyte leads to a uctuation in the cell voltage upon time. 43 In this conguration, extensive studies have been proven to be efficient over conventional H-type cells. For example, Bi 2 O 3 nanotube catalyst showed 100% selectivity at À1.05 V vs. RHE, a high current density (60 mA cm geo À2 ), and a long-term catalytic stability >48 h in 0.5 M KHCO 3 under a standard H-type cell.…”

Multi-dimensional designer catalysts for negative emissions science (NES): bridging the gap between synthesis, simulations, and analysis

“…Furthermore, as these mixed-dimensional vdW heterostructures have more surface-active sites, CO 2 bubble formation becomes an important issue. Bubble formation, particularly at high applied potentials, may block active sites causing voltage instabilities that accelerate the degradation rate of the catalysts ( Lee et al., 2020 ; Ren et al., 2020 ; Xing et al., 2021 ). To date, there have been no mechanistic studies on how CO 2 bubble formation affects the current/voltage response of catalytic systems in terms of nucleation rate, lifetime, and internal pressure of the bubbles, especially for vdW heterostructures, nor has there been an overall study of degradation mechanisms for catalysts under large applied potentials or surrounded by high-energy excitons.…”