Progress and Understanding of CO₂/CO Electroreduction in Flow Electrolyzers

Abstract

The electroreduction of CO 2 and CO into valuable chemicals and fuels powered by renewable electricity can tackle anthropogenic carbon emissions and close the carbon cycle. However, both CO 2 and CO have low solubility in aqueous electrolytes, affording their sluggish mass transport across the electrolyte. CO 2 /CO electroreduction in a flow electrolyzer can tackle this problem by directly delivering the gaseous reactant to the electrode surface. Significant progress has been made recently in simultaneously obtaining high reaction rates and high product selectivity using flow cell configurations. This perspective highlights how different flow cell designs impact CO 2 /CO electroreduction and outlines potential strategies that may further improve the cell performance. The challenges and opportunities related to fundamental and engineering aspects are also discussed.

Atomically Dispersed Metal–Nitrogen–Carbon Catalysts with d-Orbital Electronic Configuration-Dependent Selectivity for Electrochemical CO2-to-CO Reduction

“…However, its practical application has been significantly challenged by its uncontrollable product selectivity in electrochemical CO 2 RR due to the complicated reaction pathways and overdiversified products. Given that CO is the most common and simplest product, which is of high value in the C 1 chemical product chain, the electrochemical CO 2 -to-CO reduction reaction with only two electrons getting involved in the CO 2 RR could achieve high activity and high selectivity as expected. − In the past years, some noble-metal (e.g., Ag, − Au, − etc. )-based catalysts have revealed excellent electrochemical performances for CO 2 RR, which could effectively reduce CO 2 to CO at relatively low overpotentials.…”

Benchmarking of commercial Cu catalysts in CO2electro-reduction using a gas-diffusion type microfluidic flow electrolyzer

“…3,[11][12][13][14] In recent CO 2 RR studies, gas-diffusion type flow electrolyzers were widely employed to deliver industrially relevant reaction rate and selectivity by improving the mass transport of CO 2 from the gas phase to the catalyst surface. 5,[15][16][17] CO 2 RR performance with over 60% faradaic efficiency of C 2+ products at current densities 4100 mA cm À2 has been achieved in numerous recent reports. [18][19][20][21][22][23] Owing to the structural complexity of the gas-diffusion electrode (GDE) and varied configurations of flow electrolyzers employed in the literature, it is unclear whether the reported CO 2 RR performance reflects the intrinsic activity of the catalysts, as it is commonly assumed, or features of flow reactors.…”

“…Using renewable electricity to catalyse the carbon dioxide reduction reaction (CO 2 RR) has the potential to enable the sustainable production of commodity chemicals and fuels. [1][2][3][4][5][6] Cu-based materials are the most common catalysts with decent selectivity for C 2+ products, including ethylene, ethanol, acetate, and n-propanol. [6][7][8][9][10] Much effort has been devoted to the design to enhance the rate and optimize the product distribution.…”

“…[18][19][20][21][22][23] Owing to the structural complexity of the gas-diffusion electrode (GDE) and varied configurations of flow electrolyzers employed in the literature, it is unclear whether the reported CO 2 RR performance reflects the intrinsic activity of the catalysts, as it is commonly assumed, or features of flow reactors. 5,15,24,25 In this work, we evaluated the CO 2 RR performance of three commercial Cu catalysts, i.e., nanoparticle Cu (NP Cu, purchased from Sigma-Aldrich), spherical Cu (Sph Cu, purchased from Macklin), and copper oxide (CuO, purchased from Alfa Aesar), using a gas-diffusion type microfluidic flow electrolyzer that has been widely employed in CO 2 electrolysis. We showed that all three commercial catalysts were able to deliver FE of C 2+ products above 70% at 200 mA cm À2 , and notably, NP Cu could achieve near 80% FE of C 2+ products at 300 mA cm À2 .…”

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

“…Electrochemical reduction of CO 2 (CO2R) to value-added products is an element of carbon capture and utilization (CCU), which has been identified as a complementary measure to reduce CO 2 emissions . The past decade, a significant effort has been made to improve the performance metrics of the electrochemical CO2R process. − By using gas diffusion electrodes (GDEs), optimized catalyst and reaction conditions, and proper reactor engineering, we are able to obtain several CO2R products at industrial-scale current densities (CDs), high Faraday efficiencies (FEs), low cell voltages, and extended durability/stability. − The high-temperature solid oxide electrolysis cell (SOEC) for CO 2 reduction to carbon monoxide (CO) is commercialized by Haldor Topsoe, while Sunfire and others are currently bringing the co-SOEC process for syngas production to the market. In sharp contrast, the low-temperature CO 2 electrolysis process is suffering from a major drawback, which is related to the carbonation of the electrolyte as a consequence of performing CO2R in alkaline conditions to suppress the hydrogen evolution reaction (HER).…”