CHEMICAL SCIENCE

Scientists realize new carbon dioxide electrochemical capture technology


On June 28, 2023, the team of Wang Shutian of Rice University in the United States published a research paper entitled “Continuous carbon capture in an electrochemical solid electrolyte reactor” online in the journal Nature.

The research group designed a continuous electrochemical carbon dioxide capture electrolyzer. Efficient flue gas CO2 capture (440 mA cm-2, 0.137 mmol CO2 min-1 cm-2 or 86.7 kgCO2 day-1 m-2) through the high concentration of hydroxide ions formed at the catalyst/membrane interface, efficient flue gas CO2 removal efficiency (> 98%), and low energy consumption (~150 kJ/molCO2 initially) show great potential for practical applications.

The corresponding author of the paper is Wang Weitian, and the first authors are Zhu Peng and Wu Zhenyu.

Carbon dioxide capture and harvesting is a potential solution to global climate change and reduce greenhouse gas emissions. Traditional CO2 capture techniques are mainly based on physical or chemical methods, such as CO2 capture using organic amine absorbents, CO2 capture by cyclic calcination/carbonation reaction using CaO absorbents, or COF/MOF solid adsorbents. These methods can efficiently capture and store CO2, but often require higher temperatures or pressures during adsorption and regeneration and may be affected by gas composition (e.g., water vapor, NOx, SOx, CO gas) and operating conditions.

In recent years, electrochemical capture technology has become a research hotspot for reducing CO2 emissions and achieving carbon neutrality due to its potential for low energy consumption, flexibility and sustainability. Electrochemical carbon capture typically relies on redox capture media or by adjusting the pH change of solution (pH swing) to absorb and release CO2. For example, carriers with redox activity, such as quinones, have the advantage of high energy efficiency due to their rapid reduction and oxidation reaction kinetics. However, their practical application is limited by low capture rates (typically < 10 mA cm-2) and sensitivity to oxygen present in most CO2 sources.

Therefore, Wang’s group proposed a different carbon dioxide capture method, which realized continuous and modular CO2 capture of different concentrations of CO2 sources by combining O2/H2O electrolysis with porous solid electrolyte (PSE) reactors. This method has the advantages of high capture rate, high energy efficiency, insensitivity to oxygen, easy to scale, and adaptability. When oxygen molecules are reduced on an ORR catalyst (commercial Pt/C or synthetic Co monatomic catalyst) on the cathode, a large number of hydroxide ions are generated at the catalyst/membrane interface, which react rapidly with flue gas or CO2 molecules in the air to form carbonate or bicarbonate ions (Figure 1b). Driven by an electric field, these carbonate ions diffuse through an anion exchange membrane into the intermediate solid electrolyte layer. The protons diffused from the anode combine in the intermediate layer to form carbonic acid and decompose into CO2 gas, which can be continuously flushed out by the circulating water flow of the PSE layer and collected as a high-purity gas (Figure 1c).

With this OER/ORR redox electrolysis, the system does not consume or produce any chemicals externally, as the oxygen produced by the anode can be recycled back to the cathode for stoichiometric equilibrium. In addition, the CO2 capture performance is further improved by adjusting different reactor parameters. For example, the synthesis of porous Co single-atom catalysts achieves higher capture efficiency than commercial Pt/C catalysts at low concentrations of CO2, and better tolerance and stability to toxic gases such as NOx, SOx, and CO (Figure 2). The 4e−-ORR and 2e−-ORR reaction pathways were adjusted by synthesizing different single-atom catalysts to further improve the electron efficiency and CO2 capture efficiency (Figure 3).

Figure 1: Mechanism of continuous CO2 capture in a solid-state electrolyte system.

Figure 2: CO2 capture performance of synthetic Co-monatomic catalysts.

Figure 3: Parameter adjustment of the reactor and regulation of the reaction path to improve the CO2 capture efficiency and economic effect.

This study proposes a versatile carbon capture method, and the constructed solid electrolyte reactor can be implemented in many practical scenarios in the future. Notably, many electrochemical redox pairs, such as HER/HOR, have better reaction kinetics and lower overpotential than the OER/ORR pairs demonstrated by the group in this study, which will significantly reduce the operating voltage of the battery and improve carbon capture efficiency. Future research can further optimize various cell and operating parameters, such as solid electrolyte layer thickness, operating temperature and pressure, improve the catalyst of redox pairs, and adjust reaction paths to improve the energy efficiency and cost reduction of carbon capture, thus enabling large-scale practical applications of CO2 electrochemical capture. (Source: Science Network)

Related paper information:https://doi.org/10.1038/s41586-023-06060-1



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