Enhancing Efficiency of Electrochemical Carbon Capture Using Pulsed Chronopotentiometry with Hydrophilic Graphite Electrode
Achieving carbon neutrality is an urgent global goal, aiming to balance industrial development with preserving the Earth’s livability. The Intergovernmental Panel on Climate Change (IPCC) identifies carbon dioxide (CO₂) as a primary anthropogenic greenhouse gas contributing to climate change. The continuous emission of CO₂ into the atmosphere has resulted in a higher concentration (422 ppm) compared to preindustrial levels (280 ppm), leading to erratic weather patterns and extreme temperatures. Carbon capture technologies offer a practical solution to this challenge, enabling continued industrial and cultural progress while mitigating negative environmental effects. While conventional thermal methods require 230-800 kJ of thermal energy per mole of CO₂ separation, electrochemical methods provide an energy-efficient approach for the carbon capture process, operating under isothermal conditions. Recently, Seo et al. reported an electrochemical direct air capture method using redox-active Neutral Red (NR), an organic dye compound, which demonstrates high electron utilization and theoretically low energy consumption, suggesting a sustainable alternative to conventional thermal technologies. However, initial tests revealed operational voltages exceeding 2 V, attributed to limited electron transfer kinetics and transport. Two primary obstacles were identified: (1) insufficient chemical properties and active surface area in graphite felt electrodes, and (2) restricted NR transport due to low concentration.[1][2][3]Herein, we present an optimized electrochemical carbon capture operation using modified graphite felt electrodes to enhance wettability and pulsed chronopotentiometry to reduce concentration overpotentials. The carbon capture system integrates electrode material modification and pulsed chronopotentiometry to enhance electron transfer efficiency, reduce energy consumption, and address challenges such as poor wettability and NR polymerization. To improve the electrode-electrolyte interaction, graphite felt electrodes were modified by introducing oxygen-containing functional groups on their surface. This modification significantly enhanced the wettability of the electrodes, as demonstrated by water contact angle measurements, and facilitated efficient electron transfer between the electrode and electrolyte, which is critical for minimizing energy consumption. The choice of electrode materials and operational parameters was thus optimized to enable low-resistance electrochemical reactions. Cyclic voltammetry experiments revealed that the modified graphite felt exhibited a higher current response at the same voltage compared to the pristine electrode. This improvement translated into a substantial reduction in operating cell voltages, with a reduction of 19.5%, decreasing from an average of 1.18 V to 0.95 V. A notable challenge during the reduction process was the polymerization of Neutral Red (NR), which resulted in the loss of active material in the electrolyte, thereby increasing the cell voltages. To address this issue, pulsed chronopotentiometry was employed. This technique periodically applies a low opposing current, minimizing polymerization and reducing overpotential. By alternating between run and rest currents, the method effectively improved system efficiency. With pulsed chronopotentiometry, the redox reactions of NR were achieved at significantly lower operating voltages, demonstrating a 43% reduction (1.18 V) compared to constant chronopotentiometry (2.07 V) at a current density of 8 mA/cm2 and using 15% CO2.The electrochemical carbon capture system in this study employed a two-electrode configuration, featuring a customized nylon frame packed with graphite felt electrodes, with the two compartments separated by an anion exchanging membrane. The electrochemical cell was connected to two containment vessels, where consistent 15% CO2 input stream was introduced and the output measured by an FTIR CO2 sensor. A peristaltic pump was used to circulate the solution throughout the system. Two containment conditions with varying activation percentages were implemented, with a working capacity of 25% applied.The electrochemical approach using pulsed chronopotentiometry with modified graphite felt electrodes achieved operating cell potentials as low as 0.95 V, with an estimated energy consumption of 160 kJe/mol CO₂. This underscores its potential as an efficient, sustainable carbon capture strategy, highlighting the importance of electrode material modification and optimized operational strategies in enhancing energy efficiency and performance.Keywords: Electrochemistry, Carbon Capture, pH Swing, Pulsed Chronopotentiometry, Neutral Red, Graphite felt[1] IPCC, 2021: Climate Change 2021: The Physical Science Basis.Contribution of Working Group I to the Sixth Assessment Report ofthe Intergovernmental Panel on Climate Change (2021).[2] H. Seo and T. A. Hatton, Nature Communications, 14 (2023).[3] H. Seo, M. P. Nitzsche, and T. Alan Hatton, Accounts of Chemical Research, 56, 3153–3164 (2023). Figure 1
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