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학습트랜스크립트
00:00Hello everyone, and thank you for coming to my presentation.
00:06My name is Cheyyeon Lee, and today I will talk about the effect of carbon supports on
00:12the electro catalytic performance of decurrency catalysts for CO2 reduction to CO.
00:20As you can see from the title, this work focuses on decurrency type single atom catalysts.
00:28And in particular, on how different carbon supports, carbon black, carbon nanotubes, and
00:35activated nitrogen-dupped biochar influence their performance in the CO2 reduction reaction.
00:44Instead of only asking which catalyst is best, this study tries to answer a more fundamental
00:55question.
00:57How do the texture and structure properties of the carbon support, such as porosity, surface
01:03area, and conductivity affect the real electrochemical behavior of decurrency catalysts?
01:12Finally, I will discuss several key factors that explain the performance differences.
01:19Double layer capacitance, charge transfer resistance from EIS, and porosity and surface area from
01:27gas absorption measurements.
01:29At the end, I will connect these findings to our own RCC-type MEACO2-RR system and explain
01:39what they imply for future catalyst design.
01:43Let me start with a brief introduction and motivation.
01:52The electrochemical reduction of CO2 has attracted a lot of attention as a key as a way to store
02:00renewable electricity in the form of chemical fuels and feedstocks.
02:06Among the many possible products, CO is particularly important because it can be further converted
02:14to various chemicals through existing gas and fissotrop processes.
02:20Therefore, in this study, the others systemically compare three different carbon supports,
02:29carbon black, carbon nanotubes, and activated nanonitrogen-dupped biotubes.
02:35While keeping the nickel and co-ordination as similar as possible, by doing so, they can isolate
02:45the effect of the carbon support on CO2R performance, especially at high current densities, which are
02:54more relevant for practical application.
02:58On this slide, we look at the surface structure of the three recurrence catalysts, recurrence-CB,
03:10recurrence-CNT, and recurrence-AMBC.
03:14Although the exact images are shown in this text, we can imagine typical SAM or TAM images
03:24that deliver quiet different morphologies.
03:29Nickel-NCB is based on carbon black, which usually consists of nearly spherical primary particles
03:38forming aggregated and agglomerated structures.
03:43This type of sub-support often has relatively low surface area and mostly macroporous voids between particles.
03:55Nickel-NCNT is supported on carbon nanotubes.
04:00CNTs form a network of one-dimensional tubes that produce interconnected major and macropores.
04:10This tubular structure can create efficient pass-space for both electron transport and gas diffusion.
04:23Nickel-AMBC is derived from activated nitrogen biopatica.
04:30Later, we will see that even if the intrinsic activity of each nicarine site is similar,
04:39these structural features will lead to quiet different overall cell performance.
04:49Next, let us move to the chemical structure of the catalysts,
04:55which is mainly analyzed by high-resolution X-ray photoelectron spectroscopy or XPS.
05:04First, looking at the N1S spectrum, we can distinguish several types of nitrogen species on the carbon supports.
05:16Among these, pyridine N is often associated with CO2 abduration and activation,
05:25while the nickel peak near 399 E-volt is considered as the signature of the true CO2 r activated sites.
05:38Where nickel atoms coordinate with nitrogen in the carbon matrix,
05:45additional nitrogen species such as purely grapitic and oxidized N can also influence the local electronic structure and hydroplasticity.
06:00Overall, XPS confirms that all three catalysts share similar nickel and active sites,
06:09which allow us to focus on how the different carbon supports,
06:14rather than the intrinsic active site chemistry, affect the CO2 r performance.
06:21Now, let us look at the electro catalytic performance of these nickel-NC catalysts.
06:35The first set of the data is usually the linear sweep voltometry LSV curves.
06:42This curve shows how the total current density changes as we scan the potential
06:50to more negative values.
06:53All three decurrency catalysts exhibit significant cathodic currents in the CO2 saturated electrolyte,
07:03indicating active CO2 reduction.
07:07More importantly, the others evaluate the periodic efficiency of CO,
07:14parity efficiency of CO, and partial current density for CO at different applied potentials.
07:22Across a wide potential window, our drain decurrency catalysts achieve very high parity efficiency,
07:30typically around 90 to 100%.
07:33This means that almost all the current is used to produce CO,
07:38and side reactions such as hydrogen evolution are strongly suppressed.
07:47An important conclusion here is that the carbon support does not drastically change the selectivity,
07:55because the parity efficiency of CO is similar for our three catalysts at moderate current densities.
08:03Instead, the main differences appear in the cell voltage,
08:10required to reach a certain current and in the stability of a varied efficiency of CO,
08:17and at higher current densities.
08:22These observations already suggest that mass transport and electrostructure,
08:27rather than the intrinsic Nicarian kinetics are controlling the performance,
08:35especially in the high current regime.
08:38So, to understand why the performance differs,
08:45the others first analyze the double layer capacitance often denoted as CDL.
08:53CDL is obtained from cyclic photometry in a non-parodic potential region
09:01and reflects the ability of an electrosurface to accumulate the charge in the electrochemical double layer.
09:11It is commonly used as a proxy for the electrochemically active surface area.
09:19For the three Nicarian catalysts, the major CDL values are,
09:25yeah, as you can see in the picture.
09:28Yeah, so the same things.
09:30This trend directly reflects the texture properties of the carbon supports.
09:40Nicarian AMBC, with its ultra-high specific surface area and rich micro-porosity,
09:49has the largest CDL.
09:52In contrast, carbon black and CNT supports have lower surface area,
09:58resulting in smaller CDL values.
10:01Interestingly, however, the study finds no simple one-to-one correlation between CDL and the overall CO2-RR performance,
10:14especially at the high current densities.
10:18Even though Nicarian AMBC has the highest CDL,
10:23this does not automatically mean it has proportionally more active Nicarian sites.
10:30Therefore, the others conclude that CDL mainly reflects the structure and capacitive properties of the carbon supports,
10:44not necessarily the number of Nicarian active sites.
10:49This result warns us that using CDL alone as the ECSA proxy can be misreading for single atom catalysts
11:02in highly porous carbon network.
11:07The next key tool is electrochemical impedance spectroscopy ,
11:13which provides deeper insight into charge transfer and mass transport processes.
11:20The results are usually presented as Nyquist plots,
11:26where the real part of the impedance is on the x-axis and the imaginary part is on the y-axis.
11:35We can divide Nyquist plot into three frequency regions.
11:41First, high frequency region.
11:45This is the leftmost first of the plot,
11:49where the real impedance is small.
11:52Here, the impedance is dominated by the solution resistance RS,
11:57which mainly comes from the electrolyte resistance and cell configuration.
12:03In this work, our samples are around 20 to 30, indicating smaller r for all electrodes.
12:16This region reflects only the fastest process, namely ion conduction in the electrolyte.
12:23Second, mid-frequency region.
12:27In this region, we observe semicircle, whose diameter corresponds to the charge transfer resistance, RCT,
12:37at the interface between the electrode and active sites.
12:42A smaller semicircle means lower ICT and transfer electron transfer.
12:49The data show that CNT and AMBC-based catalysts have smaller semicircle, indicating lower ICT and faster charge transfer.
13:00In contrast, the carbon black-based catalyst shows a larger semicircle, meaning higher ICT and slower charge transfer,
13:12likely due to its lower conductivity and less favorable structure.
13:18Third, low-frequency region.
13:21At low-frequency region, we often see a tail or second semicircle,
13:27which is associated with Wabwag impedance, representing mass transport limitations.
13:36A large slope or extended picture in this region indicates a strong diffusion resistance for reactants and products.
13:47In this work, CB and carbon paper electrodes show larger slopes and stronger diffusion limitations,
13:59whereas CNT and AMBC electrodes show shorter or slower pitchers, implying faster mass transport.
14:12Further, connect the electrochemical behavior with the physical structure.
14:17The others analyze N2 absorption, disabsorption, isosome, and pore site distribution,
14:26often evaluated by BET and DFT methods.
14:33The key message is that hierarchical combination of micro, meso, and macro is ideal.
14:42AMBC provides a small large number of micropores for CO2 capture and the current dispersion,
14:51while CNT-based supports offer highly conductive meso and macro networks for fast transport.
15:02carbon block, with less developed porosity and lower surface area, is less favorable in both aspects.
15:12Now, let us focus on high current density behavior, which is crucial for practical CO2 electrolyzers.
15:22The study examines ferrodeficiency of CO2 and cell voltages as functions of current density from 25 to 200 milliampere per square centimeters.
15:37The trend can be summarized as follows.
15:44As a result, at industrially-relevant current densities, optimizing the carbon support structure becomes as important as optimizing the active nitrogen sites themselves.
16:02Let me summarize the main conclusions of this work before connecting them to the RCC system.
16:12Parodeficiency of CO2.
16:13Parodeficiency of CO2.
16:14All the three nickel currency catalysts supported on carbon block, CNT, and AMBC exhibit very similar parodeficiency of CO2 values.
16:27Over a wide range of potentials are current densities.
16:36This indicates that the intrinsic selectivity of the current sites toward CO2 is robust and largely independent of the carbon support.
16:48And second, energy efficiency and overpotential.
16:53The key differences among the catalysts are observed in the cell voltage and overpotential required to reach a given current density.
17:03Nickel and AMBC, in particular, achieves high current densities at lower voltages, meaning it has better energy efficiency.
17:15And then last one is design implication.
17:22Therefore, the final insight is that optimizing the texture properties of carbon support is as important as designing the nickel and active sites themselves.
17:34Different supports can enhance performance through different mechanisms, CNT through conductivity-driven effects and AMBC through surface area and confinement-driven effects.
17:55In the final part of my talk, I would like to connect these findings to RCC type MEACO2R system, which you are interested in.
18:08First, this study clearly shows that mass transport is the real bottleneck once the nickel and active slides reach a certain level of intrinsic activity.
18:30The recurrence catalysts already exhibit very high intrinsic CO2R activity to CO.
18:50So now I would like to move on from the catalyst level to process level and compare a conventional gas-based CO2R system and with the ERCC pathway.
19:02In both cases, we start from waste CO2, which is absorbed into a liquid and from CO2-rich capture solution.
19:13In contrast, in the RCC system, the CO2-capture liquid is fed directly to the electrolyzer.
19:21Finally, let me highlight pressure as one of the key operating variables for ERCC together with the cathode and the capture solution.
19:36The plot on the left shows CO-paridefuency in a gas-based CO2-R system under different conditions.
19:44Therefore, insights from gas-based CO2-R tell us that high CO2 pressure, partial pressure improves CO selectivity and disconnect can be directly applied when optimizing ERCC systems.
20:03So, yeah, thank you. Thank you very much for my presentation and I will be happy to talking about this.
20:33Good evening.
20:40Thank you.
20:45Thank you.
20:49Thank you.
20:51Thank you.
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