bluuebunny/crossref_metadata_2025 huggingface dataset:
Unveiling Transport Mechanisms of Cesium and Water in Operando Zero-Gap CO2 Electrolyzers
Authors: Joensen Bjørt , Zamora Zeledón José A. , Trotochaud Lena , Sartori Andrea , Mirolo Marta , Moss Asger Barkholt , Garg Sahil , Chorkendorff Ib , Drnec Jakub , Seger Brian , Xu Qiucheng
Published: December 2024

In zero-gap CO2 electrolyzers, maintaining the balance of water and cations is crucial. Excessive accumulation at the cathode causes performance degradation, leading to flooding and salt precipitation. Using operando wide-angle X-ray scattering and X-ray fluorescence techniques, we observed the dynamic evolution of H2O and Cs+ inside a membrane electrode assembly. While no motion of Cs+ and H2O was observed during open circuit voltage (OCV), our findings indicate that Cs+ movement across the membrane from the anode to the cathode is governed by migration and drags H2O via electroosmosis when a potential was applied. H2O diffusion then allows Cs+ diffusion further within the gas diffusion electrode. When decreasing the applied voltage, the concentration gradient causes Cs+ to quickly diffuse back to the anode. The H2O content in the macro-porous layer remains at the same level, thus showcasing an origin of gas diffusion electrode (GDE) flooding, which is one of the detrimental degradation mechanisms to these systems and result in an enhanced H2 production. By regulating the electrolyte concentration, we deconvolute the correlation of water and cations for selectivity changes. Our work underscores the significance of water/cation management strategies in zero-gap electrolyzers.
(Keynote) Copper Cathode for Electrochemical CO2 Reduction – Unanswered Questions on Reproducibility
Authors: Marshall Aaron Timothy , Heenan Alex Reynell , Tiffin Campbell Maurice
Published: December 2024

Electrocatalytic reduction of CO2 has the potential to convert CO2 into carbon-based fuels by using renewable energy. For many years, copper based cathodes have been highlighted as the quintessential electrocatalytic surface for CO2 reduction (exemplified by the work of Hori). While gas-diffusion electrodes have shown than industrially relevant reaction rates can be achieved using relatively simple cathode materials, there are still many unanswered questions regarding the behaviour of copper cathodes in aqueous solutions. In particular, a review of the literature reveals that a very wide range of product selectivities are found at seemingly similar conditions (Figure 1). Rather surprisingly this review shows that sometimes copper can have almost no activity for CO2 reduction and instead evolve almost pure H2. Our own measurements confirm this unexpected behaviour, with replicate experiments revealing occasions where identically mechanically polished copper electrodes favour hydrogen evolution over CO2 reduction. In this presentation, we will discuss the reproducibility of CO2 reduction and the steps taken to explain copper’s highly variable product selectivity.

Figure 1: Results from literature for faradaic efficiency of common CO2 reduction reaction products on polycrystalline copper (black lines) and other forms of copper (red lines) at -1 (± 0.1) V vs RHE in CO2 saturated 0.1 M KHCO3.

Figure 1
The Impact of CO2 Dynamics within the Gas Diffusion Electrode on Electrochemical CO2 Reduction in Zero-Gap MEA Operation
Authors: Kim Hyunchul , Oh Hyung-Suk , Ko Young-Jin , Lee Ung
Published: December 2024

Since the Industrial Revolution, massive amounts of generated from human industrial activities have been causing ongoing climate change and environmental impacts on Earth. Hence, there is a substantial body of research aimed at mitigating CO2 emissions to address climate change. Research on CO2 reduction has been actively conducted, focusing on electrochemical-based CO2 conversion capable of operating under high current and long-term conditions. Under high current and prolonged operation, catalyst are influenced by the concentration of CO2 within the catalytic layer. To investigate the impact of CO2 concentration, we fabricated reaction zones of flow plates used in zero-gap MEA electrolyzers in both flat and sunken shapes. The two flow plates feature an inlet with a channel to guide the incoming gas to the reaction zone and a channel within the reaction zone to distribute the gas effectively. Both the flat and sunken type feature. Both the flat and sunken shapes contain a reaction zone channel where the gas diffusion layer (GDL) is positioned at the top. However, In the sunken flow plate, gas introduced from the inlet can penetrate towards the GDL side, facilitating enhanced delivery of CO2 to the catalytic layer compared to flat flow plates. This leads to increased CO2 activity within the catalytic layer and, simultaneously, offers the advantage of easier water management, a major cause of equipment performance degradation. In this study, we confirm through simulation that the sunken shape in flow plates with serpentine channels in the reaction zone offers advantages in CO2 activity. Experimentally, we obtained partial current densities of 861 mA/cm2 and 1 A/cm2 for silver catalyst and NiNC catalyst, respectively, in the sunken serpentine structure. To analyze the reasons for the increase in these values, which are 34.5% and 18.3% higher respectively compared to the flat serpentine structure, we conducted device water discharge experiments and real-time CT imaging. Through this, we confirmed that water management is more efficient in the sunken serpentine structure. The insights and methods presented in this research are crucial for developing design principles suitable for large-scale industrial electrochemical CO2 electrolysis.

Figure 1
Temperature Effects on the Surface Dynamics of the CO2 Reduction Reaction over Copper
Authors: Brandão Victor D. , Long Oliver , Song Hakhyeon , Venkatamaran Anush , Nair Sankar , Hatzell Marta C. , Sievers Carsten , Bhargava Saket , Arora Sukaran , Villa Carlos
Published: December 2024

The electrochemical reduction of CO2 (CO2RR) has stood out as a pathway to mitigate carbon emissions and supply multi-carbon feedstocks to the chemical industry. While most CO2RR studies over copper are carried out at room temperature, heat transfer limitations in the electrolyte will result in temperature buildup near the electrode in industrial CO2 electrolyzers. Reaction temperature plays a key role in the reaction activity and product selectivity by controlling the distribution of species on the copper surface. In this study, we use surface enhanced infrared absorption spectroscopy (SEIRAS) and surface enhanced Raman spectroscopy (SERS) to investigate the effect of temperature on the dynamics of reactive intermediates in the reaction microenvironment (Fig. A).

Using SEIRAS, we showed site-specific CO coverage is dependent on temperature, and how CO migration seems to directly impact product distribution at higher temperatures. We found that increasing temperature leads to decreased CO and increased alkyl groups coverage for a given potential (Fig. B). This suggests that temperature has a direct effect on the selection of mechanistic pathways in the conversion of CO to C1 and C2 products, beyond just controlling mass transport and local CO2 availability. Using SERS, we showed that the local pH is considerably higher than their bulk values, and that higher temperatures consistently led to higher local pH values (Fig. C). The significant depletion of local hydrogen with increasing temperature indicates that local pH plays a key role in driving reaction selectivity dependence on temperature. Understanding the effect of temperature on the CO2RR surface dynamics through surface sensitive techniques is a key step to rationalize product distribution and to design solutions for enhanced C2+ production in industrial CO2 electrolyzers.

Figure 1
Ion Implantation of Copper Electrodes to Elucidate the Effect of Subsurface Oxygen and Surface Roughness for the Electrochemical CO2 Reduction Reaction
Authors: Heenan Alex Reynell , Fang Vivian , Kennedy John , Marshall Aaron Timothy
Published: December 2024

The electrochemical reduction of CO2 has the potential to be a viable method to consume anthropogenic CO2, while producing value added products such as CO and C2H4 in a carbon negative way. Copper is a unique electrocatalyst for the CO2 reduction reaction as it can produce products that require more than two electrons (such as C2H4 and C2H5OH) with reasonable selectivity. This has resulted in copper being an intensely studied catalyst over the past several decades in an attempt to understand why it is able to produce these unique products, but also to promote the production of the likes of C2H4 and C2H5OH with better selectivity, activity and stability. While excellent progress has been made, there is still plenty of debate around whether the enhanced performance of copper electrodes stems from surface roughness effects or subsurface oxygen.

In the past, these two mechanisms have been difficult to decouple because of the fact that to synthesise an electrode with subsurface oxygen, surface roughness also tends to be induced. In this work, ion implantation of neon and oxygen was used to decouple these effects. The theory was that while the oxygen ion implantation will induce subsurface oxygen sites and surface roughness, the neon ion implantation will only induce surface roughness. Interestingly, it was found that both the oxygen and neon ion implantation resulted in decreased activity and selectivity for CO and C2+, with increasing ion fluence. These decreases in performance were in spite of an increase in the surface roughness of the electrode, which means that the ion implantation affected the inherent performance of the catalyst. This was in contrast to the sample that was annealed in air which had increased surface roughness, however, the normalised activity was consistent with that of the as-made catalyst. X-ray absorption spectroscopy and x-ray photoelectron spectroscopy were used to understand the loss in performance, which showed that the as the ion fluence increased, the Cu:CuO ratio and the relative O 1s Cu2O concentration on the electrode surface increased in an equivalent fashion for both the neon and oxygen implantation. Additionally, there was also a decrease in the number of oxygen vacancies, with increasing ion fluence. This shows that while the ion implantation increased the surfaced roughness of the electrode, it was able to reduce the surface Cu2+ to Cu1+ and Cu0, which resulted in the decreased performance of the electrode, suggesting that the subsurface oxygen is the key parameter that should be optimised, over the surface roughness of the electrode.
(Invited) Reconstruction of Metal-Organic Framework-Based Heterogeneous Catalysts during CO2 Electroreduction
Authors: Nam Dae-Hyun
Published: December 2024

Electrochemical CO2 reduction reaction (CO2RR), which enables CO2 conversion into value-added fuels and chemical feedstocks, provides an avenue toward carbon neutrality and renewable energy storage. In the CO2RR, heterogeneous electrocatalysts are essential to activate substrate species and interact with reaction intermediates for efficient and selective CO2 conversion. Especially, Cu-based active sites in the catalysts enable C-C coupling via *CO dimerization for multi-carbon (C2+) chemicals production. Although judiciously controlled surface of catalysts is required to control the binding of CO2RR intermediates, the active sites of the catalysts undergo severe reconstruction during electrochemical reaction. This hinders the identification of active sites because it induces structure and phase evolution of electrocatalysts during CO2RR. Therefore, reconstruction is a major bottleneck in the development of CO2RR, and it has remained as a challenge to unveil the mechanism of reconstruction.

Here, I will present our recent efforts to understand the reconstruction of Cu-based metal-organic framework (MOF) during electrochemical CO2RR. MOFs have porous structures where the organic linkers are bonded with metal node in secondary building unit (SBU). We verified that oxidation tendency of metal ions in SBU is a key to determine the stability of MOFs. Pourbaix diagram helps to predict the trend of metal reduction in MOFs during CO2RR. Operando X-ray absorption spectroscopy (XAS) during CO2RR enabled to track the states of metal node in MOFs. We found that Cu ions in Cu-MOFs can be reduced to pure Cu states during CO2RR. This reveals the reconstruction of Cu-MOFs under reductive potential. To unveil the reconstruction behaviors of Cu active sites in the MOFs, we investigated the CO2RR of Cu benzene-1,3,5-tricarboxylate (Cu-BTC) and Cu benzene-1,4-dicarboxylate (Cu-BDC) MOFs. Unlike the Cu-BTC which resulted in the formation of C1 chemicals as major products, Cu-BDC produced C2 chemicals such as ethylene (C2H4) in CO2RR. We elucidate how the catalytic active sites of Cu-MOFs undergo the reconstruction and evolve during CO2RR. Also, we explain the how the reconstruction of Cu active sites in MOFs affects the steering of CO2RR pathway. In the concluding remarks, the future perspective in the catalyst reconstruction during CO2RR will be discussed.
Effect of Cathodic Potential in Electrochemical CO2 Reduction
Authors: Wang Lei
Published: December 2024

In this presentation, we will discuss the critical role of cathodic-potential in modulating the selectivity, activity and even stability of electroreduction of CO2 (CO2R). We will first introduce the potential-dependent selectivity in Cu-based CO(2)R, originating from a combination of pH-effect, kinetics of different *CO activation pathways, local field effect, and CO coverage effects, etc. By carefully elucidating the intricate interplays among these effects, we could leverage cathodic potential as an effective lever to steer the CO(2)R selectivity towards multi-carbon-products. Additionally, we will introduce how cathodic-potential plays affects the CO2R stability, particularly in preventing the electrolyte flooding. Specifically, we observed that CO2R kinetic-curves typically enter the mixed-control-region at approximately > 0.75 V, and then quickly transition to the CO2 mass transport-limited-region, regardless of the type of GDE used or the current density achieved. This suggests that GDE flooding is closely associated with the cathodic-potential. Inspired by this understanding, we demonstrate that an intrinsically more active catalyst capable of sustaining a sufficient CO2R current at a low cathodic potential before entering the mixed-controlled region can lead to significantly enhanced CO2R stability and improved energy efficiency.

If time allows, we will also briefly introduce two non-Cu-based systems:

(1) The potential-dependent structural-evolution of Pd-based catalysts during CO2R to formate. We found that by manipulating the valence state of Pd, one could substantially extend the cathodic-potential window for stabilizing the desired a-Pd phase, achieving robust and efficient CO2-to-formate conversion on Pd-catalysts.

(2) The potential-dependent CO2-to-methanol production on Co-Phthalocyanine. Here, the cathodic-potential is critical in inducing the structural-distortion of the Co-N4 plane, influencing the *CO binding mode and strength, which leads to the selectivity change from CO to methanol on Co-Phthalocyanine.

Overall, we wish to underscore the importance of considering cathodic potential as a crucial parameter in the design and optimization of electrochemical CO2R systems.
Activating New Reaction Pathways in Electrochemical CO2 Conversion Using Pulsing
Authors: Mayer Matthew T. , Arndt Alexander , Pardo Perez Laura Carolina , Ma Chaoqun , Bogdanoff Peter
Published: December 2024

Electrochemical CO2 conversion can result in a variety of products, often as a mixture, and controlling the product selectivity remains a key challenge. It has been shown that pulsing the electrochemical potential can lead to altered product distributions, influenced by effects on, e.g., transport, double-layer rearrangement, adsorption/desorption, and changes to electrode structure and composition (1).

Herein we report our observations using metal electrodes normally selective for the 2-electron formation of CO as major product under steady-state (potentiostatic) conditions, finding that they can produce significant amounts of higher-order products (including methane and ethylene) under the application of pulse potential waveforms. We confirm this is not due to metal impurities in the system, but is significantly affected by phenomena such as surface restructuring and accumulation of liquid products. Furthermore, time-resolved differential electrochemical mass spectrometry (DEMS) measurements reveal distinctly different transient behaviors between the different gaseous products, providing key new mechanistic insight for clarifying the roles of pulsing.

(1) Casebolt, R.; Levine, K.; Suntivich, J.; Hanrath, T. Pulse Check: Potential Opportunities in Pulsed Electrochemical CO2 Reduction. Joule
2021, 5 (8), 1987–2026. https://doi.org/10.1016/j.joule.2021.05.014.

Figure: Pulsed CO2 reduction on Ag (manuscript pending) -- a) Pulsing waveform with parameter definitions. b) Gas product evolution rates as measured by GC during continuous electrochemical pulsing of a silver foil electrode. c) DEMS study of porous Ag film electrodes, revealing product formation transient behaviors. d) Selectivity dependence on varying the cathodic step potential (Ec) while Ea is fixed.

Figure 1
Full Cell Modeling of Flooding Effects on Ionomer-Based CO2 Electrolyzers
Authors: Cross Nicholas R. , Ehlinger Victoria Marie , Goldman Maxwell , Prajapati Aditya , Moore Thomas , Clemens Auston L. , Chu An , Gutierrez Laura , Marufu Michell , Krall Eric , Duoss Eric B , Hahn Christopher , Baker Sarah
Published: December 2024

Electrochemical reduction of carbon dioxide (eCO2R) is a promising route to enable a circular economy for production of carbon-based materials using non-fossil-based feed stocks. Copper catalysts have been shown to be proficient at converting CO2 to ethylene as a precursor to polymer-based material synthesis. Production of ethylene at high faradaic efficiency and low voltage is necessary for commercial-scale viability of eCO2R as a technology, but the current state of the art does not meet these key performance indicators. We have synthesized and characterized quaternary ammonia-based polyphenylene oxide (QPPO) ionomers as alternatives to commercially available ionomers, and the QPPO ionomers showed increased faradaic efficiency towards ethylene while also decreasing full cell voltage. In this presentation, we demonstrate how continuum modeling was used to identify that underlying cause for achieving higher ethylene faradaic efficiency and lower cell voltage was the prevention of flooding of the gas diffusion layer in a zero-gap CO2 electrolyzer. We simulated two cell assemblies to elucidate the phenomena governing performance differences: one with a bare copper catalyst between the gas diffusion medium and membrane, and the other with an ionomer layer between the catalyst layer and the membrane. To validate our full cell model against experimental results for each cell assembly, we introduced a flooded region of the cathode diffusion media. By fitting the thickness of the flooded region, we were able to capture all trends for cell voltage and faradaic efficiency toward four products over three applied current densities. Voltage breakdown analysis showed that the ~150 mV lower cell voltage with the addition of the ionomer layer resulted from decreased charge and mass transfer overpotentials at the cathode due to the high aqueous CO2 concentration in the cathode catalyst layer and decrease in CO2 consumption to bicarbonate via the presence of liquid water in the gas diffusion layer. Overall, these results show the importance of incorporating liquid water into accurate modeling of CO2 electrolyzers and water management in experimental work to achieve commercial-scale electrolyzer performance.

Figure 1
Atomically Dispersed Ni-N-C Catalysts for Electrochemical Carbon Dioxide Reduction
Authors: Ko Youngdon , Osmieri Luigi , Zhang Hanguang , Zelenay Piotr
Published: December 2024

Electrochemical carbon dioxide reduction reaction (CO2RR) has the potential to play a key role in addressing major energy and environmental challenges via clean conversion of the atmospheric CO2 from combusting of fossil fuels into value-added products such as fuels and chemicals. The products generated by CO2RR vary depending on the electrocatalyst used at the CO2 electrolyzer cathode,1 which calls for the development of more active, stable, and selective CO2RR electrocatalysts. Atomically dispersed Ni-N-C catalysts have attracted attention due to their superior selectivity for CO generation.2 Their activity and selectivity towards CO2RR are influenced by the metal center and its local coordination environment in Ni-N-C catalysts.3 Ni-N-C catalysts derived from zeolitic imidazolate frameworks (ZIFs) have multiple advantages including a high specific surface area, customizable pore structures, and controllable morphologies, even after the carbonization treatment at high temperatures.

In this presentation, we will focus on ZIF-derived Ni-N-C catalysts using a ligand exchange strategy during ZIF synthesis. These ligand-exchanged ZIFs are synthesized by partially replacing 2-methylimidazole (used in ZIF-8 synthesis) with different imidazole-like ligands for the purpose of obtaining structures with increased porosity. The effects of several parameters, including ligand exchange percentage and pyrolysis temperature for synthesizing Ni-N-C catalysts will be evaluated. We will show how the physicochemical characteristics of the Ni-N-C catalyst, i.e., porosity, hydrophobicity, and density of active sites, can be tuned by varying the synthesis parameters. We will focus in particular on the optimization of porosity and accessibility of CO2 to the catalyst’ active sites to maximize CO2RR rate.

Acknowledgement

Research presented in this work has been supported by the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory under project number 20230065DR.

References

(1) Varela, A. S.; Ju, W.; Bagger, A.; Franco, P.; Rossmeisl, J.; Strasser, P. Electrochemical Reduction of CO2 on Metal-Nitrogen-Doped Carbon Catalysts. ACS Catalysis
2019, 9 (8), 7270-7284.

(2) Ju, W.; Bagger, A.; Hao, G.-P.; Varela, A. S.; Sinev, I.; Bon, V.; Roldan Cuenya, B.; Kaskel, S.; Rossmeisl, J.; Strasser, P. Understanding activity and selectivity of metal-nitrogen-doped carbon catalysts for electrochemical reduction of CO2. Nature Communications
2017, 8 (1), 944.

(3) Liang, S.; Huang, L.; Gao, Y.; Wang, Q.; Liu, B. Electrochemical Reduction of CO2 to CO over Transition Metal/N-Doped Carbon Catalysts: The Active Sites and Reaction Mechanism. Advanced Science
2021, 8 (24), 2102886.
Comprehensive Analytical Method with a Standardized Data Pipeline Enables Parallel Experiments in Electrochemical CO2 Reduction
Authors: Senocrate Alessandro , Kraus Peter , Bernasconi Francesco , Battaglia Corsin
Published: December 2024

The electrochemical reduction of CO2 (eCO2R) is a promising way to convert detrimental CO2 emissions into sustainable fuels and chemicals, and thus to achieve a net zero or net negative carbon economy.
1 Depending on catalyst type and reaction conditions, different gaseous and liquid products can be obtained during eCO2R, with their production rates significantly varying over time. Thus, for any catalytic performance analysis, it is key to assess the product distribution online during eCO2R.
2,3 However, while gaseous products are readily analyzed online by gas chromatography, liquid products are typically only assessed at the end of the reaction due to the lack of suitable automated liquid sampling and analysis methods. In addition, relevant reaction parameters such as CO2 flow rates, electrolyzer temperatures and flow pressures are seldom recorded, causing the loss of important information on catalysts, electrodes, and electrolyzer behavior.

In this work, we overcome these issues by assembling a comprehensive analytical system coupling online gas and liquid product analysis by gas and liquid chromatography (leveraging a special automated liquid sampling valve) with electrochemical protocols that assess CO2RR performance, electrolyzer cell resistance and electrode surface area. In addition, we record CO2 volumetric flow rates, electrolyzer temperatures, as well as gas and liquid flow pressures.
4 To rapidly and reproducibly handle the large and heterogeneous data volume obtained we implement a standardized data pipeline based on our own open-source software,5 which automatically parses the numerous different raw data files, composes a data set following FAIR practices,6 and post-processes and plots the data in a standard way. We validate this analytical system by carrying out eCO2R at 200 mA/cm2 on Cu gas diffusion electrodes, following the changes in selectivity with reaction time for > 12 gaseous and liquid products while recording volumetric flow rates, electrolyzer cell resistance, electrode surface area, electrolyzer temperatures and flow pressures. The modular nature of our analytical system, combined with the standardized data pipeline, allows us to freely increase the number and type of sensors used with minimal impact on the data analysis time, as well as to multiplex our analysis to 8 parallel electrolyzer cells, providing a deep understanding of the function of eCO2R catalysts, electrodes, and electrolyzers, and paving the way to accelerated discoveries.

References

[1] Senocrate, Battaglia, J. Energy Storage
2021, 36, 102373.

[2] Wang, de Araújo, Ju, Bagger, Schmies, Kühl, Rossmeisl, Strasser, Nat.
Nanotechnol.
2019, 14, 1063. [3] Löffler, Khanipour, Kulyk, Mayrhofer, Katsounaros ACS Catal.
202
0, 10, 6735.

[4] Senocrate, Kraus, Bernasconi, Battaglia, Nature Catalysis, accepted.

[5] https://dgbowl.github.io

[5] Kraus, Vetsch, Battaglia, Journal of Open Source Software
2022, 7, 4166.
Energy-Efficient Electrified Reactive Capture to Syngas Via Tuning of Morphology and Energetics of Catalyst Supports
Authors: Liu Hengzhou , Xie Ke , Sargent Edward Hartley
Published: December 2024

Direct-air capture (DAC) of CO2 often uses alkali hydroxides as sorbent, and relies on an energy-intensive thermal CaCO3/Ca(OH)2 step to release CO2 and regenerate the alkali hydroxide. Reactive capture instead converts the captured CO2 to value-add products while regenerating the capture liquid. Here we investigate the limitations of performance in prior electrochemical reactive capture systems, finding that the catalyst becomes starved of CO2 even at moderate current densities, this leading to a rapid decline in faradaic efficiency. We explored catalysts employing both microposity and micromesoporosity, finding that in the case of the best-designed supports, efficient mass transport of the carbonate feedstock is maintained up to 200 mA/cm2 current densities. Because the CO2-to-CO catalyst, metal-phthalocyanine, tends to aggregate under bias, degrading CO2 reduction activity, we then immobilized the CoPc on a polydopamine support, producing an even dispersion of catalyst on the support surface; the polydopamine further produces a desired electron-deficient Co center in the heterogenized CoPc. We report carbonate electrolysis at 200 mA cm–2 at 3.0 V with faradaic efficiency of 43% for CO with < 1% CO2 in the outlet stream. A carbonate-to-syngas system using this reaction-capture approach has a projected energy efficiency of 50% at 200 mA cm–2 when H2 is provided to form 2:1 H2:CO syngas by coupling with a water electrolyzer. Durability studies show 40 h of initial operating stability.
(Keynote) Electrochemical Conversion of Atmospheric CO2 to Value-Added Products
Authors: Ko Youngdon , Diaz-Abad Sergio , Osmieri Luigi , Zhang Hanguang , Zelenay Piotr
Published: December 2024

Climate change is an existential threat to humanity that calls for immediate reduction of CO2 concentration in the atmosphere. While drastic reduction in green-house gas emissions needs to remain the primary objective, possible integration of the direct air capture (DAC) and electrocatalytic conversion of CO2 represents a promising strategy to aid in averting a climate catastrophe. In this presentation, we will summarize the recent progress in electrochemical conversion of CO2 to value-added products at Los Alamos, in which we combine experimental and modeling approaches to tackle challenges in the development of materials for the integration of DAC with electrochemical CO2 reduction reaction (CO2RR), mostly concentrating on the conversion part. We use a “5M” (make, measure, model, machine-learn, and modify) approach to accelerate the understanding of how CO2 sorbents and CO2RR catalysts synthesis impacts their structure and performance.

Enhancing electrocatalytic activity and selectivity for the desired products are the main priorities in the development of electrocatalysts for CO2RR.1 Understanding local environment, e.g., local pH and triple phase boundary at the reaction area is also essential for long-term operation of CO2RR devices.2 We will discuss the development of atomically dispersed Ni-N-C catalysts with high selectivity for CO2 conversion to CO (faradaic efficiency in excess of 90%) and the effect that the ionomer used in the electrode preparation has on the Ni-N-C catalyst performance. In particular, we will shed light on how the ionomer properties such as hydrophobicity, local pH, and backbone structure affect the CO2RR activity and selectivity by modifying the ionomer-catalyst interface. In addition, we will outline our approach to facilitating the highly challenging integration of the DAC and CO2RR components via the use of electronically conductive carbon nanofibers with high CO2 sorption capacity and thermo-oxidative resistance.

Acknowledgement

Research presented in this work has been supported by the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory under project number 20230065DR.

References

(1) Li, Y.; Wang, H.; Yang, X.; O'Carroll, T.; Wu, G. Designing and Engineering Atomically Dispersed Metal Catalysts for CO2 to CO Conversion: From Single to Dual Metal Sites. Angewandte Chemie International Edition
2024, 63 (12), e202317884.

(2) Chen, J.; Wang, L. Effects of the Catalyst Dynamic Changes and Influence of the Reaction Environment on the Performance of Electrochemical CO2 Reduction. Advanced Materials
2022, 34 (25), 2103900.
Electrochemical CO2 Conversion to High-Valued Chemicals through a Protonic Ceramic Electrochemical Cell (PCEC)
Authors: Li Haixia , Bian Wenjuan , Wang Lucun , Wu Wei , Ding Dong
Published: December 2024

The catalytic conversion of CO2 into higher-value industrial chemicals represents a key strategy for mitigating greenhouse gas emissions. However, conventional CO2 conversion processes are severely limited by catalytic activity and thermodynamic equilibrium at low temperatures, leading to low energy efficiency and restricted applicability. Electrochemical CO2 conversion emerges as a promising avenue for both reducing carbon emissions and generating valuable chemicals simultaneously. Proton ceramic electrochemical cells (PCECs) provide a unique platform for CO2 electroreduction and hydrogenation. In this study, we propose an integrated heterogeneous structure comprising a dual-functional electro-catalyst and a PCEC electrochemical reactor. This approach aims to significantly enhance surface CO2 conversion kinetics and product selectivity. Our methodology involves optimizing the process by adjusting cell configuration, electrode (CO2 catalyst) compositions, and operational conditions to effectively convert CO2 under varying electron-driven conditions. We delve into the mechanistic insights of CO2 electroreduction pathways within dual-functional catalyst in PCECs to guide further enhancements in CO2 conversion efficiency and product selectivity. This research paves the way for a greener and economically viable approach to chemical synthesis.
Crossover Management for Practical High Efficiency Carbon Dioxide Reduction
Authors: Xi Dawei , Wang Taobo , Yan Zhifei , Zhang Zhen , Xu Hongbin , Li Ju , Nocera Daniel G , Aziz Michael J.
Published: December 2024

CO2 reduction is an important step in carbon capture, utilization, and storage (CCUS). The utilization of a membrane electrode assembly (MEA) with a gas diffusion electrode (GDE) realizes high current density CO2 reduction. However, most of the developed CO2 reduction catalysts suffer from low Faradaic efficiency when using a proton exchange membrane MEA, due to low local pH surrounding catalysts. Alternatively, with an anion exchange membrane MEA, CO2 reduction suffers from low conversion efficiency due to carbonate-bicarbonate crossover through the membrane to the anode. For continuously-running CO2 electrolyzers, the crossover of acids and cations results in low reduction efficiency and flooding of the GDE. We have designed and characterized an asymmetric membrane that prohibits carbonate-bicarbonate crossover, yet can maintain a high local pH surrounding the catalyst. The resulting MEA can achieve high Faradaic efficiency toward CO2 reduction using developed catalysts with near-zero CO2 crossover. When using oxygen evolution in the anode, we further developed an ion-blockage strategy to diminish the crossover of acids or cations during long-term operation, maintaining a relatively stable and suitable environment for CO2 reduction on GDE. The crossover management of carbonate, bicarbonate, protons and cations can lead to a long lifetime high-efficiency CO2 electrolyzer.
Identifying an Optimal Post-Capture pH for Hydroxide-Based Reactive Capture in Industrial Applications
Authors: Sun Siyu , Miao Rui Kai , Xiao Yurou Celine , Sinton David
Published: December 2024

Reactive capture - the integration of carbon dioxide (CO2) capture and upgrade - bypasses the energy-intensive CO2 regeneration step and thereby offers potential to reduce both capital and energy costs. Alkali hydroxide solutions are a common type of capture solution for reactive capture, wherein CO2 is chemically absorbed in the form of carbonate and/or bicarbonate. The composition and pH of the post-capture solution depend on the CO2 concentration of the CO2 source used and the capture duration. Lower pH levels yield higher bicarbonate concentrations, facilitating greater CO2 release during the reactive capture step and resulting in enhanced electrolysis performance. For example, direct electrochemical reduction of a pure carbonate solution (pH~12.2) has a theoretical carbon monoxide (CO) Faradaic efficiency (FE) cap at 50%, but no cap exists for a pure bicarbonate solution (pH~8.2), leading to better electrolysis performance and lower operating expenditures (OPEX) for the capture and conversion cycle. However, achieving a low pH post-capture solution with higher bicarbonate content slows the capture rate, necessitating either a bigger contactor or longer capture time, thereby increasing capital expenditures (CAPEX) for the capture step. Using a silver catalyst, we report here the electrolysis energy efficiency (EE) of CO2 to CO using a 2M potassium hydroxide solution with a post-capture pH ranging from 13.5 (hydroxide and carbonate mix) to 8.2 (pure bicarbonate). We conducted a technical-economic analysis (TEA) to assess the CAPEX and OPEX of an industrial-scale reactive capture plant that captures both point source (10%) and atmospheric (420 ppm) CO2 using 2M potassium hydroxide with different post-capture pH values. The TEA includes a sensitivity analysis to account for improvements in electrolysis performance and reduced costs due to technological advancement and economies of scale in the future. Our results demonstrate that there is an optimal post-capture pH for potassium hydroxide-based reactive capture that balances the capture cost and electrolysis performance. This study serves as a guideline for choosing an industrial relevant pH to work with for future hydroxide-based reactive capture research.
Energy-Efficient Electrified Ethylene Production from Carbonate Capture Liquid in Reactive Capture System
Authors: Chen Yuanjun , Xie Ke , Sargent Edward Hartley , Gereige Issam , Alahmed Ammar , Jamal Aqil
Published: December 2024

Direct air capture (DAC) of CO2 is typically implemented by utilizing alkali hydroxides as capture solutions to form carbonate. However, the release of CO2 and the regeneration of alkali hydroxide require an energy-intensity thermal cycle up to 900 °C. Moreover, the subsequent valorization of gaseous CO2 into products lead to additional energy demands and system complexities. Here, we present a reactive capture system – the integration of CO2 capture with electrochemical upgrade of CO2 into ethylene. We began by seeking to understand the origins of limitations of ethylene production in prior electrochemical reactive capture systems using in-situ Raman spectroscopy. We found that the CO2-starved local reaction environment on catalyst surface leads to dominant hydrogen evolution reaction, outcompeting CO2 electroreduction and suppressing C-C coupling. We therefore developed catalyst strategies to facilitate CO2 activation and promote the cooperative adsorption of key C1 intermediates for enhanced spatial availability of C1-C1 coupling. This was achieved by porous dilute alloy catalyst design and tandem catalysis system optimization. We report a 46% ethylene Faradaic efficiency (FE) with nearly 100% CO2 utilization at 200 mA cm–2 in electrochemical reactive capture system, resulting in a 65 wt% ethylene concentration in the product stream. We achieve a carbonate-to-ethylene system with an overall ethylene energy efficiency of 17% at 200 mA/cm2, which is 1.7-fold higher than the most efficient prior reports in reactive capture systems.
A Strategical Break-in of Accessible and High Surface Area Copper Cathode By Magnesium Oxide/ Hydroxide Incorporation Applied in Zero-Gap CO2RR
Authors: Tsai Ding Huei , Tu Wei-Ting , Wei-Chieh Liao , Chueh Lu Yu , Pan Yung-Tin
Published: December 2024

CO2 emissions have become a series problem since the industrial revolution, the detrimental effect of CO2 emissions raise people’s awareness in recent years. Scientists are eagerly searching the sustainable energy as the replacement of the petrochemical industry. The carbon dioxide reduction reaction (CO2RR) can reduce the CO2 amount in the atmosphere as well as generating the valuable carbon-based chemicals spontaneously, which is a strong potential way for the next generation green energy. In our work, we suggested a strategical design of the copper cathode in the zero-gap membrane electrolyte assembly (MEA) electrolyzer of CO2RR, the electrolyte-free cathodic environment caused the consequence of inefficient and ineffective activation. The magnesium oxide (MgO) and magnesium hydroxide (Mg(OH)2) incorporated with the copper oxide (CuO) as the initial catalyst (CuO-MgO/Mg(OH)2), with the manipulation of three gradually increasing potential range of cyclic voltammetry (CV) as the break-in process, the MgO/(OH)2 totally dissolved when contacting the located CO2 (g) and H2O (l) crossed from the anode which brought by the cation through the electric field attraction. The absent of the dissolved MgO/Mg(OH)2 would provide the sufficient triple-phase boundary, with the accessible reactant CO2 (g) and H2O (l) and proper local environment, the high surface area copper (HSA-Cu) eventually creating a proper condition for CO2RR. The high electrochemical surface area (ECSA) 276 μC/cm2 and 11.3 mF/cm2 had been proved in the monolayer copper oxidation redox detection and capacitance double layer (Cdl) measurement, respectively. The HSA-Cu had outstanding performance of the partial current density j
C2H4= 44.7 mA/cm2 at 3.0 V and Faradaic efficiency FEC2H4= 27.3 % at 2.8 V for C2H4 product. A 4-fold j
C2H4 and 2.5-fold FEC2H4 improvement compared with nano Cu, in equal voltage applied.
Bulk and Surface Effect of Metal Phosphides Catalysts on Hydrogen Evolution Reaction
Authors: Kong Seongyoung , Singh Prashant , Raturi Dhruv , Johnson Duane D , Kovnir Kirill
Published: December 2024

Transition metal phosphides (MPs) are emerging earth-abundant catalysts for hydrogen evolution reaction (HER) due to their promising activity and stability. Even though further development is needed to meet real-world application needs, fundamental understanding of how MP catalysts can be improved is low. In this work, we present several different approaches to uncover the relationships of bulk (electronic structure) and surface (active sites) of the catalysts with HER activity and stability. We studied well-ordered crystalline materials as model systems to elucidate the aforementioned relationships. Anionic Si/P substitution in NiSi1-xPx compounds showed that the density of the states (DOS) at EF could be one of the key determinants on HER activity. The impact of DOS was further investigated by studying two polymorphs of Fe2P where upward shift of the d-band position was shown to enhance HER activity. Several surface termination effects were demonstrated on the mm-sized single crystals of Ni2P, Co2P, and Fe2P upon facet-dependent HER activity studies. Lastly, operando X-ray absorption spectroscopy of Ni and P K-edges of Ni-P catalysts clearly demonstrated that during the HER process, reduction occurred on the catalyst surface, but reduced state was only stable under applied reductive bias and quickly oxidized after turning off the potential, and this oxidized species did not appear to return to its original state.
Atomically Dispersed Platinum Catalysts for Efficient Hydrogen Production
Authors: Park Juneseo , Yu Sungju
Published: December 2024

As the world shifts from fossil fuel-based energy industries to renewable energy industries in response to climate change caused by greenhouse gases, producing green hydrogen from water offers a solution that not only avoids greenhouse gas emissions but also serves as a clean energy carrier central to the hydrogen industry chain. However, Current hydrogen production methods are limited by low efficiency and cost-effectiveness, requiring further technological advancements. This study focuses on developing atomically dispersed platinum catalysts that enhance catalytic activity while minimizing the use of platinum in hydrogen production reactions. Compared to conventional platinum nanoparticle catalysts, the hydrogen production efficiency per unit mass of platinum increased by over 30 times, and the catalyst's long-term durability was also confirmed. Additionally, the characteristics of the highly dispersed platinum catalyst were analyzed to identify the active sites.
Non-Sacrificial Photocatalytic Water Splitting for Sustainable Hydrogen Production
Authors: Ryu Jaemin , Lee Sanghyuk , Park Juneseo , An Yeongju , Yu Sungju
Published: December 2024

Hydrogen is a promising renewable energy carrier with potential to address global energy challenges. Photocatalytic water splitting, a process that utilizes sunlight to convert water into hydrogen and oxygen, represents a carbon-neutral pathway for hydrogen production. However, the reliance of sacrificial reagents that are irreversibly consumed during the process has limited the overall efficiency and sustainability of these systems. In this study, we introduce a non-sacrificial additive that enhances hydrogen production efficiency in photocatalytic water splitting systems. This additive facilitates water decomposition while simultaneously consuming photogenerated holes, thus improving both oxidation and reduction half-reactions. Additionally, we demonstrated the stability and durability of the system under prolonged exposure to high-power illumination. Our findings show the potential of this non-sacrificial photocatalytic approach for large-scale hydrogen production.
Increasing the In Vivo Stability of Electrochemical-Aptamer Based Sensors
Authors: Leung Kaylyn , Gerson Julian , Downs Alex , Emmons Nicole , Heemstra Jen , Kippin Tod , Plaxco Kevin
Published: December 2024

The ability to measure drug, metabolite and biomarker levels in the living body, in real time, and at high frequency would revolutionize our ability to understand and diagnose disease and personalize and guide its treatment. To this end, the Plaxco group has been developing electrochemical aptamer-based (EAB) sensors, a platform technology able to measure molecules in the living body independently of the chemical or enzymatic reactivity of its targets. This has enabled the development of sensors capable of measuring both drugs (e.g., antibiotics, chemotherapeutics, psychoactive substances) and biomarkers (e.g., creatinine, urea, phenylalanine) in live rats.

Though these high time resolution measurements show promise for continuous monitoring, multiple obstacles remain. One example is the challenging environments found in the living body where EAB sensors are deployed can detrimentally affect the longevity of these sensors. As such, I will describe the mechanisms that affect the in vivo lifetime of EAB sensors and methods by which this can be greatly improved.
3-D Mapping Approach for High-Efficiency and High-Precision Latent Flaw Detection
Authors: Yamaura Daichi , Sakata Yoshitaro , Terasaki Nao
Published: December 2024

In semiconductor manufacturing, fine-polishing process plays important role in achieving high-performance products. In recent years, driven by the escalating demand for process precision, the formation of latent flaws formation, which are defects that cannot be detected by general inspection, during fine-polishing process has emerged as a critical concern. Latent flaws cannot be observed with optical or electron microscopes and require destructive inspection such as etching for reliable detection. Previously, we have reported successful detection of latent flaws by applying stress [1] or heat [2,3] to the substrate.

In this presentation, we present the development of a three-dimensional(3D) mapping approach for detecting latent flaws in glass substrates. Initially, defects were induced in a glass substrate through laser processing (532 nm). Subsequently, by observing the light scattering of the defects while adjusting the focus of the microscope, we analyzed not only the two-dimensional (2D) distribution of latent flaws but also their 3D distribution (Figure), with the addition of depth information. Understanding the depth of latent flaws is crucial, as it provides essential information for calculating the margin for shaving required for repolishing, which is necessary for removing the latent flaws and other defects. Furthermore, the 3D mapping information is anticipated to be valuable not only for optimizing polishing parameters but also for investigating any issues that may arise during the process.

The data obtained from the described methods can be incorporated into a machine learning model to predict the depth of latent flaws from the image data. Our approach enables not only highly sensitive but also highly efficient inspection and is expected to make a significant contribution to the semiconductor manufacturing industry.

[1] Yoshitaro Sakata et al. “Stress-induced light scattering method for the detection of latent flaws on fine polished glass substrates” REVIEW OF SCIENTIFIC INSTRUMENTS 85, 083303 (2014)

[2] Yoshitaro Sakata et al. “Microscopic study of stress effects around micro-crack tips using a non-contact stress-induced light scattering method” AIP ADVANCES 6, 095315 (2016)

[3] Yoshitaro Sakata et al. ” Development of a novel non-contact inspection technique to detect microcracks under the surface of a glass substrate by thermal stress-induced light scattering method” Optics & Laser Technology 90 80–83 (2017)

Figure 1