Electrochemical CO2 reduction can be used to produce a range of carbon-based small molecules, providing potential sustainable alternatives to our current use of fossil-derived feedstock chemicals. One key challenge is the difficulty to control the product selectivity of the reaction. The catalyst material plays a central role in influencing selectivity, where past experimental and computational studies revealed that different metals are characterized by favoring different major products. The two most intensively studied metals are silver and copper, with silver considered the most promising for selective production of CO, and copper known to be the only metal capable of forming significant amounts of products “beyond CO”, including hydrocarbons, alcohols, and multi-carbon species.

Our studies indicate that these generalizations do not always hold true, and that the selectivity of both Ag and Cu can be greatly altered by changes to the electrolyte and the cathode microenvironment. I will present examples of how variations in electrolyte concentration, cation type, and cell configuration can lead to formation of unconventional products (e.g. CH4 on Ag, CO on Cu). Furthermore, I will provide insight on how these effects can be dynamic in nature, revealed by using in-situ analytical techniques.

Developing efficient and selective electrocatalysts for the CO₂ reduction reaction (CO₂RR) remains a key challenge for sustainable carbon utilization. In this work, we report the synthesis of Ni-doped nitrogen-rich porous carbon materials and investigate the impact of synthesis conditions on their structural properties and electrocatalytic performance towards CO₂RR. By tuning parameters, we achieved materials with tailored porosity, nitrogen content, and well-dispersed Ni active sites.

Electrochemical evaluation was carried out in both acidic and alkaline electrolytes. The optimized Ni–N–C catalyst showed high selectivity towards CO production, with Faradaic efficiencies exceeding 95% over a wide potential range in alkaline media, and even under acidic conditions Fig.1. The combination of nitrogen coordination and Ni was found to play a crucial role in suppressing the competing hydrogen evolution reaction (HER), especially under acidic conditions where HER usually dominates [1,2].

These findings highlight the importance of precise control over synthesis parameters in designing Ni–N–C catalysts with dual electrolyte applicability for selective CO₂ electroreduction. This work provides new insights into the design of pH-universal catalysts for practical CO₂ conversion technologies.

The Haber–Bosch process has enabled large-scale ammonia synthesis for over a century, sustaining global agriculture but at a significant environmental cost, contributing nearly 2% of global CO₂ emissions [1]. As the need for sustainable alternatives grows, the electrochemical nitrate reduction reaction (E-NO₃-RR) in aqueous media is gaining traction. This process offers a dual benefit: mitigating nitrate pollution in wastewater [2] while producing ammonia under milder, potentially renewable-powered conditions.
In this work, we investigate the influence of nickel oxide morphology on its electrocatalytic performance towards E-NO₃-RR. For that purpose, three distinct preparation routes (precipitation, hydrothermal synthesis, and the reverse micelle method) were employed to generate NiO samples with varying morphologies. These materials were extensively characterized (e.g., via X-ray diffraction) and their electrochemical activity was tested employing an H-type cell with a three-electrode configuration.
NiO was selected as a baseline catalyst due to its reported role in facilitating NH₃ desorption and reducing intermediate poisoning when combined with other metals [3,4]. Our study aims to determine whether morphological differences can influence performance in terms of Faradaic efficiency and ammonia yield (μg*h^-1*mg^-1), laying the groundwork for future development of optimized or doped NiO-based systems.

Ammonia (NH₃) is indispensable for global food production and is increasingly considered a promising energy carrier due to its high volumetric energy density (4.32 kWh L⁻¹) and favorable storage properties. However, its conventional synthesis via the Haber-Bosch process (HBP) is energy-intensive, reliant on fossil fuels, and responsible for nearly 2% of global CO₂ emissions. This calls for the development of sustainable, decentralized alternatives.

Electrochemical nitrogen (E-NRR) and nitrate (E-NO₃RR) reduction reactions have emerged as promising routes for green ammonia production, leveraging renewable electricity and mild operating conditions. Notably, E-NO₃RR offers the additional benefit of converting nitrate (a common pollutant in agricultural and industrial effluents into NH₃, with increasing interest in real water applications. Despite their potential, both processes are currently limited by low selectivity, high overpotentials, and limited scalability, which are intrinsically linked to catalyst performance, electrolyte properties, and reactor design.

In this contribution, I will present the most recent advances achieved by our research group in the electrochemical conversion of nitrogenous species to ammonia. For E-NO₃RR , we have developed catalytic systems and operating strategies that improve selectivity and efficiency, including studies with real wastewater matrices. Regarding E-NRR, our work includes the investigation of lithium-mediated nitrogen reduction, where ammonia is synthesized under ambient conditions via a chemically assisted electrochemical pathway. Across both approaches, particular emphasis will be placed on the role of electrolyte engineering, material stability, and performance benchmarking, aiming to bring these technologies closer to practical implementation.

The transition to sustainable energy systems requires the development of efficient and robust catalysts capable of converting renewable electricity into chemical energy. Among these, bimetallic catalysts have garnered significant attention for their ability to enhance catalytic performance through synergies between metal constituents.^1,2 However, the complex nature of these catalysts—characterized by site-occupancy disorder—poses challenges for accurately modeling adsorption behaviors and identifying active sites. Traditional computational approaches, which typically rely on a single configuration per alloy composition, overlook the inherent structural diversity of real bimetallic catalysts under reaction conditions.

In this communication, we present a framework for addressing the statistical nature of adsorption on binary alloy surfaces, with a focus on Cu-based bimetallic alloys for C2+ product formation from CO₂ electrolysis. By introducing the concept of the "effective cutoff radius", we establish a method to efficiently sample the configurational ensemble that accurately captures the diversity of binding energies present in a Cu-based bimetallic system. This approach overcomes the limitations of traditional models that assume a uniform surface and provides a more accurate and cost-effective means of mapping adsorption chemical space on alloys. Our findings not only allow the rationalization of chemical trends in the field of CO₂ electroreduction but are envisioned to accelerate the rational design of bimetallic catalysts, offering a robust foundation for efficient computational screenings of complex materials in the future and their optimization in CO₂ electrolysis and related energy conversion applications.

The electrochemical reduction of small molecules such as O₂ and CO₂ is central to advancing sustainable energy conversion and environmental technologies. Electrochemical approaches offer a cleaner, more controllable alternative to traditional thermochemical methods. Among the various catalytic platforms, single-atom catalysts (SACs) have emerged as a powerful class of materials, offering high catalytic efficiency, tunable active sites, and efficient electron transfer. When anchored onto conductive carbon supports, SACs benefit from strong metal-support interactions and efficient charge transport, making them highly attractive for electrochemical applications. Understanding the catalytic behavior of SACs at the atomic and electronic scale is critical for designing more efficient systems. Ab initio modeling is an important tool for understanding the mechanistic pathways of SACs and linking their atomic structure to catalytic performance under electrochemical conditions. In this work, we investigate two SAC systems for the electrochemical reduction of O₂ and CO₂. The first involves Co²⁺ atoms anchored via oxygen-containing groups on reduced graphene oxide (rGO), with surrounding water molecules explicitly considered. Combined experimental and theoretical studies support a four-electron oxygen reduction pathway, confirming the high efficiency of these atomically dispersed active sites. In the second system, Ni atoms are coordinated within defective graphene structures for CO₂ reduction. Modeling is used to explore how atomic coordination and interactions with the ions in the electrolyte influence catalytic behavior.

Recent studies have observed that the bulky hydrophobic cations are able to promote the rate of the hydrogen evolution reaction, such as the tetrabutylammonium (TBA+). The addition of bulky hydrophobic cations provides a new perspective for optimizing electrochemical reaction which requires a molecular-level understanding on the underlying changes in the interfacial environment. We have developed a THz ATR spectroelectrochemical cell  to probe molecular-level details at the gold/water interface. This innovative setup reveals the potential-dependent formation of TBA-rich film at the Au/aqueous interface. The accompanying molecular dynamics simulations quantify how the balance between electrostatic and hydrophobic solvation driving forces contributes to this observed trend. Complementary molecular simulations demonstrate that above 0.6V versus Ag/AgCl, partial TBA+ desorption induced a coadsorption of TBA+/Cl- and interfacial rehydration. Our combined experimental-theoretical approach unravel the bulky hydrophobic TBA+ cations restructure the hydrogen bond network at the metal/water interface. This allows rationalizing at the molecular level the ions-induced structural changes at the interface that tune the catalytic performances.

Scalable electrocatalytic conversion of CO₂ to formate hinges on developing gas diffusion electrodes (GDEs) with high activity, selectivity, and durability. In the first study, we investigated how pulsed electrodeposition parameters modulate catalyst layer microstructure and impact CO₂ reduction performance. Lowering the duty cycle increased catalyst dispersity within the GDE’s three-dimensional matrix, improving catalyst utilization and generating smaller, denser nucleation sites. When paired with a CO₂-philic Sustainion XC-02 ionomer, these pulsed-deposited Bi-GDEs reached industrially relevant current densities (≈ 210 mA/cm²) with 94% faradaic efficiency at -1.0 V vs. RHE, superior to commercial GDEs in similar conditions. The second study tackled the stability challenge by alloying and mixing Sb into the GDE catalytic layer. Bi-based GDEs can suffer from rapid degradation in the first thirty minutes, leading to short electrode lifetimes. Our investigations revealed that adding Sb facilitates the re-deposition of the electrocatalyst during CO₂ reduction, and while the catalyst morphology in the catalytic layer changes during CO₂ reduction, the electrode activity remains nearly unchanged. In other words, the added Sb acts as a structural component in a self-repairing process, leading to elevated electrode resilience. These findings are part of an ongoing paradigm shift in energy materials design from ‘ultra stable’ materials to ‘dynamically resilient’ components and serve as an example for extending the self-repairing perspective from the electrocatalyst to a catalytic layer volume.

The electrochemical reduction of carbon dioxide (CO₂) to value-added hydrocarbons presents a promising solution to simultaneously mitigate climate change and enable renewable energy storage. Among the various target products, methane (CH₄) is particularly attractive due to its compatibility with the existing natural gas infrastructure, including storage, distribution, and consumption. Within this context, the direct electrochemical conversion of CO₂ present in biogas into CH₄ using electricity derived from intermittent renewable sources (such as solar or wind) represents a sustainable route for biogas upgrading and the production of carbon-neutral fuels, with the added advantage of eliminating the need for energy- and cost-intensive CO₂ separation processes.

This study investigates the preliminary optimization of a membrane electrode assembly-based electrolyzer for CO₂-to-CH₄ conversion, with the goal of advancing toward scalable, industrial applications for biogas upgrading. The design and configuration of the electrolyzer were systematically optimized to enhance catalytic activity, CH₄ selectivity, and long-term operational stability. Tests were conducted under conditions relevant to industrial practice, including the use of simulated biogas with varying CO₂ content. Significant advancements were achieved through the integration of nanostructured catalysts and refined process parameters, resulting in improved methane selectivity during continuous operation, thereby demonstrating the feasibility of electrochemical upgrading as a viable route for renewable fuel production, as also witnessed by a simple techno-economic analysis conducted on the system.

Carbon capture, utilization, and storage (CCUS) strategies are increasingly recognized as effective means to achieve carbon neutrality, while simultaneously enabling the conversion of CO₂ into value-added products. Among these approaches, electrochemical CO₂ reduction (CO₂RR) stands out due to its operation under mild temperature and pressure conditions and its potential to store intermittent renewable energy—such as solar or wind—in the form of chemical products like formic acid and formate [1].

The Development of Chemical Processes and Pollution Control (DePRO) research group at the University of Cantabria (Spain) has been actively involved in advancing continuous CO₂ electroreduction to formate. Over the past years, the group has systematically investigated a wide range of cathodic and anodic electrocatalysts, as well as various electrode configurations, to optimize the performance and stability of the system [2–5].

This communication presents recent advances and persistent challenges in the development of efficient continuous-flow CO₂ electroreduction systems, with a particular focus on the influence of the cathodic electrocatalytic area, an aspect that has been scarcely explored to date. All experiments were conducted under a standardized setup and operating conditions, while varying key parameters such as cathodic electrocatalysts—including Sn- [2], Bi- [3], and Sb-based materials [4]—and electrode architectures, such as planar electrodes, particulate electrodes (PE), gas diffusion electrodes (GDEs), catalyst-coated membrane electrodes (CCMEs), and membrane electrode assemblies (MEAs), operating in the gaseous-phase [6], using a geometric area of 10 cm². On the anodic side, different materials have been explored, including DSA/O₂ and Ni-based electrodes [5], with electrolysis typically coupled to the oxygen evolution reaction (OER). Both cation exchange membranes (CEM, e.g., Nafion) and anion exchange membranes (AEM, e.g., Sustainion) were tested, allowing for comparative performance analysis and identification of optimal cell configurations.

The promising results obtained by the research group have enabled the scale-up of the CO₂ electroreduction technology from a lab-scale reactor (10 cm²) to semi-industrial pilot plant configurations (100 and 1000 cm²) within the framework of various projects aimed at constructing and testing a CO₂ electrolyzer under real industrial conditions, including textile and cement plants.

During the initial scale-up to a geometric area of 100 cm², optimal performance was achieved at a current density of 200 mA·cm⁻² and a water feed rate of 15 g·h⁻¹, resulting in a formate concentration of 760 g·L⁻¹, a Faradaic efficiency of 67%, a production rate of 7 mmol·m⁻²·s⁻¹, and an energy consumption of 507 kWh·kmol⁻¹. When compared with the 10 cm² lab-scale reactor, the scaled-up system demonstrated enhanced CO₂ conversion and higher product formation rates, thereby validating the advantages of optimized flow field design and the overall scale-up strategy. Although a moderate decrease in energy efficiency was observed—mainly due to increased ohmic losses—these findings support the technical viability of gas-phase CO₂ electrolysis for formate production at larger scales.

Further improvements in cell design, materials selection, and energy management are necessary to move closer to industrial implementation. Nonetheless, these developments represent a significant step forward in the advancement and potential application of CO₂ electroreduction technologies.

The electrochemical reduction of carbon dioxide (CO₂) has emerged as a promising approach for cutting CO₂ emissions, tackling climate change, and enabling the transition toward a renewable energy-driven chemical industry. To mitigate the inefficiencies of current separation and purification processes and facilitate industrial application, direct utilization of CO₂ from point sources, such as industrial facilities or power plants, is gaining much interest.[1,2] However, such untreated exhaust gases do not possess optimal compositions[3] and are characterized by a low concentration of CO₂ (with N₂ dilutant) and several impurities (e.g., O₂, NO_x, and SO_x). Both dilution and impurities can affect performance; thus, understanding their impact is becoming critical and attracting extensive research efforts. Here, we explored the influence of CO₂ availability on a Cu₂O/SnO₂-based catalyst, tested in the presence of a potassium bicarbonate electrolyte within a 10 cm² continuous flow cell. A concentration-dependent restructuring of the pristine core-shell nano-cubes was revealed, likely responsible for the shift in selectivity from formate to CO at mild current density values, moving from 25% to 100% CO₂ in the feed. However, as the current density was increased to a value of 100 mA cm^-2, local pH effects began to dominate the CO₂ reduction reaction, specifically controlling the selective production of formate or CO. We demonstrated a stable syngas production at 100 mA cm^-2 over 8 hours of operations, with a CO to H₂ ratio higher than 1.5 at a measured cathodic potential of approximately -2 V vs Ag/AgCl. Significant effects began to manifest in the presence of 1% O₂ in the feed at low current densities. Building upon recent studies,[4] we aimed to address oxygen reduction at the cathode by playing on mass transport. The knowledge about the long-term effect of oxygen impurity on Cu₂O/SnO₂-based catalysts will guide the future design of impurity-tolerant GDEs and facilitate its practical application for electrochemical CO₂ conversion technology.

The (photo)electrochemical conversion of CO₂ into value-added chemicals and fuels is a promising strategy to provide additional energy sources to address humanity’s increasing energy needs. Among the various approaches, photoelectrochemical (PEC) CO₂ reduction is particularly attractive due to its potential for direct solar-to-chemical energy conversion. However, realizing such devices requires selective and stable multi-carbon (C₂⁺) product formation, which remains a key challenge in the field. In our recent work, we have focused on improving both the selectivity and stability of PEC systems by using novel photocathode materials and tailored interfaces.

Here, we show the power of operando spectroscopic ellipsometry (SE) to continuously track the degradation of TiO₂ protective coatings during PEC operation across a range of pH and illumination conditions.¹ In addition, we propose a novel time-resolved Kelvin probe force microscopy (KPFM) approach to enable spatially resolved mapping of surface photovoltage, which reveals the link between local microstructure and charge transport behavior.²

On the material side, we will demonstrate that ZnTe-based photocathodes, modified through a controlled electrodeposition-annealing route to generate Zn-rich surfaces, show unusual light-driven carbon product selectivity.³ Additionally, we introduce copper-tantalate (Cu₂Ta₄O₁₁, CTO) thin films, synthesized via a sodium flux-mediated technique, as a novel photocathode material. The resulting Na-doped CTO thin films, particularly after selective surface etching to remove CuO, exhibit improved ethylene selectivity and reduced photocorrosion.⁴

[1] M. Schieda, F. M. Toma et al, in preparation

[2] M. Pourmahdavi, M. Schieda, R. Raudsepp, S. Fengler, J. Kollmann, Y. Pieper, T. Dittrich, T. Klassen, and Francesca M. Toma, Correlating Local Morphology and Charge Dynamics via Kelvin Probe Force Microscopy to Explain Photoelectrode Performance, PRX Energy 2025, 4, 023010

[3] G. Zeng, G. Liu, G. Panzeri, C. Kim, C. Song, O. J. Alley, A. T. Bell, A. Z. Weber, and Francesca M. Toma, Surface Composition Impacts Selectivity of ZnTe Photocathodes in Photoelectrochemical CO2 Reduction Reaction, ACS Energy Lett. 2025, 10 (1), 34-39.

[4] A. Köche, K. Hong, S. Seo, F. Babbe, H. Gim, K.-H. Kim, H. Choi, Y. Jung, I. Oh, G. V. Krishnamurthy, M. Störmer, S. Lee, T.-H. Kim, A. T. Bell, S. Khan, C. M. Sutter-Fella, F. M. Toma, Copper Tantalate by a Sodium-Driven Flux-Mediated Synthesis for Photoelectrochemical CO₂ Reduction. Small Methods 2025, 2401432.

Innovative solutions for carbon capture and utilization are required to achieve carbon neutrality. The electrochemical reduction of CO₂ (CO2RR) offers a promising approach for converting CO₂ into valuable chemicals and fuels. However, improving the performance of this process requires the design of active, selective, and stable electrocatalysts. Atomic layer deposition (ALD) is an advanced technique that enables the precise and conformal deposition of electrocatalysts on complex substrates, such as gas diffusion layers (GDLs).

In this study, ZnO gas diffusion electrodes (GDEs) were fabricated via ALD onto carbon-based GDLs. The growth parameters were systematically optimized at a fixed deposition temperature of 160 °C by varying the pulse times of the diethyl zinc and water precursors, as well as the N₂ purge duration. Spectroscopic ellipsometry performed on Si(100) substrates revealed a linear growth rate of 0.18 Å per ALD cycle, confirming the accurate thickness control.

Scanning electron microscopy showed that the electrodes had rough, crystalline surfaces with multi-faceted, flower-like structures aggregated around the carbon black particles of the GDL. These features became more pronounced for the thicker films. X-ray diffraction confirmed the presence of hexagonal wurtzite ZnO structure on the electrode surface. Electrochemical tests in a 1 cm² flow cell reactor with 1 M KOH electrolyte demonstrated that the ZnO100 (100 ALD cycles) GDE achieved excellent selectivity to carbon monoxide, with a faradaic efficiency of ~90% at -100 mA cm^-2. To assess scalability and long-term performance, the thicker ZnO200 GDE was tested in a 5 cm² membrane electrode assembly with 0.1 M KHCO₃, where it maintained ~90% CO selectivity over 28 hours of continuous operation.

Building on these results, ongoing work aims to develop Cu-based GDEs using ALD with Copper(II) hexafluoroacetylacetonate [Cu(hfac)₂] as a precursor, with the goal of forming multi-carbon products. A supercycle ALD approach is also being explored to fabricate bimetallic  Zinc-Copper catalysts with tailored compositions to improve CO2RR selectivity.

This PhD research is part of the European Union Horizon 2021 MSCA-DN ECOMATES project, which supports the development of selective bimetallic materials and innovative processes for the  efficient electrochemical conversion of CO₂.

Electrochemical CO₂ reduction reaction (CO₂RR) presents a promising strategy to mitigate CO₂ emissions, enable carbon recycling, and synthesize high-value multi-carbon products for long-term renewable energy storage. Among various electrocatalysts, copper-based materials are extensively studied due to their unique capability to promote carbon–carbon (C–C) bond formation, which is essential for generating C₂₊ compounds. Tandem catalysis, which combines different active sites to facilitate sequential reaction steps, offers an efficient route to reduce energy barriers and simplify reaction pathways. In this study, CuAg tandem catalyst was reported to enhance electrocatalytic CO₂RR. The CuAg catalyst with 10 atomic percent silver (denoted as CuAg₁) demonstrated a high Faradaic efficiency of 50% for C₂₊ products at approximately 3V cell voltage in MEA system. Furthermore, when evaluated in a flow cell, CuAg₁ achieved an even higher Faradaic efficiency of 55% for C₂₊ products at a current density of –100 mA/cm². These results underscore the potential of CuAg as a robust and versatile catalyst suitable for a wide range of pH conditions.

The electroreduction of CO₂ (ERCO₂) into value-added products has recently gained recognition as one of the most promising strategies for CO₂ utilization from both economic and environmental perspectives. Research efforts have focused on developing catalysts, optimizing reactor designs, and refining operating conditions to improve the overall efficiency of the process. A novel and potentially transformative approach has emerged: the integration of external magnetic fields into electrochemical systems to enhance ERCO₂ performance. This strategy may significantly improve the scalability and industrial viability of the technology [1].

In this study, an initial experimental evaluation was conducted, targeting formate as the main product. A filter-press reactor with a gas diffusion electrode (GDE) cathode containing bismuth as the catalyst was employed. The system operated in a liquid-phase configuration, with a catholyte composed of 0.5 M KCl and 0.45 M KHCO₃, supplied at varying flow rates. Pure CO₂ was introduced at 200 mL min⁻¹, while the anode was fed with 1 M KOH. Magnets were placed near both the cathode and anode. Modeling showed that magnet placement significantly influenced the magnetic field strength: a single magnet near the anode produced a 20 mT field on the GDE, whereas placing two magnets at opposite reactor ends increased the field strength to 400 mT.

To explore the effect of magnetic fields on ERCO₂ performance, experiments were conducted at different catholyte flow rates (0.07, 0.15, and 0.57 mL min⁻¹ cm⁻²) while maintaining a constant current density of 200 mA cm⁻² [2]. The results demonstrated a clear enhancement in both formate concentration and Faradaic efficiency (FE) when a magnetic field was applied. Notably, the improvement was more pronounced at lower flow rates. At 0.07 mL min⁻¹ cm⁻², formate concentration increased from 18.05 to 27.25 g L⁻¹ (a 50% increase), while at 0.57 mL min⁻¹ cm⁻², the increase was approximately 20%. These improvements are attributed to the magnetohydrodynamic (MHD) effect induced by the magnetic field in the mass transfer layer between the GDE and the electrolyte. The MHD effect enhances fluid mixing and mass transport in the cathodic compartment, which is especially beneficial at low flow rates, where natural turbulence is limited.

Beyond formate production, the magnetic field-driven MHD effect presents opportunities to improve the formation of more complex products such as alcohols, methane, ethanol, and other multi-carbon (C₂+) compounds. Magnetic fields may also contribute to stabilizing key reaction intermediates, facilitating multi-electron transfer processes. Moreover, spin-related phenomena, such as the stabilization of radical pair states, should also be considered when evaluating the full impact of magnetic fields on ERCO₂ systems [1].

In summary, the integration of magnetic fields into ERCO₂ systems offers a promising route to enhance process efficiency and product selectivity. These findings represent a significant step toward the industrial implementation of electrochemical CO₂ conversion technologies.

Anion exchange membrane fuel cell (AEMFC) has significant interest due to their ability to operate without the use of precious metal catalysts and their potential for cost reduction compared to proton exchange membrane fuel cells. However, the membrane's conductivity reduction due to the presence of HCO₃^- and CO₃^2- is a problem, which are produced when CO₂ in the air dissolves into water. Conversely, research is being conducted on CO₂ collectors that take advantage of this property. While prior studies have focused on the capture of CO₂ from the atmosphere and the supply of CO₂ reduced air to living environments [1], this study proposes the utilization of the concentrated CO₂ after transportation through the AEM. That is, since the CO₂ is captured at the oxygen reduction reaction cathode, and transferred to the hydrogen oxidation anode, the concentration of CO₂ in the anode exhaust is mainly discussed here.

An AEM fuel cell with the electrode area of 6.25 cm² was utilized for measurements related to CO₂ transportation and concentration. The Pt/C catalyst was utilized as both the anode and the cathode catalyst, and the Ti mesh was employed as a current collector plate. The fuel cell was operated with the supplies of humidified air (CO₂ concentration: 400ppm) to the cathode and humidified hydrogen to the anode. The humidification was performed to achieve saturation at room temperature. The concentration ratio depended on the flow rate of the air and hydrogen. The fuel cell was operated at 100 mA and CO₂ in the air supplied to the cathode was transferred to the anode and concentrated to 4000ppm when the air and hydrogen flowrate was 600 sccm and 6 sccm, respectively.

When this device is used with a water electrolyzer operated by clean energy, the CO₂ in the air in residences and offices can be concentrated without fossil fuels. This concentrated CO₂ is useful for the recent digital and smart agriculture, that is, this can be supplied to greenhouses to grow plants.

The industrial and societal transformation towards carbon neutrality requires the development of strategies to significantly reduce greenhouse gas emissions. In this context, CO₂ electroreduction (CO₂RR) is a promising approach for converting excess electrical energy and storing it in the chemical bonds of multicarbon (C₂_⁺) products, such as alcohols and carbohydrates, using anthropogenic CO₂. Cu is currently the only class of material that can achieve significant yields of ethanol and ethylene, especially under pulsed CO₂RR conditions.[1–7^] However, to allow knowledge-driven catalyst optimisation, it is crucial to comprehensively understand the structural adaptation (near-surface) as well as the surface coverage with adsorbates under pulsed CO₂RR conditions.[3,6-7]

In this work, we use operando time-resolved X-ray diffraction and absorption, as well as surface-enhanced Raman spectroscopy (SERS), to study the formation of active structural states and adsorbates under potentiostatic and potentiodynamic conditions related to CO₂ reduction reactions (CO₂RR). We selected plasma-treated Cu foils and ZnO-decorated Cu₂O nanocubes as shape-selected electrocatalysts that can be easily prepared using a wet-chemical, ligand-free approach and demonstrate promising catalytic activity.[3-7] Our studies revealed clear correlations between catalytic performance and varying potential, as well as under a wide range of potentiodynamic reaction conditions. Correlating potential-dependent Faradaic efficiencies with insights into surface adsorbate composition obtained via in situ SERS enabled us to identify crucial, selectivity-determining adsorbates for C₂_⁺ and ethanol formation.[4,5] By varying the pulsed CO₂RR conditions (pulse profile and electrolyte composition), we demonstrate how formation of cationic Cu species as well as co-adsorption of CO and OH can be linked to alcohol formation over hydrocarbons.[3,6‑7]

We present fundamental insights to improve understanding of the implications of catalyst structure and potentiodynamic CO2RR conditions on C2+ production, which is important for scaling up the process to industrially viable conditions.

Electrochemical catalytic reactions for the energy transition (hydrogen evolution reaction (HER), carbon dioxide (CO2RR), oxygen reduction reaction (ORR), oxygen evolution reaction (OER)) attract considerable interest from the scientific community. In order to accelerate rational design of efficient catalysts with high activity, selectivity and stability, it is important to understand the fundamental mechanisms involved in the electrochemical processes. To this aim, advanced in situ / operando characterization techniques provide insight into the correlation between physical-chemical properties and the electrochemical performance. Specifically, electrochemical liquid phase transmission electron microscopy (EC-LPTEM) provides real-time morphological, structural and chemical information regarding catalytic materials under electrochemical stimulation [1]. EC-LPTEM experiments are typically performed in miniaturized liquid cell TEM holders with controlled liquid flow, where the three electrode configuration (working electrode WE, counter electrode CE, reference electrode RE) is implemented through MEMS-based technology. The stringent requirements for operation in the TEM column (electron-transparency, compatibility with high vacuum conditions) have a strong influence on the liquid cell geometry. As a result, EC-LPTEM experiments inevitably differ from the commonly used macroscopic benchmarking reactors. It is of considerable scientific interest to understand how to improve the experimental design in order to reach relevant operando conditions.

In this work, we show different approaches to the modification of the EC-LPTEM setup, with the goal of improving the experimental control of mass transport and electrochemical conditions during in situ / operando experiments.

At first, the implications of a rationally-optimized cell geometry, enhancing diffusion as main mass transport mechanism, are investigated in electrochemical experiments in aqueous electrolyte. It Is shown that with the diffusion cell geometry it is possible to perform electrochemical experiments in conditions which were previously not accessible with the standard planar EC-LPTEM cell geometry [2]. Experimental examples include the electrodeposition of Zn nanostructures for energy storage applications and the dynamical evolution of a copper-based catalyst for CO2RR applications. In the second part of this work, we focus on improving the control and stability of the electrochemical conditions during EC-LPTEM experiments. Nanostructuration of the on-chip CE and RE by electrodeposition of metallic nanostructures is presented as innovative approach for decreasing the polarization of the CE during operation while simultaneously enhancing the stability over time of the RE. The presented work aims to inspire the development of a comprehensive optimization approach of all the experimental parameters (mass trasnport, electrochemistry, radiolysis), with the aim of enhancing the capabilities of future in situ/ operando experiments.  

Recently, the search for better and more cost-effective catalysts to facilitate chemical conversion reactions for various green energy applications has driven the widespread development and adoption of operando techniques. Particularly, there is significant interest in understanding the catalysts for the electrochemical reduction of carbon dioxide and nitrogen-containing species due to their potential for generating higher-value products. The cathodic conditions of these reactions also lead to restructuring of the pre-catalysts through various processes, among which the redox transformations that occur upon potential application can result in catalyst structures that are drastically different from the pre-catalyst. Here, I will discuss my group's efforts using electrochemical liquid cell transmission electron microscopy (EC-TEM) to follow the restructuring of cubic copper(I) oxide pre-catalysts during carbon dioxide [1] and nitrate reduction [2] in a spatially and temporally resolved manner. We show that the different electrolytes used in the two reactions interestingly lead to drastically different restructuring pathways under similar applied potentials. These results illustrate how the interplay between the catalyst and electrolyte environment can not only lead to the creation of more complex catalyst motifs but also the transient stabilization of (hydr)oxide species. 

The global shift toward carbon neutrality has intensified interest in electrocatalytic reactions, such as hydrogen evolution, oxygen reduction, and particularly carbon dioxide reduction (CO₂RR), as promising strategies to reduce greenhouse gas emissions and generate valuable chemical products. In order to design catalysts with high activity, selectivity, and stability, it is essential to understand the fundamental mechanisms involved in electrochemical processes. In situ and operando approaches have emerged as powerful tools for probing catalyst properties under working conditions, enabling deeper insights into their activity, including the identification of active sites, reaction intermediates, and key transformation pathways.

Electrochemical liquid-phase transmission electron microscopy (EC-LPTEM) has gained attention for its ability to observe the evolution of the morphology and crystalline structure of materials in liquid environment, under provision of electrochemical stimulus [1]. EC-LPTEM is a highly demanding technique as it utilizes miniaturized liquid cells with integrated three-electrode configurations, which needs to be compatible with high vacuum and electron-transparent environments [2]. Electrochemical liquid-phase Raman spectroscopy can provide complementary information, in particular on surface species and their dynamic evolution during the reaction [3]. Combining EC-LPTEM with operando Raman spectroscopy provides time-resolved access to morphological, structural, and chemical information. These therefore provide direct evidence of catalyst evolution, contributing to deeper understanding of the catalyst behaviour during reaction.

In this study, we investigate the dynamic evolution of a copper-based catalyst under electrochemical CO₂ reduction conditions by EC-LPTEM, shading light on the structural and morphological changes the material undergoes during electrocatalytic activity. Complementary Raman spectroscopy is introduced to provide additional chemical insight, and the feasibility of employing a shared electrochemical cell platform to enable correlative EC-LPTEM and Raman studies is evaluated. This multimodal approach enables direct correlation of catalysts transformations with catalytic performance, offering mechanistic insights into CO₂RR on Cu-based catalysts and informing future efforts in the knowledge-driven optimization of materials for selective and stable electrocatalysis.