The electrocatalytic conversion of CO₂ into value-added fuels and chemicals is a sustainable route to recycle carbon emissions and store renewable energy.[1] Metal–organic frameworks (MOFs) are appealing for this reaction owing to their porosity, tuneable chemistry, and high density of accessible metal sites, which can be tailored across a wide range of metals and linkers.[2]

Here we explore a diverse set of MOFs as electrode materials for CO₂ conversion, including MOF-74 (M = Ni, Mg, Co, Cu), UiO-66, HKUST-1 and Cu-adenine, covering different metals, linkers and stabilities. Depending on the framework, the MOFs are used either in their pristine form or as composites incorporating conductive components to improve charge transport and stability. In all cases, the materials are deposited on carbon matrices by electrophoretic deposition and spin coating, and characterised by PXRD, N₂ adsorption, FTIR-ATR, SEM and cyclic voltammetry.

The electrodes are evaluated for two reaction pathways: the direct electroreduction of CO₂ to value-added products and the electrocarboxylation of organic substrates to carboxylic acids. Performance is assessed by controlled-potential/current electrolysis, with products quantified by gas chromatography with thermal conductivity detector and ¹H NMR to determine activity, selectivity, Faradaic efficiency and stability. This comparative study links MOF composition and electrode design to catalytic behaviour, guiding the development of efficient materials for CO₂ valorisation.

Low-temperature electrochemical CO₂ reduction reaction (CO₂RR) is a promising strategy for producing formic acid, an attractive liquid hydrogen carrier and value-added chemical. Although Bi-based catalysts are highly selective toward formate, their CO₂ conversion rate remains limited under practical electrolysis conditions. To address this issue, we initially proposed a Zr-MOF-assisted Bi catalyst design, aiming to enhance the local CO₂ availability near Bi active sites through microenvironment modulation.

First, we proposed the novel Bi with Zr-MOF (UiO-66) catalysts structure as a strategy to enhance CO₂ availability. Bi was deposited on UiO-66, a Zr-based MOF, and evaluated for CO₂RR in a flow-cell reactor under continuous CO₂ supply. The Bi/UiO-66 catalyst exhibited a 2.5–3.0-fold increase in current density compared with Bi alone while maintaining comparable Faradaic efficiency for formate production. This result suggested that the incorporation of Zr-containing components can effectively promote CO₂ conversion at Bi catalysts. However, post-electrolysis structural analyses revealed that the original UiO-66 framework was not fully retained during electrolysis. Instead, carbonate-coordinated Zr-hydroxide species were formed, indicating that the enhanced activity originates not simply from the intact MOF structure, but rather from the role of Zr-derived species in the interfacial reaction environment.

To verify this concept, Bi–Zr composite catalysts were further investigated as model systems to clarify the function of Zr species. These catalysts showed significantly higher CO₂RR current density than Bi-only electrodes. In situ Raman spectroscopy revealed a lowered surface pH for the optimized Bi/Zr composition, suggesting increased local CO₂ availability near the catalyst surface. These findings demonstrate that Zr-derived components actively modulate the CO₂ microenvironment around Bi sites, thereby improving high-rate CO₂-to-formate conversion. This study highlights Zr-based interfacial microenvironment engineering as an effective strategy for overcoming local reactant limitations in CO₂ electroreduction.

The electrochemical reduction of carbon dioxide (CO₂RR) to syngas (CO + H₂) presents a compelling strategy for defossilizing the chemical industry and advancing a circular carbon economy. However, integrating CO₂RR with downstream thermochemical processes remains a significant operational challenge [1,2]. Conventional strategies for generating ratio-tunable syngas rely heavily on modifying the catalyst composition or crystal structure during the initial synthesis stage, which restricts real-time operational flexibility and requires entirely different catalytic platforms for different target chemical outputs [3]. As underscored in our recent co‑authored collaborative review on low-temperature electrolysis scale-up, achieving on‑demand selectivity control without altering the underlying reactor architecture or catalyst configuration is essential for practical industrial deployment [2].

To address this challenge, the present work proposes a straightforward in situ activation strategy that dynamically modulates the syngas composition on a single bimetallic Cu₂O/ZnO catalyst [4]. By implementing brief potential-cycling treatments immediately before electrolysis under identical operational reaction conditions, the competitive balance between CO₂RR and the parasitic hydrogen evolution reaction (HER) can be systematically controlled [4]. Under a constant operational bias of -1.0 V_RHE, the developed catalyst yields distinct, highly stable H₂/CO molar ratios that depend entirely on the direction and polarization of the transient conditioning steps [4].

Importantly, the resulting syngas streams can be tuned to meet specific industrial benchmarks, providing a versatile interface for diverse downstream C1 chemical processing loops. The pristine, non-conditioned catalyst delivers an intermediate H₂/CO ratio of 2.5, which serves as an ideal feedstock for thermochemical methanol synthesis or Fischer-Tropsch synthesis of long‑chain hydrocarbons. When subjected to a potential cycling initiated from the anodic scan (AS), the catalyst promotes CO₂RR over water reduction, lowering the H₂/CO ratio to 0.7. This CO-rich output is perfectly tailored for industrial hydroformylation to produce valuable aldehydes and oxygenated monomers. Conversely, applying a potential cycling initiated from the cathodic scan (CS) suppresses surface defects and favors the HER, driving the H₂/CO ratio up to 5.0. This H₂-rich composition matches the demanding stoichiometric requirements needed for downstream catalytic methane synthesis.

Comprehensive ex-situ characterization indicates that the activation protocols control critical parameters, namely the copper oxidation state, the strength of the Cu-Zn electronic interaction, and surface oxygen-vacancy density, which dictate CO₂ binding strength and govern final product distribution [4]. To gain a deeper understanding of these surface dynamics, current work focuses on implementing an operando spectroelectrochemical Raman configuration. This diagnostic step aims to track the real-time structural evolution of the inorganic catalyst components and the liquid-solid interface under operational bias. Targeted parameters include monitoring the reversible Cu₂O to Cu⁰ phase transformations, evaluating structural ZnO lattice modes, and tracking variations in local carbonate/bicarbonate interfacial equilibria. Correlating these fundamental spectral trends with Faradaic efficiencies will provide a practical roadmap for evaluating surface speciation and for assessing online product-stream tuning in future electrolyzer designs.

Carbon dioxide (CO₂) conversion to produce fuels and chemicals is a promising route for reducing CO₂ emissions, thus the design of efficient and selective electrocatalysts for CO₂ reduction is essential to the development of sustainable energy conversion technologies.[1] In this work, copper-based metal–organic frameworks (Cu-MOFs)[2] were used as tuneable platforms for the design of advanced electrodes, focusing on the improvement of the catalytic performance through integration of conductive polymers. Cu-Adenine MOFs and a new Cu-Hypoxanthine coordination polymer were synthesised following the procedure described by Wang[3] and co-workers and characterised using infrared spectroscopy, X-ray diffraction and N₂ adsorption isotherms. Density functional theory (DFT) calculations were used to model the structure of the Cu-Hypoxanthine coordination polymer.

To improve electrical conductivity and catalytic activity, the synthesised materials were modified with polyaniline (PANI) via a mechanochemical approach to produce PANI-modified composites. The idea of this strategy is to enable contact between the conductive polymer and the synthesised materials while preserving their integrity.^[1] For the electrocatalytic application of these materials, it is necessary to integrate them into mechanically stable and electrically conductive electrodes. Electrophoretic deposition was used to deposit the pristine materials and the resulting PANI-modified materials onto carbon paper substrates producing uniform and adherent films. Those films were characterised by X-ray diffraction and Scanning electron microscopy.

Electrochemical performance was evaluated by linear sweep voltammetry (LSV) to assess stability and identify suitable operating potentials for CO₂ reduction.^[2] These studies provide insight into the effect of polymer incorporation on electrode activity and stability. Subsequent controlled potential electrolysis (CPE) experiments are being conducted to evaluate catalytic activity under specific conditions.

The liquid products formed during CPE were identified and quantified by ¹H NMR and liquid chromatography, while gaseous products were analysed by GC-TCD.

The urgent need to develop sustainable catalytic routes for CO₂ valorization has driven growing interest in hybrid catalytic systems. Among them, photothermocatalysis stands out as a particularly promising strategy, merging the high efficiency of thermocatalysis with the green and selective nature of photocatalysis. This synergy enables enhanced catalytic performance and substantial energy savings compared to conventional single-mode approaches.

This lecture will explore the potential of solar photothermo-catalysis for the conversion of CO₂ into solar fuels using noble metal-free catalysts. Special emphasis will be given to CeO₂- and CuOₓ-based phyllosilicates and hybrid hydrotalcite-derived systems exhibiting coupled redox and photoactive features. Furthermore, An innovative integrated process will be presented, in which CO₂ is generated from the catalytic oxidation of VOCs and subsequently transformed into solar fuels, converting air pollutants into valuable products. Finally, the different operational modes—thermo-assisted, photo-assisted, photo-driven, and photothermo-co-catalysis will be discussed, outlining the future perspectives of this emerging field.

The catalytic conversion of carbon dioxide into value-added chemicals is an important pathway toward carbon utilization and circular economy. Organic carbonates are attractive products because of their applications as green solvents, battery electrolytes, polymer precursors, and intermediates in fine-chemical synthesis. However, the thermodynamic stability and low reactivity of CO₂ require catalysts that combine high activity, selectivity, stability and low environmental impact. This work investigates the engineering design of sustainable catalysts for the conversion of CO₂ into cyclic and linear organic carbonates. Particular emphasis is placed on metal–organic frameworks (MOFs), hydrotalcite-like compounds (HTLCs) and oxide-based catalysts because of their tunable structures, accessible active sites and adjustable acid–base properties. The study focuses on the relationships among catalyst composition, active-site structure, surface acidity and basicity, pore characteristics and reaction performance. Particular attention is also given to catalysts based on earth-abundant and low-toxicity materials together with or without together solvent under mild operating conditions. Catalyst activity, product selectivity, recyclability and resistance to deactivation are evaluated to identify the main factors controlling CO₂ activation and carbonate formation [1].

The results show the importance of tailoring active-site environments and catalyst structures to improve reaction efficiency and selectivity. MOFs offer high surface areas and well-defined coordination environments, HTLC-derived materials provide tunable acid–base functionality, and mixed-metal oxides offer high thermal stability and practical recyclability. Integrating catalyst design with mechanistic understanding and process optimization provides a promising route toward scalable and energy-efficient CO₂ valorization. This work contributes to the development of more sustainable catalytic systems for producing organic carbonates while reducing reliance on fossil-derived carbon resources.

Electrochemical CO₂ reduction (CO₂RR) in zero-gap membrane electrode assemblies (MEAs) is a promising technology for industrial-scale CO production; however, its practical viability is hindered by carbonate formation and salt precipitation in neutral or alkaline environments. These phenomena deplete CO₂ reactants and obstruct active sites, limiting operational durability. While acidic media can circumvent these issues, the high proton activity typically promotes the competing hydrogen evolution reaction (HER) over CO₂RR.

In this work, we demonstrate a high-performance catalyst consisting of Ni₃S₂ nanostructures anchored on nitrogen-doped mesoporous carbon (Ni₃S₂@NMC-AL) specifically engineered for selective and stable CO conversion in acidic environments. The catalyst was synthesized via a nanocasting approach using SBA-15 as a hard template, followed by a critical acid leaching (AL) step. This purification process selectively removes unstable metallic and amorphous Ni species while preserving the sulfur-stabilized Ni₃S₂ active sites embedded within the robust, N-doped graphitic framework. Comprehensive structural characterization, including XRD, TEM-EDS, and XPS, confirmed that the Ni–S motifs are well-confined and remain stable even after exposure to harsh acidic conditions.

Performance was evaluated in a zero-gap MEA configuration under industrially relevant conditions. The optimized Ni₃S₂@NMC-AL catalyst exhibited CO Faradaic efficiencies (FE) exceeding 90% at current densities of 100 and 150 mA cm⁻². Notably, we found that CO selectivity remained largely independent of electrolyte buffer capacity (comparing KHCO₃ to K₂SO₄), indicating that performance is primarily governed by the local reaction environment and proton availability rather than bulk electrolyte identity.

By systematically tuning the anolyte pH, we identified moderate acidity (pH ≈ 3) as the optimal operating point, providing an ideal balance between suppressing HER and preventing salt deposition. Under these conditions, the catalyst achieved near-unity CO selectivity (98–99%) and exceptional long-term stability reaching 450 hours at 100 mA cm⁻². In contrast, while strongly acidic conditions (pH ≈ 1) also yielded high selectivity, they resulted in reduced durability due to accelerated HER kinetics and potential metal leaching.

These results highlight the synergistic role of Ni₃S₂ active sites, which weaken hydrogen adsorption and stabilize CO₂RR intermediates, in combination with the controlled proton transport provided by the MEA architecture. This study establishes a robust framework for designing acid-stable Ni-based catalysts and provides practical guidelines for optimizing local interfacial microenvironments in scalable CO₂ electrolysis systems.

Keywords: CO₂ reduction, Ni₃S₂ nanostructures, N-doped mesoporous carbon, Acidic CO₂RR, Zero-gap MEA, Long-term stability.

Electrochemical CO₂ reduction (CO₂RR) offers a promising route for converting greenhouse gas emissions into valuable chemicals. Among the catalysts investigated for CO₂RR, noble metals such exhibit excellent selectivity toward CO, but their high cost and limited availability hinder large-scale use. Zinc oxide (ZnO) has emerged as an attractive earth-abundant alternative due to its low cost and environmental friendliness; however, its relatively low surface area limits its CO₂ adsorption capacity. ¹. Metal-organic frameworks (MOFs) are promising materials for overcoming this limitation due to their high porosity and tunable surface chemistry. In particular, ZIF-8 exhibits high CO₂ adsorption capacity and has shown promising selectivity toward CO formation. ²

Mechanochemical synthesis, in contras with conventional solvothermal approaches,  provides a sustainable route for different MOF production by drastically reducing solvent consumption and enabling the direct use of poorly soluble metal precursors. ³ In the case of ZIF-8, mechanochemistry allow for the use of ZnO as the zinc source and its direct conversion into the ZIF-8 phase. ^4–6 Unlike conventional ZnO/ZIF-8-derived catalysts, where ZnO is typically generated by calcination of a pre-synthesized ZIF-8 sacrificial template, the mechanochemical approach enables a simple and controllable one-step conversion of ZnO into ZIF-8, providing direct control over the ZnO/ZIF-8 ratio and, consequently, the catalytic properties of the resulting materials.

Here, ZnO/ZIF-8 composites were synthesized via mechanochemistry using different grinding times (1.5 to 12 h) and optimized liquid-assisted grinding conditions, requiring only 1 μL of methanol per mg of reagent. The mechanochemical route enabled precise control over the extent of ZnO-to-ZIF-8 conversion, yielding materials containing between 58.1% (1.5 h) and 99.4% (12 h) ZIF-8, as determined by thermogravimetric analysis. The fully converted sample showed no signs of amorphization and presented a specific surface area of 1704 m² g⁻¹ (BET) and a CO₂ uptake of 1.44 mmol g⁻¹ at 273 K and 100 kPa. The resulting materials were evaluated as gas-diffusion electrodes in a membrane electrode assembly (MEA) electrolyser operating at technologically relevant current densities. While higher ZIF-8 contents enhanced CO₂ adsorption, the best CO₂RR performance was obtained for partially converted materials, demonstrating that an optimal balance between the CO₂-concentrating capability of ZIF-8 and the electrical conductivity provided by residual ZnO is required to maximize catalytic activity and CO selectivity. The optimized catalyst containing 58% ZIF-8 achieved 69% FE_CO at 250 mA cm⁻², outperforming both pristine ZnO and nearly fully converted ZIF-8-rich materials.

The escalating global CO₂ emissions from industrial processes and power generation demand urgent development of low-carbon technologies. Electrochemical CO₂ reduction (CO₂RR) offers a sustainable pathway to convert CO₂ into valuable fuels and chemicals, but its practical application is hindered by the complexity of real-world feedstocks, particularly flue gas [1]. Flue gas, a mixture of CO₂ (4–15%), nitrogen, oxygen (1–15%), and contaminants, presents significant challenges for CO₂RR due to its low CO₂ concentration, which limits solubility and mass transport, and the presence of O₂, which competes with CO₂RR via the oxygen reduction reaction (ORR), drastically reducing Faradaic efficiency even at trace levels [2].

Current strategies to mitigate these issues include hydrated ionomer coatings and polymers of intrinsic microporosity (PIMs), which selectively hinder O₂ transport while promoting CO₂ reduction [3]. However, these approaches face limitations in long-term stability and precise control over the local reaction microenvironment. Direct reactive capture (DRC) methods, such as amine scrubbing and carbonate/bicarbonate electrolytes, eliminate the need for energy-intensive CO₂ purification but suffer from poor selectivity and hydrogen evolution, impacting efficiency [4].

Non-aqueous systems, particularly those using aprotic or non-nucleophilic solvents, emerge as a promising alternative [5]. Binary solvent electrolytes, combining an aprotic solvent with a weak proton donor (e.g., water or ethanol), enable fine-tuning of the local microenvironment, enhancing CO₂ solubility and suppressing hydrogen evolution reaction (HER). These systems maintain selective CO₂ reduction pathways while providing controlled proton availability, addressing the dual challenges of low CO₂ concentration and O₂ interference.

This study introduces a binary solvent-engineered strategy for CO₂ electroreduction directly from O₂-containing flue gas. By systematically tuning the proton donor environment in acetonitrile-based electrolytes, we establish a linear correlation between HER Faradaic efficiency and hydrogen-bond donating (HBD) ability, while ORR selectivity decreases exponentially with reduced HBD strength. Theoretical calculations confirm that HBD strength moderates HER activation but strongly suppresses ORR, aligning with experimental observations. Proton-free environments, such as the dimethyl sulfide/acetonitrile (DMS/ACN) system, effectively suppress both HER and ORR due to disrupted hydrogen-bond networks. Under moderate pressures, DMS/ACN achieves near-quantitative Faradaic efficiencies for CO production even at 1% CO₂ and up to 15% O₂, with operational stability exceeding 100 hours and an energy consumption of 30.7 GJ ton⁻¹ CO. Coupled with a high-efficiency triple-junction solar cell, the system attains a solar-to-fuel conversion efficiency of ~5.5%, comparable to aqueous systems using pure CO_2r. This approach not only advances CO₂RR toward industrial relevance but also provides new mechanistic insights into selective electrocatalysis under realistic conditions.

The electrochemical reduction of CO₂ represents a promising pathway for the sustainable production of fuels and chemicals while contributing to carbon-neutral energy technologies. However, achieving high activity and selectivity toward multicarbon (C₂⁺) products remains a major challenge due to the complexity of the reaction network and the strong dependence of catalytic performance on catalyst composition, reaction intermediates, and operating conditions. In particular, efficient CO₂ conversion requires the optimization of two fundamental steps: the selective generation of CO and its subsequent transformation into multicarbon products through carbon-carbon bond formation.

Here, we present an integrated computational framework aimed at establishing catalyst design principles for CO₂ electroreduction by connecting these two key stages of the reaction pathway. The framework combines density functional theory (DFT), constant-potential simulations, and machine-learning-assisted materials screening to investigate catalyst behavior under realistic electrochemical conditions and accelerate the discovery of promising electrocatalysts.

We first investigate the origin of the remarkable selectivity of Ag-based electrocatalysts toward CO production.[1] By explicitly accounting for both thermodynamic and kinetic effects as a function of the applied potential, we demonstrate that the competition between CO₂ reduction and hydrogen evolution is governed by a subtle interplay between reaction energetics and activation barriers. The resulting mechanistic picture explains the experimentally observed transition from hydrogen evolution to highly selective CO formation and highlights the conditions required for efficient CO generation, providing a foundation for tandem CO₂-to-C₂⁺ conversion strategies.

Building on these insights, we focus on Cu-based catalysts, which are uniquely capable of promoting carbon-carbon coupling and generating multicarbon products. To explore the vast compositional space of Cu-based alloys, we developed machine-learning models trained on large DFT datasets of CO adsorption energies across different alloy compositions, surface facets, and local atomic environments.[2] The resulting models enable rapid screening of thousands of adsorption configurations while retaining predictive accuracy comparable to first-principles calculations. This approach identifies several promising alloying elements, including Ag, Au, Zn, In, Al, and Ga, capable of tuning CO adsorption toward regimes favorable for C-C coupling.[4]

To validate and rationalize these predictions, constant-potential DFT calculations were employed to investigate CO dimerization on selected CuM surfaces.[3] The simulations reveal that p-block alloying elements, particularly Al and Ga, promote electron donation to adsorbed intermediates, stabilize OCCO species, and lower the activation barrier for C-C bond formation relative to pure Cu.[3] Furthermore, a strong correlation emerges between dimerization energetics and the excess surface charge required to maintain the applied potential, identifying a physically meaningful descriptor that captures both electrostatic and covalent contributions to catalytic activity.[3]

This work provides a unified perspective on the elementary processes governing CO₂ electroreduction, bridging selective CO production and multicarbon product formation. By integrating mechanistic understanding with data-driven catalyst discovery, the proposed framework offers practical guidelines for the rational design of next-generation electrocatalysts for efficient and selective CO₂ conversion.

Currently, ethylene is the most important chemical with the largest global demand: it is mainly produced by ethane or naphtha cracking but, this is characterized by significant carbon dioxide emissions. For this reason, starting from carbon dioxide and water, different routes for ethylene production have been proposed and investigated in the literature but a complete comparative analysis is missing. In this research, we analyze ethylene production via carbon dioxide electroreduction and methanol-to-olefin process, with methanol obtained in several ways. After the modelling of these systems, economic and environmental (in term of global warming potential) analyses are conducted to develop a comparison among the investigated processes and a conventional one based on naphtha cracking. Results, located in the UK, show that the tandem process could be economically competitive (with the lowest production cost of $ 1.34 per kg of ethylene), while the methanol-to-olefin process with methanol obtained from syngas (produced through carbon dioxide-water co-electrolysis) has the best advantage for carbon dioxide emissions (with the lowest impact of −3.08 kg of CO2eq per kg of ethylene). Moreover, the most preferred energy source for the electricity supply is the nuclear one with a small-scale plant because, economic and greenhouse gas emission advantages are provided while, worse conditions are obtained when solar energy is used. Our main finding is that electrochemical processes are likely to play an important role in the future when performance improvements are realized.

Advancing the electrochemical conversion of CO₂ into value-added chemicals like formic acid requires continuous innovation in both material science and reactor engineering. While traditional systems operating in neutral or alkaline media suffer from severe carbonate formation and poor carbon utilization efficiency, transitioning to acidic media introduces the challenge of competing hydrogen evolution reactions (HER). This presentation highlights recent advances in overcoming these barriers through the synergistic integration of bimetallic catalyst development and engineered reactor architectures.

At the materials level, a carbon-free eutectic Bi-Sn (Bi_0.58Sn_0.42) gas-diffusion electrode (GDE) was developed to steer selectivity in acidic conditions. Density functional theory (DFT) calculations and experimental evaluations demonstrate that the unique Bi-Sn interfacial synergy weakens hydrogen adsorption while stabilizing formate intermediates. This innovation effectively suppresses HER, enabling the GDE to achieve a faradaic efficiency (FE) of 81.3% toward formic acid at a current density of -100 mA cm⁻² in a pH 3 electrolyte.

In a separate process-oriented approach, a continuous three-compartment electrolyser was engineered and operated. By using an extra compartment with ion-exchange resins between the electrodes, the reactor allows only pure aqueous formic acid to be collected directly at the outlet without contamination from supporting electrolyte ions. This design eliminates the need for downstream ion-separation steps while maintaining stable ionic transport. The optimized system significantly reduces ohmic resistance, achieving cell voltages of ~3.5 V, and enables the direct generation of highly concentrated formic acid up to >85 g L⁻¹.

By bridging fundamental electrocatalytic innovations with process-level reactor design, these advances provide a highly efficient, scalable platform for continuous CO₂ conversion, directly contributing to the next generation of sustainable chemical manufacturing.

The transition toward a sustainable, circular, and carbon-neutral chemical industry requires the development of efficient pathways for CO₂ utilization. Electrochemical CO₂ reduction offers a promising route to convert CO₂ into value added chemicals using renewable electricity. Among the possible products, formate stands out due to its high selectivity as a two electron product, relatively low overpotential, and versatility as a chemical intermediate. Emerging downstream pathways, such as its use as a hydrogen carrier and its integration with fermentation processes for the production of fatty acids, can significantly expand its value chain, enabling applications in personal care products and sustainable aviation fuel (SAF).

This work presents recent advances in electrochemical CO₂ to formate conversion at TNO using gas diffusion electrode Gas Diffusion Electrode (GDE) based electrolyzer systems. The study focuses on the development, optimization, and upscaling of electrolysis reactors, where key operating parameters, including electrolyte composition, current density, and cell voltage, are systematically tuned to enhance performance while maintaining compatibility with downstream processing. Different electrochemical cell configurations were evaluated, including two- and three-compartment systems, to investigate their impact on product selectivity, energy requirements, and process flexibility. Particular attention was given to GDE composition and operational strategies aimed at improving stability and mitigating performance losses associated with electrode degradation. Extended electrolysis experiments were conducted over 50–100 hours to evaluate operational stability and monitor performance evolution under continuous conditions. These studies provide insight into degradation mechanisms and define operating windows for sustained formate production. Additionally, conditioning strategies were explored to achieve target concentrations and manage impurities, ensuring compatibility with downstream applications such as fermentation.

Building on these results, a scale-up strategy is proposed toward larger cell formats (100 cm²) and subsequent validation in pilot scale platforms. Ongoing efforts aim to translate laboratory scale performance to application-relevant conditions, focusing on improved energy efficiency, stable long-term operation, and integration with downstream conversion processes.

Overall, this work contributes to the development of scalable CO₂ electrolyzer technologies and highlights the role of formate as a key intermediate for integrated carbon utilization pathways.

Tackling climate change requires not only ambitious targets but also the rapid development and deployment of practical decarbonization solutions. Among the available strategies, Carbon Capture and Utilization (CCU) has emerged as a promising pathway, enabling the transformation of waste CO₂ into valuable chemicals and fuels. This approach is especially relevant for hard‑to‑abate sectors including cement manufacturing, where a significant fraction of emissions is inherently linked to the production process and cannot be eliminated through electrification or energy efficiency measures alone.

In this context, the present work presents the design, experimental validation, and integration of an electrochemical CO₂ recycling demonstration plant tailored for cement plant flue gases. The study addresses two stages of the CCU value chain: the capture of CO₂ from industrial exhaust streams and its subsequent electrochemical conversion into formate [1, 2].

First, CO₂ capture is achieved using a membrane‑based separation system built around polymeric hollow‑fiber modules. This technology is well-suited for post‑combustion applications due to its modularity, low energy demand, and operational simplicity [3]. Experimental results show that, when treating flue gases containing 7–15% v/v CO₂, a single membrane stage increases the CO₂ concentration to approximately 18.5%. However, achieving the higher purities required for efficient downstream conversion demands a multistage configuration. Guided by predictive modelling, a three‑stage membrane reaches CO₂ concentrations above 95%, providing feed for electrochemical utilization.

The captured CO₂ is then converted into formate in a laboratory‑scale electrochemical reactor with an active area of 100 cm². The system operates using a gas diffusion electrode (GDE) based on (BiO)₂CO₃, selected for its high selectivity and improved stability under reaction conditions [4]. Long‑term operation tests, over 12 consecutive days, demonstrate system robustness. The Faradaic efficiency for formate production is initially close to 100% and gradually decreases to approximately 75% due to electrode degradation. Importantly, by-product formation remains limited, with hydrogen and carbon monoxide efficiencies consistently below 10% and 4%, respectively. Overall, the system achieves cumulative formate production exceeding 20 mol, with a stable daily output of around 1.7 mol.

To support the transition from laboratory‑scale experiments to industrial implementation, the experimental data obtained from both the capture and conversion units are used to develop predictive models. These models are integrated into a digital twin predicting key process variables, including CO₂ concentration, formate production, and system efficiency, with coefficients of determination close to 0.99. This digital framework enables real‑time monitoring, predictive control, and process optimization, enhancing the reliability and scalability of the system.

Building on these results, an integrated pilot plant is proposed, designed to process up to 20 L·min⁻¹ of captured CO₂ with an electrochemical active area of 1000 cm². The process includes flue gas conditioning, multistage membrane separation, gas compression, and direct coupling with the electrochemical reactor. Despite the promising results, several challenges remain for industrial deployment, including improving long‑term electrode durability, reducing energy consumption, and optimizing the management of unconverted CO₂ and recycled process streams.

Overall, this study demonstrates that the integration of membrane‑based CO₂ capture and electrochemical conversion is a technically viable and scalable solution for cement plant emissions. By combining experimental validation with digital twin modelling, this work provides a solid engineering foundation for advancing CCU technologies as a realistic route toward decarbonizing heavy industry and supporting the transition to more sustainable manufacturing systems.

As the primary greenhouse gas, CO₂ contributes to worldwide ecological disruption, climate instability, and economic risk. Part of the mitigation includes the increased attention on carbon capture and utilization (CCU) technologies. Among these, electrochemical CO₂ reduction (eCO₂R) has emerged as a highly promising approach for producing carbon-neutral chemicals and fuels, especially when using renewable energy. While up until now most lab-scale CO₂ reduction experiments are conducted at ambient temperatures (20-25°C), maintaining such low temperatures at an industrial scale will become challenging due to joule heating. In our study, we pushed the boundaries further than the already existing systems, opting for a higher temperature of 85°C for CO₂ reduction. This deliberate choice was made to accentuate and evaluate the changes in reaction kinetics, mass transport, and product distribution from ambient conditions and gain understanding of the thermal effects in practical electrolyzer configurations. Here, we explore the interplay between temperature, catalyst behavior and reactor design. 

We have synthesized a series of bismuth-related nano catalysts, including oxidized, metallic and carbon containing nanoparticles, and have quantitatively evaluated their performance at 85°C. The observations suggest that catalysts without carbon exhibit high initial selectivity but demonstrate diminished stability over a 24-hour timeframe compared to catalysts with a protective carbon layer. Indeed, over a 24-hour timeframe, the carbon-free catalyst showed a 20% decrease in FE, while for the carbon-containing catalyst this drop was more than halved in the same timeframe. By evaluating the role of carbon additives our results yield valuable insights into the impact of carbon additives on stability and overall performance, especially at elevated temperature. These findings uncovered important critical aspects for catalyst design, providing essential knowledge for future larger-scale applications. 

Besides catalyst design, also reactor optimization is required. Specifically, we focused on the three-phase boundary, where the eCO₂R reaction actually takes place. Logically, it is important that this boundary is at the exact location of the catalyst layer (CL). To this end, gas diffusion layers (GDLs) are specifically designed to align this boundary to the right location through variations in hydrophobic additives, thickness, porosity, etc. However, we have found that all these efforts to perfect the GDL properties can easily be forfeited if the differential pressure across it were to change as it shifts the three-phase boundary. A shift inward the GDL will result in a flooded CL, lengthening the diffusion path of the gaseous CO₂in the electrolyte to the active sites of the CL resulting in increased hydrogen evolution. Changing the temperature of the system will affect the location of the boundary layer and by optimizing the differential pressure we can shift its location back to its optimal position and increase the performance of the CO₂ electrolyzer. By optimizing the differential pressure, i.e. elevating the backpressure at gas side, it was possible to increase the system’s durability with a factor of 1.6. Besides the differential pressure, also the GDL type and composition plays a crucial role and was investigated in this work by evaluating different commercially available GDLs with/without microporous layer and with different porosity and wet proofing. By re-evaluating and optimizing the operational conditions and GDE composition, we are getting closer to making the electrochemical CO₂ reduction efficient also at elevated temperatures.

Control of fundamental interfacial processes through electrode interface and microenvironment design is key to stable and scalable CO2 electrolyzers. In this presentation, I will report on recent advances in our design and understanding of cathode/catholyte and anode interfaces in efficient and scalable PTEFE-based one-gap as well as zero-gap CO₂ electrolyzers. We will touch upon the opportunities and challenges associated with “zero-gap” vs “one-gap” cell designs based on the closed interconnection of ion and water movements across the membrane. Then, the surprising impact of the catholyte flow field design¹ in one-gap cells on product efficiency will be addressed revealing the impact of interfacial flow velocity distributions. We will discuss a recent scalable hybrid catholyte flow field/current collector design² for PTFE-based cathode interfaces for CO2 valorization into ethylene. Finally, we will give a comparative perspective on the design of AEM and BPM cell designs for zero-gap cells.^3-5

References

1. Filippi, M.; Möller, T.; Liang, L.; Strasser, P. Understanding the Impact of Catholyte Flow Compartment Design on the Efficiency of CO2 Electrolyzers. Energ Environ Sci 2023, 16, 5265-5273, 10.1039/D3EE02243A. DOI: 10.1039/D3EE02243A.
2. Filippi, M.; Möller, T.; Pastusiak, R.; Magori, E.; Paul, B.; Strasser, P. Scale-Up of PTFE-Based Gas Diffusion Electrodes Using an Electrolyte-Integrated Polymer-Coated Current Collector Approach. Acs Energy Lett 2024, 1361-1368. DOI: 10.1021/acsenergylett.4c00114.
3. Brückner, S.; Feng, Q.; Ju, W.; Galliani, D.; Testolin, A.; Klingenhof, M.; Ott, S.; Strasser, P. Design and diagnosis of high-performance CO2-to-CO electrolyzer cells. Nature Chemical Engineering 2024, 1 (3), 229-239. DOI: 10.1038/s44286-024-00035-3.
4. Brückner, S.; Ju, W.; Strasser, P. Efficient Forward‐Bias Bipolar Membrane CO2 Electrolysis in Absence of Metal Cations. Advanced Energy Materials 2025, 15, 2500186. DOI: https://doi.org/10.1002/aenm.202500186.
5. Brückner, S.; Bondarchuk, O.; Araújo, A.; Ju, W.; Cid, R.; Paz, E.; Krebs, F.; Soares, O.; Amorim, I.; Yu, Z. P.; et al. Failure mode diagnosis and stabilization of an efficient reverse-bias bipolar membrane CO2 to CO electrolyzer. Energy Environ Sci 2025, 18 (13), 6577-6586.

The integration of wastewater treatment with hydrogen production offers a promising pathway to simultaneously address environmental pollution and clean energy generation [1]. This invited presentation highlights recent advances in the use of nanoscale nickel-based electrocatalysts (NiSe and NiS) for co-electrolysis of brewery and sewage wastewater streams [2] [3]. The developed catalysts exhibit high electrocatalytic activity toward hydrogen evolution and wastewater oxidation reactions, enabling efficient hydrogen generation while facilitating the removal of organic contaminants. Replacing the conventional oxygen evolution reaction with the oxidation of wastewater constituents significantly reduces the energy demand of the electrolysis process.

The presentation will discuss catalyst design strategies, structure–activity relationships, reaction mechanisms, and pollutant degradation pathways that govern the performance of wastewater-assisted electrolysis systems. Particular attention will be given to several critical questions: Can wastewater streams become economically viable feedstocks for green hydrogen production? How do wastewater compositions influence catalyst activity, selectivity, and long-term durability? What are the dominant oxidation pathways responsible for pollutant removal? Can wastewater-assisted electrolysis reduce operational costs and carbon emissions compared with conventional water electrolysis? Finally, what scientific, engineering, and techno-economic challenges must be overcome to scale these technologies from laboratory demonstrations to industrial deployment?

The talk will provide perspectives on how wastewater-to-hydrogen technologies can contribute to circular resource utilisation, sustainable water management, and the future hydrogen economy.

Electrocatalysis is transitioning from catalyst discovery toward device-relevant operation, where meaningful benchmarking demands high current densities, extended durations, and realistic architectures such as membranes, gas diffusion electrodes (GDEs), and flow cells. In this regime, a fundamental measurement mismatch becomes dominant: the electrical variables we control (applied potential or current) are not necessarily those experienced at the catalytic interface. Significant, and often time-dependent, voltage losses arise outside the electrode surface, most notably through uncompensated solution resistance (IR drop). These losses can drift during operation, obscuring intrinsic activity and selectivity trends, distorting integrated charges and Faradaic efficiencies, and undermining reproducibility across experiments and laboratories.

We argue that robust electrolyser experimentation requires a shift in instrumentation philosophy—from traditional single–working-electrode-centric control toward electrolyser-native observability combined with closed-loop stabilisation. The first step in this transition is reliable IR compensation under high-current conditions [1]. We present a fully software-based strategy that achieves effectively 100% dynamic IR compensation using commercially available potentiostats. The method continuously determines high-frequency resistance and instantaneous DC current, and adaptively updates the applied setpoint such that the IR-corrected electrode potential remains constant throughout electrolysis.

A key advantage of this approach is its intrinsic stability under dynamically evolving conditions. In practical systems, resistance often decreases over time due to factors such as Joule heating, electrolyte redistribution, or the emergence of multiphase flow. These conditions are precisely where conventional analogue positive-feedback compensation becomes unstable, forcing users to under-compensate and accept systematic error. In contrast, our digital control strategy remains oscillation-free across such regimes, enabling accurate potential control even under strong drift.

We demonstrate the impact of this methodology in nitrate-to-ammonia electrolysis at high current density. Under conventional static partial compensation, apparent currents and inferred selectivities exhibit artefacts that can lead to erroneous mechanistic conclusions. By contrast, adaptive IR compensation stabilises operation and provides reliable potential-dependent performance metrics, directly linking observed activity to the true interfacial driving force. This establishes dynamic IR control not merely as a technical refinement, but as a prerequisite for quantitative electrocatalysis under industrially relevant conditions.

While adaptive IR compensation addresses the limitations of single-electrode measurements, practical electrolysers are inherently multi-domain systems in which cathode, separator, and anode jointly determine efficiency, stability, and failure modes. The next stage of the proposed roadmap is therefore multi-nodal electrometry: the simultaneous measurement of cathode and anode potentials relative to local reference electrodes, together with separator-associated losses and full-cell voltage. This approach enables real-time partitioning of voltage contributions, revealing where energy is dissipated as operating conditions evolve, and providing a foundation for diagnosing performance bottlenecks across the device.

Building on this enhanced observability, we outline a concept for electrolyser-centric control instrumentation that operates directly in system-relevant modes. Beyond conventional constant-current or constant-voltage control, such platforms should enable constraints aligned with practical operation, including constant-power regulation and adaptive setpoints under changing resistance or mass transport conditions. 

A further enabling component is the integration of bias-under-load, frequency-aware diagnostics into the control framework. By superimposing controlled AC perturbations—including multi-tone signals—onto the DC operating point, it becomes possible to extract impedance-informed signatures in real time during electrolysis. These dynamic measurements allow early detection of evolving transport limitations, interfacial degradation, or separator failure. 

Together, these elements define a pathway toward quantitatively reliable, system-aware electrocatalysis, bridging the gap between laboratory measurements and scalable electrochemical technologies.