Project Publications

As we publish our results, we’ll post the publications here.

You can see our related publications, which inspired FlowPhotoChem here.

Project Publications

  • Timothy Noël (2025). Interaction of light with gas–liquid interfaces: influence on photon absorption in continuous flow photoreactors. Reaction Chemistry & Engineering. DOI: https://doi.org/10.1039/D4RE00540F Download the PDF here.

  • Arnab Chaudhuri, Wouter F.C. de Groot, Jasper H.A. Schuurmans, Stefan D.A. Zondag, Alessia Bianchi, Koen P.L. Kuijpers, Rémy Broersma, Amin Delparish, Matthieu Dorbec, John van der Schaaf, Timothy Noël (2025). Scaling Up Gas–Liquid Photo-Oxidations in Flow Using Rotor-Stator Spinning Disc Reactors and a High-Intensity Light Source. Organic Process Research & Development. DOI: https://doi.org/10.1021/acs.oprd.4c00458 Download the PDF here.

  • Noémi V. Galbicsek, Attila Kormányos, Gergely Ferenc Samu, Mohd M. Ayyub, Tomaž Kotnik, Sebastijan Kovačič, Csaba Janáky, Balázs Endrődi (2024). Comparative Study of Different Polymeric Binders in Electrochemical CO Reduction. Energy & Fuels. DOI: https://doi.org/10.1021/acs.energyfuels.4c04058 Download the PDF here.

Abstract:

Electrochemical reduction of carbon monoxide offers a possible route to produce valuable chemicals (such as acetate, ethanol or ethylene) from CO2 in two consecutive electrochemical reactions. Such deeply reduced products are formed via the transfer of 4–6 electrons per CO molecule. Assuming similar-sized CO2 and CO electrolyzers, 2–3-times larger current densities are required in the latter case to match the molar fluxes. Such high reaction rates can be ensured by tailoring the structure of the gas diffusion electrodes. Here, the structure of the cathode catalyst layer was systematically varied using different polymeric binders to achieve high reaction rates. Simple linear polymers, bearing the same backbone but different functional groups were compared to highlight the role of different structural motifs. The comparison was also extended to simple linear, partially fluorinated polymers. Interestingly, in some cases similar results were obtained as with the current state-of-the-art binders. Using different surface-wetting characterization techniques, we show that the hydrophobicity of the catalyst layer─provided by the binder─ is a prerequisite for high-rate CO electrolysis. The validity of this notion was demonstrated by performing CO electrolysis experiments at high current density (1 A cm–2) for several hours using PVDF as the catalyst binder.

  • Brust, D., Wullenkord, M., Gómez, H. G., Albero, J., & Sattler, C. (2024). Experimental investigation of photo-thermal catalytic reactor for the reverse water gas shift reaction under concentrated irradiationJournal of Environmental Chemical Engineering12(5), 113372. DOI: https://doi.org/10.1016/j.jece.2024.113372 Download the PDF here.

Abstract:

An upscaled photo-thermal catalytic reactor for the heterogeneously catalysed reverse Water Gas Shift (rWGS) reaction is tested under simulated concentrated irradiation. The reactor is equipped with an aperture of 144 cm2 area covered by a quartz window, where it receives irradiation flux densities of up to 80 kW/m2 corresponding to an irradiation power input of 1 kW thereby directly irradiating a RuO2 based photo-thermal catalyst that is deposited on a porous support. The system was operated under simulated concentrated sunlight for a total of 45.5 h with 35.4 h of chemical operation. A peak CO production rate of 1.6 mol/h was achieved with an average light concentration factor of 80 in the centre of the catalyst layer. This corresponds to a solar-to-chemical efficiency – defined by the ratio of the product of molar CO production rate and reaction enthalpy for the rWGS reaction and the irradiation power input – of 1.69 %. A calculation approach to determine the catalyst surface temperature under irradiation was introduced and utilised for performance analysis leading to the discussion of design modifications and operating strategies towards performance enhancement.

  • Mohd Monis Ayyub, Attila Kormányos, Balázs Endrödi, and Csaba Janáky, Electrochemical carbon monoxide reduction at high current density: Cell configuration mattersChemical Engineering Journal, Volume 490, 15 June 2024, 151698, DOI: https://doi.org/10.1016/j.cej.2024.151698. Download the PDF here.

Abstract:

Electrochemical carbon monoxide reduction (COR) is an important link between the electrochemical CO2-to-CO reduction technology and the renewable production of C2+ chemicals. Along with the development of catalyst materials for selective and efficient COR, it is imperative to optimize electrolysis conditions and cell parameters to efficiently reduce CO at industrially relevant current density and produce concentrated product streams. This study focuses on understanding fundamental differences in reaction selectivity during COR, when the same Cu catalyst was used in three different cell configurations, namely, microfluidic, hybrid anode zero-gap, and zero-gap electrolysers. In all cases, ethylene, acetate, ethanol, and propanol formation was confirmed at industrially relevant current densities (0.5–1.2 A cm−2) at reasonable cell voltages, albeit with subtle differences. The local chemical environment at the electrode/electrolyte interface is very different in each configuration leading to different product distribution and product crossover to the anode. This stresses the importance of cell architecture and implies that comparing the catalytic activity of a catalyst studied with different cell configurations can lead to inconsistent conclusions.

  • Annechien A. H. Laporte, Tom M. MassonStefan D. A. Zondag,Prof. Dr. Timothy Noël Multiphasic Continuous-Flow Reactors for Handling Gaseous Reagents in Organic Synthesis: Enhancing Efficiency and Safety in Chemical Processes, Angewandte Chemie International Editione202316108. DOI: https://doi.org/10.1002/anie.202316108 Download the PDF here.

Abstract:

The use of reactive gaseous reagents for the production of active pharmaceutical ingredients (APIs) remains a scientific challenge due to safety and efficiency limitations. The implementation of continuous-flow reactors has resulted in rapid development of gas-handling technology because of several advantages such as increased interfacial area, improved mass- and heat transfer, and seamless scale-up. This technology enables shorter and more atom-economic synthesis routes for the production of pharmaceutical compounds. Herein, we provide an overview of literature from 2016 onwards in the development of gas-handling continuous-flow technology as well as the use of gases in functionalization of APIs.

  • Jasper H. A. SchuurmansTom M. MassonStefan D. A. ZondagProf. Dr. Pascal BuskensProf. Dr. Timothy Noël Solar-Driven Continuous CO2 Reduction to CO and CH4 using Heterogeneous Photothermal Catalysts: Recent Progress and Remaining Challenges, ChemSusChem 2023, e202301405. DOI: https://doi.org/10.1002/cssc.202301405 Download the PDF here.

Abstract:

The urgent need to reduce the carbon dioxide level in the atmosphere and keep the effects of climate change manageable has brought the concept of carbon capture and utilization to the forefront of scientific research. Amongst the promising pathways for this conversion, sunlight-powered photothermal processes, synergistically using both thermal and non-thermal effects of light, have gained significant attention. Research in this field focuses both on the development of catalysts and continuous-flow photoreactors, which offer significant advantages over batch reactors, particularly for scale-up. Here, we focus on sunlight-driven photothermal conversion of CO2 to chemical feedstock CO and CH4 as synthetic fuel. This review provides an overview of the recent progress in the development of photothermal catalysts and continuous-flow photoreactors and outlines the remaining challenges in these areas. Furthermore, it provides insight in additional components required to complete photothermal reaction systems for continuous production (e. g., solar concentrators, sensors and artificial light sources). In addition, our review emphasizes the necessity of integrated collaboration between different research areas, like chemistry, material science, chemical engineering, and optics, to establish optimized systems and reach the full potential of this technology.

  • Andrea SerfőzőGábor András CsíkAttila KormányosÁdám BalogCsaba Janáky and Balázs Endrődi, One-step electrodeposition of binder-containing Cu nanocube catalyst layers for carbon dioxide reduction, Nanoscale (2023), DOI: 10.1039/D3NR03834C. Download the PDF here.

Abstract:

To reach industrially relevant current densities in the electrochemical reduction of carbon dioxide, this process must be performed in continuous-flow electrolyzer cells, applying gas diffusion electrodes. Beyond the chemical composition of the catalyst, both its morphology and the overall structure of the catalyst layer are decisive in terms of reaction rate and product selectivity. We present an electrodeposition method for preparing coherent copper nanocube catalyst layers on hydrophobic carbon paper, hence forming gas diffusion electrodes with high coverage in a single step. This was enabled by the appropriate wetting of the carbon paper (controlled by the composition of the electrodeposition solution) and the use of a custom-designed 3D-printed electrolyzer cell, which allowed the deposition of copper nanocubes selectively on the microporous side of the carbon paper substrate. Furthermore, a polymeric binder (Capstone ST-110) was successfully incorporated into the catalyst layer during electrodeposition. The high electrode coverage and the binder content together result in an increased ethylene production rate during CO2 reduction, compared to catalyst layers prepared from simple aqueous solutions.

  • M. Toufani, H. Besic, W. Tong, P. Farràs, Exploring the role of different morphologies of β-Ni(OH)2 for electrocatalytic urea oxidation and the effects of electrochemically active surface area, Results in Chemistry (2023), DOI: https://doi.org/10.1016/j.rechem.2023.101031 Download the PDF here.

Abstract:

Ni(OH)2, as a multifunctional material, has found its applications in a great number of research areas. In particular, it is an efficient catalyst for urea oxidation reaction (UOR), which is an important alternative for oxygen evolution reaction in electrocatalytic water splitting. This work investigates the effect of materials morphology on the electrocatalytic UOR performance of β-Ni(OH)2, as well as the importance of characterising the catalysts’ surface by electrochemical active surface area. Three different morphologies (nanoflowers, nanocubes, and nanosheets) were prepared via a simple hydrothermal approach. The morphology and structure of the as-prepared samples were carefully examined by scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction. The UOR performance of β−Ni(OH)2 was evaluated by means of cyclic voltammetry, linear sweep voltammetry, Tafel analysis, and electrochemical surface area. Nanosheet Ni(OH)2 electrocatalyst exhibits higher current density responses (28.3 mA cm-2 ECSA at 1.6 V vs. RHE) and a lower slope in the Tafel plot (72.6 mV dec-1). Consequently, due to the exposure of more active sites to the reactants, the Ni(OH)2 electrode with nanosheet morphology displayed higher electrocatalytic performance during UOR compared to the nanoflower and nanocube samples.

  • Yong Peng, Horatiu Szalad, Pavle Nikacevic, Giulio Gorni, Sara Goberna, Laura Simonelli, Josep Albero, Nuria Lopez and Hermenegildo Garcia (2023). Co-doped hydroxyapatite as photothermal catalyst for selective CO2 hydrogenation. Applied Catalysis B: Environmental, 333, 122790. DOI: https://doi.org/10.1016/j.apcatb.2023.122790  Repository link here. Download the PDF here.

Abstract:

The rational design and in deep understanding of efficient, affordable and stable materials to promote the light-assisted production of fuels and commodity chemicals is very appealing for energy crisis and climate change amelioration. Herein, we have prepared a series of Co-doped hydroxyapatite (HAP) catalysts with different Co content. The materials structure has been widely investigated by XRD, FT-IR, HRTEM, XPS, XAS, as well as computational simulations based on Density Functional Theory (DFT) with PBE functional. At low Co loading, there is a partial substitution of Ca cations in the HAP structure, while higher loadings promote the precipitation of small (∼ 2 nm) Co nanoparticles on the HAP surface. For the optimal Co content, a constant CO rate of 62 mmol·g−1·h−1 at 1 sun illumination and 400 °C, with the material being stable for 90 h. Visible and NIR photons have been determined responsible of the light-assisted activity enhanced. Mechanistic studies based on both experimental and DFT simulations show that H2 preferentially adsorbs to metallic Co, while CO2 adsorbs to the HAP surface oxygen. Moreover, both direct photo- and plasmon-driven contributions have been separated in order to study their mechanisms independently.

Graphical Abstract

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Co-doped hydroxyapatite has been demonstrated visible light photo-assisted activity of CO2 hydrogenation to CO. Experimental and computation investigation have confirmed the partial substitution of Ca ions in the hydroxyapatite structure. Mechanistic studies have determined both direct photo- and plasmon-driven catalysis occurs depending on the Co doping level. These materials have been also demonstrated to be very stable under operational conditions.

  • Gumaa A. El-Nagar, Flora Haun, Siddharth Gupta, Sasho Stojkovikj, Matthew T. Mayer, "Unintended cation crossover influences CO2 reduction selectivity in Cu-based zero-gap electrolysers" Nat Commun 14, 2062  (2023). April 12, 2023 DOI: https://doi.org/10.1038/s41467-023-37520-x. Download the PDF here.

Abstract:

Membrane electrode assemblies enable CO2 electrolysis at industrially relevant rates, yet their operational stability is often limited by formation of solid precipitates in the cathode pores, triggered by cation crossover from the anolyte due to imperfect ion exclusion by anion exchange membranes. Here we show that anolyte concentration affects the degree of cation movement through the membranes, and this substantially influences the behaviors of copper catalysts in catholyte-free CO2 electrolysers. Systematic variation of the anolyte (KOH or KHCO3) ionic strength produced a distinct switch in selectivity between either predominantly CO or C2+ products (mainly C2H4) which closely correlated with the quantity of alkali metal cation (K+ ) crossover, suggesting cations play a key role in C-C coupling reaction pathways even in cells without discrete liquid catholytes. Operando X-ray absorption and quasi in situ X-ray photoelectron spectroscopy revealed that the Cu surface speciation showed a strong dependence on the anolyte concentration, wherein dilute anolytes resulted in a mixture of Cu+ and Cu0 surface species, while concentrated anolytes led to exclusively Cu0 under similar testing conditions. These results show that even in catholyte-free cells, cation effects (including unintentional ones) significantly influence reaction pathways, important to consider in future development of catalysts and devices.

Download a PDF of the lay summary here.

Title: Unintended cation crossover influences CO2 reduction selectivity in Cu-based zero-gap electrolysers

Authors of summary and organization: Matthew Mayer, Helmholtz-Zentrum Berlin

Aims

We aimed to understand the origins of cell performance degradation which is caused by salt precipitate formation in membrane-electrode assemblies for CO2 conversion. We hypothesized that decreasing the electrolyte concentration would decrease the movement of cations through the membrane which contributes to this degradation.

Why is this important?

The influence of electrolyte cations on electrochemical reactions is well studied in laboratory scale experiments, but questions remain about how cations impact the behaviors of industrially relevant device configurations. This represents a knowledge gap between fundamental and applied research. Understanding cation effects in membrane-electrode assembly devices is critical for advancing the technology of CO2 conversion in practical devices.

What methods were used?

Gas diffusion electrodes with copper catalysts were studied in a membrane-electrode assembly cell using anion exchange membranes. Their electrochemical CO2 conversion activities were tested using a range of electrolyte concentrations. Gas chromatography was used to determine the production of various products.

What was learned?

We observed that the distribution of major products of CO2 conversion was strongly dependent on the electrolyte concentration, and this correlated with the amount of undesired cation crossover through the membrane. High concentrations gave lots of crossover and resulted in production of C2+ products like ethylene, whereas low concentrations exhibited minimal crossover and produced predominantly carbon monoxide. Thus, even in the absence of electrolyte at the cathode, CO2 electrolyzer performance is highly dependent on the presence or absence of electrolyte ions passing through the membrane.

How could this research benefit citizens, society and other researchers?

These findings show researchers in this field that the electrolyte concentrations most often used do not lead to effective ion exclusion by ion exchange membranes, and that lower concentrations can result in drastically different electrode behaviors. This new insight will help further the development of electrochemical approaches to CO2 conversion as a route toward a carbon-neutral society.

Link to full paper/abstract https://www.nature.com/articles/s41467-023-37520-x

  • Isaac Holmes-Gentle, Saurabh Tembhurne, Clemens Suter, Sophia Haussener, "Kilowatt-scale solar hydrogen production system using a concentrated integrated photoelectrochemical device"Nat Energy (2023). April 10, 2023 DOI: https://doi.org/10.1038/s41560-023-01247-2. Download the PDF here.

Abstract:

The production of synthetic fuels and chemicals from solar energy and abundant reagents offers a promising pathway to a sustainable fuel economy and chemical industry. For the production of hydrogen, photoelectrochemical or integrated photovoltaic and electrolysis devices have demonstrated outstanding performance at the lab scale, but there remains a lack of larger-scale on-sun demonstrations (>100 W). Here we present the successful scaling of a thermally integrated photoelectrochemical device—utilizing concentrated solar irradiation—to a kW-scale pilot plant capable of co-generation of hydrogen and heat. A solar-to-hydrogen device-level efficiency of greater than 20% at an H2 production rate of >2.0 kW (>0.8 g min−1) is achieved. A validated model-based optimization highlights the dominant energetic losses and predicts straightforward strategies to improve the system-level efficiency of >5.5% towards the device-level efficiency. We identify solutions to the key technological challenges, control and operation strategies and discuss the future outlook of this emerging technology.

Download a PDF of the lay summary here.

Title: Kilowatt-scale solar hydrogen production system using a concentrated integrated photoelectrochemical device

Authors of summary and organization: Isaac Holmes-Gentle, Sophia Haussener, EPFL

Aims

This study aims to demonstrate the potential of a thermally- integrated photoelectrochemical device at scale which utilizes solar concentration to produce hydrogen, oxygen and heat. Notably, this work demonstrates this technology at the kilowatt scale whilst achieving a high device-level solar-to-hydrogen efficiency.

Why is this important?

Hydrogen is an important industrial chemical feedstock and energy vector. Current production of hydrogen is dominated by carbon- intensive methane reforming (often referred to as “grey hydrogen”) and it is essential that we move towards CO2-free hydrogen production (“green hydrogen”). Solar energy is a large and sustainable resource and therefore solar energy-derived fuels and chemicals are particularly attractive. In order to develop solar fuel technologies, it is important to move from lab-scale research to pilot-scale demonstrators, such as described in this study.

What methods were used?

A pilot-scale system was developed and constructed on EPFL campus and comprised of a 7 m-diameter solar parabolic dish, an integrated photo-electrochemical reactor placed in the focal point of the dish and various auxiliary components such as pumps and heat exchangers. An experimental campaign was conducted over a number of days under a variety of meteorological conditions.

What was learned?

The pilot plant achieved performed well in a number of metrics over the experimental campaign – 20.3% device-level solar-to-fuel efficiency, 5.5% system-level solar-to-fuel efficiency and 35.3% system-level thermal efficiency where the Gibbs free energy is used to calculate solar-to-fuel efficiencies. We investigated various control strategies for the operation of the solar dish and discovered that water flowrate control was a promising method for stabilising water temperatures under varying solar irradiance. We also overcame a number of design challenges in the integration and construction of the reactor unit.

How could this research benefit citizens, society and other researchers?

This pilot-scale demonstrator presents a scalable approach to high performance thermally integrated photovoltaic-electrolysis system as a pathway to a more sustainable future.

Link to full paper/abstract https://www.nature.com/articles/s41560-023-01247-2

  • Attila Kormányos, Balázs Endrődia, Zheng Zhanga, Angelika Samua, László Méraia, Gergely F. Samua, László Janováka, and Csaba Janáky, "Local hydrophobicity allows high-performance electrochemical carbon monoxide reduction to C2+ products" EES. Catal., 2023, March 13, 2023, DOI: https://doi.org/10.1039/D3EY00006K  Download the PDF here.

Abstract:

While CO can already be produced at industrially relevant current densities via CO2 electrolysis, the selective formation of C2+ products seems challenging. CO electrolysis, in principle, can overcome this barrier, hence forming valuable chemicals from CO2 in two steps. Here we demonstrate that a mass-produced, commercially available polymeric pore sealer can be used as a catalyst binder, ensuring high rate and selective CO reduction. We achieved above 70% Faradaic efficiency for C2+ products formation at j = 500 mA cm−2 current density. As no specific interaction between the polymer and the CO reactant was found, we attribute the stable and selective operation of the electrolyzer cell to the controlled wetting of the catalyst layer due to the homogeneous polymer coating on the catalyst particles’ surface. These results indicate that sophistically designed surface modifiers are not necessarily required for CO electrolysis; hence the capital costs can be significantly decreased.

  • Yong Peng, Josep Albero, Antonio Franconetti, Patricia Concepción and Hermenegildo García, "Visible and NIR Light Assistance of the N2 Reduction to NH3 Catalyzed by Cs-promoted Ru Nanoparticles Supported on Strontium Titanate" ACS Catal. 2022, 12, 9, 4938–4946, April 12, 2022, DOI: https://doi.org/10.1021/acscatal.2c00509  Download the PDF here.

Abstract:

NH3 production accounts for more than 1% of the total CO2 emissions and is considered one of the most energy-intensive industrial processes currently (T > 400 °C and P > 80 bars). The development of atmospheric-pressure N2 fixation to NH3 under mild conditions is attracting much attention, especially using additional renewable energy sources. Herein, efficient photothermal NH3 evolution in continuous flow upon visible and NIR light irradiation at near 1 Sun power using Cs-decorated strontium titanate-supported Ru nanoparticles is reported. Notably, for the optimal photocatalytic composition, a constant NH3 rate near 3500 μmolNH3 gcatalyst–1 h–1 was achieved for 120 h reactions, being among the highest values reported at atmospheric pressure under 1 Sun irradiation.

  • Gumaa A. El-Nagar, Fan YangSasho StojkovikjStefan Mebs, Siddharth Gupta, Ibbi Y. Ahmet, Holger Dau, and Matthew T. Mayer, "Comparative Spectroscopic Study Revealing Why the CO2 Electroreduction Selectivity Switches from CO to HCOO at Cu–Sn- and Cu–In-Based Catalysts" ACS Catal.2022, 12, XXX, 15576–15589 5 December 2022 DOI: https://doi.org/10.1021/acscatal.2c04419 Download the PDF here.

Abstract:

To address the challenge of selectivity toward single products in Cu-catalyzed electrochemical CO2 reduction, one strategy is to incorporate a second metal with the goal of tuning catalytic activity via synergy effects. In particular, catalysts based on Cu modified with post-transition metals (Sn or In) are known to reduce CO2 selectively to either CO or HCOO depending on their composition. However, it remains unclear exactly which factors induce this switch in reaction pathways and whether these two related bimetal combinations follow similar general structure–activity trends. To investigate these questions systematically, Cu–In and Cu–Sn bimetallic catalysts were synthesized across a range of composition ratios and studied in detail. Compositional and morphological control was achieved via a simple electrochemical synthesis approach. A combination of operando and quasi-in situ spectroscopic techniques, including X-ray photoelectron, X-ray absorption, and Raman spectroscopy, was used to observe the dynamic behaviors of the catalysts’ surface structure, composition, speciation, and local environment during CO2 electrolysis. The two systems exhibited similar selectivity dependency on their surface composition. Cu-rich catalysts produce mainly CO, while Cu-poor catalysts were found to mainly produce HCOO. Despite these similarities, the speciation of Sn and In at the surface differed from each other and was found to be strongly dependent on the applied potential and the catalyst composition. For Cu-rich compositions optimized for CO production (Cu85In15 and Cu85Sn15), indium was present predominantly in the reduced metallic form (In0), whereas tin mainly existed as an oxidized species (Sn2/4+). Meanwhile, for the HCOO-selective compositions (Cu25In75 and Cu40Sn60), the indium exclusively exhibited In0 regardless of the applied potential, while the tin was reduced to metallic (Sn0) only at the most negative applied potential, which corresponds to the best HCOO selectivity. Furthermore, while Cu40Sn60 enhances HCOO selectivity by inhibiting H2 evolution, Cu25In75 improves the HCOO selectivity at the expense of CO production. Due to these differences, we contend that identical mechanisms cannot be used to explain the behavior of these two bimetallic systems (Cu–In and Cu–Sn). Operando surface-enhanced Raman spectroscopy measurements provide direct evidence of the local alkalization and its impact on the dynamic transformation of oxidized Cu surface species (Cu2O/CuO) into a mixture of Cu(OH)2 and basic Cu carbonates [Cux(OH)y(CO3)y] rather than metallic Cu under CO2 electrolysis. This study provides unique insights into the origin of the switch in selectivity between CO and HCOO pathways at Cu bimetallic catalysts and the nature of surface-active sites and key intermediates for both pathways.

Download a PDF of the lay summary here.

Title: Comparative Spectroscopic Study Revealing Why the CO2 Electroreduction Selectivity Switches from CO to HCOOat CuSn- and Cu–In-Based Catalysts.

Author of summary and organization:

Gumaa A. El-Nagar

Young Investigator Group Electrochemical Conversion of CO2, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, Berlin 14109, Germany

Aims

To investigate the selectivity change from CO to HCOO- on increasing the In/Sn content in the Cu-M bimetallic system. We also study whether these two related bimetal combinations follow similar general structure–activity trends.

Why is this important?

It provides a novel understanding of what factors affect the selectivity of bimetallic catalyst system helping to design more selective catalysts for future applications.

What methods were used?

Product Analysis: GC-Headspace; HPLC
Material characterisation: SEM, In-situ Raman, XRD, Quasi In-situ XPS, In-situ XAS
Catalyst synthesis: Dynamic Hydrogen Bubble Technique, Electrodeposition

What was learned?

Cu rich systems produce CO predominantly whereas Cu poor system produce HCOO-.
Whilst both the Cu rich systems gave similar selectivity the surface speciation was different for both the bimetallic systems.

Therefore, identical mechanisms can’t be used to explain the behaviour of these two bimetallic systems.

How could this research benefit citizens, society and other researchers?

CO2 conversion is an essential step in closing the anthropogenic carbon cycle. The main challenges affecting electrochemical CO2 conversion are product selectivity and production rates. This research sheds new light on product selectivity mechanisms across different bimetallic systems.

Link to full paper/abstract https://pubs.acs.org/doi/full/10.1021/acscatal.2c04419

  • Tom M. Masson, Stefan D. A. Zondag, Michael G. Debije, and Timothy Noël, "Rapid and Replaceable Luminescent Coating for Silicon-Based Microreactors Enabling Energy-Efficient Solar Photochemistry" ACS Sustainable Chem. Eng. 2022, XXXX, XXX, XXX-XXX, 4 August 2022 DOI: https://doi.org/10.1021/acssuschemeng.2c03390 Download the PDF here.

Abstract:

The sun is the most sustainable source of photons on the earth but is rarely used in photochemical transformations due to its relatively low and variable intensity, broad wavelength range, and lack of focus. Luminescent solar concentrator-based photomicroreactors (LSC-PMs) can be an answer to all these issues, but widespread adoption is plagued by challenges associated with their complicated manufacturing. Herein, we developed a new strategy to accelerate and ease the production of LSC-PMs by depositing a thin luminescent film on commercially and widely available silicon-based microreactors. The protocol is fast and operationally simple, and the luminescent coating can be easily removed and replaced. This enables rapid tuning of the luminescent coating to fit the requirements of the photocatalytic system and to increase the photon flux inside the microreactor channels.

    • Etienne BoutinMahendra PatelEgon KecsenovitySilvan SuterCsaba Janáky, and Sophia Haussener, "Photo-Electrochemical Conversion of CO2 Under Concentrated Sunlight Enables Combination of High Reaction Rate and Efficiency". Advanced Energy Materials, 15 June 2022 DOI: https://doi.org/10.1002/aenm.202200585 Download the PDF here.

    Abstract:

    Photo-electrochemical production of solar fuels from carbon dioxide, water, and sunlight is an appealing approach. Nevertheless, it remains challenging to scale despite encouraging demonstrations at low power input. Higher current densities require notable voltage input as ohmic losses and activation overpotentials become more significant, resulting in lower solar-to-CO conversion efficiencies. A concentrated photovoltaic cell is integrated into a custom-made heat managed photo-electrochemical device. The heat is transferred from the photovoltaic module to the zero-gap electrolyzer cell by the stream of anodic reactant and produce synergetic effects on both sides. With solar concentrations up to 450 suns (i.e., 450 kW m−2) applied for the first time to photo-electrochemical reduction of CO2, a partial current for CO production of 4 A is achieved. At optimal conditions, the solar-to-CO conversion efficiency reaches 17% while maintaining a current density of 150 mA cm−2 in the electrolyzer and a CO selectivity above 90%, representing an overall 19% solar-to-fuel conversion efficiency. This study represents a first demonstration of photo-electrochemical CO2 reduction under highly concentrated light, paving the way for resource efficient solar fuel production at high power input.

    Download a PDF of the lay summary here.

    Title: Concentrating sunlight to store energy efficiently while recycling CO2.

    Authors of summary and organizations: Etienne Boutin, Mahendra Patel, Egon Kecsenovity, Silvan Suter, Csaba Janáky, and Sophia Haussener,
    Ecole Polytechnique Fédérale de Lausanne and University of Szeged

    Aims

    In this paper, we demonstrate that concentrated sunlight can power a CO2 photo-electrolyzer, a device that stores solar energy by converting CO2 into fuels.

    Why is this important?

    This study is the first report of concentrated sunlight usage for the photo-electrochemical reduction of CO2. It shows that high efficiency can be maintained in compact, high power density devices.

    What methods were used?

    In this study, we used concentrated sunlight to increase the efficiency and the surface footprint of a photovoltaic (PV) absorber. This PV was powering a CO2 electrolyzer that was taking advantage of the excess heat produced on the PV to enhance the efficiency.

    What was learned?

    We learned and demonstrated that increased power density was not necessarily associated with lower energy conversion efficiency. We also learned that concentrated sunlight is a promising strategy to decrease material costs associated with CO2 electrolysis.

    How could this research benefit citizens, society and other researchers?

    This study constitutes a new milestone on the way towards solar-to-molecule conversion at a relevant industrial scale. Such a technology aims at supporting the deployment of renewable energies by storing peak energy into fuel or other platform chemicals.

    Link to full paper/abstract https://onlinelibrary.wiley.com/doi/10.1002/aenm.202200585

    • Arnab ChaudhuriStefan D. A. ZondagJasper H. A. SchuurmansJohn van der Schaaf, and Timothy Noël, "Scale-Up of a Heterogeneous Photocatalytic Degradation Using a Photochemical Rotor–Stator Spinning Disk Reactor". Organic Process Research & Development Article ASAP DOI: 10.1021/acs.oprd.2c00012 Download the PDF here.

    Abstract:

    Many chemical reactions contain heterogeneous reagents, products, byproducts, or catalysts, making their transposition from batch to continuous-flow processing challenging. Herein, we report the use of a photochemical rotor–stator spinning disk reactor (pRS-SDR) that can handle and scale solid-containing photochemical reaction conditions in flow. Its ability to handle slurries was showcased for the TiO2-mediated aerobic photodegradation of aqueous methylene blue. The use of a fast rotating disk imposes high shear forces on the multiphase reaction mixture, ensuring its homogenization, increasing the mass transfer, and improving the irradiation profile of the reaction mixture. The pRS-SDR performance was also compared to other lab-scale reactors in terms of water treated per reactor volume and light power input.

    Download a PDF of the lay summary here.

    Title
    Scale-Up of a Heterogeneous Photocatalytic Degradation Using a Photochemical Rotor-Stator Spinning Disk Reactor

    Author of summary and organization  Stefan D. A. Zondag, Universiteit van Amsterdam

    Aims
    The aim of this research is to expand the possibilities of continuous-flow photochemistry. Currently, large-scale and solid-containing (heterogeneous) photochemistry is underrepresented in this field because of the associated complications in processing. The goal is to enable this type of chemistry at larger scale, tackling both the current scale-up and solids-handling issues encountered in this field.

    Why is this important?
    The use of solid catalysts in flow chemistry is plagued by clogging and poor mixing, resulting in limited reported applications and inhibiting large-scale incorporation. This causes researchers to investigate alternatives without solids. Apart from the time and effort this requires, this introduces more complex and costly separation methods in comparison to the easy separation of solids from liquids by filtration.

    What methods were used?
    A custom reactor is used to demonstrate solid-containing photochemical wastewater purification. This purification uses a non-toxic solid catalyst, air or oxygen and wastewater. The reactor contains a window to allow light to shine into the system. A fast rotating disk inside the reactor ensures that the solids are efficiently mixed with the wastewater and gas in such a way that they cannot settle and clog the reactor.

    What was learned?
    The custom reactor, called the “photochemical rotor-stator spinning disk reactor”, enabled the continuous processing of the complex solid-liquid-gas mixture. This was achieved by the efficient mixing provided by the rotating disk, effectively preventing clogging of the reactor at all tried conditions. This design provides a basis for process intensification for this type of photochemical transformation.

    How could this research benefit citizens, society and other researchers?
    Continuous processing in photochemistry is regarded as a relatively new and sustainable development. This field can contribute greatly to pharmaceutical and industrial chemistry, both in reducing energy consumption due to the mild reaction conditions and reduction of generated waste. However, the issues associated with scaling up and solids handling inhibit widespread application. This research contributes to bridging the gap of lab-scale to large-scale, bringing us closer to more sustainable process intensification in the future of the field.

    Link to full paper/abstract https://doi.org/10.1021/acs.oprd.2c00012

    • Laura C. Pardo Pérez, Alexander Arndt, Sasho Stojkovikj, Ibbi Y. Ahmet, Joshua T. Arens, Federico Dattila, Robert Wendt, Ana Guilherme Buzanich, Martin Radtke, Veronica Davies, Katja Höflich, Eike Köhnen, Philipp Tockhorn, Ronny Golnak, Jie Xiao, Götz Schuck, Markus Wollgarten, Núria López, Matthew T. Mayer, "Determining Structure-Activity Relationships in Oxide Derived CuSn Catalysts During CO2 Electroreduction Using X-Ray Spectroscopy". Adv. Energy Mater. 2103328 (2021) DOI: 10.1002/aenm.202103328. Download the PDF here.

    Abstract:

    The development of earth-abundant catalysts for selective electrochemical CO2 conversion is a central challenge. CuSn bimetallic catalysts can yield selective CO2 reduction toward either CO or formate. This study presents oxide-derived CuSn catalysts tunable for either product and seeks to under-stand the synergetic effects between Cu and Sn causing these selectivity trends. The materials undergo significant transformations under CO2 reduction conditions, and their dynamic bulk and surface structures are revealed by correlating observations from multiple methods—X-ray absorption spectroscopy for in situ study, and quasi in situ X-ray photoelectron spectroscopy for surface sensitivity. For both types of catalysts, Cu transforms to metallic Cu0under reaction conditions. However, the Sn speciation and content differ significantly between the catalyst types: the CO-selective catalysts exhibit a surface Sn content of 13 at. % predominantly present as oxidized Sn, while the formate-selective catalysts display an Sn content of 70 at. % consisting of both metallic Sn0 and Sn oxide species. Density functional theory simulations suggest that Snδ+ sites weaken CO adsorption, thereby enhancing CO selectivity, while Sn0 sites hinder H adsorption and promote formate production. This study reveals the complex dependence of catalyst structure, composition, and speciation with electrochemical bias in bimetallic Cu catalysts.

    • , "Fe clusters embedded on N-doped graphene as a photothermal catalyst for selective CO2 hydrogenation". Chemical Communications, 57, 10075-10078 (2021) DOI: https://doi.org/10.1039/D1CC03524J. Download the PDF here.

    Abstract:

    In comparison with the Co analog, small Fe clusters incorporated in a graphene matrix exhibit a photo-assisted increase of 110% in reverse water gas shift CO2 hydrogenation under UV-Vis light irradiation. Available data indicate that the photo-assistance derives from light absorption by the N-doped graphene followed by charge recombination at the Fe clusters, increasing their local temperature.

    • Ádám Vass, Attila Kormányos, Zsófia Kószó, Balázs Endrődi, and Csaba Janáky, "Anode Catalysts in CO2 Electrolysis: Challenges and Untapped Opportunities". ACS Catal. 2022, 12, XXX, 1037–1051 (2022). DOI: https://doi.org/10.1021/acscatal.1c04978. Download the PDF here.

    Abstract:

    The field of electrochemical carbon dioxide reduction has developed rapidly during recent years. At the same time, the role of the anodic half-reaction has received considerably less attention. In this Perspective, we scrutinize the reports on the best-performing CO2 electrolyzer cells from the past 5 years, to shed light on the role of the anodic oxygen evolution catalyst. We analyze how different cell architectures provide different local chemical environments at the anode surface, which in turn determines the pool of applicable anode catalysts. We uncover the factors that led to either a strikingly high current density operation or an exceptionally long lifetime. On the basis of our analysis, we provide a set of criteria that have to be fulfilled by an anode catalyst to achieve high performance. Finally, we provide an outlook on using alternative anode reactions (alcohol oxidation is discussed as an example), resulting in high-value products and higher energy efficiency for the overall process.

    • Gergely F. Samu and Csaba Janáky, "Photocorrosion at Irradiated Perovskite/Electrolyte Interfaces". J. Am. Chem. Soc., 142, 52, 21595–21614 (2020). DOI: https://doi.org/10.1021/jacs.0c10348. Download the PDF here.

    Abstract:

    Metal−halide perovskites transformed optoelectronics research and development during the past decade. They have also gained a foothold in photocatalytic and photoelectrochemical processes recently, but their sensitivity to the most commonly applied solvents and electrolytes together with their susceptibility to photocorrosion hinders such applications. Understanding the elementary steps of photocorrosion of these materials can aid the endeavor of realizing stable devices. In this Perspective, we discuss both thermodynamic and kinetic aspects of photocorrosion processes occurring at the interface of perovskite photocatalysts and photoelectrodes with different electrolytes. We show how combined in situ and operando electrochemical techniques can reveal the underlying mechanisms. Finally, we also discuss emerging strategies to mitigate photocorrosion (such as surface protection, materials and electrolyte engineering, etc.).

    • Ádám Vass, Balázs Endrődi, Gergely Ferenc Samu, Ádám Balog, Attila Kormányos, Serhiy Cherevko, and Csaba Janáky, "Local Chemical Environment Governs Anode Processes in CO2 Electrolyzers." ACS Energy Lett. 2021, 6, XXX, 3801–3808, DOI: https://doi.org/10.1021/acsenergylett.1c01937
      Download the PDF here.

    Abstract:

    A major goal within the CO2 electrolysis community is to replace the generally used Ir anode catalyst with a more abundant material, which is stable and active for water oxidation under process conditions. Ni is widely applied in alkaline water electrolysis, and it has been considered as a potential anode catalyst in CO2 electrolysis. Here we compare the operation of electrolyzer cells with Ir and Ni anodes and demonstrate that, while Ir is stable under process conditions, the degradation of Ni leads to a rapid cell failure. This is caused by two parallel mechanisms: (i) a pH decrease of the anolyte to a near neutral value and (ii) the local chemical environment developing at the anode (i.e., high carbonate concentration). The latter is detrimental for zero-gap electrolyzer cells only, but the first mechanism is universal, occurring in any kind of CO2 electrolyzer after prolonged operation with recirculated anolyte.

    • Tom M. Masson, Stefan D. A. Zondag,  Michael G. Debije, Timothy Noel, "The development of luminescent solar concentrator-based photomicroreactors: a cheap reactor enabling efficient solar-powered photochemistry". Photochem Photobiol Sci (2021). DOI: https://doi.org/10.1007/s43630-021-00130-x. Download the PDF here.

    Abstract:

    Sunlight strikes our planet every day with more energy than we consume in an entire year. Therefore, many researchers have explored ways to efficiently harvest and use sunlight energy for the activation of organic molecules. However, implementation of this energy source in the large-scale production of fine chemicals has been mostly neglected. The use of solar energy for chemical transformations suffers from potential drawbacks including scattering, reflections, cloud shading and poor matches between the solar emission and absorption characteristics of the photochemical reaction. In this account, we provide an overview of our efforts to overcome these issues through the development of Luminescent Solar Concentrator-based PhotoMicroreactors (LSC-PM). Such reactors can efficiently convert solar energy with a broad spectral distribution to concentrated and wavelength-shifted irradiation which matches the absorption maximum of the photocatalyst. Hence, the use of these conceptually new photomicroreactors provides an increased solar light harvesting capacity, enabling efficient solar-powered photochemistry.

    • Tom M. Masson, Stefan D. A. Zondag, Koen P. L. Kuijpers, Dario Cambié, Michael G. Debije, Timothy Noel, "Development of an off-grid solar-powered autonomous chemical mini-plant for producing fine chemicals." ChemSusChem 10.1002/cssc.202102011, DOI: https://doi.org/10.1002/cssc.202102011
      Download the PDF here.

    Abstract:

    Photochemistry using inexhaustible solar energy is an eco-friendly way to produce fine chemicals outside the typical laboratory or chemical plant environment. However, variations in solar irradiation conditions and the need for an external energy source to power electronic components limits the accessibility of this approach. In this work, a chemical solar-driven “mini-plant” centered around a scaled-up luminescent solar concentrator photomicroreactor (LSC-PM) was built. To account for the variations in solar irradiance at ground level and passing clouds, we designed a responsive control system that rapidly adapts the flow rate of the reagents to the light received by the reaction channels. Supplying the plant with solar panels, integrated into the module by placing it behind the LSC to utilize the transmitted fraction of the solar irradiation, allows this setup to be self-sufficient and fully operational off-grid. Such a system can shine in isolated environments and in a distributed manufacturing world, allowing to decentralize the production of fine chemicals.

    • Laura Buglioni, Fabian Raymenants, Aidan Slattery, Stefan D. A. Zondag, and Timothy Noël, "Technological Innovations in Photochemistry for Organic Synthesis: Flow Chemistry, High-Throughput Experimentation, Scale-up, and Photoelectrochemistry." Chem. Rev. 2021,  XXXX, XXX, XXX-XXX, DOI: https://doi.org/10.1021/acs.chemrev.1c00332
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    Abstract: Photoinduced chemical transformations have received in recent years a tremendous amount of attention, providing a plethora of opportunities to synthetic organic chemists. However, performing a photochemical transformation can be quite a challenge because of various issues related to the delivery of photons. These challenges have barred the widespread adoption of photochemical steps in the chemical industry. However, in the past decade, several technological innovations have led to more reproducible, selective, and scalable photoinduced reactions. Herein, we provide a comprehensive overview of these exciting technological advances, including flow chemistry, high-throughput experimentation, reactor design and scale-up, and the combination of photo- and electro-chemistry.

    • Larissa O. Paulista, Josep Albero, Ramiro J.E. Martins, Rui A. R. Boaventura, Vitor J. P. Vilar, Tania F. C. V. Silva and Hermenegildo Garcia, "Turning Carbon Dioxide and Ethane into Ethanol by Solar-Driven Heterogeneous Photocatalysis over RuO2– and NiO-co-Doped SrTiO3." Catalysts 2021, 11(4), 461 DOI: https://doi.org/10.3390/catal11040461
      Download the pdf here.

    Abstract: The current work focused on the sunlight-driven thermo-photocatalytic reduction of carbon dioxide (CO2 ), the primary greenhouse gas, by ethane (C2H6), the second most abundant element in shale gas, aiming at the generation of ethanol (EtOH), a renewable fuel. To promote this process, a hybrid catalyst was prepared and properly characterized, comprising of strontium titanate (SrTiO3 ) co-doped with ruthenium oxide (RuO2 ) and nickel oxide (NiO). The photocatalytic activity towards EtOH production was assessed in batch-mode and at gas-phase, under the influence of different conditions: (i) dopant loading; (ii) temperature; (iii) optical radiation wavelength; (vi) consecutive uses; and (v) electron scavenger addition. From the results here obtained, it was found that: (i) the functionalization of the SrTiO3 with RuO2 and NiO allows the visible light harvest and narrows the band gap energy (ca. 14–20%); (ii) the selectivity towards EtOH depends on the presence of Ni and irradiation; (iii) the catalyst photoresponse is mainly due to the visible photons; (iv) the photocatalyst loses > 50% efficiency right after the 2nd use; (v) the reaction mechanism is based on the photogenerated electron-hole pair charge separation; and (vi) a maximum yield of 64 µmol EtOH gcat −1 was obtained after 45-min (85 µmol EtOH gcat −1 h −1 ) of simulated solar irradiation (1000 W m−2 ) at 200 ◦C, using 0.4 g L−1 of SrTiO3:RuO2:NiO (0.8 wt.% Ru) with [CO2 ]:[C2H6 ] and [Ru]:[Ni] molar ratios of 1:3 and 1:1, respectively. Notwithstanding, despite its exploratory nature, this study offers an alternative route to solar fuels’ synthesis from the underutilized C2H6 and CO2.