Current and Future Catalytic Interfaces for Electrochemical CO2 Reduction/Trendbericht Physikalische Chemie (2/3)

Dem Ursprung des Lebens nähern sich Forschende aus zwei Richtungen: von der frühen Erde zu den ersten Biomolekülen und von heute zum Genom alter Organismen. CO₂ lässt sich elektrochemisch reduzieren; damit sich das lohnt, müssen Katalysatormaterialien Moleküle mit mindestens zwei Kohlenstoffatomen bilden. Für die elektrokatalytischen Grenzflächen gibt es nun neue additive Fertigungsverfahren. Um Infrarotspektren von Molekülen vollständig zu simulieren, braucht es viel Rechenkapazität – daher gibt es Kniffe, die sogar IR-Signaturen von Proteinen zuverlässig simulierbar machen könnten.

Current and Future Catalytic Interfaces for Electrochemical CO₂ Reduction

Without active reduction of atmospheric CO₂ levels the global effects of climate change are impossible to mitigate. Electrochemical CO₂ reduction is among the most efficient ways to tackle this challenge, but it requires catalytic materials capable of generating valuable chemicals (hydrocarbons, alcohols) with chains of two or more carbon atoms to reach economic viability. Efficient, selective and high-throughput electrocatalytic materials are urgently needed to meet this goal. We describe here the essential variables for catalyst design – specifically, chemical composition, electronic properties, and geometric confinement between individual catalytic components – in light of recent opportunities offered by new bottom-up additive manufacturing techniques to fabricate new electrocatalytic interfaces.

A growing demand for CO₂ recycling

The urgent need to mitigate global climate change caused by anthropogenic carbon dioxide accumulation in the Earth‘s atmosphere requires the development of technologies capable of reducing CO₂ levels. Current climate models indicate that merely reducing CO₂ emissions is insufficient, highlighting the necessity of active carbon dioxide removal strategies. Electrochemical CO₂ reduction (CO₂RR) is a promising approach to addressing this challenge by converting waste CO₂ into valuable chemicals. In this process, electrical energy – ideally sourced from renewable sources – drives the transformation of thermodynamically stable carbon dioxide into hydrocarbons, alcohols, and other useful compounds that can be utilized in the chemical industry, transportation, and energy sectors. For CO₂RR to become economically viable, electrocatalytic interfaces must exhibit high efficiency, stability, and selectivity toward desired products. Here, we present several key factors influencing CO₂RR catalyst design and outline potential future directions for catalyst design using advanced additive manufacturing methods.

Metallic CO₂RR electrocatalysts

Electrochemical CO₂RR research started in the 1950s with mercury-based cathodes producing formic acid, setting the stage for further research into metallic catalysts.¹⁾ More recent studies have highlighted that noble metals such as Ag and Au can convert CO₂ to CO with high faradaic efficiencies.²⁾ These metals adsorb and activate CO₂ at the surface, but high costs make their perspectives for industrial applications in CO₂RR less favourable. Alternatively, Zn has emerged as a cost-effective option for CO₂ to CO conversion. The ability of metals to catalyze CO₂ reduction is governed by their interaction with reaction intermediates, which depends on their electronic structure and how the surface atoms are arranged. Metals with weak CO₂ binding affinity (Au, Ag) adsorb reaction intermediates sufficiently to produce CO but not enough to reduce them further and form longer carbon chains. Thus, they are recognized as selective catalysts for CO production. Transition metals can vary in selectivity: some (like Sn and Pb) stabilize *OCHO and produce formates³⁾, while others (such as Cu) retain *CO leading to hydrocarbons. Differences in the adsorption and desorption of *CO₂ and *CO on various metals determine at what stage the reaction stops and which product is produced.

Among the various metallic catalysts, copper stands out due to its ability to convert CO₂ to a wide range of products, from single-carbon products like CO and CH₄, to higher-value C₂₊ hydrocarbons and alcohols.

Unique among metals, copper can catalyze C–C coupling at reasonable rates due to its optimal *CO binding energy. Techno-economic analyses suggest that C₂₊ products are more attractive due to their higher costs and overall larger market size compared to C₁ products.⁴⁾ However, copper‘s efficiency in CO₂RR is limited by its unselective nature, often resulting in up to 16 different by-products.

Bimetallic Cu-based catalysts

The search for improved CO₂RR catalytic systems has led to interest in bimetallic catalysts that utilize the unique properties of copper in a tandem with another metal to enhance catalytic performance. One promising approach is to combine copper with Pd, Au, Ag, or Zn. Since these metals efficiently reduce CO₂ into CO, while copper converts CO into higher-value C₂₊ products, a bimetallic interface between them should, in principle, perform better than each of the metals alone. The reasons for this improvement include electronic and proximity (so-called “spillover”) effects.

Leveraging electronic effects

Alloying Cu with a second metal reorganizes the catalyst’s electronic structure, which can alter the binding energies of intermediates on the catalyst surface. When two metals form an alloy or share an interface at the atomic level, electrons redistribute due to the differences in electronegativity and electronic structure of the crystal. This shifts the d-band center or adsorption energetics of surface atoms, thereby tuning the catalytic behaviour.⁵⁾ In simple terms, the presence of a second metal can either donate electron density to Cu or withdraw it, and each scenario has predictable effects on reaction intermediates.⁶⁾

For example, Pd is more electronegative and has a high affinity for hydrogen; when alloyed with Cu, Pd partly donates its electron density.⁷⁾ Density functional theory (DFT) calculations have shown that in a Cu–Pd alloy, charge transfer from Pd to Cu leads to a downward shift in Cu’s d-band center, resulting in weaker binding of CO on the CuPd surface compared to pure Cu. This electronic modification has a profound impact on selectivity. Weaker CO adsorption means that once CO is formed, it is less likely to remain and become protonated on the surface; instead, it desorbs more readily. Experimental studies confirm that Cu–Pd catalysts typically favour CO as the final product and suppress hydrocarbon formation,⁸⁾ reducing the conversion of CO to CH₄ or CH₃CH₂OH.

Taking advantage of catalyst geometry

Geometric confinement refers to physical structures, such as nanopores, trenches, or layered catalyst architectures, that restrict the local reaction volume. This can raise the local pH and retain key intermediates (like *CO) near the surface, promoting C–C coupling. Recent studies systematically varied the shape and size of confined spaces on a Cu catalyst and found that this steers the reaction towards different products. Notably, methane and ethanol selectivities were sensitive to the shape (degree of enclosure) of the confined pocket, while ethylene generation depended predominantly on the dimensions (size) of the confinement.⁹⁾ This suggests that a narrowly confined cavity favours pathways to C₂H₄, likely by keeping *CO and *CH_x intermediates close, whereas more open shapes allow pathways to CH₄ or ethanol. The local confinement creates a high concentration of both hydroxide ions and reaction intermediates near the Cu surface, essentially forming a microreactor that pushes the reactivity towards multi-carbon products.

Spillover Effect

Another advantage of bimetallic catalysts is that intermediates can be generated in situ and subsequently transferred between the two metals – the spillover effect. In CO₂RR on Cu-based bimetallics, as CO₂ is reduced to CO (typically more easily on metals like Au, Ag, or Pd), the CO intermediate can “spill over” onto Cu sites, which then catalyze C–C coupling or subsequent protonation steps. This creates a tandem sequence at the molecular scale within an integrated catalyst particle or surface. Unlike the macroscopic tandem of physically separate catalysts, spillover in a true bimetallic occurs over short, possibly atomic distances. Experimental evidence of CO spillover has been directly observed. For instance, a Cu–Pd catalyst with a high density of Cu/Pd interface sites was found to produce exceptionally high C₂₊ product output.¹⁰⁾

Future approaches in catalyst synthesis

To manipulate all the aforementioned effects, new approaches in CO₂RR catalyst design are needed. Until now, colloidal synthesis remains perhaps the most popular catalyst preparation method – not just for CO₂RR. Generally, this approach is simple and can be performed without specialized equipment in a standard flask or other types of chemical reactors. It allows for the production of large quantities of catalyst, offers a high degree of control over the colloid shape, size and size distribution, morphology (crystal structure), chemical composition, and even the distribution of the catalyst’s components. Bimetallic alloy¹¹⁾ and core-shell¹²⁾ nanoparticles incorporating various metals in combination with Cu have been successfully synthesized and exhibited improved (shifted towards C₂₊) product distribution. Confinement effects can also be achieved: nanocavities¹³⁾, hollow spherical¹⁴⁾ and cubic¹⁵⁾ multi-shell structures have demonstrated higher C₂₊ yield compared to solid Cu nanoparticles.

Although they are very versatile, colloidal catalysts offer limited geometry. A different way to generate high-surface area electrocatalysts with complex shapes is achieved by directly modifying the metal surface of the electrode. Nanowire arrays¹⁶⁾, nanoporous metals¹⁷⁾, and bubble-templated foams¹⁸⁾ can be produced by etching or (electro)deposition on initially planar surfaces. However, bimetallic interfaces are more difficult to produce with these methods.

In this light, recent advances in metal 3D printing at micro- and nanoscale^19,20) offer an interesting perspective for the preparation of catalytic materials of the future.

As we speculate here, these emerging approaches can help prepare catalytic interfaces with well-defined geometry, chemical composition and distribution of metallic components, which would help achieve appropriate geometric confinement and tune electronic and spillover effects for better performance in CO₂RR.

Electrochemical additive manufacturing (e-AM) is a growing family of techniques for the fabrication of 3D out-of-plane metallic structures. This determines the achievable resolution, with microscale or even sub-microscale features being commonplace when using nozzles with sufficiently small openings. Reliable operation, however, requires integration with special feedback mechanisms that allow tracking of metal growth to synchronize the nozzle movement with metal deposition. Automated nozzle retraction, when implemented with nanoscale nozzles, enables the printing of high aspect ratio Cu pillars, zigzags (Figure a, p. 70), and overhangs (Figure b, p. 70).²¹⁾ The features, however, are not limited to simple geometrical shapes. With voxel-by-voxel (a voxel is a 3D equivalent of planar structural element commonly known as pixel) and layer-by-layer printing routines, one can produce a variety of complex shapes, including hollow objects²²⁾ intersecting rings²³⁾, coils²⁴⁾, and even microscale replicas of famous macroscopic artefacts (Figure c–f, p. 70)²⁵⁾. With the current level of resolution, structures with voxel sizes of 50²⁶⁾ and even 25 nm²⁷⁾ are possible (Figure j, k, p. 70).

Importantly for CO₂RR, e-AM’s primary fabrication material is Cu, which is electroplated with a low quantity of impurities. Depending on the choice of the e-AM technique, either polycrystalline structures with a limited number of defects (voids)^23,27) or porous structures²⁸⁾ could be produced. The materials library for e-AM continuously grows and offers printing with more metals or their alloys: Pt^29,30), Au³¹⁾, Ni and Ag²³⁾ (Figure f–i, p. 70), as well as bimetallic Co/Cu³²⁾, Cu/Ag³³⁾, Ni/Cu³⁴⁾, Ni/Mn and Ni/Co¹¹⁾. In addition, multi-material processing capacity of e-AM also becomes available³³⁾.

These advances in high resolution 3D printing offer a vast playground for creating catalytic interfaces. The advantage of such bottom-up fabrication lies in the possibility to shape metallic structures with optimized designs for geometric confinement with a high degree of control. Electrochemistry allows tunability of the chemical composition and recent multi-material e-AM could be particularly suited for creating catalytic interfaces with enhanced activity and selectivity. Although these techniques cannot yet satisfy manufacturing needs at large scale, the possibilities to modulate catalytic interfaces with nanoscale resolution and a high degree of tunability are very attractive for systematic investigation.

Three questions for the author: Dmitry Momotenko

Your research in 140 characters?

My group is working on the development of electrochemical techniques for small scale 3D printing, chemical sensing, and functional imaging.

Which method has been used more frequently in the last twelve months that you also need for your research?

Differential electrochemical mass-spectrometry is an emerging technique for research in electrocatalysis, capable to interface electrochemistry with very sensitive analysis. It is not yet a wide-spread method, but we need it for our work on electrochemical CO₂ reduction.

How do you manage to combine family life with a career? This is very difficult. My wife and son live in a different country (Switzerland), which makes this already difficult problem in academia even more complex.

Dmitry Momotenko Dmitry Momotenko is leading the Electrochemical Nanotechnology Group at the University of Oldenburg, currently funded by an ERC Starting Grant. He studied analytical chemistry at Moscow State University and obtained his PhD at EPFL in Lausanne in 2013. He then moved to the University of Warwick, where he received a Marie Curie Fellowship. In 2017, he joined ETH Zürich as an independent group leader with an Ambizione Grant. Co-author Polina Evstigneeva is pursuing a PhD in Momotenko‘s group. She studied chemistry at Moscow State University and obtained her Specialist degree in fundamental and applied Chemistry in 2024. She completed her diploma research at the N.D. Zelinsky Institute of Organic Chemistry (RAS).

• ¹ T. E. Teeter, P. Van Rysselberghe, J. Chem. Phys. 1954, 22, 759–760
• ² R. Kostecki, J. Augustynski, Ber. Bunsenges. Phys. Chem. 1994, 98, 1510–1515
• ³ M. Serafini, F. Mariani, F. Basile et al., Nanomaterials 2023, 13, 1723
• ⁴ H. Shin, K. U. Hansen, F. Jiao, Nat. Sustain. 2021, 4, 911–919
• ⁵ A. Vasileff, C. Xu, Y. Jiao et al., Chem. 2018, 4, 1809–1831
• ⁶ B. Hammer, Y. Morikawa, J. K. Nørskov, Phys. Rev. Lett. 1996, 76, 2141–2144
• ⁷ T. Takashima, T. Suzuki, H. Irie, Electrochim. Acta 2017, 229, 415–421
• ⁸ T. Adit Maark, B. R. K. Nanda, J. Phys. Chem. C 2016, 120, 8781–8789
• ⁹ Y. Chen, Z. Fan, J. Wang et al., J. Am. Chem. Soc. 2020, 142, 12760–12766
• ¹⁰ X.-Q. Li, G.-Y. Duan, X.-X. Yang et al., Fundam. Res. 2022, 2, 937–945
• ¹¹ C. Shen, Z. Zhu, D. Zhu et al., Nanotechnology 2022, 33, 265301
• ¹² J. R. C. Junqueira, P. B. O’Mara, P. Wilde et al., ChemElectroChem 2021, 8, 4848–4853
• ¹³ T.-T. Zhuang, Y. Pang, Z.-Q. Liang et al., Nat. Catal. 2018, 1, 946–951
• ¹⁴ C. Liu, M. Zhang, J. Li et al., Angew. Chem. Int. Ed. 2022, 61, e202113498
• ¹⁵ D. Tan, J. Zhang, L. Yao et al., Nano Res. 2020, 13, 768–774
• ¹⁶ M. Ma, K. Djanashvili, W. A. Smith, Angew. Chem. Int. Ed. 2016, 55, 6680–6684
• ¹⁷ A. J. Welch, J. S. DuChene, G. Tagliabue et al., ACS Appl. Energy Mater. 2019, 2, 164–170
• ¹⁸ S. Vesztergom, A. Dutta, M. Rahaman et al., ChemCatChem 2021, 13, 1039–1058
• ¹⁹ J. Hengsteler, G. P. S. Lau, T. Zambelli et al., Electrochem. Sci. Adv. 2022, 2, e2100123
• ²⁰ J. Hengsteler, K. A. Kanes, L. Khasanova et al., Annu. Rev. Anal. Chem. 2025, 29
• ²¹ D. Momotenko, A. Page, M. Adobes-Vidal et al., ACS Nano 2016, 10, 8871–8878
• ²² L. Hirt, S. Ihle, Z. Pan et al., Adv. Mater. 2016, 28, 2311–2315
• ²³ C. van Nisselroy, C. Shen, T. Zambelli et al., Addit. Manuf. 2022, 53, 102718
• ²⁴ G. Ercolano, T. Zambelli, C. van Nisselroy et al., Adv. Eng. Mater. 2020, 22, 1900961
• ²⁵ G. Ercolano, C. van Nisselroy, T. Merle et al., Micromachines (Basel) 2020, 11, doi: 10.3390/mi11010006
• ²⁶ M. Menétrey, C. Kupferschmid, S. Gerstl et al., Small 2024, 20, 2402067
• ²⁷ J. Hengsteler, B. Mandal, C. van Nisselroy et al., Nano Lett. 2021, 21, 9093–9101
• ²⁸ M. Menétrey, L. Koch, A. Sologubenko et al., Small 2022, 18, 2205302
• ²⁹ J. Hu, M.-F. Yu, Science 2010, 329, 313–316
• ³⁰ A. P. Suryavanshi, M.-F. Yu, Nanotechnology 2007, 18, 105305
• ³¹ P. Schürch, D. Osenberg, P. Testa et al., Mater. Des. 2023, 227, 111780 Y
• ³² Lei, X. Zhang, W. Nie et al., J. Electrochem. Soc. 2021, 168, 112507
• ³³ A. Reiser, M. Lindén, P. Rohner et al., Nat. Commun. 2019, 10, 1853
• ³⁴ C. Wang, M. E. Hossain Bhuiyan, S. Moreno et al., ACS Appl. Mater. Interfaces 2020, 12, 18683–18691

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