Probing the life cycle of copper electrocatalysts with X-ray scattering

Electrocatalytic conversion powered by renewable energy is expected to play a key role in the energy transition by enabling the recycling of industrial chemical waste, such as through electrochemical CO₂ reduction. However, electrocatalyst materials exhibit structural changes under operational conditions, leading to a gradual decline in conversion efficiency.

The structural transformations responsible for electrolyser degradation remain largely unexplored. These changes occur across multiple length scales, from atomic-to-nanometre scale restructuring and deformation of the electrocatalyst to macroscopic degradation phenomena, such as flooding, at the micrometre-to-millimetre scale. Gaining a comprehensive understanding of electrocatalyst stability requires simultaneous insights across these length scales, posing a significant experimental challenge.

Various techniques are available to study the dynamics of electrocatalysts under operational conditions, each offering distinct advantages and limitations in terms of spatiotemporal resolution and compatibility with aqueous electrochemical environments.

Surface-sensitive vibrational spectroscopy and ensemble X-ray characterization are widely used to investigate adsorbed reaction intermediates and electrocatalyst structures. Synchrotron X-rays are particularly well-suited for in-situ structural and compositional analysis, as high photon energies enable deep penetration into practical electrocatalyst samples. Additionally, multiple X-ray techniques, such as diffraction and absorption spectroscopy, can be combined in a single experiment to provide complementary insights. However, studies that concurrently resolve structural and compositional transformations across multiple length scales remain limited.

Compared to diffraction and spectroscopy, wide-angle and small-angle X-ray scattering (WAXS/SAXS) remains underutilized for electrocatalyst characterization, despite its potential for multiscale in-situ analysis. WAXS provides insights into crystal structure and crystalline domain size, whereas SAXS offers information on particle size, shape, and volume. 

This study employed simultaneous WAXS and SAXS measurements to investigate the structural evolution of copper oxide electrocatalysts. A custom electrochemical cell was designed for X-ray scattering measurements in transmission mode (Figure 1a), minimizing interference from the electrolyte and the glassy carbon electrode substrate while facilitating the detection of scattered X-rays. The experimental setup at beamline ID02 enabled the simultaneous acquisition of SAXS and WAXS signals. The SAXS detector was positioned 31 m from the sample, while WAXS data was collected concurrently using a detector located approximately 0.12 m away (Figure 1b). 

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Fig. 1: a) Schematic representation of the custom electrochemical cell used for the in-situ X-ray scattering experiments. The detectors display representative 2D in-situ WAXS and SAXS patterns, along with the length scales probed by each technique. Dashed arrows indicate azimuthal integration, while solid arrows represent the scattering vector q. b) Photograph of the electrochemical cell inside the ID02 experiment hutch. Labels: 1 = electrochemical cell, 2 = pump, 3 = electrolyte with CO₂ bubbler, 4 = WAXS detector (protective shield), 5 = opening of the SAXS vacuum flight tube, and 6 = X-ray beam. c) Differential WAXS patterns relative to the mean of the first 10 diffractograms (recorded over the first 3.4 s). Blue regions correspond to negative features, while red regions indicate positive features. d) Six representative SAXS patterns (dots) with corresponding fits (solid lines), recorded during the first 60 seconds of the reaction (0, 5, 10, 20, 40, 60 s; vertically offset for clarity). The purple and green dashed lines indicate the position of the second minimum for the first and last patterns, respectively. The model was fitted to the q-value range highlighted in grey. e,f) Schematic representations of structural changes observed via in-situ X-ray scattering for (e) activated and (f) degraded micron-sized Cu₂O electrocatalyst particles.
 

The experiments began with pristine, well-defined copper oxide particles supported on a thin glassy carbon electrode. These particles were immersed in an aqueous electrolyte containing dissolved CO₂, which was continuously refreshed to maintain consistent reaction conditions and prevent gas bubble accumulation. Upon applying a negative potential, copper oxide was reduced, forming metallic copper particles that retained the morphology of the initial oxide precursor. CO₂ reduction to ethylene, methane, and CO was catalysed at undercoordinated surface sites of these activated copper particles. However, prolonged operation led to a gradual decline in catalytic activity.

The combined WAXS/SAXS analysis revealed that this deactivation correlated with surface roughening on ~100 nm length scales. The activation and deactivation dynamics of micron-sized Cu₂O octahedral and cubic electrocatalyst particles were monitored over timescales ranging from milliseconds up to 30 minutes using detailed X-ray scattering models for particles of varying sizes and morphologies (Figures 1c and 1d).

Additional models were developed to simulate the high-quality X-ray scattering patterns obtained during catalyst degradation. The experimental scattering data closely matched modelled patterns of surface roughening (Figures 1e and 1f), whereas models based on sintering and partial dissolution exhibited less agreement. Complementary in-situ Raman spectroscopy confirmed the presence of undercoordinated surface sites at the start of the reaction (Figure 1e), which gradually evolved into more planar surface configurations. These structural changes resulted in reduced CO₂ reduction activity and an increased tendency for hydrogen evolution (Figure 1f).

This study highlights the complex relationship between electrocatalyst structure and performance during electrochemical CO₂ reduction, demonstrating the effectiveness of multiscale in-situ X-ray scattering in capturing activation and deactivation mechanisms. These findings lay the groundwork for the rational design of electrocatalyst materials with enhanced stability and selectivity for CO₂ reduction.

Principal publication and authors
Multiscale X-ray Scattering Elucidates Activation and Deactivation of Oxide-derived Copper Electrocatalysts for CO₂ Reduction, J. de Ruiter (a), V.R.M. Benning (b), S. Yang (a), B.J. den Hartigh (a), H. Wang (a), P.T. Prins (a), J.M. Dorresteijn (a), J.C.L. Janssens (a), G. Manna (c), A.V. Petukhov (d), B.M. Weckhuysen (a), F.T. Rabouw (a,b), W. van der Stam (a), Nat. Comm. 16, 373 (2025); https://doi.org/10.1038/s41467-024-55742-5
(a) Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science and Institute for Sustainable and Circular Chemistry, Faculty of Science, Utrecht University (The Netherlands)
(b) Soft Condensed Matter, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht University (The Netherlands)
(c) ESRF 
(d) Physical and Colloid Chemistry group, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht University (The Netherlands)