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X-ray imaging tracks catalyst degradation in CO2 electrolysers

• Converting CO2 into fuels and chemicals requires catalysts that remain stable under industrially relevant electrolysis conditions. • Operando X-ray imaging at beamline ID31, combining wide- and small-angle scattering with X-ray fluorescence, was used to track catalyst evolution inside working CO2 electrolysers under accelerated stress testing. • The results identify distinct degradation pathways in silver and gold catalysts, guiding the development of more durable electrocatalysts for CO2 electrolysis.

The challenge

Electrochemical CO2 reduction into fuels or chemicals is a promising route to closing the carbon cycle and mitigating industrial emissions. Among the available technologies, membrane-electrode assembly (MEA)- based CO2 electrolysers show the greatest potential for industrial deployment because of their high efficiency and compact design. However, their performance stability over time remains a significant barrier to scale-up.

Catalyst degradation is one of the main causes of performance loss, but the processes leading to it are complex. During electrolysis, chemical, mechanical, and electrochemical transformations occur simultaneously across different cell components. Traditional durability

tests often struggle to disentangle catalyst degradation from other issues, such as salt precipitation or gas diffusion layer flooding [1,2]. Understanding when and how degradation begins – before large performance drops occur – is crucial for developing robust, long- lasting CO2 electrolysers. Achieving this requires an experimental approach capable of probing structural and compositional changes directly within the device while it operates under industrially relevant conditions.

The experiment

At beamline ID31, a new operando X-ray characterisation platform was developed specifically for MEA-based CO2 electrolysers (Figure 65). The system integrates wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and X-ray fluorescence (XRF), enabling simultaneous, time-resolved monitoring of crystallite growth, nanoparticle agglomeration, and ion migration across the electrode layers during CO2 electrolysis. This multi-modal approach allows degradation processes to be tracked spatially and temporally, revealing how catalysts evolve during realistic operating conditions.

To accelerate degradation while avoiding secondary artefacts such as salt precipitation, a pulsed accelerated stress test (AST) protocol was introduced. The method alternates between short periods of high current density and relaxation intervals, mimicking the intermittent power supply typical of renewable energy sources. These controlled fluctuations place stress on the catalyst layer and support structure while preserving stable

Fig. 65: Schematic of the operando X-ray

characterisation setup. Customised

synchrotron cell used to monitor MEA-based CO2 electrolysis. The design

enables simultaneous WAXS, SAXS, and

XRF measurements, allowing real-time tracking of crystal

structure, particle size, and ion movement

across catalyst layers.

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