A recent study in Nature Materials explores how copper-based catalysts (Cu2O) change during nitrate electroreduction (NO3RR) to ammonia. Researchers investigated which catalyst species are active and how their structure shifts under different conditions using correlated operando microscopy and spectroscopy.
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Developments in Electrocatalytic Technologies
Electrocatalysis is an important tool for sustainable energy, helping convert pollutants into valuable chemicals. The nitrate reduction reaction is particularly relevant for reducing freshwater pollution from agricultural runoff while offering an alternative way to produce ammonia—an essential industrial chemical and a potential green hydrogen carrier.
Copper-based catalysts like Cu2O are of interest because their nitrate adsorption properties improve reaction efficiency. However, identifying the active species during NO3RR is complex, as these catalysts undergo significant structural and compositional changes throughout the reaction.
Examining Catalyst Behavior
To address this, researchers used advanced operando microscopy and spectroscopy techniques to monitor Cu2O cube restructuring during NO₃RR. They combined electrochemical liquid cell transmission electron microscopy (EC-TEM) with other methods, including electrochemical liquid cell transmission X-ray microscopy (EC-TXM), hard X-ray absorption spectroscopy (XAS), and Raman spectroscopy. This allowed them to track structural and chemical changes in real time under different reaction conditions.
The Cu2O cubes were synthesized through electrodeposition onto carbon working electrodes, producing well-defined structures averaging 250 nm in size. The experiments were conducted with applied potentials ranging from -0.2 V to -0.6 V versus the reversible hydrogen electrode (RHE) to analyze structural changes and catalyst-electrolyte interactions.
Key Findings and Insights
The study identified three main processes influencing Cu₂O restructuring during NO₃RR: dissolution, copper redeposition, and reduction to metallic copper. The researchers found that Cu2O could coexist with metallic copper under moderately reductive conditions, likely due to the formation of surface hydroxides.
Changes in morphology depended on the applied potential. At -0.2 V RHE, the Cu2O cubes remained stable. However, at more cathodic potentials, dissolution and redeposition became more noticeable. At -0.4 V RHE, complete dissolution occurred after 140 minutes, while at -0.5 V RHE, it happened within 90 minutes. This restructuring behavior was different from what was observed during carbon dioxide reduction (CO2RR), where catalyst fragmentation was more common.
The electrolyte also played a key role in restructuring dynamics and ammonia selectivity. Catalyst-electrolyte interactions affected local pH, influencing copper species stability and catalytic performance. The findings suggest that metallic copper is the active phase driving ammonia production, while the stability of Cu2O affects reaction selectivity.
Relevance for Sustainable Chemistry
This research helps refine electrocatalysts for nitrate reduction and other electrochemical applications. A clearer understanding of copper-based catalyst behavior during NO₃RR can improve ammonia production while reducing environmental impact.
The study also highlights how electrolyte selection influences catalytic performance, suggesting new directions for improving electrocatalytic processes in energy storage, carbon capture, and sustainable chemical synthesis.
Future research should focus on understanding catalyst behavior in different electrolytic environments. These efforts will not only expand knowledge of electrocatalytic processes but also contribute to developing sustainable technologies to tackle environmental challenges.
Journal Reference
Yoon, A., et al. (2025). Revealing catalyst restructuring and composition during nitrate electroreduction through correlated operando microscopy and spectroscopy. Nat. Mater. DOI: 10.1038/s41563-024-02084-8, https://www.nature.com/articles/s41563-024-02084-8
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