Scientists have made a breakthrough in electrocatalysis. Their recent study reveals how catalysts can exist in unexpected forms during nitrate reduction. These findings could lead to the creation of more effective catalysts.
Researchers from the Interface Science Department at the Fritz Haber Institute of the Max Planck Society, in conjunction with beamline experts from the Helmholtz-Zentrum Berlin, have made significant strides in electrocatalysis. Their findings, published in the journal Nature Materials, provide insights into how catalysts can manifest in unanticipated forms during the nitrate reduction process. Titled “Revealing Catalyst Restructuring and Composition During Nitrate Electroreduction through Correlated Operando Microscopy and Spectroscopy,” this study could facilitate the development of more efficient catalysts.
Understanding Catalysts: The Key to Better Chemical Reactions
Catalysts are essential substances that accelerate chemical reactions without being consumed in the process. They play a vital role in various industrial applications, including fuel production and pharmaceuticals manufacturing. However, understanding catalyst behavior during their operation has posed a challenge. Similar to how a chameleon adapts its color to its surroundings, catalysts can alter their structure and composition when an electric potential is applied. Traditionally, it has been assumed that like a chameleon, catalysts quickly revert to their most active form upon activation.
A Multi-Modal Approach to Study Catalysts
This research team utilized a distinctive blend of advanced techniques to demonstrate that this assumption does not hold true under certain circumstances. They employed electrochemical liquid cell transmission electron microscopy (EC-TEM) to observe cubic Cu2O pre-catalysts during the nitrate reduction reaction, aimed at generating green ammonia. This approach enabled them to visualize the changes in the catalysts, particularly the cubic Cu2O pre-catalysts, throughout the reaction. They also combined X-ray microscopy/spectroscopy with Raman spectroscopy to determine if the pre-catalysts transformed into the expected Cu metal phase during the reaction and whether this transformation occurred uniformly across all nanocatalyst particles.
Key Findings: The Role of Redox Kinetics
A noteworthy discovery from the study is that the Cu2O cubes do not swiftly transition to the preferred metallic state; instead, they can remain as a combination of Cu metal, Cu oxide, and Cu hydroxide for an extended duration during operation. The makeup of this mixture and the shape of the resulting catalysts are significantly influenced by the applied electric potential, the surrounding chemical environment, and the duration of the reaction.
Implications for Ammonia Selectivity
One major reason for exploring nitrate reduction is to assess its potential for converting waste nitrates back into ammonia, a crucial component in fertilizers for food production. Previously, efforts to optimize this process have relied on the assumption that catalysts would adopt their most favorable forms during reactions. This new research will pave the way for designing Cu-based pre-catalysts that are more effective at producing ammonia.
Dr. See Wee Chee, a group leader at the Interface Science Department and the study’s corresponding author, remarked, “It is surprising that we observe different phases during the reaction, especially when we begin with a single form of the catalyst. What’s more, this mixed state can persist for a long time, providing valuable insight for designing more efficient catalysts.”
This research further illustrates how advanced real-time observation techniques that capture local chemical variations can enhance our understanding of the complex nature of catalysts in action.
Prof. Beatriz Roldán, director of the Interface Science Department at the FHI and co-corresponding author, noted: “Currently, ammonia is produced through the gas-phase Haber-Bosch thermal catalysis method, which occurs at moderate temperatures (450-550 °C) but under high pressures (150 bar), requiring significant amounts of fossil-based H2. Our challenge was to find an alternative method for ammonia synthesis with lower carbon emissions, which we accomplished by pursuing a direct electrocatalytic route powered by renewable electricity.”
