The Goldilocks Zone of Cobalt Reactivity: Navigating the Balance of Stability and Reactivity in Cobalt Oxides
As the world shifts towards more sustainable energy solutions, cobalt oxides have emerged as key players in innovative technologies, particularly in fields like artificial photosynthesis and advanced battery systems. These materials are critical for catalytic processes and energy storage; however, utilizing their potential poses a challenge: achieving an optimal balance between chemical reactivity and stability.
Recent research from John Anderson's laboratory, published in the Journal of the American Chemical Society (JACS), tackles this complexity by successfully stabilizing a molecule with two cobalt centers in the +4 oxidation state, a feat that has proven elusive for many in the scientific community.
Anderson articulates the dual nature of cobalt oxides, likening their behavior to "two sides of the same coin." In catalytic applications, cobalt centers in these oxides are pushed to high oxidation states, facilitating the spontaneous generation of oxygen. Conversely, when utilized in batteries, the goal is to realize these same high oxidation states without generating oxygen.
Therefore, studying cobalt oxides in this “Goldilocks” zone where they are highly oxidized but stable enough to examine has proven tricky. Pushing the oxidation states of model complexes used to study cobalt oxides can often lead to decomposition. Anderson elaborates, “When you create these highly oxidizing intermediates, they start to break down the supporting structure around the metal center, leading to its failure.”
To address this challenge, the study led by Joseph Schneider, a former graduate student in Anderson's lab and now a Postdoctoral Fellow at UC Berkeley, presents a novel ligand specifically engineered to enhance the stability of cobalt centers.
“The key innovation here was developing a new ligand with fluorinated groups adjacent to the binding site,” Anderson explains.
This innovative approach leverages the notorious stability of polyfluorinated alkyl substances (pfas), which are prevalent environmental contaminants. While fluorinated compounds often raise environmental concerns, the Anderson lab’s study highlights their significant durability which helps to stabilize highly oxidized cobalt complexes. With their investigation, the research team cleverly transformed a pressing environmental issue into a scientific breakthrough.
By optimizing the electronic environment surrounding the cobalt center, Schneider and Anderson were able to stabilize a dicobalt dioxygen core where the cobalt centers are in highly oxidized cobalt(IV) states. This newfound stability enables researchers to explore high-oxidation states more clearly, unlocking insights into essential catalytic behaviors.
“A good catalyst does not exist for very long due to its reactivity,” says Schneider.
He further states, “We needed to stabilize it for study to learn what these things look like and understand their chemistry better.”
While commercial applications may not be on the immediate horizon, the Anderson lab’s study lays a crucial groundwork for the development of stable cobalt centers, potentially advancing battery technology. Enhanced stability could also mitigate the degradation issues currently limiting battery performance and longevity.
Anderson underscores the uniqueness of cobalt complexes, noting, “There's not been a lot of work with high-valent cobalt. These complexes are unique and hard to extrapolate from. But I think it's important that we can start painting a picture of what the chemistry of cobalt(IV) states looks like.”
The lab intends to further investigate the chemistry of these stabilized compounds, seeking to uncover new reactions and applications that were previously thought to be out of reach. For now, their findings provide a vital reference point for ongoing research into the chemical behaviors of cobalt oxides.
Citation - Isolation and Crystallographic Characterization of an Octavalent Co2O2 Diamond Core
Joseph E. Schneider, Shilin Zeng, Sophie W. Anferov, Alexander S. Filatov, and John S. Anderson
Journal of the American Chemical Society 2024 146 (34), 23998-24008, DOI: 10.1021/jacs.4c07335