Novel Strategies for Recycling and Regeneration of Materials for Energy and Sustainability

The reliance on critical elements that are at the heart of clean energy technologies stems from their unique properties that makes them highly active, selective, and stable. In order to best utilize our limited critical element resources, we need to find better ways to reduce, replace, and recover critical elements such as Cobalt and Nickel, employed in high energy density Li-ion batteries, as well as Platinum and Iridium used as catalysts in fuel cells and electrolyzers, respectively. These drivers spark new opportunities either to repurpose materials from end-of-life electrochemical devices as part of recycling processes or to explore interface dynamics at the atomic scale to regenerate active sites functionality. In this talk we will discuss these strategies by first presenting results on the use of spent Li-ion cathode materials as catalysts for electrochemical advanced oxidation processes and second, by discussing how controlled surface dissolution can lead to deactivation and reactivation of MoS_x catalysts for H₂ evolution reaction (HER). In the first part of our talk, LiCoO₂ is used as a catalyst in aqueous media for the simultaneous destruction of Bisphenol A (BPA), an important organic pollutant found in water streams. By revealing the changes in the electrode surface composition during the very first polarization steps we can produce CoO_xH_y surface moieties that are effective in removing >90% BPA from the electrolyte within 1 hour, even at initial parts per billion levels of BPA. Due to the activity-stability relationships present during water oxidation reactions, we show how this process can be further modulated to generate Co ions that can be recovered and recycled. In the second part of this talk we will discuss the activity-stability trends found on MoS₂ and MoS_x materials during HER as replacement for precious metal catalysts such as Pt and Ir. The selective dissolution of S observed during H₂ evolution leads to catalyst deactivation, while high potential excursions induce selective dissolution of Mo that regenerate the active sites for HER. We demonstrate many cycles of active site deactivation and regeneration while establishing the role of material loss as the eventual complete degradation pathway of these materials. We will discuss alternative strategies to recover not only the active sites but the catalyst material as a whole, which holds the promise of achieving active and virtually infinitely stable electrochemical materials.