Aqueous Redox Active Molecular Materials Mediating Proton-Coupled-Electron-Transfer for Sustainable Energy Applications

This work presents a systematic exploration of aqueous redox-active molecular systems designed to mediate proton-coupled electron transfer (PCET) across multiple interfaces, with a focus on advancing sustainable energy technologies. Redox-active aqueous molecules, if proton coupled,^1,2 can function as carriers for hydrogen atoms (one proton alone with one electron). Our recent research has focused on harnessing the potential of anthraquinone-based aqueous solutions for electrochemical hydrogen storage under ambient conditions. In particular, we demonstrated a highly efficient, reversible aqueous electrochemical system that operates with near-perfect Faradaic efficiency and offers significant advantages for stationary hydrogen storage applications.³ This system employs anthraquinone disulfonate (AQDS) as a redox mediator, facilitating hydrogen storage through PCET with a minimal energy cost and high Coulombic efficiency across a wide range of current densities.
Building upon this foundation, we extended the application of PCET processes to electrochemical hydrogen production systems that incorporate both aqueous and nonaqueous phases.⁴ In this work, we successfully achieved high-efficiency interfacial molecular mediation by utilizing aqueous-nonaqueous phase boundaries, enabling efficient interfacial PCET for selective nonaqueous hydrogenation reactions. By employing a heterogeneous molecular catalytic process, we ensured nearly 100% selectivity and efficiency in the interfacial PCET, overcoming limitations such as over-reduction and product contamination inherent in conventional methods.
We are currently developing a system that uses aqueous redox molecules to mediate PCET at the aqueous-solid interface, with hydrogen atoms subsequently transferred into a nonaqueous phase to drive hydrogenation at the solid-nonaqueous interface. The integration of aqueous electrochemistry with nonaqueous hydrogenation processes represents a promising pathway for the development of sustainable and scalable energy solutions. The tunability of the redox molecules involved in this system provides further potential for optimization across a range of energy storage and conversion applications, contributing to the broader field of materials science by addressing key challenges in interfacial catalysis and molecular mediation.

1. Dawei Xi,* Abdulrahman M. Alfaraidi,* Jinxu Gao, Thomas Cochard, Luana CI Faria, Zheng Yang, Thomas Y. George et al. "Mild pH-decoupling aqueous flow battery with practical pH recovery." Nature Energy 9, no. 4 (2024): 479-490.
2. Dawei Xi, Zheng Yang, Abdulrahman M. Alfaraidi, Yan Jing, Roy G. Gordon, and Michael J. Aziz. "Single-membrane pH-decoupling aqueous batteries using proton-coupled electrochemistry for pH recovery." Energy Advances 3, no. 8 (2024): 1911-1918.
3. Taobo Wang,* Dawei Xi,* and Michael J. Aziz. "Electrochemical Hydrogen Storage under Ambient Conditions in Aqueous-Soluble Organics." ACS Applied Energy Materials 7, no. 15 (2024): 6578-6584.
4. Dawei Xi,* Yuheng Wu,* Yuli Li, Ricahrd Y. Liu and Michael J. Aziz. "Electrifying Industrial Hydrogen Peroxide Production via Interfacial Molecular Mediation" Preprint on Research Square. https://doi.org/10.21203/rs.3.rs-4986886/v1