Finding the Right TEMPO: Multi-Objective Virtual Screening and Experimental Validation of TEMPO Derivatives for Aqueous Redox Flow Battery Catholytes

ChemRxiv

Abstract

We formulate the discovery of aqueous redox flow battery catholytes as a multi-objective optimization problem and introduce a virtual screening framework that simultaneously considers redox potential, chemical stability, and synthetic accessibility. Applied to a library of 182 TEMPO derivatives, the workflow identified a diverse set of high-ranking candidates, including the previously unexplored methyl carbamate-TEMPO (MC-TEMPO) and diethylamino-TEMPO (DEA-TEMPO). Furthermore, the screening revealed a moderate correlation between redox potential and predicted degradation resistance, indicating an intrinsic trade-off between these properties. For established TEMPO derivatives, the framework reproduced relative performance trends reported within independently studied series. Across the broader library, the highest-ranked candidates reflected a non-intuitive balance of electrochemical performance, stability, and synthetic accessibility rather than optimization of redox potential alone. MC-TEMPO and DEA-TEMPO were subsequently synthesized and experimentally characterized, providing a prospective test of the computational predictions. Cyclic voltammetry validated the redox potential predictions, with measured values closely matching the calculated values. During 130 h potentiostatic holds under sustained oxidizing conditions, MC-TEMPO showed no measurable electrochemical or molecular degradation, whereas DEA-TEMPO underwent a substituent-specific degradation pathway not captured by the initial screening model. Together, these results show that multi-objective catholyte discovery can prioritize molecules that would be overlooked by redox-potential optimization alone and provides a framework for the computationally guided design of organic redox flow battery catholytes.

Authors 5

1. Daniel Willimetz Aachen Integrated Fuel and Science Center

   Fraunhofer Institute for Algorithms and Scientific Computing · RWTH Aachen University

   Affiliation as printed

   Department of Virtual Material Design, Fraunhofer Institute for Algorithms and Scientific Computing, Schloss Birlinghoven 1, Sankt Augustin, 53754, Germany

   MODES, The Integrated Fuel and Science Center, RWTH Aachen University, Schinkelstraße 8, Aachen, 52062, Germany

2. Žak Ruben Šinkovec

   University of Cambridge

   Affiliation as printed

   Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, CB3 0AS, UK

3. Jan Hamaekers

   Fraunhofer Institute for Algorithms and Scientific Computing

   Affiliation as printed

   Department of Virtual Material Design, Fraunhofer Institute for Algorithms and Scientific Computing, Schloss Birlinghoven 1, Sankt Augustin, 53754, Germany

4. Alexei A. Lapkin

   University of Cambridge · The Cambridge Centre for Advanced Research and Education in Singapore

   Affiliation as printed

   Cambridge Centre for Advanced Research and Education in Singapore (CARES Ltd), #05-05 CREATE Tower, 1 Create Way, 138602, Singapore

   Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, CB3 0AS, UK

   Innovation Centre in Digital Molecular Technologies, University of Cambridge, Lensfield Road, CB2 1EW, UK

5. Abhishek Khetan Aachen Integrated Fuel and Science Center

   RWTH Aachen University

   Affiliation as printed

   MODES, The Integrated Fuel and Science Center, RWTH Aachen University, Schinkelstraße 8, Aachen, 52062, Germany