The Role of Nitrogen-Doping and Surface Topology of Biobased Carbon Electrodes for Iron-Based Redox-Flow Batteries

To redefine our material sources in a circular economy, it is key the utilization of extensively available biomass wastes, as new carbon mines. A plethora of applications that valorize biomass, and implement biomass-derived materials (i.e., biobased), are being intensively investigated, e.g., biofuels, biodegradable polymers, carbon fibers, battery electrodes.¹ Hydrochar, produced from hydrothermal and pyrolysis processing of biomass is an alternative avenue to produce more sustainable carbon materials for energy storage, while it provides new routes for biomass waste valorization.² Hydrochar’s structure is predominantly aromatic, rich in nitrogen atoms, and highly porous, which are valued features for carbon electrodes,³ such as those in redox flow batteries.⁴ However, the fundamental mechanisms underlying the performance of biobased electrodes are still unclear. To achieve better understanding of the structure-property relationship of hydrochar-derived carbon electrodes in iron-based redox flow batteries, we performed density functional calculations (DFT) calculations of iron redox species and hydrochar model systems with different surface features. We explored the effect of quaternary nitrogen functional groups, surface curvature, endo- and exo- absorption sites at the surface, and curvature radius, as well as the effect of iron spin multiplicity. Our results suggest that the interaction between iron and biobased carbon electrodes not only depend on the surface curvature or nitrogen content, but also on the spin multiplicity of the metal ion.<br/><br/>1. A. Bachs-Herrera, D. York, T. Stephens-Jones, I. Mabbett, J. Yeo and F. J. Martin-Martinez, <i>iScience</i>, 2023, <b>26</b>, 106549.<br/>2. S. A. Nicolae, H. Au, P. Modugno, H. Luo, A. E. Szego, M. Qiao, L. Li, W. Yin, H. J. Heeres, N. Berge and M.-M. Titirici, <i>Green Chem.</i>, 2020, <b>22</b>, 4747–4800.<br/>3. S. Liu, J. Tian, L. Wang, Y. Zhang, X. Qin, Y. Luo, A. M. Asiri, A. O. Al-Youbi and X. Sun, <i>Adv. Mater.</i>, 2012, <b>24</b>, 2037–2041.<br/>4. C. T.-C. C. Wan, D. López Barreiro, A. Forner-Cuenca, J.-W. W. Barotta, M. J. Hawker, G. Han, H.-C. C. Loh, A. Masic, D. L. Kaplan, Y.-M. M. Chiang, F. R. Brushett, F. J. Martin-Martinez and M. J. Buehler, <i>ACS Sustain. Chem. Eng.</i>, 2020, <b>8</b>, 9472–9482.