Exploration of Biomass-Derived Activated Carbons for Use in Vanadium Redox Flow Batteries

Increasing redox reaction rates on carbon electrodes is an important step to reducing the cost of all-vanadium redox flow batteries (VRFBs). Biomass-derived activated carbons (ACs) hold promise as they may obviate the need for post-synthetic modifications common to conventional materials. While initial efforts have shown that these materials can enhance VRFB performance, the wide selection of potentially inexpensive feedstocks and synthesis routes lead to a collection of electrocatalytic materials with disparate physical, chemical, and electrochemical properties, challenging the development of generalizable design principles. Here, we employ a hydrothermal processing (HTP) technique to produce elementally diverse ACs, varying biomass feedstock composition, and HTP temperature. Specifically, we study ACs derived from chitin, which contain nitrogen and oxygen functionalities, and ACs derived from pine wood, which contain oxygen functionalities. Using Vulcan XC72 as a comparator, we apply spectroscopic, electrochemical, and computational techniques, finding electrochemically accessible surface area, rather than the heteroatom composition, to be the more representative performance indicator. Evaluation of the best-performing AC in a VRFB reveals ∼100 mW cm-2 improvement in peak power density when deposited into felt electrodes. The feedstock-processing-property relationships studied in this work represent a systematic approach to advancing biomass-based functional materials for use in energy applications.