(Energy Technology Division Graduate Student Award sponsored by Bio-Logic) Designer Porous Carbon Electrodes for Redox Flow Batteries

Abstract

Redox flow batteries (RFBs) hold promise for efficiently storing and delivering electricity at the grid-scale, offering opportunities to complement and ultimately supplant fossil fuels with sustainable, but variable, energy sources.[1] However, widespread deployment of RFBs is hindered by their prohibitive cost, which depends, at least in part, on reactor performance. Thus, improving cell performance characteristics by targeting critical system components is an effective strategy towards realizing an energy infrastructure powered by renewable resources. In particular, porous carbon electrodes are vital components of RFBs, simultaneously fulfilling multiple crucial roles.[2] The electrode provides surface area for redox reactions to occur, distributes the electrolyte, determines the pressure drop, and cushions the cell during compression; thus, electrode properties are directly coupled with the RFB electrochemical and fluid dynamic performance. However, the commercial materials utilized in advanced flow batteries – typically papers, cloths, or felts – possess low surface area (~0.1 – 10 m2 g-1), poor aqueous wettability, and suboptimal surface chemistry, motivating efforts into electrode engineering. Current approaches for improving the electrode largely focus on post-process modification of pre-existing fiber-bed substrates which, although effective, may ultimately be incremental, as achievable properties are limited by the underlying material. While findings from prior art have furthered knowledge about the role of electrode interfacial chemistry and microstructure in cell performance, greater paradigm shifts may be necessary to unlock transformative advances and to enable chemistry-specific electrode design.In this talk, I will present three concurrent efforts towards rationally designing electrodes with property sets favorable for RFBs. First, I describe a method of refining the interfacial properties of commercial carbon electrodes through conformal deposition of conductive polymers with nanometric thicknesses, analyzing potential benefits of these coatings towards enhanced performance of iron-based redox couples.[3,4] Second, I discuss a strategy to produce sustainably sourced, elementally diverse, and high surface area electrocatalysts derived from biomass.[5] Findings from this work are coupled with modeling efforts to guide the effective utilization of high surface area electrocatalysts. Lastly, I outline a scalable, bottom-up synthetic method for producing tunable electrode microstructures that achieve pore network configurations inaccessible to classic fibrous electrodes. The fabricated scaffolds offer compelling opportunities as platforms for microstructure-function studies and potentially as performance materials.[6,7] While the focus of these efforts is RFBs, the methods, implications, and techniques for these concepts may ultimately be applicable to a diverse portfolio of convection-driven electrochemical systems that benefit from engineered transport layers. Acknowledgements This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. CTW acknowledges additional funding from the National Science Foundation Graduate Research Fellowship Program under Grant No. 1122374. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.