Electrode Treatments for Redox Flow Batteries: An Industrial Perspective
Authors: Agarwal Harsh , Roy Esha , Singh Nirala , Klusener Peter A. A. , Stephens Ryan , Zhou Qin (Tracy) 
Published: September 2023

Renewables sources of energy like solar and wind are expected to supply ~35% of the total electricity demand by 2050.1 The intermittent nature of solar and wind necessitates the development of energy storage technologies. Redox flow batteries (RFBs) are a promising technology for storing energy over several hours to days; however, RFBs suffer from inefficiencies in part due to the overvoltages at the electrode surface. Vanadium redox flow batteries (VRFBs) are the most commercialized RFB chemistry till date due to the use of same element both sides of battery, eliminating the issue of cross-contamination. Carbon felts (CFs) are the most commonly used electrodes in RFBs due to their high conductivity and porous nature. More than 70 electrode treatments for VRFBs alone have been previously shown to reduce the overvoltages and improve performance of VRFBs. Some of these CF electrode treatments include thermal, acid/base, elemental doping, and loading with electrocatalysts.2–5 However, the differences in the operating conditions between treatment studies in literature makes the comparison among different treatments very difficult. Additionally, the complexity associated with each treatment makes identification of industrially implementable treatments extremely challenging.
In this talk, I will discuss our efforts to tackle the above problem by comparing treatments under similar operating conditions and accounting for the treatment complexity. We compare the VRFB performance, stability, and economic feasibility with various CF treatments, and treatment complexity to identify the most promising industrially implementable treatments. We extract the round-trip energy efficiencies (EE) of VRFBs using CFs with (and without) various treatments from literature at laboratory and industrial scale. The performance is evaluated using the EE at various operating current densities and stability is identified based on the change in EE per cycle. Economic feasibility of a treatment is measured based on the affordable capital cost (ACC) obtained from an in-house techno-economic model. ACC is defined as the maximum capital cost that can be invested in a treatment without an increase in the overall capital cost of VRFB without treated electrodes. The treatment complexity is measured using the number of steps and the process units required in a treatment. Based on carefully chosen metrics for satisfying the performance, stability, economic feasibility, and treatment complexity criteria, we identify the high performing, stable, and economic feasible treatments that are easy to implement industrially. We conduct a cost analysis of these promising treatments by utilizing the similarities in production of carbon fibers and CFs. We encourage the RFB community to standardize of RFB testing procedures for fast industrial implementation of CF treatments as we move towards a society powered by renewable energy.

References:

(1) International Energy Outlook 2021.
(2) Amini, K. et al.
Adv. Funct. Mater.
2020, 30 (23), 1910564.
(3) Sun, B. et al.
Electrochim. Acta
1992, 37 (13), 2459–2465.
(4) Sun, B. et al.
Electrochim. Acta
1992, 7, 1253–1260.
(5) Wu, T. et al.
J. Solid State Electrochem.
2012, 16, 579–585.