(103c) Designing Electrocatalysts for Vanadium-Based Flow Batteries for Renewable Energy Storage

The world’s growing population and rising standard of living will continue to increase energy demand. To satisfy energy demand, fossil fuels are burned at an incredible rate, emitting 35 billion tons of CO₂ in 2017. There are technologies capable of satisfying energy demand without CO₂ emissions, such as solar or wind, but they are intermittent in energy generation, thus their energy must be stored to match demand.

Vanadium-based redox flow batteries (VRFBs) are a promising technology to store renewable electricity. VRFBs (e.g., all vanadium, V-Ce, V-Br) have been tested on benchtop and at pilot scales. The main challenge for the widespread adoption of VRFBs is cost, which can be reduced by increasing the current densities without decreasing energy storage efficiency. Electrocatalysts have been used to accelerate the V²⁺/V³⁺ redox reaction in VRFBs (shown in Equation 1), but a mechanistic understanding of the V²⁺/V³⁺ redox reaction is still unclear.

V²⁺ V³⁺ + e^- with E⁰(V²⁺/V³⁺) = -0.255 V vs. SHE

One possible mechanism on carbon, metal oxides, and metals involves the exchange of the vanadium ion with H (present as OH on carbon or metal oxides and metal-H on metals), where this exchange reaction acts as an intermediate step in the V²⁺/V³⁺ reduction or oxidation reaction.

We will discuss experimental measurements of V²⁺/V³⁺ redox activity on different electrocatalysts (e.g., glassy carbon, Au, Bi) and compare the results to density functional theory calculations of hydrogen adsorption. Our hypothesis is that the strength of the bound hydrogen should correlate with the electrocatalyst reaction rate, if H_ads plays a role in the V²⁺/V³⁺ reaction. For metals, the energy of the adsorbed hydrogen intermediate is well-known to correlate with the hydrogen evolution activity (an undesired side-reaction in vanadium-based RFBs),^1,2 so we will use this to eliminate certain metals from consideration. Of the metals reported currently to be active for the V²⁺/V³⁺ redox reaction (i.e., Bi,^3–7 Sb⁸, Cu,⁹ Sn¹⁰) all bind hydrogen very weakly according to our DFT calculations. We will discuss if other ‘descriptors’ (such as vanadium ion adsorption strength) are required to understand the V²⁺/V³⁺ reaction rates on metal surfaces.

References

(1) Nørskov, J. K.; Bligaard, T.; Logadottir, A.; Kitchin, J. R.; Chen, J. G.; Pandelov, S.; Stimming, U. Trends in the Exchange Current for Hydrogen Evolution. J. Electrochem. Soc. 2005, 152 (3), J23.

(2) Parsons, R. The Rate of Electrolytic Hydrogen Evolution and the Heat of Adsorption of Hydrogen. Trans. Faraday Soc. 1957, 54 (0), 1053–1063.

(3) Yang, X.; Liu, T.; Xu, C.; Zhang, H. H.; Li, X.; Zhang, H. H. The Catalytic Effect of Bismuth for VO2+/VO2+ and V3+/V2+ Redox Couples in Vanadium Flow Batteries. J. Energy Chem. 2017, 26 (1), 1–7.

(4) Suárez, D. J.; González, Z.; Blanco, C.; Granda, M.; Menéndez, R.; Santamaría, R. Graphite Felt Modified with Bismuth Nanoparticles as Negative Electrode in a Vanadium Redox Flow Battery. ChemSusChem 2014, 7 (3), 914–918.

(5) Park, M.; Ryu, J.; Cho, J. Nanostructured Electrocatalysts for All-Vanadium Redox Flow Batteries. Chem. - An Asian J. 2015, 10 (10), 2096–2110.

(6) Flox, C.; Murcia-López, S.; Carretero, N. M.; Ros, C.; Morante, J. R.; Andreu, T. Role of Bismuth in the Electrokinetics of Silicon Photocathodes for Solar Rechargeable Vanadium Redox Flow Batteries. ChemSusChem 2017, 8028, 125–129.

(7) Liu, T.; Li, X.; Nie, H.; Xu, C.; Zhang, H. Investigation on the Effect of Catalyst on the Electrochemical Performance of Carbon Felt and Graphite Felt for Vanadium Flow Batteries. J. Power Sources 2015, 286, 73–81.

(8) Shen, J.; Liu, S.; He, Z.; Shi, L. Influence of Antimony Ions in Negative Electrolyte on the Electrochemical Performance of Vanadium Redox Flow Batteries. Electrochim. Acta 2015, 151, 297–305.

(9) Wei, L.; Zhao, T. S.; Zeng, L.; Zhou, X. L.; Zeng, Y. K. Copper Nanoparticle-Deposited Graphite Felt Electrodes for All Vanadium Redox Flow Batteries. Appl. Energy 2016, 180, 386–391.

(10) Mehboob, S.; Mehmood, A.; Lee, J.-Y.; Shin, H.-J.; Hwang, J.; Abbas, S.; Ha, H. Y. Excellent Electrocatalytic Effects of Tin through: In Situ Electrodeposition on the Performance of All-Vanadium Redox Flow Batteries. J. Mater. Chem. A 2017, 5 (33), 17388–17400.