One possible solution to prevent catalyst poisoning is through a protective oxide coating on its surface. ALD was chosen due to its highly controllable, conformal deposition, but also as it can be applied to a wide range of commercial catalysts, making it highly applicable for real world applications. Vanadium oxide was deposited on a commercial 50% Pt/C catalyst via ALD, chosen for its precise control in both layer thickness and conformality on the surface of the catalyst. XPS, HRTEM and HAADF-STEM confirmed the ALD process had deposited vanadium oxide species selectively on the Pt.
The stability of the material in the presence of bromide/tribromide solution was tested via XPS, ICP-AES and electrochemistry. The uncoated Pt/C is unactive towards Hads after 180 seconds, and completely dissolved after 600 seconds, whereas the coated samples could still adsorb H after 600 seconds. XPS and ICP-AES showed that after an initial mass loss the V2O5 coating is stabilized on the Pt surface, preventing the bromide species from reaching and dissolving the Pt.
The coating had a positive effect on the HOR. The kinetics were assessed via RDE HOR polarization in an alkaline electrolyte, as they’re too fast to be measured via RDE in acid electrolytes. The mass activities of the coated samples increased as the coating thickness increased, up to 156% for the sample coated with 720 ALD cycles. The CV shows enhanced H and O adsorption/desorption on the Pt, indicating that the improvement of HOR kinetics is due to the interface between the Pt and the oxide.
This demonstrates that oxide coating can be used to protect the catalysts in corrosive electrolytes without inhibiting HOR/HER. Whilst it has been demonstrated for bromine poisoning of Pt, this approach should be applicable to many poisoning problems facing other catalysts/applications. ALD is an ideal technique to produce these materials due to selective, controllable deposition. The oxide coating tested here also increased HOR kinetics in alkaline electrolytes, reducing the amount of Pt needed for good performance.
(1) Li, Q.; He, R.; Gao, J.-A.; Jensen, J. O.; Bjerrum, N. J. The CO Poisoning Effect in PEMFCs Operational at Temperatures up to 200°C. J. Electrochem. Soc. 2003, 150 (12), A1599. https://doi.org/10.1149/1.1619984.
(2) Stühmeier, B. M.; Selve, S.; Patel, M. U. M.; Geppert, T. N.; Gasteiger, H. A.; El-Sayed, H. A. Highly Selective Pt/TiOx Catalysts for the Hydrogen Oxidation Reaction. ACS Appl. Energy Mater. 2019, 2 (8), 5534–5539. https://doi.org/10.1021/acsaem.9b00718.
(3) Singh, N.; McFarland, E. W. Levelized Cost of Energy and Sensitivity Analysis for the Hydrogen-Bromine Flow Battery. J. Power Sources 2015, 288, 187–198. https://doi.org/10.1016/j.jpowsour.2015.04.114.
(4) Saadi, K.; Nanikashvili, P.; Tatus-Portnoy, Z.; Hardisty, S.; Shokhen, V.; Zysler, M.; Zitoun, D. Crossover-Tolerant Coated Platinum Catalysts in Hydrogen/Bromine Redox Flow Battery. J. Power Sources 2019, 422, 84–91. https://doi.org/10.1016/J.JPOWSOUR.2019.03.043.
(5) Tucker, M. C.; Cho, K. T.; Spingler, F. B.; Weber, A. Z.; Lin, G. Impact of Membrane Characteristics on the Performance and Cycling of the Br2-H2 Redox Flow Cell. J. Power Sources 2015, 284, 212–221. https://doi.org/10.1016/j.jpowsour.2015.03.010.
(6) Hardisty, S. S.; Frank, S.; Zysler, M.; Yemini, R.; Muzikansky, A.; Noked, M.; Zitoun, D. Selective Catalyst Surface Access through Atomic Layer Deposition. ACS Appl. Mater. Interfaces 2021. https://doi.org/10.1021/ACSAMI.1C20181.