Electrical energy storage technologies are needed when significant fraction of intermittent renewable energy sources such as wind and solar are integrated into the electrical grids. The hydrogen-bromine (H₂-Br₂) reversible fuel cell system is one of the promising technologies because of its high round-trip conversion efficiency, high power density capability and low cost. In a hydrogen bromine fuel cell, while carbon surface can be for the bromine reactions, a noble metal such as platinum is needed for the hydrogen reactions. Since platinum is not stable in HBr/Br₂ environment and HBr and Br₂ are expected to cross from the bromine electrode to the hydrogen electrode during operation, a more durable and active catalysts is needed for the hydrogen reactions. Rh_xS_y catalysts have been found to be stable in the HBr/Br₂ environment and as active as platinum per active area.^{1, 2}

Commercial Rh_xS_y catalysts have large and broad particle sizes (12-40 nm) and consequently low mass specific active area (< 10 m²/g) for HOR. To address this problem, we explore the core-shell approach used by others ³ as a way to increase the mass specific area of these Rh_xS_y catalysts. Figure 1 shows the mass specific active surface area (ECSA) of the core-shell and commercial Rh_xS_y catalysts, and Table 1 shows a comparison of the mass specific ECSA and durability of commercial 20 wt. % Pt/C and commercial and core-shell Rh_xS_y catalysts. These results show that the core shell Rh_xS_y catalyst has much higher mass specific ECSA than commercial Rh_xS_y catalyst and superior durability over platinum catalyst. This presentation will discuss the approach used to synthesis the core-shell Rh_xS_y catalyst and the characteristics and performance of this catalyst.

Figure 1. CV of core-shell and commercial Rh_xS_y catalysts, measured in 1M H₂SO₄ at 10mV/s

 

 

	KU Core-Shell RhxSy/C		20 wt.% Pt/C		Commercial RhxSy/C
Time in 1M HBr (hr)	m2/g	%	m2/g	%	m2/g	%
0	61.4	100	127.3	100	7.8	100
24	60.2	98	82.7	65
48	58.4	97	42.2	51

 

Table 1. Durability in 1M HBr solution of Pt/C and commercial and core-shell RhxSy catalysts

 

 

References

1. Anna Ivanovskaya, Nirala Singh, Ru-Fen Liu, Haley Kreutzer, Jonas Baltrusaitis, Trung Van Nguyen, Horia Metiu, Eric W McFarland, “Transition Metal Sulfide Hydrogen Evolution Catalysts for Hydrobromic Acid Electrolysis,” Langmuir, 29(1), 480-492 (2013).
2. Jahangir Masud, Trung Van Nguyen, Nirala Singh, Eric McFarland, Myles Ikenberry, Keith Hohn, Chun-Jern Pan, and Bing-Joe Hwang, “A RhxSy/C Catalyst for the Hydrogen Oxidation and Hydrogen Evolution Reactions in HBr,” J. Electrochem. Soc., 162 (4), F455-F462 (2015).
3. Hee-Young Park, Tae-Yeol Jeon, Jong Hyun Jang, Sung Jong Yoo, Kug-Seung Lee, Yoon-Hwan Cho, Kwang-Hyun Choi, Yong-Hun Cho, Namgee Jung, Young-Hoon Chung and Yung-Eun Sunga, “Hydrogen Oxidation Reaction Activity of Sub-Monolayer Pt-Shell/Pd-Core Nanoparticles,” J. Electrochem. Soc., 160 (1), H62-H66 (2013).

 

Acknowledgements

The work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000262 and the National Science Foundation under Grant No. EFRI-1038234 and No. 1416874, as a sub-award from Proton Onsite.