NiMo As Non-Precious Metal Catalyst for Hydrogen Oxdiation Reaction in Alkaline Media

Abstract

Fuel cell is environment-friendly power source which has high efficiency in generating electricity. Polymer electrolyte fuel cell uses hydrogen as a fuel that only produces water as byproduct which does not cause any pollution. Currently, commercialized Nafion-based polymer electrolyte membrane fuel cell (PEMFC) applied Pt/C as both cathode and anode catalyst which cause cost inefficiency in manufacturing fuel cell stack. Anion exchange membrane fuel cell (AEMFC) is being developed to combine advantages of both PEMFC and traditional alkaline fuel cell (AFC). By adopting solid membrane as electrolyte, leakage problem and insoluble salt precipitation could be solved. Furthermore, alkaline condition enhances oxygen reduction reaction (ORR) kinetics which obstructs cell power in PEMFC. However, stability of membrane is still in issue, and hydrogen oxidation reaction (HOR) kinetics are significantly diminished [1], which leads to higher Pt loading. This research is focusing at slow HOR kinetics and reducing catalyst cost by replacing Pt into non-precious metals such as transition metals. One of the well-known HOR catalyst for alkaline fuel cell is nickel. Several studies show nickel has catalytic activity of hydrogen oxidation in alkaline media [2,3], but it’s not enough to overcome precious metals such as platinum. Therefore, diverse researches tried to enhance activity of nickel by expanding surface area or doping other elements [4]. However, these catalytic activities were only tested in 6 M KOH, 60~80 ℃ condition, which is identical to real cell operating condition. NiMo catalyst was synthesized by electrodeposition method which is cost-effective way to produce. Nickel chloride is used for nickel source, and sodium molybdate worked as molybdenum source. Galvanostatic electrodeposition was applied to synthesize NiMo catalyst. Rotating disk electrode (RDE) was used to remove evolved hydrogen efficiently. HOR activity was measured in hydrogen saturated 0.1 M KOH solution. RDE was used to control diffusion with 1600 rpm speed. Experiment was held at room temperature. To remove capacitive current, steady state polarization method was applied for measuring HOR activity. Figure 1 shows HOR current of commercial Pt/C, electrodepositied NiMo, Ni. Adding small amount of Mo in Ni increases HOR current significantly. At overpotential of 20 mVRHE, Pt/C shows current density of 1.12 mA/cm2, where NiMo has 0.86 mA/cm2which is about 77% of Pt/C HOR activity. Reference [1] W. Sheng, et al., J. Electrochem. Soc. 157 (11), B1529 (2010) [2] T. Tomida, et al., J. Electrochem. Soc. 136 (11), 3296 (1989) [3] H. K. Lee, et al., Mat. Chem. Phys., 55, 89 (1998) [4] J. A. Linnekoski, J. Fuel Cell Sci. Tech., 4, 45 (2007) Figure 1