Comparing Different Nanoparticles Protecting Layers That Can Slow Down the Degradation of Pd-Ni Based Catalyst during Hydrogen Oxidation Reaction (HOR) in Alkaline Media

Abstract

Alkaline fuel cell (AFC) technology has several advantages over the mature Proton exchange membrane fuel cell (PEMFC), notably its low cost, coming from the use of non-Pt catalysts. [1] Gencell Energy is one of the very few companies that invest in AFC, with a specialty on membraneless AFC that can be used at extreme weather condition without compromising their lifetime and efficiency, where it is impossible to use PEMFC. The 6.6 M KOH electrolyte of membraneless AFC drive is a key to its robustness [2,3], but it is a highly corrosive environment, in which the HOR catalyst on the anode side can deactivate. Based on previously reports, Pd-Ni is a good candidate for HOR in high pH compared to Pt-based catalysts [4,5]. Yet, after long-term operation, Pd-Ni still suffer severe particle detachment and passivation. To increase the durability of such catalyst, forming a protecting layer that covers the nanoparticle is necessary, without hindering the HOR activity. [6,7] This work presents a variety of protecting layers that cover the Pd-Ni particles to slow down the degradation. An example of HOR activity for one of the Pd-Ni capped is presented in Figure 1. The Pd-Ni capped generation 1 (G1)/ Vulcan XC72 needs an activation using prolonged potential cycling in Ar (typically 300 CVs from 0.1-1.23 V vs. RHE, 100 mV/s). Once the catalyst is fully activated, accelerated stress tests (AST) are performed up to 3300 cycles to track the durability of the catalyst. As shown, after 21 AST runs (which corresponds to 3150 CVs), the catalyst still maintains its HOR activity. It will be shown that different cover layers (varying in type and thickness of the cover) enable to modulate the materials’ activation and durability. In any case, the HOR activity and rate of degradation of Pd-Ni with different protecting layers is tracked using IL-TEM, XRD and XPS pre and post AST.(1) Simon, C.; Hanzlik, M.; Gasteiger, H. A.; Schuler, T.; Durst, J.; Siebel, A.; Hasche, F.; Herranz, J.; Rheinlander, P. J. Hydrogen Oxidation and Evolution Reaction (HOR/HER) on Pt Electrodes in Acid vs. Alkaline Electrolytes: Mechanism, Activity and Particle Size Effects. ECS Trans. 2014, 64 (3), 1069–1080.(2) Gülzow, E. Alkaline Fuel Cells. Fuel Cells 2004, 4 (4), 251–255.(3) Gouérec, P.; Poletto, L.; Denizot, J.; Sanchez-Cortezon, E.; Miners, J. H. The Evolution of the Performance of Alkaline Fuel Cells with Circulating Electrolyte. J. Power Sources 2004, 129 (2), 193–204.(4) Sankar, S.; Anilkumar, G. M.; Tamaki, T.; Yamaguchi, T. Binary Pd−Ni Nanoalloy Particles over Carbon Support with Superior Alkaline Formate Fuel Electrooxidation Performance. ChemCatChem 2019, 11 (19), 4731–4737.(5) Zhao, Y.; Wang, G.; Xiao, L.; Lu, J.; Zhuang, L. Hydrogen Oxidation Reaction on Pd-Ni(OH)2 Composite Electrocatalysts in an Alkaline Electrolyte. ChemistrySelect 2020, 5 (26), 7803–7807.(6) Yang, Y.; Sun, X.; Han, G.; Liu, X.; Zhang, X.; Sun, Y.; Zhang, M.; Cao, Z.; Sun, Y. Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel-Based Metal–Organic Framework. Angew. Chemie - Int. Ed. 2019, 58 (31), 10644–10649.(7) Gao, Y.; Peng, H.; Wang, Y.; Wang, G.; Xiao, L.; Lu, J.; Zhuang, L. Improving the Antioxidation Capability of the Ni Catalyst by Carbon Shell Coating for Alkaline Hydrogen Oxidation Reaction. ACS Appl. Mater. Interfaces 2020, 12 (28), 31575–31581. Figure 1