Novel Anode Catalysis for Ammonia Solid Oxide Fuel Cell

Abstract

Ammonia (NH3) is attractive as a hydrogen carrier and a suitable fuel for solid oxide fuel cells (SOFCs) because it has high hydrogen density and can be easily liquefied at an ambient temperature., However, the activity of conventional Ni cermet anodes of SOFCs for NH3 oxidation is much lower than that when H2 is used as a fuel [1]. It is necessarily to improve the anode activity for NH3 oxidation for realizing NH3-fueled SOFCs. There are many studies on the Ni-based anodes for NH3-SOFCs. However, the number of report on the bimetallic anode for NH3-SOFCs is limited. Previously, we have investigated the activity of Ni-M (M = Fe, Mo ,Ta, W and Nb) cermet anodes for NH3-SOFCs at temperature of 700 - 900 °C [2-5]. In these studies, we found that the anode polarization was greatly improved by transition metal additives, which favored the formation of metal (and/or alloy) nitrides in the anode under operation condition. Furthermore, the activation energy of NH3 oxidation at the anode was strongly dependent on the metal additive, suggesting that a metal-nitrogen biding energy of catalysis was related to the catalytic activity for NH3 oxidation. Among these anodes, Ni-Fe and Ni-Mo cermet anodes were highly active for the electrochemical oxidation of NH3 at 700 °C and expected for the active anode of NH3-SOFCs at intermediate temperature. In this study, we further investigated the effects of Fe and Mo additives to Ni cermet anode on the cell performance at temperature of 500 - 600 °C. Fig.1 shows the current density versus voltage (I–V) curves for the electrolyte supported cells: Ni40-Fe60/SDC, Ni97-Mo3/SDC and Ni/SDC|LSGM|SSC at 600 °C. The thickness of LSGM electrolyte was 300 µm. The cell performance was significantly improved by the addiction of Fe and Mo as shown in Fig.1. The formation of alloy nitrides in both Ni-Fe and Ni-Mo anodes was observed under operation condition. The role of alloy nitrides in the NH3oxidation will be discussed. Acknowledge This work was supported by “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan and by JSPS-KAKENHI Grant Number C16K05958. Reference [1] Q. Ma et al., J. Power Sources 161 (2006) 95. [2] W. Akimoto et al., Solid State Ionics 256 (2013) 1. [3] M. Hashinokuchi et al.,Solid state Ionics 285(2016) 222. [4] M. Hashinokuchi et al., ECS Transactions 68 (2015) 2739. [5] R. Yokochi et al., ECS Transactions 68 (2015) 2745. Figure 1