Ammonia as an SOFC Fuel

Abstract

SOEC operation using ammonia as a fuel was investigated. At high temperatures (T>800oC) cell performance closely resembles performance in equivalent gas mixtures of N2 and H2. Between 600 oC < T < 750 oC, however, a mild impeding effect of presence of ammonia on the hydrogen oxidation rate is observed. Further, the fuel cell durability when operating on ammonia was tracked over test periods between 2000 and 6000 hours at different temperatures. In general, degradation rates observed in ammonia were similar to degradation rates observed when operating in a 1:3 gas mixture of N2/H2. Some morphological changes in the fuel electrode support and auxiliary Ni-meshes were observed after test. These indicate Ni-nitride formation and whereas this is detrimental to the Ni-mesh, it did not affect overall cell performance. Experiments with ammonia operation at stack level were also conducted illustrating the potential to realize a stack cooling by internal ammonia cracking.