Coking-resistant Ce_0.8Ni_0.2O_2-δ internal reforming layer for direct methane solid oxide fuel cells

The development of direct methane solid oxide fuel cells (SOFCs) is severely hindered by the deactivation of conventional Ni-based anodes due to carbon fouling. Here, a Ce_0.8Ni_0.2O_2-δ (CNO) internal reforming layer is imposed on conventional Ni-Sm_0.2Ce_0.8O_2-x (SDC) anodes for direct methane SOFCs. In CNO, there are two types of Ni species which are segregated NiO dispersed over the CNO and incorporated Ni²⁺ in the ceria lattice, respectively. The Ni²⁺ dopants are stable in wet hydrogen at 650 °C; however, the segregated NiO is reduced into Ni under the same conditions. With the doping of Ni²⁺ into the ceria lattice, surface oxygen vacancies are generated in CNO. For the stability testing in wet methane (∼3 mol% H₂O in methane) at 650 °C and 0.2 A cm⁻², the voltage of the conventional Ni-SDC anode decreases by 43.1% in approximately 26 h, whereas the CNO internal reforming layer operates stably for 40 h. In wet methane at 650 °C, with the addition of the CNO internal reforming layer, the polarization resistance of the Ni-SDC anode reduces by 22.3% from 0.0917 to 0.0712 Ω cm², and the maximum current density of it increases from 614 to 664 mW cm⁻².