Carbon-tolerant Ni-based cermet anodes modified by proton conducting yttrium- and ytterbium-doped barium cerates for direct methane solid oxide fuel cells

Abstract

Conventional Ni-based cermet anodes such as Ni-gadolinia doped ceria (Ni-GDC) suffer from low carbon deposition resistance in direct methane solid oxide fuel cells (SOFCs). Here we show that impregnating proton conducting perovskites like BaCe_0.9Y_0.1O_3−δ (BCY) and BaCe_0.9Yb_0.1O_3−δ (BCYb) in Ni-GDC not only improves the initial polarization performance but also, most importantly, significantly enhances the stability in wet methane fuel (3% H₂O in CH₄) by inhibiting carbon deposition and formation. In wet methane, the voltage of the cell with the conventional Ni-GDC anode decreases rapidly from 0.58 to 0.15 V within 6 h at 200 mA cm⁻² and 750 °C. In contrast, in the case of the cells with BCY + Ni-GDC and BCYb + Ni-GDC anodes, the cell voltage is essentially constant at 0.62–0.65 V over a period of 48 h tested under identical conditions. The microstructure and Raman spectroscopy analysis reveal that the impregnated fine BCY and BCYb particles are preferentially distributed on the surface of the Ni grains in the Ni-GDC anode, decreasing the exposed surface of Ni grains and inhibiting carbon deposition. Also, the proton conducting and fine BCY and BCYb particles can adsorb and decompose water, which in turn reacts with deposited carbon to form CO and H₂, alleviating the carbon deposition problem in the anode and thus significantly improving the cell stability of direct methane SOFCs.