NiCo and NiCu Based-Materials for Hydrogen Production and Electro-oxidation Reactions

Ni1-xCoxO-CGO, Ni1-xCuxO-CGO, CuOCGO and NiO-CGO composites powders were obtained by a one-step synthesis method and their catalytic activities in dry reforming of methane (CH4+CO2) for hydrogen production were evaluated. X-ray diffraction (XRD) analysis of composite powders confirmed NiO, Co3O4, CuO and Ce0.9Gd0.1O1.95 cubic phases. XRD results also showed the formation of nanocrystalline materials. Cobalt-based materials showed higher surface area values (SBET) than copper-based materials. According to temperature programmed reduction (TPR) analyses, Ni0.6Co0.4O-CGO (NiCo0.4) and Ni0.4Co0.6O-CGO (NiCo0.6) catalysts have higher reduction capacity and stronger metal/support interaction than Ni0.6Cu0.4O-CGO (NiCu0.4) and Ni0.4Cu0.6O-CGO (NiCu0.6) materials. Rietveld refinement analyses for NiCo0.4, NiCo0.6 and NiCu0.4 reduced catalysts, confirmed the presence of Ni-Co and Ni- Cu alloys. These factors are important for enhanced catalytic activity avoiding carbon deposition. NiCo0.4 and NiCo0.6 catalysts had higher conversions of CH4 and CO2 than Ni-CGO and Cu-based catalysts. NiCo-based catalyst showed a better resistance to carbon deposition. NiCo0.4 had high H2/CO ratio and the best reaction selectivity below 600 ºC. The electrocatalytic activity of NiCo0.4/CGO/NiCo0.4 screen-printed symmetrical cells from hydrogen and synthetic biogas (CH4+CO2) electro-oxidation reaction was studied by impedance spectroscopy in the temperature range between 650 and 850 ºC. The polarization resistance was influenced by the atmosphere conditions. Total polarization resistances (Rp) of 0.96 and 36.10 Ω cm2 were obtained at 750 °C for H2 and biogas atmospheres, respectively. The activation energy (Ea) was lower when H2 was used (0.92 eV). The hydrogen oxidation reaction occurs more easily than the dry reforming of methane.

Keywords: Alloy, Carbon Deposition, Dry Reforming of Methane, One Step Synthesis, Electro-Oxidation Reaction, Hydrogen, Impedance Spectroscopy Surface Area, Metal/Support Interaction, Reduction Capacity.