Various simple and layered perovskites have been extensively investigated as promising cathode materials for metal‐air batteries and fuel cells, because of their tunable structural, electronic, and chemical properties. However, the electrocatalytic activity of perovskite oxides towards the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) must be improved by increasing the slow kinetics and by decreasing the overpotential associated with those reactions. Doping with other transition metals such as Ni, Mn, Fe and Cu represents one of the effective chemical methods to improve the catalytic activity of perovskite oxides. Herein, we investigate Ni‐doped cobalt‐based double perovskites, PrBa0.5Sr0.5Co2‐xNixO5+δ (x=0, 0.1, 0.2 and 0.3), as promising cathode materials for rechargeable alkaline Zn‐air batteries. PrBa0.5Sr0.5Co1.9Ni0.1O5+δ (PBSCN1) shows low Tafel slopes (OER: 83 mV dec−1 and ORR: 67 mV dec−1), favorable onset potentials (OER: 1.513 V vs. RHE at 1 mA cm−2 and ORR: 0.720 V vs. RHE at −1 mA cm−2), and high limiting currents (OER: 25.20 mA cm−2 and ORR: −5.67 mA cm−2). In addition, it shows improved discharge‐charge performances for a full‐cell Zn‐air battery. The enhanced electrochemical properties of PBSCN1 could be achieved by the high concentration of surface oxygen species, and the coexistence of different chemical states of cobalt cations caused by the presence of nickel cations in the lattice. Based on these results, PrBa0.5Sr0.5Co1.9Ni0.1O5+δ could be considered a promising cathode material for Zn‐air battery systems.
This work studied an effect of anionic precursor on the preparation of active and fine nickel metal catalysts for syngas methanation. Nickel catalysts were pr¬epared by impregnation-co-precipitation method. Nickel hydrate salts of Ni(NO3)2·6H2O, NiSO4·6H2O and NiCl2·6H2O were used as a metal catalyst precursor, and the obtained catalysts were named as Ni/Al (N), Ni/Al (S) and Ni/Al (Cl), respectively. Methanation synthesis of carbon monoxide was carried out in a fixed bed stainless reactor. Prior to experiment, the catalyst powder was pressed into tablets, then crushed and sieved to use 0.5-0.9 mm particles. Reactions were performed at the temperature of 350 °C in the pressure of 3 atm of H2:CO syngas (the molar ratio of 3:1) with the GHSV of 3000 h-1. In the present methanation conditions, the Ni/Al (N), Ni/Al (S) and Ni/Al (Cl) catalysts gave the CH4 selectivity of 93%, 18% and 91% (vol.), respectively. The XRD and ICP-OES analysis clarified that although the Ni/Al (S) catalyst contained a similar nickel amount of 17.4 wt % to other two catalysts, its metal distribution was poor. Also the low activity of the Ni/Al (S) catalyst was caused by the contamination of remained sulfur from sulfate precursor. This work also examined an influence of catalyst activation temperature pre-synthesis. The Ni/Al (N) catalyst was reduced by pure hydrogen gas at different temperatures of 350 ºС, 400 ºС or 450 ºС. The catalyst activated at 400 ºС produced the highest CH4 amount of 0.087 mmol·g-1cat for the duration of 1h methanation. An initial temperature of methane formation was the lowest for the Ni/Al (N) catalyst which was activated at 400 ºС among three catalysts.
The high cost and limited availability of the precious metal catalysts required for catalysing the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in metal–air batteries restrict the marketing of these clean energy technologies.
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