Low temperature synthesis of NiO/CoO nanostructures to enhance their low temperature oxygen reduction catalysis

"Thermal expansion and cold contraction" are common occurrences in nature. Resulting from "thermal expansion and cold contraction" reaction, strain effect is created, which affects the oxygen reduction reaction (ORR) activities of fuel cell catalysts. Nevertheless, the "thermal expansion and cold contraction" effects of catalysts have rarely been investigated. Herein, the influence of "thermal expansion and cold contraction" strains upon ORR activities of NiO/CoO catalysts is investigated. Experimental and first-principles calculations reveal that, when NiO/CoO are synthesized and used as catalysts under low temperature ice/water environment, there is virtually no strain effect created, and abundant active sites contribute to the good low temperature ORR activities of NiO/CoO catalysts (onset potential: 0.736 V, halfwave potential: 0.659 V). When high temperature synthesized NiO/CoO catalysts are used at low temperature, however, small amounts of active sites are created. Moreover, the adsorption activity of NiO(222) and CoO(311) stepped active sites are weakened by compressive strain of lattice contraction, which reduces their ORR activities. The "low temperature synthesis and low temperature catalysis" route proposed by this paper paves a new road for the synthesis and design of low-temperature catalysts.