Hierarchical pine tree-like α-MnO2 architectures are prepared by a facile one-step method without any template. The hierarchical α-MnO2 is composed of branched α-MnO2 short nanorods assembled onto the backbone of an α-MnO2 long nanowire. Time-dependent experiment shows that the growth process of the branched α-MnO2 nanostructures is the formation of β-MnOOH and then the transformation to a α-MnO2 branched structure in a step by step manner. Owing to its specific structure features, the hierarchical pine tree-like α-MnO2 exhibits superior catalytic performance in the catalytic combustion of dimethyl ether with a light-off temperature (T10) at 169 °C and a complete conversion temperature (T90) of 235 °C, which is far better than commercial MnO2.
Developing efficient, low-cost and bifunctional catalysts with predominant durability for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is an extraordinary challenge in the preparation of green hydrogen energy by electrochemical water splitting. Three-dimensional (3D) transition metal compounds have become a research hotspot as OER electrocatalysts , which can replace noble metal oxides such as RuO 2 and IrO 2 to reduce application costs. Herein, we synthesized a novel three-dimensional pine-tree-like bimetallic sulfide arrays on nickel foam (FeCoS/NF) using various optimization strategies such as morphology optimization, in situ growth and introduction of heterogeneous structures. The as-synthesized FeCoS/NF electrocatalyst only requires relatively low overpotential of 156 mV to achieve a current density of 20 mA cm −2 for OER, with a Tafel slope of only 37 mV dec −1 . It also has a small charge transfer resistance, an electrochemical surface area and good electrochemical stability in alkaline electrolytes . The excellent performance of FeCoS/NF can be attributed to the synergistic effect and amorphous phase of FeCoS as well as the well-defined pine-tree-like array architecture with a large surface area, abundant active sites, and sufficient gas and electrolyte diffusion channels.
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