Unraveling the precise location and nature of active sites is of paramount significance for the understanding of the catalytic mechanism and the rational design of efficient electrocatalysts. Here, we use well-defined crystalline cobalt oxyhydroxides CoOOH nanorods and nanosheets as model catalysts to investigate the geometric catalytic active sites. The morphology-dependent analysis reveals a ~50 times higher specific activity of CoOOH nanorods than that of CoOOH nanosheets. Furthermore, we disclose a linear correlation of catalytic activities with their lateral surface areas, suggesting that the active sites are exclusively located at lateral facets rather than basal facets. Theoretical calculations show that the coordinatively unsaturated cobalt sites of lateral facets upshift the O 2p-band center closer to the Fermi level, thereby enhancing the covalency of Co-O bonds to yield the reactivity. This work elucidates the geometrical catalytic active sites and enlightens the design strategy of surface engineering for efficient OER catalysts.

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Effective nonprecious metal catalysts are urgently needed for hydrogen evolution reaction (HER). The hybridization of N-doped graphene and a cost-effective metal is expected to be a promising approach for enhanced HER performance but faces bottlenecks in controllable fabrication. Herein, a silica medium-assisted method is developed for the high-efficient synthesis of single-layer N-doped graphene encapsulating nickel nanoparticles (Ni@SNG), where silica nanosheets molecule sieves tactfully assist the self-limiting growth of single-layer graphene over Ni nanoparticles by depressing the diffusion of gaseous carbon radical reactants. The Ni@SNG sample synthesized at 800 °C shows excellent activity for HER in alkaline medium with a low overpotential of 99.8 mV at 10 mA cm–2, which is close to that of the state-of-the-art Pt/C catalyst. Significantly, the Ni@SNG catalyst is also developed as a binder-free electrode in magnetic field, exhibiting much improved performance than the common Nafion binder-based electrode. Therefore, the magnetism adsorption technique will be a greatly promising approach to overcome the high electron resistance and poor adhesive stability of polymer binder-based electrodes in practical applications.

Materials with different wettability features have attracted intensive attention due to their outstanding performances and the broad application prospects. In this work, we report an applicable and economical surface thermal oxidation method for fabricating copper oxide nanotip arrays with tunable wettability: superhydrophobicity of Cu2O nanotip array (Cu2O NA) and superhydrophilicity of CuO nanotip array (CuO NA). The superhydrophobic Cu2O NA surface presented a high water contact angle (WCA) of 161.1° and ultralow water sliding angle nearly 0°, which is an applicable property for droplet transportation in microfluidic devices. Meanwhile, the CuO NA surface exhibited a near 0° WCA as well as ultrashort wetting time for water, which indicates that the CuO NA is a promising material for oil/water separation. The dramatically transformed wettability of the two surfaces is contributed by the synergetic effect of the special convex hierarchical micro–nano structure and the nature of surface materials. The superior water affinity of CuO is attributed by the hydrolysis process, which was demonstrated by the density functional theory simulation. In addition, The Cu2O NA presented outstanding chemical and mechanical enduring reliability under harsh environments. The cost-effective fabricating process, easily controlled wettability, and special wetting performance make the Cu oxide nanotip arrays promising materials for microfluid devices and oil/water separation.

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