On‐again, off‐again personality: Superhydrophobic conducting polypyrrole (PPy) films are synthesized through a facile electrochemical process. The PPy films exhibit an extended porous structure with both coarse‐ and fine‐scale roughness (see image). By controlling the electrical potential, PPy films can be switched between the oxidized state and the neutral state, resulting in reversibly switchable superhydrophobic and superhydrophilic properties.

The development of efficient and cost-effective catalysts to catalyze a wide variety of electrochemical reactions is key to realize the large-scale application of renewable and clean energy technologies. Owing to the maximum atom-utilization efficiency and unique electronic and geometric structures, single atom catalysts (SACs) have exhibited superior performance in various catalytic systems. Recently, assembled from the functionalized organic linkers and metal nodes, metal-organic frameworks (MOFs) with ultrafine porosity have received tremendous attention as precursors or self-sacrificing templates for preparing porous SACs. Here, the recent advances toward the synthesis strategies for using MOF precursors/templates to construct SACs are systematically summarized with special emphasis on the types of central metal sites. The electrochemical applications of these recently emerged MOF-derived SACs for various energy-conversion processes, such as oxygen reduction/evolution reaction (ORR/OER), hydrogen evolution reaction (HER), and CO 2 reduction reaction (CO 2 RR), are also discussed and reviewed. Finally, the current challenges and prospects regarding the development of MOF-derived SACs are proposed.

Exploring efficient and cost-effective catalysts to replace precious metal catalysts, such as Pt, for electrocatalytic oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) holds great promise for renewable energy technologies. Herein, we prepare a type of Co catalyst with single-atomic Co sites embedded in hierarchically ordered porous N-doped carbon (Co-SAS/HOPNC) through a facile dual-template cooperative pyrolysis approach. The desirable combination of highly dispersed isolated atomic Co-N4 active sites, large surface area, high porosity, and good conductivity gives rise to an excellent catalytic performance. The catalyst exhibits outstanding performance for ORR in alkaline medium with a half-wave potential (E1/2) of 0.892 V, which is 53 mV more positive than that of Pt/C, as well as a high tolerance of methanol and great stability. The catalyst also shows a remarkable catalytic performance for HER with distinctly high turnover frequencies of 0.41 and 3.8 s−1 at an overpotential of 100 and 200 mV, respectively, together with a long-term durability in acidic condition. Experiments and density functional theory (DFT) calculations reveal that the atomically isolated single Co sites and the structural advantages of the unique 3D hierarchical porous architecture synergistically contribute to the high catalytic activity.

Herein, we report efficient single copper atom catalysts that consist of dense atomic Cu sites dispersed on a three-dimensional carbon matrix with highly enhanced mesoporous structures and improved active site accessibility (Cu-SA/NC­(meso)). The ratio of +1 to +2 oxidation state of the Cu sites in the Cu-SA/NC­(meso) catalysts can be controlled by varying the urea content in the adsorption precursor, and the activity for ORR increases with the addition of Cu1+ sites. The optimal Cu1+-SA/NC­(meso)-7 catalyst with highly accessible Cu1+ sites exhibits superior ORR activity in alkaline media with a half-wave potential (E 1/2) of 0.898 V vs RHE, significantly exceeding the commercial Pt/C, along with high durability and enhanced methanol tolerance. Control experiments and theoretical calculations demonstrate that the superior ORR catalytic performance of Cu1+-SA/NC­(meso)-7 catalyst is attributed to the atomically dispersed Cu1+ sites in catalyzing the reaction and the advantage of the introduced mesoporous structure in enhancing the mass transport.

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We report the preparation and use of the three-dimensionally ordered mesoporous Ni sphere arrays (3D-OMNiSA) as a highly effective OER catalyst in alkaline electrolyte. The 3D-OMNiSA is fabricated through lyotropic liquid crystal templating within a polymer inverse opal. The prepared 3D-OMNiSA catalyst exhibits a low overpotential of 254 mV at 10 mA cm −2 and a small Tafel slope of 39 mV decade −1 , better than the commercial precious RuO 2 catalyst. The mass activity (166.5 A g −1 ) and turnover frequency (0.0281 s −1 ) of 3D-OMNiSA are about 4.3 and 2.2 times that of RuO 2 , respectively. Additionally, this 3D-OMNiSA catalyst shows a high durability under harsh water oxidation cycling test. The outstanding OER performance of the 3D-OMNiSA could be attributed to the large surface area, efficient mass and charge transport, and high structural stability arising from the unique 3D hierarchical porous structure of the 3D-OMNiSA consisting of ordered close-packed mesoporous spheres.

Nickel and gold meshes having three-dimensional periodicity at optical wavelengths and nanoscale structural fidelity have been prepared by electrodeposition within closepacked silica sphere arrays.There is major current interest in the fabrication of nanoporous metal arrays. [1][2][3][4] Routine access to such materials could impact a variety of areas including photonics, magnetics, catalysis, electrochemical applications and thermoelectrics. Recent reports have described the formation of 3-D metal meshes within colloidal silica or polymer membranes through the use of molten metal infiltration, nanoparticle infiltration and electroless methods. 4-6 Though metal electrodeposition methods have been effectively used for membranes with one-dimensional pore structures, 7 the extension of this technique to threedimensional structures has not been reported. This electrochemical method has the major advantage of readily producing well defined metal meshes of materials melting at such high temperatures that melt infiltration is prohibited by template structural instability. Herein, we describe the use of this approach for the fabrication of nickel and gold arrays having three-dimensional periodicity at optical wavelengths.Silica membranes (opal) were prepared by published methods. 8 Silica spheres with a diameter of ca. 300 nm diameter were initially prepared from tetraethylorthosilicate (TEOS). The spheres were then formed into close-packed lattices through a sedimentation process over several months. This precipitate was then sintered at 120 °C for two days and then 750 °C for 4 h, producing a robust opalescent piece that could be readily cut into smaller sections. Electrodes were formed from the opal (typically 7 3 10 3 1.5 mm) by first depositing ca. 0.5 mm thick copper films on one side of the piece by magnetron sputtering. A length of wire was attached to the copper backing with silver paste (Ted Pella, Inc.) and the copper/wire side of the electrode, as well as the edges, were sealed off with neoprene glue (Elmer's). For metal deposition, the electrodes were immersed into nickel or gold plating solutions (Technic, Inc.) with a platinum wire counter electrode. Electrodeposition was carried out by a constant current method over a 36 h period; a low current density (0.50 mA cm 22 ) was used in an effort to achieve even deposition within the opal membrane. Low current densities such as that used here have been found to be effective in the growth of nanowires. After deposition, the opal was washed thoroughly with distilled water and the neoprene layer peeled off. To remove the silica matrix, the metal-opal pieces were soaked in a 2% HF solution for 24 h. This resulted in a dark opalescent metal membrane (ca. 100 mm thick). Scanning electron micrographs (SEM) were obtained on a JEOL JSM 5410 SEM. Magnetic measurements on the nickel mesh were performed on a Quantum Design MPMS-5S SQUID susceptometer. The mesh was fixed between two pieces of Kapton tape and placed in a commercially available soda straw. No correction for t...

A novel polyaniline nanofibre supported platinum (Pt) nanoelectrocatalyst is developed for direct methanol fuel cells (DMFCs). Polyaniline nanofibres (PaniNFs) with a 60 nm diameter are synthesized by a scalable interfacial polymerization without the use of a template or functional dopant. PaniNF supported Pt electrocatalyst (Pt/PaniNFs) and carbon black supported Pt electrocatalyst (Pt/C) are prepared by an ethylene glycol (EG) reduction method. The Pt nanoparticles deposited onto PaniNFs have a smaller diameter (1.8 versus 2.3 nm by XRD) and narrower particle size distribution (1.5-3 nm versus 1-5 nm by TEM) than the Pt nanoparticles deposited onto carbon black. The Pt/PaniNFs catalyst shows a higher electrochemical active surface area (ECSA) and higher methanol oxidation reaction (MOR) catalytic activity than the Pt/C.