Developing highly active electrocatalysts with low cost and high efficiency for hydrogen evolution reactions (HERs) is of great significance for industrial water electrolysis. Herein, a 3D hierarchically structured nanotubular copper-doped nickel catalyst on nickel foam (NF) for HER is reported, denoted as Ni(Cu), via facile electrodeposition and selective electrochemical dealloying. The as-prepared Ni(Cu)/NF electrode holds superlarge electrochemical active surface area and exhibits Pt-like electrocatalytic activity for HER, displaying an overpotential of merely 27 mV to achieve a current density of 10 mA cm and an extremely small Tafel slope of 33.3 mV dec in 1 m KOH solution. The Ni(Cu)/NF electrode also shows excellent durability and robustness in both continuous and intermittent bulk water electrolysis. Density functional theory calculations suggest that Cu substitution and the formation of NiO on the surface leads to more optimal free energy for hydrogen adsorption. The lattice distortion of Ni caused by Cu substitution, the increased interfacial activity induced by surface oxidation of nanoporous Ni, and numerous active sites at Ni atom offered by the 3D hierarchical porous structure, all contribute to the dramatically enhanced catalytic performance. Benefiting from the facile, scalable preparation method, this highly efficient and robust Ni(Cu)/NF electrocatalyst holds great promise for industrial water-alkali electrolysis.

The bottom-up fill of copper in fine via holes is reported in electroless copper plating with the addition of bis͑3-sulfopropyl͒ disulfide ͑SPS͒. When the concentration of SPS in the plating bath was varied from 0.05 to 0.5 mg/L with a plating time of 10 min, the ratio of the Cu thickness at the bottom of the hole (T b ) to that at the surface (T s ), called the bottom-up ratio, increased from 1.05 to 2.8 for a 1.0 m hole. The bottom-up ratio increases with SPS concentration and decreases with an increase in hole diameter. X-ray diffraction structure analyses and cross-sectional transmission electron microscopy observations indicated that the grain size of Cu film was reduced by the SPS addition, but Cu͑111͒ texture was enhanced by the SPS addition. Bottom-up fill may be attributed to a higher SPS concentration at the surface than at the bottom of the holes due to SPS incorporation in the Cu film and diffusion-limited flux of SPS molecules into fine holes.Copper ͑Cu͒ is used widely as an interconnection metal in ultralarge-scale integration ͑ULSI͒ circuits due to its lower resistivity and superior resistance against electromigration compared to conventional aluminum alloys. The present damascene copper interconnections are fabricated by electroplating on a sputtered Cu seed layer. To produce void-free and seamless fill for high-aspect-ratio trenches and via holes, superfill or bottom-up fill, in which the deposition rate at the bottom of the hole is higher than at the surface, is necessary. Cu electroplating baths containing additives, such as chloride ion, polyethylene glycol ͑PEG͒, bis͑3-sulfopropyl͒ disulfide ͑SPS͒, 3-mercapto-1-propanesulfonate ͑MPSA͒, or Janus Green B ͑JGB͒, have yielded desirable plating characteristics. 1-8 Inhibition to Cu deposition in the Cl-PEG-SPS system is due primarily to the combination of PEG and chloride ions, 2-5 with acceleration attributed to SPS. However, a major premise of the superfill deposition of electroplating is a continuous sputtered Cu seed layer. Because a shrinkage in dimensions occurs for next generation interconnections, forming a continuous sputtered Cu film on the sidewalls of fine via holes becomes more difficult as sputtering suffers from poor step coverage. Consequently, copper electroless plating and chemical vapor deposition ͑CVD͒ are the most promising processes for the formation of a seed layer for electroplating. 9-15 Bottom-up filling of submicrometer features by iodine-catalyzed CVD was reported by Shim et al., 9 Hwang and Lee, 10 and Josell et al.,11 but adhesion between the copper film and the barrier metal layer was poor and the deposition rate was slow. Copper electroless plating, which does not require a sputtered Cu seed layer, is an efficient means of filling high aspect ratio holes and has became increasingly important. 12-15 However, when the hole diameter is less than 70 nm, filling the highaspect-via-hole with normal electroless plating is difficult.Many studies report bottom-up fill of Cu in electroplating baths using additives, but few r...

Hindered by sluggish kinetics and large overvoltages of direct hydrazine oxidation, energy-efficient electrolytic hydrogen generation from whole cell hydrazine electrolysis still remains a great challenge. Herein, we present a 3D hierarchically nanotubular Ni–Cu alloy on nickel foam (Ni­(Cu)/NF) and demonstrate its high efficiency and strong durability for the hydrazine oxidation reaction (HzOR) with a required potential of merely 86 mV to afford a current density of 100 mA cm–2 in alkaline hydrazine aqueous solution. The normalization of HzOR polarization curves for Ni­(Cu)/NF manifests that the superlarge electrochemical active surface area (ECSA) with an 18-fold increase is the main contributor to the excellent HzOR performance. The superior cell performance makes Ni­(Cu)/NF a good alternative transition-metal-based electrocatalyst for utilization in the HzOR electrolyzer. The remarkable performance toward the hydrogen evolution reaction (HER) of Ni­(Cu)/NF allows the use of a superior bifunctional electrocatalyst for electrolytic hydrogen production via HzOR and HER. In a two-electrode electrolyzer cell employing Ni­(Cu)/NF to function as the cathode and anode, an extremely low cell voltage of 0.41 V is required to afford 100 mA cm–2 with remarkable long-term stability.

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Global-scale application of water-splitting technology for hydrogen fuel production and storage of intermittent renewable energy sources has called for the development of oxygen- and hydrogen-evolution catalysts that are inexpensive, efficient, robust, and can withstand frequent power interruptions and shutdowns. Here, we report the controlled electrodeposition of porous nickel-iron hydroxylphosphate (NiFe-OH-PO) nanobelts onto the surface of macroporous nickel foams (NF) as a bifunctional electrocatalyst for efficient whole-cell water electrolysis. The NiFe-OH-PO/NF electrode shows both high water oxidation and water reduction catalytic activity in alkaline solutions and is able to deliver current densities of 20 and 800 mA cm at overpotentials of merely 249 and 326 mV for oxygen-evolution reaction, current densities of 20 and 300 mA cm at overpotentials of only 135 and 208 mV for hydrogen-evolution reaction. Further, in a two-electrode water electrolytic cell, the bifunctional NiFe-OH-PO/NF electrodes can obtain the current densities of 20 and 100 mA cm at an overall cell potential of only 1.68 and 1.91 V, respectively. Remarkably, the NiFe-OH-PO/NF catalyst also represents prolonged stability under both continuous and intermittent electrolysis and can be used for oxygen evolution and hydrogen evolution reversibly without degradation.