Nitrogen-doped porous carbon encapsulates multivalent cobalt-nickel as oxygen reduction reaction catalyst for zinc-air battery.

In this study, we present a bimetallic ion coexistence encapsulation strategy employing hexadecyl trimethyl ammonium bromide (CTAB) as a mediator to anchor cobalt-nickel (CoNi) bimetals in nitrogen-doped porous carbon cubic nanoboxes (CoNi@NC). The fully encapsulated and uniformly dispersed CoNi nanoparticles with the improved density of active sites help to accelerate the oxygen reduction reaction (ORR) kinetics and provide an efficient charge/mass transport environment. Zinc-air battery (ZAB) equipped CoNi@NC as cathode exhibits an open-circuit voltage of 1.45 V, a specific capacity of 870.0 mAh g-1, and a power density of 168.8 mW cm-2. Moreover, the two CoNi@NC-based ZABs in series display a stable discharge specific capacity of 783.0 mAh g-1, as well as a large peak power density of 387.9 mW cm-2. This work provides an effective way to tune the dispersion of nanoparticles to boost active sites in nitrogen-doped carbon structure, and enhance the ORR activity of bimetallic catalysts.

Nickel induced in situ growth of nickel hydroxide nanoflakes on reduced graphite oxide with high energy and power density.

Layered hexagonal Ni(OH)2 nanoflakes have been successfully fabricated on the surface of reduce graphite oxide (rGO) via nickel induced in situ growth in this study. The layers number and size of Ni(OH)2 nanoflakes could be controlled by adjusting the concentration of Ni2+ precursors with nickel as active site on rGO surface. In the three electrode systems, the composite showed a relatively high specific capacitance achieved 1012.2 F∙g-1 at current density of 1 A∙g-1 with coulombic efficiency of 98.3%. As assembled in asymmetric devices (Ni(OH)2 nanoflakes loaded on rGO as positive electrode and active carbon as negative electrode), the maximum specific capacitance reaches to 260.9 F∙g-1 at current density of 0.5 A∙g-1 and the energy density can be maintained at 71.1 Wh∙kg-1 at power density of 26.95 kW∙kg-1 with good rate capability and acceptable cycling stability.