Multifunctional bayberry-like composites consisting of CoFe encapsulated by carbon nanotubes for overall water splitting and zinc–air batteries

The rational design of high-performance electrocatalysts with multiple functions based on earth-abundant elements for energy storage and conversion devices is highly demanded but remains a significant challenge. Herein, porous bayberry-like architectures constructed from CoFe alloy nanoparticles encapsulated within nitrogen-doped carbon nanotubes (N-CNTs) were developed by a room-temperature coprecipitation procedure, followed by an annealing process under a nitrogen atmosphere. The synergistic coupling effect between the alloys and in situ formed N-CNTs within the architectures not only provided abundant active sites and accelerated electron/proton transfer but also effectively optimized the adsorption energy of the reaction intermediates. As a result, the as-developed CoFe@N-CNTs-800 exhibited an excellent trifunctional electrocatalytic activity for the hydrogen evolution reaction and oxygen evolution reaction with overpotentials of 115 and 306 mV at 10 mA cm−2, respectively, as well as the oxygen reduction reaction with a half-wave potential of 0.847 V vs. the reversible hydrogen electrode (RHE). As a proof-of-concept, CoFe@N-CNTs-800-assembled water splitting cells could drive a current density of 10 mA cm−2 at a voltage of 1.64 V, lower than that of the Pt/C‖IrO2/C couple (1.65 V). Furthermore, a CoFe@N-CNTs-800 air cathode-based zinc–air battery exhibited a very small charge–discharge voltage gap of 0.79 V (at 10 mA cm−2) and a high energy density of 938.1 mW h g−1.