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Bimetallic cobalt/iron nitrides embedded into N,S-codoped carbon nanotubes (CoN/FeN@N,S-C-800) was prepared by pyrolysis of a Fe-glu coated tetrazole energetic {Co 4 (OH) 2 (SO 4)(bdt) 2 (H 2 O) 4 }. Benefiting from high specific surface area (728.2 m2 g−1) and enriched active sites (cobalt/iron nitrides and N,S-C), CoN/FeN@N,S-C-800 exhibits a superior ORR/OER catalytic activity with a low Δ E of 0.75 V. Liquid and all-solid-state ZABs catalyzed by CoN/FeN@N,S-C-800 display tremendous potentials in portable device. [Display omitted] • A tetrazole energetic {Co 4 (OH) 2 (SO 4)(bdt) 2 (H 2 O) 4 } is synthesized. • CoN/FeN@N,S-C-800 consists of cobalt/iron nitrides and N,S-CNTs. • CoN/FeN@N,S-C-800 can offer abundant mass/electron transfer channels. • CoN/FeN@N,S-C-800 displays a small potential difference Δ E of 0.75 V. • CoN/FeN@N,S-C-800-based ZAB exhibits a low voltage gap of 0.55 V. Exploring highly effcient bifunctional oxygen catalysts is a central issue for rechargeable Zn–air batteries. Herein, bimetallic cobalt/iron nitrides in situ embedded into nitrogen, sulfur-codoped carbon nanotubes (CoN/FeN@N,S-C-800) was firstly developed by pyrolysis of a Fe-glucosamine coated tetrazole energetic metal − organic framework. Due to the significant nitrogen (5.38at%) dopant content, the synergistic effect between bimetallic nitrides, and interconnected N, S-codoped carbon nanotubes, the as-prepared CoN/FeN@N,S-C-800 exhibits an ultra-high half-wave potential (0.865 V) for oxygen reduction reaction (ORR) and a low overpotential (385 mV) for oxygen evolution reaction (OER). The assembled liquid Zn–air battery affords a high peak power density of 168.3 mW cm−2 and a low voltage gap of 0.55 V after 600 cycles (100 h). Impressively, an all-solid-state ZAB catalyzed by CoN/FeN@N,S-C-800 affords a high OCV of 1.354 V, and three all-solid-state ZABs in series can successfully light LED (~2.2 V), displaying tremendous potentials in portable devices. [ABSTRACT FROM AUTHOR]

Rational design of non-noble metal-based bifunctional electrocatalysts for hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) is still a challenge in water splitting. Herein, a MOF-on-MOF (MOF = metal-organic framework) strategy is developed to obtain trimetal-based nitrogen-doped carbon nanotubes arrays loaded on nickel foams (denoted as FeNiCo@NC/NF). Benefiting from the superior compositional and structural feature, FeNiCo@NC/NF self-supported electrodes exhibit excellent bifunctional HER and OER activity with a low overpotential of 145 and 245 mV at 10 mA cm−2. When simultaneously used as cathode and anode for water splitting, it only requires 1.61 V to achieve 10 mA cm−2 and even outperforms the benchmark electrode couple of Pt/C||RuO 2 at higher current densities. Studies discover that trimetallic FeNiCo nanoparticles can provide more synergetic metal active sites, interconnected N-doped carbon nanotubes arrays can offer more effective electron transports channels, and conductive Ni foam substrate can reduce the internal impedance of the material. Density functional theory (DFT) calculations also demonstrate that FeNiCo@NC/NF electrode possesses a favorable Gibbs free energy of hydrogen adsorption (ΔG H*) value of −0.13 eV, which is benefit for its superior HER activity. Overall, our work reports an efficient self-supported electrode for hydrogen/oxygen evolution reactions and water splitting. • Synergistic effect among trimetals and N-dopants enhances HER/OER activities. • N-CNTs could offer more effective electron transports channels. • Hierarchical structure ensures super-fast evolution and escape of H 2 and O 2. • Without polymer binder reduces the internal impedance of the material. • ΔG H* = −0.13 eV further manifests their superior HER activity. [ABSTRACT FROM AUTHOR]