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The development of highly active and stable non-noble catalysts for oxygen evolution reaction (OER) is of great importance to advance the sustainable energy conversion devices, but is still a huge challenge. Herein, we have developed an efficient multistep strategy to synthesize a unique hybrid nanostructure by directly growing Ni–Fe selenides nanoparticles onto nitrogen-doped carbon nanotubes (Ni–Fe–Se/N-CNTs), which can act as an in situ-derived electrocatalyst for the efficient and stable OER. It has been discovered that the Ni–Fe bimetallic selenides are in situ converted into the corresponding oxides/peroxides during the OER process, which are responsible for the high activity for OER. The remaining Ni–Fe selenides and the N-CNTs with excellent conductivity, and the strong interaction between active species and N-CNTs also contribute to the fast electron transfer of electrocatalysts and the robust durability. As expected, the as-prepared nanohybrids exhibit a low overpotential of 215 mV at the current density of 10 mA cm−2 and excellent stability in 1.0 M KOH electrolyte. This work underscores the importance of using bimetallic selenide as the efficient template for designing highly active and robust bimetallic species for OER.

A robust trifunctional electrocatalyst based on N-doped graphitic carbon nanosheets encapsulated with CoFe alloy nanocrystals (CoFe@NC/NCHNSs) is synthesized, which exhibits a positive half-wave potential (E1/2) of 0.92 V for oxygen reduction reaction (ORR), and low overpotentials of 285 mV and 120 mV at 10 mA cm−2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The superior trifunctional electrocatalytic performance can be accredited to the synergetic effect of the rich CoFe alloy sites and the high-content doping of graphitic N, as evidenced with theoretical calculations and experimental results. The introduction of Co and Fe species in the synthesis of the CoFe@NC/NCHNSs catalyst plays the important roles of both anchoring N in the carbon matrix and generating graphitic N species, which critically promote the formation of high-content graphitic-N and therefore further boost the electrocatalytic activity. Impressively, with the as-prepared trifunctional catalyst, the assembled liquid Zn-air batteries and water electrolyzers exhibit excellent catalytic activity and durability, and the solid-state Zn-air batteries show a high-power density up to 125 mW cm−2, demonstrating a great potential of this kind of devices for practical applications.

Rational engineering electrode structure to achieve an efficient triple-phase contact line is vital for applications such as in zinc-air batteries and water electrolysis. Herein, a facile "MOF-in situ-leaching and confined-growth-MOF" strategy is developed to construct a breathable trifunctional electrocatalyst based on N-doped graphitic carbon with Co nanoparticles spatially confined in an inherited honeycomb-like macroporous structure (denoted as Co@HMNC). The unique orderly arranged macroporous channels and the "ships in a bottle" confinement effect jointly expedite the triple transport, endowing the catalysts with fast reaction kinetics. As a result, the obtained Co@HMNC catalyst presents superb trifunctional performance with a positive half-wave potential (E1/2 ) of 0.90 V for oxygen reduction reaction (ORR), and low overpotentials of 318 and 51 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) at 10 mA cm-2 , respectively. The Co@HMNC-based liquid Zn-air battery reaches a large specific capacity of 859 mA h gZn-1 , a high-power density of 198 mW cm-2 , and long-term stability for 375 h, suggesting its promise for actual applications.