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[Display omitted] The bifunctional efficient electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are in urgent need for the advanced overall water splitting (OWS) device. Restricted by the thermodynamic limitations of the catalytic active center for OER and the reaction kinetics limitations induced by the structure of the electrocatalysts, the development of OWS catalysts requires more effort. Herein, a porous carbon-based bimetal electrocatalyst of Mo 0.84 Ni 0.16 -Mo 2 C@NC nanosphere is prepared by hydrothermal treatment of PMo 12 @PVP@Zn/Ni-ZIF which is synthesized via one-pot self-assembled hydrothermal method. Our study confirms that the Mo-Ni alloy and Mo 2 C nanoparticles homogeneously distribute in nitrogen-rich carbon-based materials. Furthermore, the porous structure exposes rich active sites and increases the effective specific area for redox reactions. The obtained Mo 0.84 Ni 0.16 -Mo 2 C@NC catalyst requires low overpotentials of 151 and 285 mV to reach a current density of 10 mA cm−2 towards the water reduction and oxidation in 1 M KOH solution, respectively, and possesses good catalytic stability for one day. This work introduces an advanced method for the synthesis of the bimetal electrocatalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • A weak-strong coetching strategy is developed for metal–organic frameworks. • Hollow nanopompoms structure is obtained and can be maintained upon pyrolysis. • Pyrolyzed nanopompoms allow for efficient electron transfer applications. • Heterophases increase active sites and promotes electrocatalytic performance. • Nanopompoms catalyst has desirable bifunctional performance for Zn-air batteries. The rational structure and composition design of bifunctional electrocatalysts for oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) is crucial for rechargeable metal–air batteries. Here, we report controlled structural transitions of metal–organic frameworks through a weak-strong competitive coordination strategy for high-performance electrocatalysts. Upon the introduction of potassium ferricyanide (PF) and/or phosphomolybdic acid (POM), cubic zeolitic-imidazole framework-67 (Cube-67) undergoes both chemical and macroscopic morphology changes, i.e., from nanocubes to hollow nanopompoms, where PF and POM act as the weak chelator (i.e., for finer structures) and the strong chelator (i.e., shape-directing agent), respectively. After calcination, the hierarchically structured nanopompoms display tunable and high-performance OER and ORR catalytic activities suitable for Zn–air batteries that display a long-term charge–discharge cycling stability. This work not only holds promise for clean-energy applications but provides a design principle for engineering advanced electrocatalysts by effectively tuning their structural and chemical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • A weak-strong coetching strategy is developed for metal–organic frameworks. • Hollow nanopompoms structure is obtained and can be maintained upon pyrolysis. • Pyrolyzed nanopompoms allow for efficient electron transfer applications. • Heterophases increase active sites and promotes electrocatalytic performance. • Nanopompoms catalyst has desirable bifunctional performance for Zn-air batteries. The rational structure and composition design of bifunctional electrocatalysts for oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) is crucial for rechargeable metal–air batteries. Here, we report controlled structural transitions of metal–organic frameworks through a weak-strong competitive coordination strategy for high-performance electrocatalysts. Upon the introduction of potassium ferricyanide (PF) and/or phosphomolybdic acid (POM), cubic zeolitic-imidazole framework-67 (Cube-67) undergoes both chemical and macroscopic morphology changes, i.e., from nanocubes to hollow nanopompoms, where PF and POM act as the weak chelator (i.e., for finer structures) and the strong chelator (i.e., shape-directing agent), respectively. After calcination, the hierarchically structured nanopompoms display tunable and high-performance OER and ORR catalytic activities suitable for Zn–air batteries that display a long-term charge–discharge cycling stability. This work not only holds promise for clean-energy applications but provides a design principle for engineering advanced electrocatalysts by effectively tuning their structural and chemical properties. [ABSTRACT FROM AUTHOR]

• A high-performance ORR/OER catalyst is prepared by using corn stalks as precursor. • FeN x and FeC x originated from Fe, N-dual doped improve catalytic performance. • The Fe-MNC catalyst achieves an excellent performance for Zn-air batteries. [Display omitted] The development of affordable and perdurable electrocatalysts for oxygen reduction/evolution reaction (ORR/OER) has been considered as an alternative to address the global energy crisis and grievous environmental pollution. Therefore, exhaustively developing low-cost bifunctional electrocatalysts is of significance especially derived from the ubiquitous carbonous biomass materials. Here, an advanced catalyst of Fe, N-dual doped mesoporous and microporous carbon nanosheets (Fe-MNC) is synthesized by using Fe-pyridine coordination complex as the sources of Fe, N and corn stalk soot as the support. The Fe-MNC possesses vigorous electrocatalytic performance for ORR with an E 1/2 of 0.85 V. Moreover, for OER, the overpotential is as low as 309 mV at the current density (j) of 10 mA cm−2 and the Tafel slope is 127 mV dec−1. What's more, a rechargeable Zn-Air battery is constructed based on Fe-MNC as the air cathode. This work not only establishes an easy access and sustainable way to produce a cost-cutting and highly efficient ORR/OER catalyst, but also paves a new way for a greater value-added utilization of biomass carbon for sustainable energy conversation. [ABSTRACT FROM AUTHOR]

• Corn stalks was used as the precursor of electrocatalyst. • Electrocatalyst (NPCSS) is featured with a few-layer N-doped porous carbon nanosheets. • NPCSS shows outstanding water splitting electrocatalysis. The environmental crisis of the earth's living has led to in-depth research on energy generation and conversion, and electrocatalytic water splitting appeared suitable for sustainable energy cycles and conversion. Here, a N-doped few-layer porous carbon nanosheets catalyst (labeled as NPCSS) with high specific surface area, enormous active sites and high atom ratio of pyridinic/pyrrolic N was obtained by pyrolysis of mixture of corn stalks soot and melamine. Compared with corn stalks soot during pyrolysis without melamine, the NPCSS is featured with more electrochemically active sites and smaller mass transfer resistance, leading to a superior water splitting activity in 1 M KOH solution. NPCSS shows outstanding water splitting performance with small overpotentials of 195 mV and 358 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at the current density (j) of 10 mA cm−2, respectively. Our method realizes the high value-added utilization of biomass carbon. [ABSTRACT FROM AUTHOR]