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Using a 2D Co-based MOF as precursor, a core-shell nanostructure consisting of Co3O4 nanoparticles and N-doped carbon matrix (Co3O4@N/C) was prepared by hydrothermal reaction between the carbonized MOF product and graphitic carbon nitride (g-C3N4) nanosheet. The Co3O4@N/C nanocomposite combines the advantages of N-doped carbon nanomaterials (high nitrogen content, good conductivity and high stability) and Co3O4 nanoparticles (high electrocatalytic activity), thus showing excellent catalytic performance for oxygen reduction reaction (ORR). The Co3O4@N/C presents an almost same onset potential and half wave potential with Pt/C, but more positive than those for the N-undoped counterpart. The electron transfer number of 3.73 for Co3O4@N/C is closer to 4, but bigger than that for the N-undoped product (3.53), indicating that the Co3O4@N/C catalyst gives rise to a nearly 4e mechanism. The Co3O4@N/C shows better methanol tolerance and long-term durability than the N-undoped product and Pt/C catalyst. The excellent ORR performance originates from the synergistic interaction between Co3O4 and N-doped carbon in core-shell structure. This study might give a good method for the synthesis of MOF-derived carbon nanocomposite for ORR electrocatalyst.

Developing high-efficient non-noble metal electrocatalysts toward oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), water-splitting, and the zinc-air battery is essential but challenging. Zeolitic imidazole frameworks (ZIFs) are generally employed as ideal platforms for the design and fabrication of energy-related catalysts by exploiting their porous structure with high surface area and flexibility. This work presents the preparation of NiFe-bimetallic species decorated N-doped porous carbon composite (NiFe@NPC) through pyrolyzing the NiFe-coordinated ZIF precursor. The obtained NiFe@NPC shows a larger surface area and porous nanostructure comprising the active bimetallic species evenly distributed in the conductive carbon matrix. The nanocomposite demonstrates excellent trifunctional catalytic activity toward ORR, OER, and HER. For ORR, NiFe@NPC offers a half-wave potential value of 0.87 V, which is positively shifted by 30 mV relative to that of Pt/C in 1 M KOH. NiFe@NPC exhibits OER activity with superior overpotential, reaction kinetics, and durability to those of IrO2. It also demonstrates the desirable HER activity with a low overpotential of 150 mV at 10 mA/cm2 and excellent durability in an acidic electrolyte. Additionally, the water-splitting configuration and zinc-air battery assembled with NiFe@NPC catalyst reveal superior performance to noble-metal catalysts. Such excellent electrocatalytic performance can be attributed to the distinct chemical composition of evenly distributed bimetallic active sites on highly conductive carbon sheets, and the porous nanostructure with large surface area and fast mass transfer.

Zeolitic imidazole frameworks (ZIF) and ultrathin layered double hydroxide nanosheets (LDHNS) have drawn growing attention in the electrocatalysis field. Combining the merits and maximizing the electrocatalytic activity of each building block in the corresponding composite is imperative but challenging. This work thus proposes a simple strategy for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (LDHNS@ZIF-67) without an additional Co2+ source. Thanks to the ultrathin nature, CoAl-LDHNS provide more Co reactive sites for the ordered growth of ZIF-67 nanocrystals on this 2D matrix via coordination interactions between Co2+ and 2-methylimidazole. The obtained LDHNS@ZIF-67 provides more convenient pathways to rapid electron transportation between the basal electrode and analytes. Hence, the modified electrode can be applied for the truly simultaneous detection of naphthol isomers by differential pulse voltammetry. α-naphthol and β-naphthol exhibit irreversible oxidation peaks at 0.327 and 0.487 V vs. saturated calomel electrode, respectively, making their simultaneous detection feasible. The voltammetric responses of both isomers are linear in concentrations ranging from 0.3 to 150 μM with limits of detection of 62 and 94 nM, respectively. The sensor exhibits advantages including good reproducibility, stability, selectivity, and practicability for the simultaneous detection of naphthol isomers in real water samples.

A Co-metal–organic-framework (MOF) crystal has been hydrothermally synthesized. Then the corresponding Co/nitrogen-doped porous carbon (Co/NPC) composite is fabricated by direct pyrolyzation of MOF without any precursor additive. The results reveal that the MOF-derived Co/NPC exhibits a porous structure with a surface area of 412 m2 g−1 and a narrow pore size distribution (from 1.8 to 4.9 nm). The doped N mainly occurs in pyridine N and graphitic N types with total content as 4.11 at.%, which is originated from the N-based ligands in MOF. As an efficient oxygen reduction reaction (ORR) catalyst, Co/NPC shows a more positive onset potential (0.91 V vs. RHE) with a diffusion-limited current density of 5.46 mA cm−2 at 0.3 V (vs. RHE). The rotating disk electrode and rotating ring-disk electrode results suggest that the Co/NPC catalyst experiences a nearly 4e pathway with a stronger methanol tolerance and better durability than commercial Pt/C catalyst in 0.1 M KOH. The excellent ORR catalytic activity of Co/NPC can be attributed to the N-doped porous carbon structure with incorporated metallic Co active species. This work affords a new strategy for preparation of non-noble metal ORR catalysts employing MOF as a precursor.