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In this study, cobalt-iron selenides embedded in porous carbon nanofibers (CoFe2Se4/PCF), derived from Prussian blue analogues, was prepared as a novel phenolic sensor. The obtained CoFe2Se4/PCF nanocomposites show three-dimensional (3D) networks nanostructures that can supply a desirable conductive network to accelerate electron transfer and avoid the aggregation of CoFe2Se4 nanoparticles. Electrochemical detection of hydroquinone (HQ), catechol (CC) and resorcinol (RS), at CoFe2Se4/PCF modified glassy carbon electrode (GCE) were researched. The results show the obtained 3D CoFe2Se4/PCF/GCE exhibits excellent electrochemical properties towards the simultaneous testing trace of HQ, CC and RS. The obtained electrode provides wide linear ranges of 0.5–200, 0.5–190 and 5–350 μM and low detection limit of 0.13, 0.15 and 1.36 μM for HQ, CC and RS, respectively. The as-prepared phenolic sensor displays satisfied selectivity and long-term storage stability. In addition, the constructed sensor can be used to determine HQ, CC and RS in actual samples.

Exploring highly active, inexpensive and robust electrocatalysts for oxygen reduction reaction (ORR) is of great significance as a competitive alternative to noble metal-based catalysts in energy conversion and storage devices. In the present study, we design a novel ORR electrocatalyst of iron-cobalt (FeCo) alloy nanoparticles embedded on N-doped porous carbon nanofibers (FeCo@PCNF-T) by electrospinning of [Polyacrylonitrile (PAN)/Prussian blue analogues/CaCO3] and post-calcination treatment. The obtained catalysts with bimetallic active sites show unique three-dimensional (3D) hierarchical meso/macropores structures. FeCo alloy nanoparticles are encapsulated into graphitic carbon that can increase stability and provide additional catalytic active sites. Under the optimized condition, FeCo@PCNF-800 displays excellent ORR electrocatalytic activity in alkaline solutions, with a more positive half-wave potential (E1/2 of 0.854 V vs RHE) and larger limited-diffusion current density (j of 6.012 mA cm−2) than those of 20 wt% Pt/C (E1/2 of 0.849 V and j of 5.710 mA cm−2). In addition, FeCo@PCNF-800 also exhibits comparable ORR electrocatalytic activity in acidic solutions to those of 20 wt% Pt/C with onset potential and half-wave potential as more positive as 0.843 V vs RHE and 0.739 V vs RHE, respectively. Moreover, FeCo@PCNF-800 exhibits excellent tolerance towards methanol, stability and a four-electron pathway in both basic and acidic solutions. The excellent ORR electrocatalytic activity performance of FeCo@PCNF-800 is attributed to the synergistic effect of the FeCo alloy nanoparticles and N-doped porous carbon nanofibers. The synergistic effect can improve the mass and charge transport capability and increase active sites of FeCo-N-C. Furthermore, this work offers a new insight for the reasonable design and development of efficient non-noble metal electrocatalysts for challenging electrochemical energy-related technologies.

In this work, a novel enzyme-free glucose and hydrogen peroxide (H2O2) sensor based on Ni3N nanoparticles on conductive 3D graphene aerogels (Ni3N/GA) has been successfully synthesized by using hydrothermal reaction, freeze-dried and then calcined under NH3 atmosphere. The obtained Ni3N/GA composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption isotherms and electrochemical methods. The results show the obtained 3D Ni3N/GA composites exhibit excellent electrochemical performance toward glucose oxidation and H2O2 reduction with larger catalytic rate constant Kcat value of 3.75 × 103 M−1 s −1 and 1.24 × 103 M−1 s −1, respectively. As a glucose sensor, the obtained electrode provides a wide detection range of 0.1–7645.3 μM, fast response time within 3 s, high sensitivity of 905.6 μA mM-1 cm-2 and low detection limit of 0.04 μM. For detection of H2O2, this prepared sensor offers a wide detection range (5 μM–75.13 mM), fast response time (within 5 s), sensitivity (101.9 μA mM-1 cm-2) and low detection limit (1.80 μM). This enzyme-free glucose and H2O2 sensor display satisfactory selectivity, reproducibility and long-term storage stability. Additionally, the sensor can also be used for glucose and H2O2 detection in human blood serum. The results demonstrate that 3D GA nanostructures provide an enviable conductive network for efficient charge transfer and avoid Ni3N nanoparticles aggregation, which is advantageous for electrocatalytic applications.

Porphyrinic iron metal-organic framework (pFeMOF) was combined with different kinds of carbon matrices, including porous graphene (PG), ordered mesoporous carbon (OMC) and macroporous carbon (MPC) via a simple one-step hydrothermal method. The introduction of carbon substrates improves the electrical conductivity and stability of pFeMOF. The presence of carbon also reduces the size of pFeMOF crystallites, leading to more active sites. The catalysts were used to electrocatalysis of hydrogen evolution reaction (HER) and the reduction of hydrogen peroxide (H2O2). Electrochemical measurements show that pFeMOF/PG has better electrocatalytic efficiency than pFeMOF/OMC, pFeMOF/MPC and pFeMOF. The HER on pFeMOF/PG displays a small onset potential of −34.37 mV vs. reversible hydrogen electrode (RHE), a low Tafel slope of 73.06 mV dec−1, a small over-potential of 154.71 mV at 10 mA cm−2. The catalytic effect for H2O2 is also satisfied. The linearity range of H2O2 is as wide as 5–4310 μM, and the sensitivity is as high as 77.38 μA mM−1. Such splendid performances may be attributed to the crumpled structure of PG leading to evenly and smaller pFeMOF. Furthermore, abundant hierarchical pores of pFeMOF/PG result in larger electrochemically surface areas. Our work may provide a new approach to design efficient non-precious metal catalysts.

A novel porphyrinic iron metal-organic framework (pFeMOF)-decorated ordered mesoporous carbon (OMC) was developed to detect hydrogen peroxide (H2O2) released from viable cells. The pFeMOF/OMC hybrid materials were synthesized via a simple one-step hydrothermal method. Fe (III) ion could coordinate with carboxylates of porphyrin groups strongly, leading to more stable MOFs. Because of the mimic peroxidase property of pFeMOF, amplified electrochemical signal could be obtained. The carbon skeleton of OMC revealed a function of restriction for the growth of pFeMOF crystallites, resulting in more active sites to reduce H2O2. The increased amount of mesopores brings faster diffusion. Moreover, the electrical conductivity and stability has been improved due to the introduction of OMC. The electrocatalytic reduction of H2O2 displayed two segments linearity range from 0.5 to 70.5 μM and 70.5 to 1830.5 μM, with high sensitivity of 67.54 μA mM−1 in the range of low concentration and 22.29 μA mM−1 of high concentration as well as a low limit of detection (LOD) as 0.45 μM. In addition, the pFeMOF/OMC/glassy carbon electrode (GCE) exhibited outstanding property to resist interference, long-term stability and repeatability. Due to these excellent analytical performances, the as-prepared biosensor was applied to detect H2O2 released from living cells with satisfactory outcome. These results display that this new nanocomposite has the potential to fabricate electrochemical sensing platform for nonenzymatic biosensing.

In this work, a novel porphyrinic metal-organic framework-based composite has been successfully synthesized by a simple one-step solvothermal method through growing Zr-PorMOF on macroporous carbon (MPC). Porphyrin-base MOFs combining the structural adjustable of MOFs and the specific catalytic activity of biomimetic catalysts play an important role in electrocatalysis. A series of characterization show that the roles of MPC as follow: (1) MPC could avoid the agglomeration of Zr-PorMOF particles and increase the specific surface area; (2) MPC could improve the electrochemical stability of Zr-PorMOF particles; (3) MPC could reduce the electron transfer resistance. Therefore, MPC plays the role of the conductive bridges to provide facile charge transport. The obtained Zr-PorMOF/MPC composites exhibit much better electrocatalytic activity for the reduction of hydrogen peroxide (H2O2) than the pristine Zr-PorMOF due to the synergy of Zr-PorMOF and MPC. This enzyme-free H2O2 sensor shows two linear relationships in the ranges 0.5–137 μM (R2 = 0.991, sensitivity = 66 μA mM−1) and 137–3587 μM (R2 = 0.993, sensitivity = 16 μA mM−1), with a low over-potential at −0.2 V, a fast response time within 1 s and a low limit of detection (LOD) of 0.18 μM. Moreover, Zr-PorMOF/MPC composites were used to simultaneously detect uric acid (UA), xanthine (XA) and hypoxanthine (HX). These three substances are degradation products of purine metabolism. In addition, Zr-PorMOF/MPC composites can be used to develop multifunctional biosensors.