Research Progress in ZIF-8 Derived Single Atomic Catalysts for Oxygen Reduction Reaction

Multilayer Porous Fe/Co-N-MWCNT Electrocatalyst For Rechargeable Zinc-Air Batteries

The design of efficient, stable, low-cost non-precious metal-based electrocatalysts with enhanced oxygen reduction reaction (ORR) activity has garnered significant attention in the scientific community. This study introduces a novel electrocatalyst, Fe/Co-N-MWCNT, synthesized through the in-situ growth of ZIF-8 and Fe/Co-Phen on multi-walled carbon nanotubes (MWCNTs), followed by pyrolysis at varying temperatures to optimize its properties. The inclusion of Fe and Co during the pyrolysis process facilitated the creation of metal active sites and Fe-Co, enhancing electron transfer and ORR activity. Compared to Pt/C (E1/2=0.854 V, JL=4.90 mA cm-2), Fe/Co-N-MWCNT exhibited a similar half-wave potential (E1/2=0.812 V) and an improved limiting current density (JL=5.37 mA cm-2). Moreover, Fe/Co-N-MWCNT displayed remarkable stability, showing only a 7 mV negative shift in E1/2 after 2000 cycles. Ampere response testing indicated a current decay of only 7.8 % for Fe/Co-N-MWCNT after 10000 s, while Pt/C experienced a decay of about 18.4 %. The exceptional catalytic stability of Fe/Co-N-MWCNT positions it as a promising candidate for rechargeable zinc-air batteries, attributed to its high pyridinic nitrogen content, unique structure, and abundant metal active sites.

g-C3N4 promoted MOF-derived Fe single atoms anchored on N-doped hierarchically porous carbon for high-performance Zn-air batteries

Exploring efficient, easy-to-manufacture, and inexpensive bifunctional electrocatalysts with abundant accessible active sites is crucial for rechargeable zinc-air batteries (ZABs). Herein, we report the strategy consisting of the space confinement and pore-making engineering to fabricate single-atom catalyst enriched with Fe-N4 sites anchored on N-doped hierarchically porous carbon (Fe-NC-C3N4). The optimized Fe-NC-C3N4 exhibits excellent oxygen reduction/evolution reaction (ORR/OER) activities with a half-wave potential (E1/2) of 0.90 V vs. RHE and a promising low overpotential of 0.305 V vs. RHE at 10 mA·cm-2 in alkaline electrolyte. These superior catalytic activities are attributed to the combined effect between the atomic active sites and the well-balanced micro-meso-macropore structures. The homemade liquid Zn-air battery (ZAB) assembled with Fe-NC-C3N4 catalyst displays a power density of 133.59 mW·cm-2 and a significant energy density of 882.58 mAh·g-1, exceeding those of the equipment with commercial Pt/C-RuO2 (56.82 mW·cm-2 and 643.87 mAh·g-1, respectively). Particularly, the corresponding flexible wearable ZAB manifests outstanding foldability and cyclical stability. This work opens a new perspective for the structural design of single-atom catalysts in the energy storage and conversion area.

Evaluating the Oxygen Electrode Reactions of La Single-Atom Catalysts with the N/C Coordination Effect

There is a growing demand for bifunctional electrocatalysts for oxygen electrodes in rechargeable metal-air batteries. This article investigates the bifunctional activity of La single-atom catalysts with N/C coordination (LaNxC6-x@Gra) using density functional theory (DFT). The augmentation of N coordination will result in enhanced synthetic stability. The coordination between nitrogen and carbon (N/C) has a significant influence on the working stability of the system under consideration. In the context of active atoms, the coordination between nitrogen and carbon (N/C coordination) has a significant impact on the electronic structure. This, in turn, influences the adsorption performance and catalytic activity of the catalysts. In the case of stable coordination environments, a correlation exists between the f-orbital center (εf) and the overpotential (η) via the adsorption free energy of intermediates (ΔG*ads). This correlation serves as a useful tool for predicting catalytic performance. The LaNxC6-x@Gra exhibits remarkable bifunctional activity due to its complementary performance, with an overpotential for the oxygen reduction reaction (ηORR) of 0.66 V and an overpotential for the oxygen evolution reaction (ηOER) of 0.43 V. This makes it a promising candidate for use as a bifunctional electrocatalyst in oxygen electrodes.

Xerogel-Derived Manganese Oxide/N-Doped Carbon as a Non-Precious Metal-Based Oxygen Reduction Reaction Catalyst in Microbial Fuel Cells for Energy Conversion Applications

Current study provides a novel strategy to synthesize the nano-sized MnO nanoparticles from the quick, ascendable, sol-gel synthesis strategy. The MnO nanoparticles are supported on nitrogen-doped carbon derived from the cheap sustainable source. The resulting MnO/N-doped carbon catalysts developed in this study are systematically evaluated via several physicochemical and electrochemical characterizations. The physicochemical characterizations confirms that the crystalline MnO nanoparticles are successfully synthesized and are supported on N-doped carbons, ascertained from the X-ray diffraction and transmission electron microscopic studies. In addition, the developed MnO/N-doped carbon catalyst was also found to have adequate surface area and porosity, similar to the traditional Pt/C catalyst. Detailed investigations on the effect of the nitrogen precursor, heat treatment temperature, and N-doped carbon support on the ORR activity is established in 0.1 M of HClO4. It was found that the MnO/N-doped carbon catalysts showed enhanced ORR activity with a half-wave potential of 0.69 V vs. RHE, with nearly four electron transfers and excellent stability with just a loss of 10 mV after 20,000 potential cycles. When analyzed as an ORR catalyst in dual-chamber microbial fuel cells (DCMFC) with Nafion 117 membrane as the electrolyte, the MnO/N-doped carbon catalyst exhibited a volumetric power density of ~45 mW m2 and a 60% degradation of organic matter in 30 days of continuous operation.

Synthesis of Se single atoms on nitrogen-doped carbon as novel electrocatalyst for sensitive nonenzymatic sensing of hydrogen peroxide

Single-atom catalysts received increasing attention due to their maximum atom utilization efficiency. However, metal-free single atoms have not been used to construct electrochemical sensing interfaces. In this work, we demonstrated the use of Se single atoms (SA) as electrocatalyst for sensitive electrochemical nonenzymatic detection of H2O2. Se SA was synthesized and anchored on nitrogen-doped carbon (Se SA/NC) via a high-temperature reduction strategy. The structural properties of Se SA/NC were characterized by transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical techniques. The results showed that Se atoms were uniformly distributed on the surface of the NC. The obtained SA catalyst exhibited excellent electrocatalytic activity toward H2O2 reduction, and can be used to detect H2O2 in a wide linear range from 0.04 mM to 11.1 mM with a low detection limit of 0.018 mM and high sensitivity of 403.9 µA mM-1 cm-2. Moreover, the sensor can be used for the quantification of H2O2 concentration in real disinfectant samples. This work is of great significance for expanding the application of nonmetallic single-atom catalysts in the field of electrochemical sensing. Se single atoms (Se SA) as novel electrocatalyst were synthesized and anchored on nitrogen-doped carbon (NC) for sensitive electrochemical nonenzymatic detection of H2O2.

Metal-Organic Framework-Derived Atomically Dispersed Co-N-C Electrocatalyst for Efficient Oxygen Reduction Reaction

In this work, an atomically dispersed cobalt-nitrogen-carbon (Co-N-C) catalyst is prepared for the oxygen reduction reaction (ORR) by using a metal-organic framework (MOF) as a self-sacrifice template under high-temperature pyrolysis. Spherical aberration-corrected electron microscopy is employed to confirm the atomic dispersion of high-density Co atoms on the nitrogen-doped carbon scaffold. The X-ray photoelectron spectroscopy results verify the existence of Co-N-C active sites and their content changes with the Co content. The electrochemical results show that the electrocatalytic activity shows a volcano-shaped relationship, which increases with the Co content from 0 to 0.99 wt.% and then decreases when the presence of Co nanoparticles at 1.61 wt.%. The atomically dispersed Co-N-C catalyst with Co content of 0.99 wt.% shows an onset potential of 0.96 V vs. reversible hydrogen electrode (RHE) and a half-wave potential of 0.89 V vs. RHE toward ORR. The excellent ORR activity is attributed to the high density of the Co-N-C sites with high intrinsic activity and high specific surface area to expose more active sites.

Rationalizing Structural Hierarchy in the Design of Fuel Cell Electrode and Electrolyte Materials Derived from Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are arguably a class of highly tuneable polymer-based materials with wide applicability. The arrangement of chemical components and the bonds they form through specific chemical bond associations are critical determining factors in their functionality. In particular, crystalline porous materials continue to inspire their development and advancement towards sustainable and renewable materials for clean energy conversion and storage. An important area of development is the application of MOFs in proton-exchange membrane fuel cells (PEMFCs) and are attractive for efficient low-temperature energy conversion. The practical implementation of fuel cells, however, is faced by performance challenges. To address some of the technical issues, a more critical consideration of key problems is now driving a conceptualised approach to advance the application of PEMFCs. Central to this idea is the emerging field MOF-based systems, which are currently being adopted and proving to be a more efficient and durable means of creating electrodes and electrolytes for proton−exchange membrane fuel cells. This review proposes to discuss some of the key advancements in the modification of PEMs and electrodes, which primarily use functionally important MOFs. Further, we propose to correlate MOF-based PEMFC design and the deeper correlation with performance by comparing proton conductivities and catalytic activities for selected works.