Cobalt and Iron Complexes with N-heterocyclic Ligands as Pyrolysis Precursors for Oxygen Reduction Catalysts

Co-N-C/C Bifunctional Electrocatalyst for Dual Applications in Seawater Electrolysis and Catalyst in Hydrazine Fuel Cells

The convergence of water electrolysis and alkaline fuel cells offers captivating solutions for sustainably harvesting energy. The research explores both hydrazine-assisted seawater electrolysis (hydrazine oxidation reaction (HzOR) and hydrogen production reaction (HER)), as well as alkaline hydrazine fuel cell reactions (HzOR and Oxygen reduction reaction (ORR)) by using a bifunctional cobalt polyaniline derived (Co PANI/C) catalyst. The catalyst shows excellent performance for hydrazine-assisted seawater electrolysis in harsh seawater environments to produce H2 as fuel with nearly 85% Faradaic efficiency and during alkaline HzOR, the bifunctional catalyst generates H2 with 95% Faradaic efficiency by acting as both anode and cathode side catalyst. Also, the same catalyst requires only a potential of 0.34 V versus RHE and 0.906 V versus RHE for HzOR and ORR, respectively, in 1 m KOH, which makes this overall process useful for a Hz/O2 fuel cell.

Cobalt-Imidazole Complexes: Effect of Anion Nature on Thermochemical Properties

A solvent-free method was proposed for the synthesis of hexaimidazolecobalt(II) nitrate and perchlorate complexes-[Co(C3H4N2)6](NO3)2 and [Co(C3H4N2)6](ClO4)2-by adding cobalt salts to melted imidazole. The composition, charge state of the metal, and the structure of the resulting complexes were confirmed by elemental analysis, XPS, IR spectroscopy, and XRD. The study of the thermochemical properties of the synthesized complexes showed that [Co(C3H4N2)6](NO3)2 and [Co(C3H4N2)6](ClO4)2 are thermally stable up to 150 and 170 °C, respectively. When the critical temperature of thermal decomposition is reached, oxidative two-stage gasification is observed. In this case, the organic component of the [Co(C3H4N2)6](NO3)2 complex undergoes almost complete gasification to form Co3O4 with a slight admixture of CoO, which makes it attractive as a component of gas-generation compositions, like airbags.

Morphological and structural design through hard-templating of PGM-free electrocatalysts for AEMFC applications

This study delves into the critical role of customized materials design and synthesis methods in influencing the performance of electrocatalysts for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). It introduces a novel approach to obtain platinum-free (PGM-free) electrocatalysts based on the controlled integration of iron active sites onto the surface of silica nanoparticles (NPs) by using nitrogen-based surface ligands. These NPs are used as hard templates to form tailored nanostructured electrocatalysts with an improved iron dispersion into the carbon matrix. By utilizing a wide array of analytical techniques including infrared and X-ray photoelectron spectroscopy techniques, X-ray diffraction and surface area measurements, this work provides insight into the physical parameters that are critical for ORR electrocatalysis with PGM-free electrocatalysts. The new catalysts showed a hierarchical structure containing a large portion of graphitic zones which contribute to the catalyst stability. They also had a high electrochemically active site density reaching 1.47 × 1019 sites g-1 for SAFe_M_P1AP2 and 1.14 × 1019 sites g-1 for SEFe_M_P1AP2, explaining the difference in performance in fuel cell measurements. These findings underscore the potential impact of a controlled materials design for advancing green energy applications.

Fine tuning of porphyrin based-paddlewheel framework by imidazole derivative to boost electrochemiluminescence performance

Precise tuning the structure of catalytic center is of great importance for the construction of enhanced electrochemiluminescence (ECL) emitters and the development of ECL amplification strategies, which is a key factor in improving the sensitivity of biosensors. In this work, we report the enhanced ECL emitters based on the porphyrin-based paddlewheel framework (PPF) with axial coordinated imidazole-like ligands (PPF/X, X = 2-methylimidazole (MeIm), imidazole (Im), benzimidazole (BIM)). In this system, the electron-donating ability of the axial ligands is positively correlated to its coordination ability to the paddlewheel units and the catalytic ability of the axially coordinated paddlewheel units. In addition, the electrochemical and ECL behavior of PPF/X (X = MeIm, Im, BIM) with different axial coordinated ligands are explored.

High-performance electrocatalyst based on polyazine derived mesoporous nitrogen-doped carbon for oxygen reduction reaction

Nitrogen-doped porous carbon materials have high potential in metal-free electrocatalysts, which is essential for several renewable energy conversion systems. Herein, we report a convenient and environment-friendly method to fabricate a nitrogen doped mesoporous carbon (NMC) using a nonionic surfactant of Pluronic F127 micelles as the template and a Schiff-base polymer (polyazine) as the precursor. The synthesized NMCs were of spheric morphology and mesoporous structures with surface area up to 1174 m² g⁻¹ and high level of nitrogen (2.9–19 at%) and oxygen (4.9–7.4 at%) simultaneously doped. The electrochemical data of NMCs were analyzed in the context of the BET and XPS information. A correlation between ORR activity and the pyridinic-N was found. The NMC-700 demonstrate the highest electrocatalytic activity for ORR among the studied materials, which can be ascribed to the reasonable surface area and mesoporous structure, as well as the most abundant touchable pyridinic-N, thus providing more effective active sites for the oxygen reduction. In comparsion to the control sample, the NMC-700 provides the ORR electrocatalytic activity approximate to that of commercial Pt/C catalyst with a highly long-term stability.

Nitrogen-doped porous carbon materials have high potential in metal-free electrocatalysts, which is essential for several renewable energy conversion systems.

Iron-/Nitrogen-Doped Electrocatalytically Active Carbons for the Oxygen Reduction Reaction with Low Amounts of Cobalt

Transition-metal-doped carbon catalysts are promising Pt-free alternatives for low-temperature fuel cells. They are frequently obtained from sacrificial N-rich zeolitic imidazolate frameworks (ZIFs) doped with Co and Fe. The optimal low loading of metals has to be achieved to guarantee the competitive efficiency and facilitate an inquiry into the mechanism of their catalytic activity. We report on microwave-assisted solvothermal synthesis of Zn,Co-ZIFs with a relatively low (1-15 mol %) Co loading, which were further enriched with Fe(II). Materials were pyrolyzed at 700 °C to form catalytically active carbons bearing metal nanoparticles confined in structured carbon. The electrochemistry test of carbons for the oxygen reduction reaction (ORR) in perchloric acid demonstrated their high efficiency even at low cobalt contents. The initial loading of 10 mol % was found efficient, leading to the production of catalytically active carbons allowing for four-electron path of ORR.

Biomorphic CoNC/CoOx Composite Derived from Natural Chloroplasts as Efficient Electrocatalyst for Oxygen Reduction Reaction

Natural chloroplasts containing big amounts of chlorophylls (magnesium porphyrin, Mg-Chl) are employed both as template and porphyrin source to synthesize biomorphic CoNC/CoO_x composite as electrocatalyst for the oxygen reduction reaction (ORR). Cobalt-substituted chlorophyll derivative (Co-Chl) in chloroplasts is first obtained by successively rinsing in hydrochloric acid and cobalt acetate solutions. After calcining in nitrogen to 800 °C, Co-Chl is transferred to CoNC; while other parts of chloroplasts adsorbed with Co ions are transferred to CoO_x retaining the microarchitecture of chloroplasts. The abundant active CoNC sites are protected by circumjacent biocarbon and CoO_x to avoid leakage and agglomeration, and at the same time can overcome the poor conductivity weakness of CoO_x by directly transporting electrons to the carbonaceous skeleton. This unique synergistic effect, together with efficient bioarchitecture, leads to good electrocatalytical performance for the ORR. The onset and half-wave potentials are 0.89 and 0.82 V versus reversible hydrogen electrode, respectively, with better durability and methanol tolerance than that of commercial Pt/C. Different from the traditional concept of biomorphic materials which simply utilize bioarchitectures, this work provides a new example of coupling bioderivative components with bioarchitectures into one integrated system to achieve good comprehensive performance for electrocatalysts.

Investigation of Earth-Abundant Oxygen Reduction Electrocatalysts for the Cathode of Passive Air-Breathing Direct Formate Fuel Cells

The development of direct formate fuel cells encounters important obstacles related to the sluggish oxygen reduction reaction (ORR) and low tolerance to formate ions in Pt-based cathodes. In this study, electrocatalysts formed by earth-abundant elements were synthesized, and their activity and selectivity for the ORR were tested in alkaline electrolyte. The results showed that carbon-encapsulated iron-cobalt alloy nanoparticles and carbon-supported metal nitrides, characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD), do not present significant activity for the ORR, showing the same half-wave potential of Vulcan carbon. Contrarily, nitrogen-doped carbon, synthesized using imidazole as the nitrogen source, showed an increase in the half-wave potential, evidencing an influential role of nitrogen in the ORR electrocatalysis. The synthesis with the combination of Vulcan, imidazole, and iron or cobalt precursors resulted in the formation of nitrogen-coordinated iron (or cobalt) moieties, inserted in a carbon matrix, as revealed by X-ray absorption spectroscopy (XAS). Steady-state polarization curves for the ORR evidenced a synergistic effect between Fe and Co when these two metals were included in the synthesis (FeCo-N-C material), showing higher activity and higher limiting current density than the materials prepared only with Fe or Co. The FeCo-N-C material presented not only the highest activity for the ORR (approaching that of the state-of-the-art Pt/C) but also high tolerance to the presence of formate ions in the electrolyte. In addition, measurements with FeCo-N-C in the cathode of an passive air-breathing direct formate fuel cells, (natural diffusion of formate), showed peak power densities of 15.5 and 10.5 mW cm−2 using hydroxide and carbonate-based electrolytes, respectively, and high stability over 120 h of operation.

From Enzymes to Functional Materials-Towards Activation of Small Molecules

The design of non-noble metal-containing heterogeneous catalysts for the activation of small molecules is of utmost importance for our society. While nature possesses very sophisticated machineries to perform such conversions, rationally designed catalytic materials are rare. Herein, we aim to raise the awareness of the overall common design and working principles of catalysts incorporating aspects of biology, chemistry, and material sciences.

Transition metal–phosphorus-based materials for electrocatalytic energy conversion reactions

This review illustrates the recent developments of transition metal–phosphorus-based materials for electrocatalytic energy conversion reactions.

Cobalt/nitrogen co-doped porous carbon nanosheets as highly efficient catalysts for the oxygen reduction reaction in both basic and acidic media

Cobalt/nitrogen co-doped porous carbon nanosheets as highly-efficient catalysts for ORR in both basic and acidic electrolytes have been prepared by using cobalt porphyrin based conjugated microporous polymer nanosheet as a precursor.

Enhanced power generation using nano cobalt oxide anchored nitrogen-decorated reduced graphene oxide as a high-performance air-cathode electrocatalyst in biofuel cells

Power generation was improved using nano cobalt oxide anchored nitrogen-decorated graphene as oxygen reduction electrocatalyst in biofuel cells.