Construction of FeCo2O4@N-Doped Carbon Dots Nanoflowers as Binder Free Electrode for Reduction and Oxidation of Water

Mesoporous Single Atom-Cluster Fe-N/C Oxygen Evolution Electrocatalysts Synthesized with Bottlebrush Block Copolymer-Templated Rapid Thermal Annealing

Current electrocatalysts for oxygen evolution reaction (OER) are either expensive (such as IrO2, RuO2) or/and exhibit high overpotential as well as sluggish kinetics. This article reports mesoporous earth-abundant iron (Fe)-nitrogen (N) doped carbon electrocatalysts with iron clusters and closely surrounding Fe-N4 active sites. Unique to this work is that the mechanically stable mesoporous carbon-matrix structure (79 nm in pore size) with well-dispersed nitrogen-coordinated Fe single atom-cluster is synthesized via rapid thermal annealing (RTA) within only minutes using a self-assembled bottlebrush block copolymer (BBCP) melamine-formaldehyde resin composite template. The resulting porous structure and domain size can be tuned with the degree of polymerization of the BBCP backbone, which increases the electrochemically active surface area and improves electron transfer and mass transport for an effective OER process. The optimized electrocatalyst shows a required potential of 1.48 V (versus RHE) to obtain the current density of 10 mA/cm2 in 1 M KOH aqueous electrolyte and a small Tafel slope of 55 mV/decade at a given overpotential of 250 mV, which is significantly lower than recently reported earth-abundant electrocatalysts. Importantly, the Fe single-atom nitrogen coordination environment facilitates the surface reconstruction into a highly active oxyhydroxide under OER conditions, as revealed by X-ray photoelectron spectroscopy and in situ Raman spectroscopy, while the atomic clusters boost the single atoms reactive sites to prevent demetalation during the OER process. Density functional theory (DFT) calculations support that the iron nitrogen environment and reconstructed oxyhydroxides are electrocatalytically active sites as the kinetics barrier is largely reduced. This work has opened a new avenue for simple, rapid synthesis of inexpensive, earth-abundant, tailorable, mechanically stable, mesoporous carbon-coordinated single-atom electrocatalysts that can be used for renewable energy production.

Fe3+ in a tetrahedral position determined the electrocatalytic properties in FeMn2O4

As an electrocatalyst for the oxygen evolution reaction (OER) for water decomposition purposes, spinel ferrite materials have gained a lot of attention from many researchers. Herein, we document a co-precipitation synthesis of antitypical spinel nanoparticles (FeMn2O4) by post-annealing at different temperatures to enable modulation of the cationic oxidation state and tuning of the conversion degree for efficient and good OER performance. The electrocatalytic activity test shows that the sample annealed at 500 °C has the most optimal catalytic activity with an overpotential of 360 mV at a current density of 10 mA cm-2 and a Tafel slope as low as 105.32 mV dec-1. The formation of FeOOH during in situ OER promotes the catalytic activity of the catalysts. More importantly, according to the results of Brunauer-Emmett-Teller normalization, we demonstrate that the activity of the catalyst is also inseparable from the internal crystal structure. This work broadens the field of research on the electrocatalysis of spinel manganese ferrites.

Electrochemical Performance of Iron-Doped Cobalt Oxide Hierarchical Nanostructure

In this study, hydrothermally produced Fe-doped Co3O4 nanostructured particles are investigated as electrocatalysts for the water-splitting process and electrode materials for supercapacitor devices. The results of the experiments demonstrated that the surface area, specific capacitance, and electrochemical performance of Co3O4 are all influenced by Fe3+ content. The FexCo3-xO4 with x = 1 sample exhibits a higher BET surface (87.45 m2/g) than that of the pristine Co3O4 (59.4 m2/g). Electrochemical measurements of the electrode carried out in 3 M KOH reveal a high specific capacitance of 153 F/g at a current density of 1 A/g for x = 0.6 and 684 F/g at a 2 mV/s scan rate for x = 1.0 samples. In terms of electrocatalytic performance, the electrode (x = 1.0) displayed a low overpotential of 266 mV (at a current density of 10 mA/cm2) along with 52 mV/dec Tafel slopes in the oxygen evolution reaction. Additionally, the overpotential of 132 mV (at a current density of 10 mA/cm2) and 109 mV with 52 mV/dec Tafel slope were obtained for x = 0.6 sample towards hydrogen evolution reaction (HER). According to electrochemical impedance spectroscopy (EIS) measurements and the density functional theory (DFT) study, the addition of Fe3+ increased the conductivity at the electrode–electrolyte interface, which substantially impacted the high activity of the iron-doped cobalt oxide. The electrochemical results revealed that the mesoporous Fe-doped Co3O4 nanostructure could be used as potential electrode material in the high-performance electrochemical capacitor and water-splitting catalysts.

Advances in Electrochemical and Catalytic Performance of Nanostructured FeCo2 O4 and Its Composites

It is well established that the excessive and uncontrolled use of fossil fuels and organic chemicals have put a risk to the earth's environment and the life that sustains within it. Carbon-free, sustainable, alternative energy technologies have therefore become the prime focus of current research. Smart inorganic materials have emerged as the potential solution to suffice energy needs and remediate the organic pollutants discharged to the environment. One such promising, versatile material is FeCo₂ O₄ which has gained immense research interest in the present decade due to its high efficiency and performance in energy and environmental applications. Innovative material design strategies involving the interplay of nanostructured morphology, chemical composition, redox surface states, and defect engineering have significantly enhanced both electrochemical and catalytic properties of FeCo₂ O₄ . Therefore, this review article aims to provide the first-ever comprehensive account of the latest research and developments in design-synthesis strategies, characterization techniques, and applications of nanostructured FeCo₂ O₄ and its composites in various electrochemical as well as catalytic applications. A detailed account of the nanostructured FeCo₂ O₄ and its composites in various energy storage and conversion devices such as supercapacitors (SCs), batteries, and fuel cells has been presented. Furthermore, a special section has been devoted to highlight the role of FeCo₂ O₄ in enhancing the sluggish reaction kinetics of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in water splitting application. This review also highlights the role of nanostructured FeCo₂ O₄ in photocatalytic waste water treatment, gas sensing, and dual-phase membrane technologies wherein FeCo₂ O₄ has demonstrated promising performance.

Fe(III) Ions-Assisted Aniline Polymerization Strategy to Nitrogen-Doped Carbon-Supported Bimetallic CoFeP Nanospheres as Efficient Bifunctional Electrocatalysts toward Overall Water Splitting

It remains an urgent demand and challenging task to design and fabricate efficient, stable, and inexpensive catalysts toward sustainable electrochemical water splitting for hydrogen production. Herein, we explored the use of Fe(III) ion-assisted aniline polymerization strategy to embed bimetallic CoFeP nanospheres into the nitrogen-doped porous carbon framework (referred CoFeP-NC). The as-prepared CoFeP-NC possesses excellent hydrogen evolution reaction (HER) performance with the small overpotential (η₁₀) of 81 mV and 173 mV generated at a current density of 10 mA cm^-2 in acidic and alkaline media, respectively. Additionally, it can also efficiently catalyze water oxidation (OER), which shows an ideal overpotential (η₁₀) of 283 mV in alkaline electrolyte (pH = 14). The remarkable catalytic property of CoFeP-NC mainly stems from the strong synergetic effects of CoFeP nanospheres and carbon network. On the one hand, the interaction between the two can make better contact between the electrolyte and the catalyst, thereby providing a large number of available active sites. On the other hand, it can also form a network to offer better durability and electrical conductivity (8.64 × 10^-1 S cm^-1). This work demonstrates an efficient method to fabricate non-noble electrocatalyst towards overall water splitting, with great application prospect.