Reinterpreting volcano correlations in bio-inspired Electrocatalysts: The role of active site availability in oxygen reduction

Generation, characterization, and reactivity of a phthalocyanine iron–oxo complex

Metal–nitrogen–carbon (M–N–C) molecular catalysts attract attention for the hydrogen evolution reaction (HER) owing to their well‐defined active sites and structural tunability. However, previous studies prioritize intramolecular regulation, leaving the cooperative role of intermolecular interactions insufficiently understood. Herein, we design and synthesize three Fe–N–C molecules, including iron phthalocyanine (FePc) and two pyridinic‐N–incorporated FePc derivatives (FeTAP and FeOM), and elucidate their structure–activity relationships via integrated structural and electronic analyses to enable performance prediction. We demonstrate that pyridinic‐N incorporation drives Fe centers from Fe 2+ to a more positively charged Fe 2+δ state, creating an “oxidation‐state reservoir” that promotes rapid electron transfer and proton adsorption for HER. Moreover, overall activity is governed by the balance between intramolecular electronic regulation and intermolecular π–π interactions: FePc is limited by weak intramolecular regulation; FeOM exhibits strong intramolecular effects but weakened intermolecular coupling; and FeTAP optimizes this balance, delivering the highest HER activity. Electrochemical measurements corroborate the predictions and further reveal that an optimal level of pyridinic‐N achieves the intra‐/intermolecular balance, thereby accelerating HER kinetics on these Fe–N–C catalysts. These findings provide a predictive basis and a clear design guideline centered on intra‐/intermolecular balance for molecular electrocatalysts.

The electrochemical reduction of nitrate (NO3-) to ammonia (NH3) offers a sustainable route for nitrogen cycle remediation and decentralized NH3 production. In this work, we systematically investigated the impact of electronic structure and wettability in regulating the catalytic performance of molecular catalysts using functionalized iron phthalocyanines (FePc-R, R = NH2, COOH, CN, and t-Bu) supported on carbon nanotubes. The strongly hydrophilic FePc-NH2/CNT (electron-donating functional group-containing) catalyst achieved a maximum Faradaic efficiency of 94.1% at -0.6 VRHE and a partial current density of 83.9 mA cm-2 toward NH3 at -0.9 VRHE. In contrast, strongly hydrophilic FePc-COOH/CNT and weakly hydrophilic FePc-CN/CNT, containing electron-withdrawing functional groups, delivered a lower performance across all potentials. Density functional theory (DFT) calculations revealed that electron-donating functional groups elevate the Fe-center HOMO level, facilitating hydrogenation of NHx intermediates and enhancing turnover frequency. In situ X-ray absorption spectroscopy (XAS) confirmed that Fe-N4 coordination in FePc-NH2/CNT remains stable across all tested potentials, while electron-withdrawing functional group-containing catalysts (FePc-COOH/CNT and FePc-CN/CNT) exhibited Fe-Fe cluster formation at -0.8 and -0.7 VRHE, respectively. Furthermore, coupled mass transport and reaction modeling indicated that more hydrophilic surfaces reduce the diffusion layer thickness, promoting NO3- accessibility and NH3 formation. Together, these findings decoupled the synergistic role of electronic tuning and wettability control in governing both activity and stability, providing mechanistic design principles for molecular and heterogeneous catalysts in the reduction of electrochemical NO3- to NH3.

Here we propose an innovative approach for the fabrication of hybrid p–n heterojunction diodes based on iron phthalocyanine (FePc) and zinc oxide (ZnO) on solid and flexible substrates using Al doped ZnO (AZO) as a transparent electrode. We combined transparent conductive thin films of ZnO with organic semiconductors represented by FePcs deposited by means of physical deposition, such as magnetron sputtering (MS), for undoped and doped ZnO thin films, and molecular beam epitaxy (MBE) for FePc deposition. The structural, optical and morphological properties of the fabricated hybrid diodes were assessed by X-ray diffraction (XRD), ellipsometric measurements, scanning tunneling microscopy (STM) and Raman techniques. Key electrical parameters such as current density and rectifying ratio (RR) were determined from the current density-voltage characteristic (J-V), which provided insights into the charge transport mechanisms and the organic/inorganic heterojunction interface. Moreover, by electrical impedance spectroscopy (EIS) measurements, we calculated the capacitance value of a p-n heterojunction and we assessed the equivalent circuit parameters of the heterojunction devices under equilibrium conditions. The results demonstrated the potential of combining inorganic transparent oxides with organic semiconductors for the development of flexible and transparent hybrid optoelectronic devices with improved efficiency.

ABSTRACT The assembly between carbon materials and transition metals has been proved to be a promising way to build electrocatalysts with good activity and stability, especially those with biomimetic metallophthalocyanine bearing M‐N 4 active sites. Herein, through direct pyrolysis of Enteromorpha and subsequent solvent impregnation, we demonstrate the successful synthesis of a composite consisting of electrochemically active iron phthalocyanine and N, S codoped graphene‐like Carbon. This biomass‐derived electrocatalyst is low‐cost and more facile in preparation, and its typical features like biomimetic multi‐shell structure, high specific area, and heteroatom doping enable it to serve as not only a promising cathode material for oxygen reduction reaction (ORR), leading to excellent half‐wave potential of 0.9 V. Further combination of ORR with iodide oxidation reaction (IOR) greatly enhances energy efficiency, as the assembled Zn‐air/iodide hybrid battery (ZAIHB) exhibits high open‐circuit voltage of 1.59 V and gravimetric capacity of 756 mAh g − 1 .

Iron phthalocyanine doped dual hydrogel network enables sensitive and selective electrochemical detection of neuro-related analytes

Synergistic nitrogen, boron co-doping in graphene support to optimize FeN4 active site in iron phthalocyanine for oxygen reduction reaction: A DFT study

Iron phthalocyanine nanozyme enhances photodynamic antibacterial activity via enzyme-mimicking catalysis

Recent advances in scanning tunneling microscopy have enabled quantum-coherent control of single surface spins via all-electric electron spin resonance (ESR). Such control requires magnetoelectric coupling, since spin resonance is a magnetic effect. We show that a magnetic tip induces a bias-dependent exchange field on a localized Anderson impurity via virtual particle exchange with the magnetic lead. This field differs from the Heisenberg exchange and can be tuned, reversed, or suppressed by the bias voltage. Our model reproduces bias-controlled resonance shifts for individual electron spin S = 1/2 titanium atoms and iron(II) phthalocyanine molecules. Their distinct bias responses provide unambiguous spectroscopic identification of different magnetic species through their characteristic electrochemical parameters. The exchange field is the magnetoelectric mechanism behind all-electric ESR and enables spin control for atomic-scale spin-based quantum technologies via electric fields.

Precise modulation of spin states of single-atom catalysts (SACs) offers a promising route to fine-tune peroxide activation behaviors and selectivity toward different oxidation pathways. Here, we report a spin-tunable Fe SAC composed of iron phthalocyanine (FePc) axially coordinated via oxygen bridges (-O-) onto annealed nanodiamond (AND), denoted as FePc-O-AND. The axial oxygen coordination induces a spin transition from high-spin (t2g5eg3) to an intermediate-spin (t2g4eg2) state. This transition generates an unoccupied Fe 3dz2 orbital that enables oriented electron transfer to peracetic acid (PAA) via hydroxyl oxygen coordination. In situ synchrotron-based Fourier-transform infrared spectroscopy (SR-FTIR) reveals a distinct PAA activation pathway involving inner-sphere complexation and a non-radical electron-transfer mechanism. As a result, the FePc-O-AND/PAA system drives a non-radical electron-transfer pathway with a high reaction rate (2.11 min-1), selectively converting phenolic pollutants into high-molecular-weight polyphenolic products (n ≥ 5). Density functional theory (DFT) calculations reveal that axial oxygen coordination in FePc-O-AND enhances PAA adsorption energy (-0.89 eV) and induces a favorable inner-sphere interaction with the hydroxyl oxygen, thereby facilitating effective PAA activation. The FePc-O-AND/PAA system exhibits strong resistance to water matrix interferences and maintains high performance over 130 h of continuous-flow operation. These findings establish axial coordination-mediated spin-state regulation as a powerful strategy for engineering SACs for sustainable water purification and recycling of micropollutants.

The vibrational landscape of adsorbed molecules is central to understanding surface interactions at the atomic scale, influencing phenomena from catalysis to molecular electronics. Recent advances in atomic-scale tip-enhanced Raman spectroscopy (TERS) have enabled vibrational mapping of single molecules with subnanometer spatial resolution, providing unprecedented insights into molecule-surface interactions by confining light in plasmonic picocavities. Here, we exploit TERS in a cryogenic scanning tunneling microscope junction to perform Raman hyperspectral mapping of single iron phthalocyanine (FePc) molecules in three nonequivalent adsorption configurations on Ag surfaces. We explore the changes in the vibrational modes of FePc molecules adsorbed on two distinct silver crystal terminations with differing symmetry, Ag(111) and Ag(110), revealing how subtle variations in the adsorption geometry due to substrate anisotropy can strongly influence molecular vibrations, lifting the degeneracy of individual normal modes. Our findings not only demonstrate the first use of subnanometer TERS mapping across different symmetry configurations but also provide a deeper understanding of how site-specific vibrational properties are intimately linked to local atomic environments. This capability paves the way for precisely tailoring surface interactions and controlling chemical reactions on the atomic scale.

Phthalocyanines (Pc) complexes are versatile, highly conjugated planar macrocycles known for robust thermal stability and tunable electronic properties, making them valuable in catalysis, sensing, and energy applications. Herein, we report the synthesis of novel chromium(II) and iron(II) phthalocyanines bearing peripheral 2-mercaptobenzothiazole (2-MBT) substituents. The 2-MBT groups introduce sulfur- and nitrogen-containing aromatic thiolate functionality to the macrocycle periphery, aimed at extending π-conjugation and modulating the electronic structure of the phthalocyanine core. This functionalization strategy is expected to tailor the optical and redox characteristics of the complexes. Structural characterization via elemental analysis, Fourier-transform infrared (FT-IR), ultraviolet–visible (UV–Vis), and 1 HNMR spectroscopy confirmed successful formation of the macrocyclic complexes. Notably, the disappearance of the phthalonitrile C≡N stretching band in FT-IR indicated complete cyclotetramerization into the MPc framework. The UV–Vis spectra exhibited characteristic Q-bands at 683 nm and B-bands at 300–350 nm, consistent with π–π* transitions of the conjugated ring. Thermogravimetric analysis revealed that both complexes remain highly thermally stable up to 250°C before undergoing stepwise exothermic decomposition. Electrochemical studies cyclic voltammetry and square-wave voltammetry in dimethylformamide, showed multiple quasi-reversible redox processes associated with both the phthalocyanine π-system and the central metal ions. These findings demonstrate that the 2-MBT-functionalized phthalocyanines are thermally robust and redox-active, with promising potential for electrocatalysis and catalysis.

Atomically dispersed Fe-N-C catalysts with well-defined iron-nitrogen coordination exhibit fantastic promise for the oxygen reduction reaction (ORR). However, achieving their scalable synthesis while preventing iron aggregation and performance degradation remains a critical challenge. Here, we demonstrate a highly efficient confined flash Joule heating (CFJH) technique for the scalable and ultrafast synthesis of Fe-N-C catalysts. The coal-derived porous carbons are efficient in confining iron phthalocyanine (FePc) molecules, suppressing their migration and iron aggregation during ultrafast CFJH treatment. This process facilitates the conversion of FePc into atomically dispersed FeN4 sites embedded within a graphitization-enhanced carbon framework. Mechanistic studies reveal that, compared to an FePc precursor, these integrated FeN4 sites exhibit a shifted rate-determining step with optimized adsorption/desorption of oxygen intermediates, leading to a reduced energy barrier for efficient 4e- oxygen reduction. The resulting catalyst exhibits impressive ORR activity in alkaline media with a high half-wave potential (0.90 V vs RHE) and remarkable durability (94.5% retention over 100 h). The assembled zinc-air battery delivers a peak power density of 277.6 mW cm-2 and sustains stable operation for over 900 h, outperforming the Pt/C + IrO2 benchmark. Scalable production is achieved at a rate of 0.5 kg h-1, establishing a facile and industrially viable route for synthesizing high-performance atomically dispersed catalysts.

Covalent organic frameworks (COFs) such as iron phthalocyanine (FePc) have been considered as potential electrocatalysts. Herein, we provide important insights into modulating the intrinsic activity of FePc COFs for the oxygen reduction reaction (ORR) by adjusting their stacking configuration. The eclipsed, AA-stacked and the staggered, AB-stacked FePc COF configurations were obtained via adjusting the interlayer interaction forces. Electrochemical studies reveal that the AA-stacked FePc COF exhibits a half-wave potential of 0.856 V vs RHE, which is 0.195 V higher than that of the AB-stacked FePc COF. The assembled zinc-air battery, using AA-stacked FePc COF as the cathode, demonstrates a high cell voltage of 1.64 V vs Zn2+/Zn alongside with a superior specific capacity of 935.79 mA h-1gZn-1. The upshift in the valence band center and the high effective magnetic moment in the eclipsed, AA-stacked FePc COF suggest that the states are occupied at high energy levels, indicating a high-spin state of Fe. Density functional theory calculations suggest that the long-range spin channels aligned with iron columns in the eclipsed, AA-stacked FePc COF facilitate the spin-selective charge transport through interlayer band dispersion. The mechanism associated with the high-spin state of Fe promotes the cleavage of the *OO and *OOH intermediates, accelerating the ORR kinetics. Our study reveals that the stacking order of FePc COFs is important for modulation of the charge transfer and electron spin states, showing how to control the spin electronic characteristics of COFs through the stacking configuration-dependent interlayer interactions.

New iron(II) phthalocyanine complexes featuring long-chain alkyldiamine axial ligands have been synthesized, isolated, and comprehensively characterized by single-crystal X-ray diffraction and multinuclear NMR spectroscopy ( 1 H, 13 C, and 15 N), among other techniques. In tetrahydrofuran solution, these complexes exist in a dynamic equilibrium between mononuclear ( M ) and variable amounts of linear ( D ) and cyclic ( Cy ) polynuclear assemblies, depending on concentration and ligand stoichiometry, while maintaining a six-coordinate Fe(II) environment across all assemblies. Quantum-chemical calculations reveal the energetic minima associated with each assembly, providing a coherent picture of the structure–stability relationships that govern nuclearity and aggregation in solution. Long-chain alkyldiamines act as programmable axial linkers that control the nuclearity of low-spin Fe(II) phthalocyanines, establishing a dynamic equilibrium between monomeric, dimeric, and cyclic assemblies in THF. Multinuclear NMR and PGSE diffusion measurements, complemented by DFT calculations, rationalize the structure–stability relationships governing aggregation. • Controlled nuclearity switching in Fe(II) phthalocyanines via axial diamines. • Stoichiometry- and concentration-dependent equilibria between monomeric, dimeric and cyclic species in solution. • PGSE diffusion NMR identifies mono- and polynuclear FePc assemblies. • DFT calculations rationalize stability and aggregation of FePc complexes.

The curvature change of the support can control the induced local stress strain and directly change the properties and performance of the layered materials. Herein, we successfully in situ grew graphdiyne (GDY) on the surface of carbon nanotubes (CNTs) to form a heterojunction material with curved structure and highly surface-active. Our results indicated that the surface-grown GDY can deform into a curved-GDY (cGDY) due to internal stress. Such structural rearrangement regulates the charge distribution on interface of graphdiyne/CNTs and increases the charge density of Csp─Csp bonds within bent diacetylene linkages (-Csp≡Csp-Csp≡Csp-). While loading iron phthalocyanine (FePc) to this bent surface, the interactions and the interfacial repulsive force in the system were greatly enhanced, resulting in the elevated energy level of Fe 3dz2, which was beneficial to the adsorption of O2, and the hybridization between Fe (3dxz, 3dyz, and 3dz2) and *OO (2px, 2py, and 2pz) orbitals, significantly enhancing activation of O2. Therefore, compared with the FeN4 moiety on pure CNTs or GDY, this heterojunction structure through axial π─bond tuning demonstrates superior performance with a half-wave potential of 0.905V and a Tafel slope of 31.7mV dec-1.

Janus carbonaceous assembly of biomimetic wettability-gradient air electrode for optimizing zinc-air battery kinetics.

ABSTRACT Appropriate deposition of metal complex‐based catalysts on solid carriers sometimes results in considerably higher catalytic activity than that of the metal complex alone, due to interactions between the complex and the solid. These catalysts could be a part of single‐molecule catalysts (SMCs) or site‐isolated molecular complex catalysts (SIMCs). Herein, we report a solid‐supported metal complex catalyst for CH 4 oxidation at room temperature. Specifically, μ‐nitrido‐bridged iron phthalocyanine dimer deposited on conductive carbon black can oxidatively activate the chemically stable C─H bond of CH 4 with high efficiency even at 25°C in an aqueous solution containing H 2 O 2 as an oxidant. Its catalytic activity for CH 4 oxidation is much higher than that of the commonly used Fenton reaction with Fe 2+ and H 2 O 2 under the same conditions. Such high catalytic oxidizing activity is attributable to the interaction between the specific surface sites of carbon black and the high‐valent iron‐oxo species of the catalyst molecule.

Cocatalyst-free dual-functional catalysis for four-electron transfer oxidation of hydrazine induced by an organic p–n bilayer comprising perylene derivative and iron phthalocyanine