Regulating the Active Sites of Metal–Phthalocyanine at the Molecular Level for Efficient Water Electrolysis: Double Deciphering of Electron‐Withdrawing Groups and Bimetallic

Abstract

Electrocatalysts based on precious metals of Pt, Ir, Ru, and their oxides are considered to be the most effective materials for accelerating the water oxidation process, but the high cost and scarcity limited the large-scale applications. Therefore, it is necessary to develop efficient, low-cost, and durable electrocatalysts to replace precious metal catalysts. [3] As we know, in the electrocatalytic reaction of two electrons and four electrons, the activation of H 2 O and the adsorption of reaction intermediates by the active site are essential. [2b,4] For OER, the kinetic rate may be limited by the weak oxygen-binding state of the metal, and the strong bonding ability may limit the proton-electron transfer to *OH and *O. [5] On the other hand, the Volmer-Heyrovsky step will be limited by the weak or strong bonding ability during HER. [6] According to the above discussion, the adsorption capacity of the active site to reaction intermediates plays a crucial role in electrocatalytic performance, the weaker and stronger adsorption capacity will also have an adverse impact on the activity of electrocatalysis. Hence, the construction of customizable electronic structures for efficient bifunctional electrocatalysts is irresistibly attractive but still challenging.Among various electrocatalysts, metallic phthalocyanine compounds (MPc, M = Fe, Co, Ni Cu, etc.) have many advantages Implementing a molecular modulation strategy for metallic phthalocyanines (MPc) without losing the activity of the metal center and inducing a multifunction characteristic in electrocatalytic remains a challenge. Herein, a series of 2D CuCo bimetallic polymerized phthalocyanine modified with strong electron-withdrawing groups (CuCoPc-g, g = F, Cl, Br, NO 2 ) for water oxidation in the alkaline electrolyte is designed and simply synthesized. The experimental results testify that the bimetallic design can perform electronic adjustment once and introduce the second active sites to get bifunctional characteristics, and then the electronic structure of the active center can be regulated by electron-withdrawing groups for a second time to achieve the optimal state. These electrons that transfer in the active center of inner metal can generate space-charged regions and the design of the polymer can stabilize active site region to maintain long-term electrolytic stability and high activity. This study precisely regulates the electronic structure of MPc at the molecular level and provides insight into the multifunctional design of polymeric macrocyclic electrocatalysts.

Atomically Dispersed Fe Sites Regulated by Adjacent Single Co Atoms Anchored on N‐P Co‐Doped Carbon Structures for Highly Efficient Oxygen Reduction Reaction

“…materials, featuring N-coordinated metal centers, have been developed as promising catalysts due to their resemblance to bio-porphyrin structures. [16,17] The unique geometric configuration of MN 4 species could provide a valuable opportunity to investigate the correlation between their electronic properties and structures. [18] However, the symmetric electron distribution and inherent electronic structure of MN 4 catalysts, along with their single-metal-atom active sites, present challenges in breaking the linear scaling relationship between the adsorption energies of different reaction intermediates to improve their catalytic activities.…”

FeN3S1─OH Single‐Atom Sites Anchored on Hollow Porous Carbon for Highly Efficient pH‐Universal Oxygen Reduction Reaction

“…Nitrogen-coordinated iron atoms on carbon matrix (Fe-Nx-C) electrocatalysts possess cost-effectiveness, tunable atomic structure, and outstanding catalytic activities, which are considered to be the most promising alternative to noble metal catalysts. [5,6] Among them, symmetrical Fe─N 4 architectures in Fe-N X -C singleatom catalysts (SACs) dominate ORR activities, attributed to their structural similarity to bio-porphyrins, which has been testified by density functional theory (DFT) calculations [7,8] However, on the basis of previous research, [9][10][11] the symmetrical N atoms with higher electronegativity are not conducive to the adsorption and desorption of oxygen-containing intermediates, leading to unsatisfactory catalytic activities of Fe-N 4 -C SACs. Therefore, the optimization of the electronic structure is still challenging in the enhancement of the electrocatalytic activities for Fe-N 4 -C SACs.…”

Unusual Ligand Assistance in Molecular Electrocatalysis via Interfacial Proton Charge Assembly

“…The global energy crisis due to the extensive use of fossil fuels has already become a ubiquitous problem, making the domain of renewable energy conversion a hot research topic for the global scientific community. − In this regard, electrochemical transformation via electrocatalysis has become an area of research focus because of its potential to convert abundant feedstocks into value-added products. − This has in turn led to the design and development of various metal-based and molecular electrocatalysts. − Molecular electrocatalysts such as phthalocyanines and porphyrins have gained a lot of attention mainly because of their superior chemical and thermal stability and highly flexible optoelectronic nature. − For these reasons, the metallophthalocyanines have been explored for catalysis, like the MEROX process for the sweetening of oils to electrocatalysis in fuel cells and air batteries, with undeniable importance in electrochromism, the pigment industry, sensing, solar cells, and photodynamic therapy (cancer treatment). − It is already known that the electrochemical performance of the phthalocyanines can be affected by the redox properties of the central metal which in turn can be altered by changing the metal center or by altering the type, number, and position of the substituents on the macrocyclic ligand. − It has also been observed that electron-withdrawing functionalities such as −NO 2 , −CN, −COOH, and −Cl favor oxidation reactions like water electrolysis, oxidation of thiols, ascorbic acid oxidation, peroxide oxidation, etc. − On the other hand, electron-donating substituents like t -Bu, −NH 2 , and −OH favor reductive electrocatalysis such as carbon dioxide reduction, oxygen reduction, nitrogen reduction, etc. − Therefore, a correlation between electrocatalytic capability and inductive effect of the ligand functionality has already arrived, which is widely chosen as a benchmark for designing new molecular platforms for electrochemical transformations.…”