Electrochemical properties and biomimetic activity of water-soluble meso-substituted Mn(III) porphyrin complexes in the electrocatalytic reduction of hydrogen peroxide

Hydrogen Peroxide Fuel Cells and Self-Powered Electrochemical Sensors Based on the Principle of a Fuel Cell with Biomimetic and Nanozyme Catalysts

The operating principle of a fuel cell is attracting increasing attention in the development of self-powered electrochemical sensors (SPESs). In this type of sensor, the chemical energy of the analyzed substance is converted into electrical energy in a galvanic cell through spontaneous electrochemical reactions, directly generating an analytical signal. Unlike conventional (amperometric, voltammetric, and impedimetric) sensors, no external energy in the form of an applied potential is required for the redox detection reactions to occur. SPESs therefore have several important advantages over conventional electrochemical sensors. They do not require a power supply and modulation system, which saves energy and costs. The devices also offer greater simplicity and are therefore more compatible for applications in wearable sensor devices as well as in vivo and in situ use. Due to the dual redox properties of hydrogen peroxide, it is possible to develop membraneless fuel cells and fuel-cell-based hydrogen peroxide SPESs, in which hydrogen peroxide in the analyzed sample is used as the only source of energy, as both an oxidant and a reductant (fuel). This also suppresses the dependence of the devices on the availability of oxygen. Electrode catalyst materials for different hydrogen peroxide reaction pathways at the cathode and the anode in a one-compartment cell are a key technology for the implementation and characteristics of hydrogen peroxide SPESs. This article provides an overview of the operating principle and designs of H2O2-H2O2 fuel cells and H2O2 fuel-cell-based SPESs, focusing on biomimetic and nanozyme catalysts, and highlights recent innovations and prospects of hydrogen-peroxide-based SPESs for (bio)electrochemical analysis.

Polarized Bimetallic Site Synergy in Ionic Structures of Cu(II), Fe(III), and Mn(III) Porphyrins: Electrochemistry and Catalytic Hydrogenation of Nitroaromatics

Binuclear catalytic sites attained in a controlled way with complementary and cooperative metal ion centers are highly relevant in the development of new or enhanced catalytic processes. Herein, binuclear sites carrying Fe(III), Cu(II), or Mn(III) metal ions with a polarized structure have been prepared using the ionic self-assembly of oppositely charged metalloporphyrins. Binary porphyrin structures (BIPOS) have been prepared based on metalloporphyrin cations carrying pyridinium or methylpyridinium groups in conjugation with metalloporphyrin anions carrying sulfonatophenyl groups. BIPOS carrying [cation/anion] tecton pairs of [Cu/Fe], [Fe/Cu], [Cu/Cu], [Fe/Fe], [Mn/Fe], [Fe/Mn], and [Mn/Mn] have been compared. Electrochemical interaction and enhanced catalytic behavior are noticeable for BIPOS [Fe/Cu], [Fe/Fe], and [Mn/Fe] carrying a Fe center and [less electronegative/more electronegative] metal ion centers in the [cation/anion] porphyrin ionic pairs. For high-performance BIPOS, cyclic voltammograms showed a greater separation of the cathodic and anodic peaks, within ΔEp = 0.095-0.125 V, and the rate constants for the catalytic reduction of 4-nitrophenol were within k = 0.380-0.535 min-1/mg of catalyst, significantly superior to the related individual metalloporphyrins. Inverse heterobimetallic [Cu/Fe] and [Fe/Mn] and the homometallic BIPOS [Cu/Cu] and [Mn/Mn] were significantly less active or inefficient. A [Fe/Cu] material could be reused in at least 5 catalytic cycles, maintaining catalytic activity; the best catalysts were also active in the reduction of nitrobenzene to aniline in mild conditions (visible light, 30 °C, 0.5 mol % catalyst), and an [Fe/Fe] catalyst showed 100% aniline yield after 2 h.

Intrinsic Multienzyme-like Activities of the Nanoparticles of Mn and Fe Cyano-Bridged Assemblies

This study investigates the intrinsic multienzyme-like properties of the non-stabilized nanocrystalline nanoparticles of manganese-doped Prussian blue (Mn-PB) nanozymes and Prussian blue (PB) nanozymes in chemical and electrocatalytic transformations of reactive oxygen species. The effect of manganese doping on the structural, biomimetic, and electrocatalytic properties of cyano-bridged assemblies is also discussed.

Porphyrinic MOF Film for Multifaceted Electrochemical Sensing

Electrochemical sensors are indispensable in clinical diagnosis, biochemical detection and environmental monitoring, thanks to their ability to detect analytes in real‐time with direct electronic readout. However, electrochemical sensors are challenged by sensitivity—the need to detect low concentrations, and selectivity—to detect specific analytes in multicomponent systems. Herein, a porphyrinic metal‐organic framework (PP‐MOF), Mn‐PCN‐222 is deposited on a conductive indium tin oxide (ITO) surface. It affords Mn‐PCN‐222/ITO, a versatile voltammetric sensor able to detect redox‐active analytes such as inorganic ions, organic hazardous substances and pollutants, including nitroaromatics, phenolic and quinone‐hydroquinone toxins, heavy metal ions, biological species, as well as azo dyes. As a working electrode, the high surface area of Mn‐PCN‐222/ITO enables high currents, and therefore leverages highly sensitive analysis. The metalloporphyrin centre facilitates analyte‐specific redox catalysis to simultaneously detect more than one analyte in binary and ternary systems allowing for detection of a wide array of trace pollutants under real‐world conditions, most with high sensitivity.