Oxygen Electroreduction Reaction Research Articles

Cu-porphyrin-based polymers in electroreduction reactions of gases

In this work, the electrochemical properties of Cu-complexes of di- and tri-amino-substituted tetraphenylporphyrins in dichloromethane were investigated by the cyclic voltammetry method. Electrooxidation of porphyrins in a dichloromethane solution produced polyporphyrin films on the electrode. The formation of polymers occurs through the amino groups of phenyl substituents with the generation of phenazine and dihydrophenazine fragments. The surface morphology and thickness of polyporphyrin films were studied using a scanning electron microscope. The surface of the poly-Cu5,15-di(4′-aminophenyl)-10,20-diphenylporphyrin film is a network of fibers of about 5 µm long and 0.2–0.3 µm thick. The film thickness is 14 µm. The surface of poly-Cu5,10,15-tri(4′-aminophenyl)-20-phenylporphyrin has large branched agglomerates of indefinite shape; the film thickness is 22 µm. The catalytic activity of the obtained polyporphyrin films in oxygen and carbon dioxide electroreduction reactions were evaluated. Poly-Cu5,10,15-tri(4′-aminophenyl)-20-phenylporphyrin was found to be more catalytically active in both reactions, which is evidently associated with a more developed surface of the polymer.

Oxygen Electroreduction Reaction on Iron, Nitrogen-doped Nanocarbons: Structure – Reactivity Relationship

Theoretical calculations at the revPBE0-D3(PCM)/def2-TZVP level were performed to investigate the mechanism of the oxygen reduction reaction (ORR) on the FeN4-doped NCMs (graphene, single-walled (6,6)-armchair and (12,0)-zigzag carbon nanotubes) as catalysts. The effect of the support and relative orientation of FeN4 fragment in the catalyst structure on the ORR activity and stability of the differently adsorbed successive intermediates (O2*, HO2*, O*, HO*, H2O2*, H2O*) is discussed. Special attention is given to the possible poisoning effect of CO. The relative catalytic activity of the metal center and the adjacent C2 site of the carbon support are analyzed depending on the structure of the support. The metal catalytic center on the armchair nanotube and graphene supports is prone to deactivation by poisoning with CO, whereas in the zigzag nanotube supported catalyst the metal center is tolerant to CO. The four-electron mechanism of ORR is shown to be preferable over the two-electron mechanism in both acidic and alkaline media, both on the metal and C2 centers.

Electrochemically produced films based on individual porphyrins and bimetallic composites: Morphology and electrocatalytic properties in the reaction of oxygen electroreduction

In this work, we obtained polyporphyrin films based on Fe(III)Cl-5,10,15,20-tetrakis(4-pyridyl)porphyrin and Mn(III)acetate-5,10,15,20-tetrakis(4-pyridyl)porphyrin and composite films on their basis by electrooxidation-induced electrochemical polymerization. The obtained films produced uniform coatings. Spectral analysis showed that the composite films were enriched with iron complexes. Comparative analysis of the prepared films demonstrated differences between the morphologies of the composite film and films of individual metal complexes. The oxygen electroreduction process on the obtained materials proceeded at more positive values than that on carbositall. The effective number of transferred electrons demonstrated that replacing catalysts based on individual porphyrins with the bimetallic composite changed the process mechanism: while the four-electron mechanism competed with subsequent two-electron reactions on the Fe(III)Cl-5,10,15,20-tetrakis(4-pyridyl)porphyrin and Mn(III)acetate-5,10,15,20-tetrakis(4-pyridyl)porphyrin films, on the bimetallic composite the process mainly represented a four-electron reaction.

Edge defects-regulated FeCo metalic sites confined in N-doped carbon polyhedron as an efficient ORR catalyst for durable Zn-air battery

Metal sites or nanoparticles immobilized on MOF-derived porous carbon matrix have gained enormous attention for oxygen electroreduction reaction (ORR), but they still suffered from the insufficient catalytic performance. Herein, we introduced edge defects to regulate the ORR performance of N-doped carbon polyhedron-supported FeCo bimetallic catalysts via a facile NaCl/KCl-assisted pyrolysis. HR-TEM, HAADF-STEM, Raman spectra, XPS and EPR analysis confirmed the existence of uniform FeCo atoms and edge defects within N-doped porous carbon polyhedrons and their mutual effect helped promoting ORR performance. The resulting FeCo-NC-30 exhibited more excellent ORR activity with E1/2 of 0.86 V, and faster kinetic process with a higher kinetic current density, Jk,E = 0.85V = 7.15 mA/cm2. As a cathode catalyst, it delivered a desirable power density of 196.9 mW/cm2, comparable to Pt/C, in home-made Zn-air batteries. Our findings demonstrated that the electronic tuning effect caused by carbon edge defects and synergistic bimetallic interactions is beneficial for enhancing ORR activity.

Synergistic effect of two metal porphyrins in a polymer catalyst for oxygen electroreduction

This work considers the formation and catalytic properties of films of individual hydroxyphenyl porphyrin complexes with manganese (manganese(III) acetate 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (MnAc(4-OHPh)P)) and iron (iron(III) chloride 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (FeCl(4-OHPh)P)) and their composites. The films of individual metalloporphyrins and bimetallic composites were obtained by superoxide-assisted electrochemical deposition in dimethylsulfoxide solutions. The formation of the bimetallic (Mn + Fe) porphyrin composite was confirmed by spectral methods. An analysis of the atomic-force microscopy results showed that the composite films consisted of larger globules and were rougher than those of individual porphyrins. The electroactive surface areas of the individual porphyrin films and the composite were significantly different from each other. The mechanism and kinetics of the oxygen electroreduction reaction (ORR) on the films of individual porphyrins and bimetallic composite were evaluated using a rotating disk electrode. The kinetic current density of the Tafel slope and the position of the ORR current wave on the surface of the poly-(MnAc(4-OHPh)P + FeCl(4-OHPh)P) composite indicate smaller kinetic limitations and lower overvoltage on this material than on carbositall and films of individual porphyrins. The smaller kinetic limitations and better energy characteristics can be explained by the synergistic effect produced by the combined action of the Mn- and Fe- catalytically active centers during ORR on the composite film.

Revisit to Grain Boundary Effect in Pt Nanocrystals toward the Oxygen Electroreduction Reaction

AbstractThe effect of catalytic surface defects in the oxygen reduction reaction (ORR) has been extensively studied to enhance the performance of proton‐exchange‐membrane fuel cells. Platinum (Pt)‐based nanocatalysts have been used to overcome the poor performance of ORR, and Sabatier‐type activity plots have been used to identify the optimal adsorption properties for ORR intermediates on the catalytic surface. Grain boundaries (GBs) within the nanostructures have been identified as the optimal active sites for ORR due to their reasonable coordination number and high oxygen residence time. However, oxidation of Pt atoms exposed at GB sites and leaching of non‐noble metals from bimetallic Pt alloys have been identified as the “Achilles Heel” of GB‐containing nanocatalysts. In this concept, we revisit the effect of GBs on nanocatalysts, summarize the mechanism of GBs towards ORR, and suggest outlooks for improving ORR for future design of nanocatalysts.

The Effect of Pretreatment on a PtCu/C Catalyst's Structure and Functional Characteristics.

This research focuses on studying the effects of various pretreatment types on a PtCu/C catalyst synthesized by the co-deposition of metal precursors. The treatment in a 1 M HNO3 solution for 1 h is shown to result in a slight increase in activity in the oxygen electroreduction reaction (both the mass activity and specific activity calculated for the value of the electrochemically active surface area). The sample obtained after the thermal treatment, which is carried out at 350 °C under an argon atmosphere for 1 h, demonstrates 1.7 times higher specific activity than the sample before the treatment. The durability testing results obtained by the stress testing method in a potential range of 0.6-1.4 V during 2000 cycles show that the PtCu/C catalysts after both the acid treatment and the thermal treatment are characterized by higher residual activity than the sample in the "as-prepared" state.

Boosting the dynamic reconstitution of FeCu–N4 sites via doping of bimetal nanoparticles during oxygen electrocatalysis

Dual metal atom catalysts with nitrogen coordination are emerging as promising materials that can be substituted for platinum group-based catalysts employed for the oxygen electroreduction reaction.

Influence of caprolactam on the tin electrodeposition on a dispersed carbon support and preparation of Pt/(SnO2/C) catalysts

Composite SnO2/C materials obtained by electrodeposition of tin on Vulcan XC72 particles were used to fabricate a platinum catalyst for the oxygen electroreduction reaction (ORR). Thermogravimetry and X-ray diffraction methods made it possible to determine the composition of materials and the size of platinum and tin oxide crystallites. The use of the SnO2/C composite obtained in the presence of e-caprolactam (CPL) as a support made it possible to increase the electrochemically active surface area (ESA) of platinum and the mass activity of the Pt/SnO2/C catalyst in ORR.

Palladium-containing catalysts based on mesostructured material of the cmk type in the reaction of oxygen electroreduction

Palladium-containing catalysts based on mesostructured material of the cmk type in the reaction of oxygen electroreduction

Polymer materials based on metal-free hydroxy- and aminophenyl porphyrin as potential catalysts: Preparation and properties

Hydroxy- and aminophenylporphyrin polymer films have been obtained by a superoxide-assisted electrochemical deposition method. This paper demonstrates the effect of the porphyrin structure on the film morphology and electrocatalytic properties of the prepared materials. A catalytic activity series of the synthesized metal-free electropolymers has been defined for the oxygen electroreduction reaction in an aqueous alkaline medium. It is shown that the samples prepared from 2H-5,10,15,20-tetrakis(3-aminophenyl)porphyrin possess the highest catalytic activity.

2H-5,10,15,20-tetrakis(3-aminophenyl)porphyrin films: Electrochemical formation and catalyst property testing

• Tetra(3-aminophenyl)porphyrin films were formed via superoxide-assisted method; • Ab initio applies for adsorption energy analysis on the catalytic site; • 3-aminophenyl porphyrin based films show promising ORR activity; • Calculations indicate on the same ORR mechanism as experiments. Polymer films based on 2H-5,10,15,20-tetrakis( 3 -aminophenyl)porphyrin have been successfully prepared by superoxide-assisted electrochemical deposition method from dimethyl sulfoxide solutions. Investigation of the deposition process and obtained films demonstrates typical for superoxide-assisted method mechanism of polymer formation, which leads to phenazine type bridges between porphyrin moieties. The density functional theory method has been used to model a polymer chain fragment and an analysis of natural bond orbital has been carried out. According to the calculations, the charge density distribution on the carbon skeleton of the obtained polymer resembles the distribution of charges on carbon materials doped with nitrogen, which are considered as promising catalysts for the oxygen electroreduction. Thus, the energy of adsorption of O 2 and OOH species (intermediates of oxygen electroreduction) on potential catalytic centers of the model polymer fragment has been calculated. The calculation results indicate predominantly two-electron pathway of O 2 reduction. A catalytic activity of poly-2H-5,10,15,20-tetrakis( 3 -aminophenyl)porphyrin films has been shown for the oxygen electroreduction reaction in an aqueous alkaline medium

Excess dopant effect in platinum‐based alloys toward the oxygen electroreduction reaction

AbstractDoping the PtNi octahedra with trace amount of transition metals has recently been shown to significantly improve the activity and durability of the oxygen reduction reaction (ORR). However, the role of excessive amounts of doped elements on ORR performance is unclear. In this work, PtNi octahedra were synthesized with and without excess Mo dopant. Also, spherical PtNi nanoparticles containing excess Co dopant were synthesized. The ORR performance revealed that PtNiMo octahedra and PtNiCo nanoparticles showed inferior ORR activities compared to bimetallic PtNi octahedra. Based on the electrochemical analysis, we found that unfavorable oxygen‐binding strengths of PtNiMo and PtNiCo catalysts decrease the ORR performances.

Understanding catalytic activity trends of atomic pairs in single-atom catalysts towards oxygen reduction reactions

Single-atom catalysts are regarded as the most promising materials for oxygen electroreduction reactions. However, their rational development is hindered by challenges such as determining the reaction mechanism and modulating the electronic configuration at the orbital level. Using density functional theory (DFT) calculations, in this work we investigate the catalytic activities of 13 transition metal single-atom (TM1)-doped titanium dioxide (TM1@TiO2) nanosheets toward the oxygen reduction reaction (ORR). Based on the scaling relationships between ORR intermediates, the number of theoretical d-valence electrons of TM1 atoms could be used to directly predict the ORR activities. The overall synergy of TM1 and Ti active sites (TM1-Ti1 atomic pairs) can effectively decrease the theoretical overpotential by reducing the bonding contribution of dz2-sp orbital pairs in TM1-OH bonds. This work paves the way toward a better understanding of orbital interactions between active sites and adsorbates, which will promote the discovery and design of candidate materials with desirable catalytic activities.

Understanding electronic configurarions and coordination environment for enhanced ORR process and improved Zn-air battery performance

Electronic configurations and coordination environment of catalysts play the crucial roles for oxygen reduction reaction (ORR). However, most of current efforts have been focused on the geometry design and recognition of active sites, resulting in the rare studies on the intrinsic activity of reaction sites and the synergistic effects between metal centers and external environment. Herein, a dual performance optimization of iron phthalocyanine (FePc) molecules is realized via introducing reduced graphene oxide (rGO) as the carrier. Coupling of rGO and Fe-N4 moiety can further boost Fe 3d electron spin state transition and C 2p charge delocalization. The higher spin state of Fe ions and more Fe-N4 local charge accelerate the electron transfer between Fe sites and adsorbed reactants/intermediates, rendering in an enhanced ORR performance. Under alkaline conditions, the ORR activity (Tafel slope of 39.1 mV dec−1 and an onset potential of 0.98 V vs. RHE) and durability of optimal catalyst exceed commercial Pt/C and many reported Fe-N-C electrocatalysts. Both liquid and solid state Zn-air batteries driven by this catalyst also exhibit satisfactory practical application potential. This work provides a novel insight into the Fe 3d orbitals electronic structure and internal charge whereabouts of catalyst in oxygen electroreduction reactions.

The electrochemical activation mode as a way to exceptional ORR performance of nanostructured PtCu/C materials

The nanostructured PtCux/C catalysts with an average nanoparticle size of 3–5 nm, which significantly surpass in activity the commercial Pt/C analog in the oxygen electroreduction reaction (ORR), were obtained by the chemical reduction. A detailed analysis of the activation potentials range effect on the catalysts electrochemical performance in particular, on the microstructure of bimetallic catalysts with small nanoparticles, has been carried out. The upper potential limit, which limited the range of the electrode activation potentials, had a significant effect on the PtCu/C catalysts mass activity and specific activity in the ORR, but does not affect to the electrochemically surface area and materials compositions. Thus, an important phenomenon has been noted in which materials with the same composition differ significantly in their functional characteristics in the ORR, depending on the electrochemical activation conditions. Original approach to electrochemical study is presented, which helps to understand the effect of the activation potentials range on the surface layers reorganization of bimetallic nanoparticles in catalysts.

Synthesis, Photo- and Electrocatalytic Properties of Nanostructured Y-TiO2 Films

The electrocatalytically active films based on nanodispersed titanium dioxide modified by Y3+ ions and synthesized by the sol-gel method were characterized by the X-ray diffraction (XRD) and ultraviolet-visible photocurrent spectra. Electrocatalytic properties of the TiO2 and Y-TiO2 electrodes were investigated during the process of oxygen electro-reduction. The XRD results indicated that the TiO2 and Y-TiO2 powders with the yttrium content of 0.5–5 mol% calcined at 500 °C had an anatase crystal structure, with the crystallite size of 10–12 nm. The electrodes based on the Y-TiO2 films were photosensitive in a wavelength range of 250–400 nm. For all investigated samples with the Y (III) content of ≤ 5 mol%, both an increase in the photocurrent quantum yield and a shift of spectra towards longer wavelengths vs. those of the undoped TiO2 were observed. The photocurrent quantum yield for the Y-TiO2 samples first increased and then decreased with increasing the Y (III) content, and reached its maximum with 2% Y-TiO2 films. It was found that doping of the TiO2 films by Y (III) improves the catalytic activity of the Y-TiO2 electrodes in the reaction of oxygen electroreduction. A correlation between photo- and electrocatalytic properties and structural changes occurring in the TiO2 films upon yttrium doping has been revealed.

Influence of Heat Treatment on the Microstructure and Functional Characteristics of PtCu/C Catalysts

PtCu/C electrocatalysts with different compositions, obtained by the method of the combined reduction of metal precursors, are heat treated at a temperature of 350°C in an argon atmosphere. The study by X-ray powder diffraction and transmission electron microscopy shows an increase in the average size of nanoparticles after heat treatment, which explains a decrease in the value of the electrochemically active surface area of the catalysts. An increase in the specific activity of the catalysts in the reaction of oxygen electroreduction after heat treatment is shown. The study by stress testing in the potential range of 0.6–1.4 V shows an increase in the stability of the heat-treated catalyst in comparison with the material in the “as prepared” state. A decrease in the amount of dissolved copper from the catalyst nanoparticles after heat treatment during electrochemical activation is shown, which also indicates an increase in catalyst stability.

Kinetics of Nanoparticles Nucleation/Growth and Control of the Pt/C Catalysts Microstructure and Activity

A kinetic analysis of the complex Pt(IV) ions reduction has been carried out for two common liquid-phase synthesis methods, in which formaldehyde and formic acid are used as reducing agents. The character of the influence of temperature, the nature of the reducing agent and solution components, the atmosphere composition, and the carbon support have been established. This made it possible to optimize the synthesis conditions and obtain Pt/C catalysts with ultrasmall nanoparticles, significantly exceed commercial analogs in their morphology, durability, and activity in the oxygen electroreduction reaction.

UV-assisted anchoring of gold nanoparticles into TiO2 nanotubes for oxygen electroreduction

• Au nanoparticles are deposited on TiO 2 nanotubular layers via photocatalytic reduction. • ORR overvoltage of photodeposited AuNPs is lower than AuNPs loaded from colloids. • ORR overvoltage of AuNPs-TNT depends on size, concentration and structure of AuNPs. Gold nanoparticles (AuNPs) have been deposited on titania nanotubular layers (TNT) via photocatalytic deposition, and the activity of the obtained AuNPs-TNT systems toward oxygen electroreduction reaction (ORR) in an alkaline medium has been studied and compared with the activity of AuNPs-TNT composites prepared from Au colloidal solutions. Two photodeposition methods were utilized for anchoring of AuNPs: direct UV-irradiation of a TNT electrode immersed into a HAuCl 4 containing solution (TNT-Au1 composites) and initial adsorption of AuCl 4 − ions on TNT followed by UV-irradiation (TNT-Au2 composites). The size, spatial distribution, structure and surface of AuNPs deposited on TNT layers were studied via scanning and transmission electron microscopy, optical spectroscopy and underpotential deposition of lead ad-atoms on gold. It was found that these parameters depend on the photodeposition method. The TNT-Au2 composites have smaller size, higher surface concentration and more uniform distribution of AuNPs in the TNT layers as compared with the TNT-Au1 systems. The electrocatalytic efficiency of Au-TNT electrodes in ORR was found to depend on various factors such as doping level of TNT support (governed by annealing temperature), AuNPs size and their loading amount. The electroreduction of oxygen was observed at less negative potentials when Au nanoparticles were grown on the TNT surface by photoreduction in comparison with the TNT electrodes modified with AuNPs from sols. The enhanced activity of the photocatalytically prepared AuNPs-TNT composites can be explained by the consolidation of the interface between gold nanoparticles and TiO 2 support and the absence of ligands on the AuNPs surface.