Electrocatalytic Oxygen Reduction Reaction Research Articles

Ultrafast synthesis of nanocrystalline spinel oxides by Joule-heating method

Spinel oxides, with the formula AB2O4 (A and B represent metal ions) perform superior electrocatalytic characteristic when A and B are transition metals like Co, Fe, Mn, etc. Abundant researches have been attached to the structure designments while methods are often energy-intensive and inefficient. Here, we devised a universal strategy to achieve rapid synthesis of nanocrystalline spinel materials with multiple components (Co3O4, Mn3O4, CoMn2O4 and CoFe2O4 are as examples), where phase formation is within 15 s. Under the Joule-heating shock, a crack-break process of microcosmic phase transformation is observed by in-situ transmission electron microscopy. The half-wave potential values of Co3O4JH, Mn3O4JH, CoMn2O4JH and CoFe2O4JH in the electrocatalytic oxygen reduction reaction were 0.77, 0.78, 0.79 and 0.76, respectively. This suggests that the Joule heating is a fast and efficient method for the preparation of spinel oxide electrocatalysts.

Anchoring Fe Species on the Highly Curved Surface of S and N Co‐Doped Carbonaceous Nanosprings for Oxygen Electrocatalysis and a Flexible Zinc‐Air Battery

AbstractOxygen reduction reaction (ORR) is of critical significance in the advancement of fuel cells and zinc‐air batteries. The iron‐nitrogen (Fe−Nx) sites exhibited exceptional reactivity towards ORR. However, the task of designing and controlling the local structure of Fe species for high ORR activity and stability remains a challenge. Herein, we have achieved successful immobilization of Fe species onto the highly curved surface of S, N co‐doped carbonaceous nanosprings (denoted as FeNS/Fe3C@CNS). The induction of this twisted configuration within FeNS/Fe3C@CNS arose from the assembly of chiral templates. For electrocatalytic ORR tests, FeNS/Fe3C@CNS exhibits a half‐wave potential (E1/2) of 0.91 V in alkaline medium and a E1/2 of 0.78 V in acidic medium. The Fe single atoms and Fe3C nanoparticles are coexistent and play as active centers within FeNS/Fe3C@CNS. The highly curved surface, coupled with S substitution in the coordination layer, served to reduce the energy barrier for ORR, thereby enhancing the intrinsic catalytic activity of the Fe single‐atom sites. We also assembled a wearable flexible Zn‐air battery using FeNS/Fe3C@CNS as electrocatalysts. This work provides new insights into the construction of highly curved surfaces within carbon materials, offering high electrocatalytic efficacy and remarkable performance for flexible energy conversion devices.

Anchoring Fe Species on the Highly Curved Surface of S and N Co-Doped Carbonaceous Nanosprings for Oxygen Electrocatalysis and a Flexible Zinc-Air Battery.

Oxygen reduction reaction (ORR) is of critical significance in the advancement of fuel cells and zinc-air batteries. The iron-nitrogen (Fe-Nx ) sites exhibited exceptional reactivity towards ORR. However, the task of designing and controlling the local structure of Fe species for high ORR activity and stability remains a challenge. Herein, we have achieved successful immobilization of Fe species onto the highly curved surface of S, N co-doped carbonaceous nanosprings (denoted as FeNS/Fe3 C@CNS). The induction of this twisted configuration within FeNS/Fe3 C@CNS arose from the assembly of chiral templates. For electrocatalytic ORR tests, FeNS/Fe3 C@CNS exhibits a half-wave potential (E1/2 ) of 0.91 V in alkaline medium and a E1/2 of 0.78 V in acidic medium. The Fe single atoms and Fe3 C nanoparticles are coexistent and play as active centers within FeNS/Fe3 C@CNS. The highly curved surface, coupled with S substitution in the coordination layer, served to reduce the energy barrier for ORR, thereby enhancing the intrinsic catalytic activity of the Fe single-atom sites. We also assembled a wearable flexible Zn-air battery using FeNS/Fe3 C@CNS as electrocatalysts. This work provides new insights into the construction of highly curved surfaces within carbon materials, offering high electrocatalytic efficacy and remarkable performance for flexible energy conversion devices.

Investigating the effect of CeO2 on the radical scavenging activity of Pt@CoOx/NC@CeO2 during the electrocatalytic oxygen reduction reaction in acidic and alkaline environments

Researchers have concentrated on developing electrocatalysts that are especially designed to minimise oxygenated radicals generated in partial oxygen reduction reactions (ORRs).

Catalytic reduction of oxygen to water by non-heme iron complexes: exploring the effect of the secondary coordination sphere proton exchanging site.

In this study, we prepared non-heme FeIII complexes (1, 2, and 3) of an N4 donor set of ligands (H2L, Me2L, and BPh2L). 1 is supported by a monoanionic bispyridine-dioxime ligand (HL). In 2 and 3, the primary coordination sphere of Fe remained similar to that in 1, except that the oxime protons of the ligand were replaced with two methyl groups and a bridging -BPh2 moiety, respectively. X-ray structures of the FeII complexes (1a and 3a) revealed similar Fe-N distances; however, they were slightly elongated in 2a. The FeIII/FeII potential of 1, 2, and 3 appeared at -0.31 V, -0.25 V, and 0.07 V vs. Fc+/Fc, respectively, implying that HL and Me2L have comparable donor properties. However, BPh2L is more electron deficient than HL or Me2L. 1 showed electrocatalytic oxygen reduction reaction (ORR) activity in acetonitrile in the presence of trifluoroacetic acid (TFAH) as the proton source at Ecat/2 = -0.45 V and revealed selective 4e-/4H+ reduction of O2 to H2O. 1 showed an effective overpotential (ηeff) of 0.98 V and turnover frequency (TOFmax) of 1.02 × 103 s-1. Kinetic studies revealed a kcat of 2.7 × 107 M-2 s-1. Strikingly, 2 and 3 remained inactive for electrocatalytic ORR, which established the essential role of the oxime scaffolds in the electrocatalytic ORR of 1. Furthermore, a chemical ORR of 1 has been investigated using decamethylferrocene as the electron source. For 1, a similar rate equation was noted to that of the electrocatalytic pathway. A kcat of 6.07 × 104 M-2 s-1 was found chemically. Complex 2, however, underwent a very slow chemical ORR. Complex 3 chemically enhances the 4e-/4H+ reduction of O2 and exhibits a TOF of 0.24 s-1 and a kcat value of 2.47 × 102 M-1 s-1. Based on the experimental observations, we demonstrate that the oxime backbone of the ligand in 1 works as a proton exchanging site in the 4e-/4H+ reduction of O2. The study describes how the ORR is affected by the tuning of the ligand scaffold in a family of non-heme Fe complexes.

A twisted carbonaceous nanotube as the air-electrode for flexible Zn-Air batteries.

Exploring electrocatalysts with high-efficiency oxygen reduction reaction (ORR) is significant for practical applications of fuel cells and metal-air batteries. In this work, a twisted core@shell material has been prepared with helical polypyrrole nanotubes (HPPys) as the core and coordination polymers (CPs) as the shell. After the pyrolysis process, a dense twisted carbon layer was formed by the reaction of CP and HPPy at its interface under Ar. The derived twisted carbonaceous nanotube exhibits good performance in both electrocatalytic ORR and OER. When used as the air-electrode in a flexible Zn-air battery, the battery shows good performance and stability.

Scalable synthesis of N-doped graphene-oxide-supported FeCo(OH)x nanosheets for efficient Co-doped Fe3O4 nanoparticle-based oxygen reduction reaction electrocatalysis

An innovative intermediate-control-method for layered FeCo(OH)x enables selective formation of well-dispersed Fe3O4 nanoparticles on NRGO, yielding spinel (Co)Fe3O4 after 900 °C-calcination with supreme ORR activity and stability.

Morphological and structural design through hard-templating of PGM-free electrocatalysts for AEMFC applications.

This study delves into the critical role of customized materials design and synthesis methods in influencing the performance of electrocatalysts for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). It introduces a novel approach to obtain platinum-free (PGM-free) electrocatalysts based on the controlled integration of iron active sites onto the surface of silica nanoparticles (NPs) by using nitrogen-based surface ligands. These NPs are used as hard templates to form tailored nanostructured electrocatalysts with an improved iron dispersion into the carbon matrix. By utilizing a wide array of analytical techniques including infrared and X-ray photoelectron spectroscopy techniques, X-ray diffraction and surface area measurements, this work provides insight into the physical parameters that are critical for ORR electrocatalysis with PGM-free electrocatalysts. The new catalysts showed a hierarchical structure containing a large portion of graphitic zones which contribute to the catalyst stability. They also had a high electrochemically active site density reaching 1.47 × 1019 sites g-1 for SAFe_M_P1AP2 and 1.14 × 1019 sites g-1 for SEFe_M_P1AP2, explaining the difference in performance in fuel cell measurements. These findings underscore the potential impact of a controlled materials design for advancing green energy applications.

Double coordination shell modulation of nitrogen-free atomic manganese sites for enhancing oxygen reduction performance

The rational design and fabrication of the active sites of single-atom catalysts (SACs) remains the main breakthrough for efficient electrocatalytic oxygen reduction reaction (ORR). Although metal-nitrogen-carbon (M-N-C) materials have been...

Carbon-coated FeCoNi nanocatalysts for the electrocatalytic oxygen reduction reaction

Developing low-cost, high-activity transition metal-based oxygen reduction electrocatalysts to replace noble metals in oxygen reduction reactions continues to pose a notable difficulty in the field of research.

Tuning the performance of Fe-porphyrin aerogel-based PGM-free oxygen reduction reaction catalysts in proton exchange membrane fuel cells.

Fe-N-C catalysts are currently the leading candidates to replace Pt-based catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells. To maximize their activity, it is necessary to optimize their structure to allow high active site density on one hand, and hierarchical porous structure that will allow good mass transport of reactants and products to and from the active sites on the other hand. Hence, the hierarchical structure of the catalyst plays an important role in the balance between the electrochemical active site density and the mass transport resistance. Aerogels were synthesized in this work to study the interplay between these two parameters. Aerogels are covalent organic frameworks with ultra-low density, high porosity, and large surface area. The relative ease of tuning the composition and pore structure of aerogels make them prominent candidates for catalysis. Herein, we report on a tunable Fe-N-C catalyst based on an Fe porphyrin aerogel, which shows high electrocatalytic oxygen reduction reaction activity with tunable hierarchical pore structure and studied the influence of the porous structure on the overall performance in proton exchange membrane fuel cells.

Selective oxygen reduction reaction: mechanism understanding, catalyst design and practical application.

The oxygen reduction reaction (ORR) is a key component for many clean energy technologies and other industrial processes. However, the low selectivity and the sluggish reaction kinetics of ORR catalysts have hampered the energy conversion efficiency and real application of these new technologies mentioned before. Recently, tremendous efforts have been made in mechanism understanding, electrocatalyst development and system design. Here, a comprehensive and critical review is provided to present the recent advances in the field of the electrocatalytic ORR. The two-electron and four-electron transfer catalytic mechanisms and key evaluation parameters of the ORR are discussed first. Then, the up-to-date synthetic strategies and in situ characterization techniques for ORR electrocatalysts are systematically summarized. Lastly, a brief overview of various renewable energy conversion devices and systems involving the ORR, including fuel cells, metal-air batteries, production of hydrogen peroxide and other chemical synthesis processes, along with some challenges and opportunities, is presented.

Component-controlled synthesis of PdxSny nanocrystals on carbon nanotubes as advanced electrocatalysts for oxygen reduction reaction.

Pd-based bimetallic or multimetallic nanocrystals are considered to be potential electrocatalysts for cathodic oxygen reduction reaction (ORR) in fuel cells. Although much advance has been made, the synthesis of component-controlled Pd-Sn alloy nanocrystals or corresponding nanohybrids is still challenging, and the electrocatalytic ORR properties are not fully explored. Herein, component-controlled synthesis of PdxSny nanocrystals (including Pd3Sn, Pd2Sn, Pd3Sn2, and PdSn) has been realized, which are in situ grown or deposited on pre-treated multi-walled carbon nanotubes (CNTs) to form well-coupled nanohybrids (NHs) by a facile one-pot non-hydrolytic system thermolysis method. In alkaline media, all the resultant PdxSny/CNTs NHs are effective at catalyzing ORR. Among them, the Pd3Sn/CNTs NHs exhibit the best catalytic activity with the half-wave potential of 0.85 V (vs. RHE), good cyclic stability, and excellent methanol-tolerant capability due to the suited Pd-Sn alloy component and its strong interaction or efficient electronic coupling with CNTs. This work is conducive to the advancement of Pd-based nanoalloy catalysts by combining component engineering and a hybridization strategy and promoting their application in clean energy devices.

Vacancy Defects Inductive Effect of Asymmetrically Coordinated Single-Atom Fe─N3 S1 Active Sites for Robust Electrocatalytic Oxygen Reduction with High Turnover Frequency and Mass Activity.

The development of facile, efficient synthesis method to construct low-cost and high-performance single-atom catalysts (SACs) for oxygen reduction reaction (ORR) is extremely important, yet still challenging. Herein, an atomically dispersed N, S co-doped carbon with abundant vacancy defects (NSC-vd) anchored Fe single atoms (SAs) is reported and a vacancy defects inductive effect is proposed for promoting electrocatalytic ORR. The optimized catalyst featured of stable Fe─N3 S1 active sites exhibits excellent ORR activity with high turnover frequency and mass activity. In situ Raman, attenuated total reflectance surface enhanced infrared absorption spectroscopy reveal the Fe─N3 S1 active sites exhibit different kinetic mechanisms in acidic and alkaline solutions. Operando X-ray absorption spectrareveal the ORR activity of Fe SAs/NSC-vd catalyst in different electrolyte is closely related to the coordination structure. Theoretical calculation reveals the upshifted d band center of Fe─N3 S1 active sites facilitates the adsorption of O2 and accelerates the kinetics process of *OH reduction. The abundant vacancy defects around the Fe─N3 S1 active sites balance the OOH* formation and *OH reduction, thus synergetically promoting the electrocatalytic ORR process.

Real-time diagnostic synthesis of nitrogen-doped carbon-coated VC@C(Nx) core-shell nanoparticles by DC arc plasma as efficient ORR electrocatalysts

The high complexity and cost of synthesis methods, along with the instability of catalytic activity, pose significant challenges in the search for viable non-precious metal alternatives to commercial Pt/C catalysts for oxygen reduction reaction (ORR). In this study, we employed a highly efficient and cost-effective method, namely, DC arc plasma, to synthesize carbon-coated vanadium carbide (VC@C) core-shell nanoparticles in a one-step process. The synthesized VC@C material was subsequently nitrogen-doped using urea as a nitrogen (N) source in a tube furnace, resulting in the formation of N-doped carbon-coated VC [VC@C(Nx)] catalysts for ORR electrocatalysis in alkaline media. Real-time optical emission spectroscopy (OES) analysis offers an in-depth comprehension of the energy states involved in the synthesis process of VC@C nanocrystalline powders. Highlighting the plasma states at various stages throughout the synthesis, provides a solid basis for dissecting the formation of VC@C nanoparticles and elucidating the intricate nature of their core-shell structures. Compared to the VC@C catalyst, the VC@C(N10) catalyst exhibited a significant improvement in both half-wave and onset potential, approaching the performance levels comparable to Pt/C catalysts. Moreover, VC@C(N10) demonstrated superior ORR kinetics, stability, and methanol tolerance. The exceptional performance of VC@C(N10) could be primarily attributed to the introduction of nitrogen doping, which generated more active sites and enhanced the synergistic cooperation between the VC core and the nitrogen-doped carbon shell. Additionally, the protective effect from the carbon shell prevented corrosion and oxidation of the VC core. This study represents a new exploration in the quest for the development of stable and efficient non-precious metal catalysts for ORR applications.

Construction and electrocatalytic performance of lignin-based Ag/FC catalysts

This investigation presents a comprehensive exploration of the synthesis and characterization of Ag/FC catalysts for the electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The catalysts were prepared using the electrospinning technique, with lignin, silver nitrate, and polyacrylonitrile (PAN) as precursor materials. The morphology and structure of the catalysts were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results showed that the Ag/FC-900 catalyst, synthesized with a mass ratio of 5:1:5 for lignin, silver nitrate, and PAN, exhibited remarkable ORR and OER activities in alkaline media. Specifically, the half-wave potential of the ORR was recorded at 0.78 V, accompanied by a maximum current density of 4.5 mA/cm2 with a Tafel slope of 95.9 mV/dec. The catalyst exhibited a potential of 1.48 V at a current density of 10 mA/cm2 in OER. Furthermore, the Ag/FC-900 catalyst displayed exceptional stability and methanol tolerance, surpassing the performance of the commercial Pt/C catalyst. These findings propose that the Ag/FC catalyst possesses significant potential as a dual-functional electrocatalyst.

A robust asymmetric diatomic electrocatalyst for oxygen reduction reaction in both acidic and alkaline media

Herein, an asymmetric diatomic site oxygen reduction reaction (ORR) electrocatalyst with atomically dispersed Fe and Cu species co-anchored on porous nitrogen-doped polyhedra carbon was successfully prepared through a facile cooperation of post-adsorption and two-step pyrolysis method. Density functional theory (DFT) calculations reveal that the asymmetric FeCu dual atomic site experiences a symmetry destruction of electron transfer due to the existing Cu-N4 sites and thus results in the electron redistribution in FeSACuSA/NC, contributing significantly to the optimization of intermediates adsorption and acceleration of kinetics during ORR process. Attributed to the structural advantages of FeSA-N4&CuSA-N4 sites and highly porous carbon matrix, the FeSACuSA/NC catalyst exhibits excellent electrocatalytic ORR performance with half-wave potentials (E1/2) of 0.86 and 0.88 V versus reversible hydrogen electrode in 0.1 M HClO4 and 0.1 M KOH solutions as well as high durability. Moreover, FeSACuSA/NC-based H2/O2 fuel cell and zinc-air battery present superior performance with high peak power density.

Electrochemical investigations and antimicrobial activity of Au nanoparticles photodeposited on titania nanoparticles

Titanium oxide nanopowder (TiO2 NPs) was synthesized via anodization in 0.7 M perchloric acid then annealed in nitrogen at 450 °C for 3 h to prepared the Titanium Oxide Nitrogen annealed nanoparticles (TiO2 NPs-N2) powder as catalytic support. Using a photodeposition process, gold was added with isopropanol as a sacrificial donor and H[AuCl4] acid, producing gold nanoparticles on nitrogen-annealed titanium oxide nanoparticles (Au-NPs on TiO2-NPs-N2). The mass loading of Au NPs was 2.86 × 10−4 (g/cm2). TEM images of Au NPs on TiO2-NPs-N2 suggest circular particles with a tendency to agglomerate. Cyclic voltammetry (CV) was used to investigate the electrocatalytic performance of the Au NPs/TiO2-NPs-N2 catalysts in ferrocyanide, KOH, and H2SO4, and the results were compared to those of a polycrystalline Au electrode that is readily accessible in the market. In KOH, H2SO4, and (2 M KOH + 0.1 M glycerol) solutions, the Au NPs/TiO2-NPs-N2 electrode displayed a startlingly high electrocatalytic performance. Using CV, the electrocatalytic oxygen reduction reaction (ORR) of Au NPs/TiO2-NPs-N2 and Au-NPs against glycerol oxidation in basic media was studied. The results indicated that Au NPs/TiO2-NPs-N2 is a promising support material for improving the electrocatalytic activity for acidic and basic oxidation. The electrode made of Au NPs/TiO2-NTs-N2 has steady electrocatalytic activity and may be reused repeatedly. TiO2 NPs and Au NPs/TiO2NPs-N2 showed satisfactory antibacterial activity against some human pathogenic bacteria using the disc diffusion method.

Facet engineering of a two-dimensional metal-organic framework with uniquely oriented layered-structure for electrocatalytic oxygen reduction reaction

The properties of metal–organic framework (MOF) nanocrystals are highly dependent on their sizes, morphologies, and exposed facets. Facet engineering of MOFs offers an efficient strategy to tailor the active sites and optimize the catalytic activity of both MOFs and their derivatives. In this study, we prepared 1D zeolitic imidazolate framework-nanorod (ZIF-NR) through facet engineering of the parental 2D ZIF-L. The introduction of cetyltrimethylammonium bromide (CTABr) surfactant into the synthesis solution hindered the crystal growth along the c-axis of leaf-like ZIF-L, resulting in the formation of 1D ZIF-NR. The derived Co nanoparticle encapsulated N doped carbon nanorod (denoted as Co-NCR) exhibited high activity and stability for electrocatalytic oxygen reduction reactions and Zn-air batteries. Facet engineering of a 2D MOF with a uniquely oriented layered structure demonstrates the possibility of designing novel electrocatalysts.

Pyridinic and Pyrrolic-N induced carbon nanotubes support bimetallic oxide nanoparticles as high-performance electrocatalysts for oxygen reduction reaction

In-expensive MnO2-based nanostructure has been considered the ideal electrode material for oxygen reduction reaction (ORR) in fuel cell technology. Regardless of their highly active ORR performance, the fuel cross-over capacity and stability of MnO2-based catalysts are still far from satisfying. Herein, we report the highly active SnO2 nanoparticles (NPs) integrated on N-induced carbon nanotube (SnO2@NC) are combined with MnO2 nanoparticles through the electrodeposition to form effective nanostructured in which the MnO2 NPs and SnO2@NC in situ grown on a glassy carbon electrode (MnO2/SnO2@NC) with well-controlled reaction parameters, that exhibits superior ORR activity for the first time. We assessed the marginal role of pyridinic-N and pyrrolic-N in the electrocatalytic ORR activity, synthesis of MnO2/SnO2 bimetallic oxide electrocatalysts, and distribution behavior of NPs. Bimetallic MnO2/SnO2@NC electrode has unique synergistic interactions between MnO2/SnO2 NPs and NC support, which increases electro-active sites, and fast charge transfers towards ORR as compared to other as-prepared electrodes on account of the rational design of the electrode-electrolyte interface plays a significant role in expediting the ORR kinetics. Additionally, the surface nanostructure features, crystalline structure, as well as electronic chemical states of the MnO2/SnO2 NPs embedded in N-induced CNTs, were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Furthermore, bimetallic MnO2/SnO2@NC nanostructure leads an outstanding ORR performance in the 0.1 M KOH electrolyte, delivering a halfwave potential (-0.878 V) and remarkable limiting current density (-4.14 mA cm−2) and much better tolerance to the ethanol cross-over effect with high stability. Thus, the present strategy opens a new path to the design of a pyridinic-N and pyrrolic-N-oriented bimetallic oxide nanostructure as a high-active electrocatalyst for ORR application.