Oxygen Reduction Catalysis Research Articles

One-step complexation and self-template strategy to synthesis bimetal Fe/Mn–N doped interconnected hierarchical porous carbon for enhancing catalytic oxygen reduction reaction

Currently, it is still a challenge in the research of fuel cells and zinc-air battery to use a facile method to prepare efficient and low-cost cathode oxygen reduction reaction (ORR) catalysts to replace the precious metal Pt-based catalyst. Herein, we reported a one-step complexation of ethylenediaminetetraacetic acid disodium (EDTA-2Na) with transition metals (M) and self-template strategy to synthesis an bimetal Fe/Mn–N doped interconnected hierarchical porous carbon material for efficient catalytic ORR. In addition to being a carbon source, EDTA-2Na can very well fix M atoms in the carbon precursory by complexation, which is beneficial for M atoms to be anchored in the carbon structure by N atoms, thus forming the M-Nx catalytic active site. During pyrolysis, meanwhile, Na ions in EDTA-2Na not only acted as self-template to form the interconnected porous structure but also separated M atoms from each other, which also suppressed the aggregation and growth of the M atoms. More importantly, the prepared bimetal Fe/Mn–N doped interconnected hierarchical porous carbon (Fe/Mn–NIHPC) showed better catalytic ORR performance (half-wave potentials of 0.86 V vs. RHE) than those prepared by single metal elements (Fe or Mn). And Fe/Mn–NIHPC also exhibited better catalytic ORR activity and durability, compared with the Pt/C (20 wt%) catalyst.

Highly effective bi‐functional electrochemical activity of Ag 2 O‐PrO 2 / γ‐Al 2 O 3 electrocatalysts towards OER and ORR

The oxygen reduction and evolution reaction (ORR/OER), are the keystones for many energy generating and storage devices, have influence with many electrocatalytic reactions. The sluggish kinetics of these reaction is a challenging situation on the surface of electrodes which imposes large over-potential and affects the energy output of fuel cells. Although the platinum-based electrode materials have excellent activity toward ORR/OER but their high cost limits commercialization of fuel cells. To deal with this problem, platinum-free electrode materials has aroused the considerations of scientists. The present work is proposed to study the oxygen reduction reaction and water oxidation on the surface of xAg2O-yPrO2/γ-Al2O3/Glassy-Carbon. The ORR was studied electrochemically via cyclic voltammetry on the surface of these nano-catalysts while the OER was investigated via cyclic voltammetry and linear sweep voltammetry in alkaline media. The mechanism of ORR on catalysts surface was enquired and the results indicate that ORR followed two electrons pathway in case of 10PrO2/γ-Al2O3/Glassy-Carbon while four electrons reduction pathway is identified on surface of others catalysts which divulged that addition of silver with praseodymium shifted the mechanism from 2e− to 4e− pathway. The electrocatalysts featured the stability during multiple scans and no corrosion of electrode in OER/ORR is observed. Different kinetic parameters for both reactions are determined which affirmed that both ORR and OER on the active surface of catalysts is irreversible and diffusion controlled. 4Ag2O-6PrO2/γ-Al2O3 is indicated to be proficient electro-catalyst among other members of the series, having greater value of mass transport and diffusion coefficients. The bi-functionality of all electrocatalysts are verified by their electrochemical responses in alkaline medium. The catalytic reduction of oxygen and oxidation of water by these electro-catalysts imitates their potential as electrode material in batteries and unitized regenerative fuel cells (URFC) technology for energy production as substitute of platinum electrode.

Engineering asymmetric Fe coordination centers with hydroxyl adsorption for efficient and durable oxygen reduction catalysis

Single-atom Fe catalysts are a promising substitute to Pt catalysts for oxygen reduction reaction (ORR). Adjusting metal energy level through direct atomic interface regulation can effectively improve catalytic performance but still in its infancy. Herein, highly active nitrogen and sulfur dual-coordinated asymmetric Fe center anchored in carbon nanoparticles were developed. Spontaneously absorbed OH ligand is steadily anchored in asymmetric atomic interface, constructing new FeN3S-OH moiety. Theoretical calculations reveal that the incorporated S atom combined with OH ligand as energy level modifier effectively activate Fe center by electronic modulation and d-band center shift, rendering improved ORR activity of FeNSC-2Fe with E1/2 of 0.913 V in alkaline, 0.806 V in acidic and 0.711 V in neutral media. The FeNSC-2Fe-based device displays high power density of 306 mW cm−2 in Zn-air battery and 2485 mW m−2 in microbial fuel cell. This work provides a new perspective for the controllable synthesis and performance optimization for electrocatalysts.

Nanostructured Mn-doped Zn N C @reduced graphene oxide as high performing electrocatalyst for oxygen reduction reaction

Future fuel cells and metal-air batteries will benefit greatly from revealing self-supported electrodes with efficient oxygen reduction reaction (ORR) activity and durability. However, noble metal catalysts are expensive and unstable, necessitating research into novel metal-organic framework (MOF)-based topologies that can catalyse oxygen reduction reactions (ORR). In this work, the synthesis of nitrogen-doped carbon (NC) is derived from zeolitic imidazolate frameworks (ZIFs) and a novel Mn-doped ZnN[email protected] is synthesized using a self-templated solvothermal method and their performance in an alkaline medium for oxygen reduction reaction (ORR) is studied. The nanostructured composite outperformed the commercial Pt/C catalyst in terms of both material resources and application efficacy. The Mn/ZnNC @30% rGO exhibit outstanding performance for ORR in KOH, with a more positive cathodic peak of 0.78 V vs RHE and an onset potential of 0.97 V vs RHE, which are characteristics that suggest the possibility of reducing ORR overpotentials. The improved electrochemical performance, small Tafel slopes and methanol tolerance are ascribed to the interdependent effect of the N-doped carbon (NC) and the Mn/Zn active sites. Novel architecture, tunable porosities, template directed growth and remarkable electrocatalytic performance of Mn-doped ZnN[email protected] make it a good aspirant for energy applications.

Few-layered nitrogen-doped graphene wrapped three-dimensional titanium oxide flower as a robust support for Pt nanoparticles in catalyzing oxygen reduction reaction

• Few-layered nitrogen-doped graphene wrapped 3D flower-like TiO 2 is synthesized. • The anti-corrosion support has a high surface area and electronic conductivity. • Pt-TiO 2 @N-Gr-800 exhibits superior ORR activity, stability, and CO tolerance. • Pt-TiO 2 @N-Gr-800 shows a strong metal and support interaction. Carbon materials are commonly used as electrocatalyst supports in fuel cells. Nevertheless, carbon corrosion is a severe concern under strong acidic and oxidizing environments. Hence, developing a robust catalyst support is critical to ensuring fuel cells stability. Herein, we report a unique support of few-layered nitrogen-doped graphene wrapped three-dimensional (3D) flower-like anatase TiO 2 (TiO 2 @N-Gr) via in-situ polymerizing dopamine on the surface of a 3D-TiO 2 flower precursor, followed by pyrolysis. After loading Pt nanoparticles, Pt-TiO 2 @N-Gr-800 exhibits comparable ORR activity to the commercial Pt/C catalyst (E 1/2 = 0.91 V RHE ), superior stability in a 30 K cycling stability test and strong CO resistance capability. The outstanding performance of the Pt-TiO 2 @N-Gr-800 catalyst is attributed to the strong anti-corrosion property and high electronic conductivity of the nanocomposite support, as well as a strong metal and support interaction. The unique flower-like scaffold is also of great advantage for mass transfer. This work provides a facile strategy to synthesize robust nanocomposite supports for fuel cells.

Synergistic effect of doping and defect in achieving white light emission and oxygen reduction catalysis in Ce1-xSmxPO4

Multifunctional materials owing to their efficacy to perform more than one job have attracted the attention of global materials science community to resolve the issue of material crunch and reduce the work load. Here, in this work, we have demonstrated the suitability of CePO4:Sm3+ (CPOS) phosphor for white light luminophore and oxygen reduction catalyst. Raman spectroscopy confirmed the stabilization of monoclinic phase for CPOS. White light emission with correlated color temperature (CCT) favoring cool white feature in CPOS is endowed by inefficient host to dopant energy transfer (HDET). X-ray photoelectron spectroscopy (XPS) suggested presence of both Ce3+ and Ce4+ in CPOS with later in lower fraction. XPS results also showed the presence of surface oxygen in CPOS which along with mixed oxidation state of cerium on the surface may be aiding CPOS to work as electrocatalysts for oxygen reduction reaction (ORR). The best electrocatalytic performance was achieved with 1.0% Sm doped sample which has higher concentration of oxygen associated with Ce (IV) on the surface.

Recent progress in design and fabrication of SOFC cathodes for efficient catalytic oxygen reduction

Solid oxide fuel cells (SOFCs) are highly promising energy conversion devices. However, the performance and efficiency of current SOFC devices are still limited by inadequate oxygen reduction activity in the cathode, which has been recognized as a great challenge for SOFCs to achieve high power output at low operating temperatures. This has stimulated intensive efforts to develop more efficient cathodes for enhanced catalytic oxygen reduction. This article reviews recent advances in design and fabrication of cathodes for efficient SOFCs, with emphasis on (1) engineering cathode microstructures, (2) fabrication techniques to prepare cathode layers, and (3) strategies to address segregation and poisoning issues.

Fungus-Based MnO/Porous Carbon Nanohybrid as Efficient Laccase Mimic for Oxygen Reduction Catalysis and Hydroquinone Detection.

Developing efficient laccase-mimicking nanozymes via a facile and sustainable strategy is intriguing in environmental sensing and fuel cells. In our work, a MnO/porous carbon (MnO/PC) nanohybrid based on fungus was synthesized via a facile carbonization route. The nanohybrid was found to possess excellent laccase-mimicking activity using 2,2′-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) as the substrate. Compared with the natural laccase and reported nanozymes, the MnO/PC nanozyme had much lower Km value. Furthermore, the electrochemical results show that the MnO/PC nanozyme had high electrocatalytic activity toward the oxygen reduction reaction (ORR) when it was modified on the electrode. The hybrid nanozyme could catalyze the four-electron ORR, similar to natural laccase. Moreover, hydroquinone (HQ) induced the reduction of oxABTS and caused the green color to fade, which provided colorimetric detection of HQ. A desirable linear relationship (0–50 μM) and detection limit (0.5 μM) were obtained. Our work opens a simple and sustainable avenue to develop a carbon–metal hybrid nanozyme in environment and energy applications.

Facile Synthesis of Surfactant-Induced Platinum Nanospheres with a Porous Network Structure for Highly Effective Oxygen Reduction Catalysis.

Developing a facile and eco-friendly method for the large-scale synthesis of highly active and stable catalysts toward oxygen reduction reaction (ORR) is very important for the practical application of proton exchange membrane fuel cells (PEMFCs). In this paper, a mild aqueous-solution route has been successfully developed for the gram-scale synthesis of three-dimensional porous Pt nanospheres (Pt-NSs) that are composed of network-structured nanodendrites and/or oval multipods. In comparison with the commercial Pt/C catalyst, X-ray photoelectron spectroscopy (XPS) demonstrates the dominant metallic-state of Pt and electrochemical impedance spectroscopy (EIS) indicates the substantial improvement of conductivity for the Pt-NSs/C catalyst. The surfactant-induced porous network nanostructure improves both the catalytic ORR activity and durability. The optimal Pt-NSs/C catalyst exhibits a half-wave potential of 0.898 V (vs. RHE), leading to the mass activity of 0.18 A mgPt -1 and specific activity of 0.68 mA cm-2 which are respectively 1.9 and 5.7 times greater than those of Pt/C. Moreover, the highly-active Pt-NSs/C catalyst shows a superior stability with the tenable morphology and the retained 78% of initial mass activity rather than the severe Pt aggregation and the only 58% retention of the commercial Pt/C catalyst after 10000 cycles.

Activation of Main‐Group Antimony Atomic Sites for Oxygen Reduction Catalysis

The catalytic activity of main-group metal is hard to promote because of the intrinsic lack of host d orbitals available to be combined. Herein, under the guidance of theoretical predictions, we find atom-dispersed antimony sites (Sb-N4 moieties) can be activated to achieve high oxygen reduction reaction (ORR) activity using a functional group regulation strategy. Correspondingly, we manage to synthesize a main-group Sb single-atom catalysts (SACs) that comprises Sb-N4 active moieties functionalized by epoxy groups in the second microenvironment and incorporated in N-doped graphene (Sb1 /NG(O)). The electron-rich epoxy group can adjust the electronic structure of Sb-N4 active moieties, thereby optimizing the adsorption of the intermediate. The Sb SACs are comparable to industrial Pt/C under alkaline conditions. This discovery provides new opportunities to manipulate and improve the catalytic activity of main-group-element electrocatalysts.

Activation of Main‐Group Antimony Atomic Sites for Oxygen Reduction Catalysis

AbstractThe catalytic activity of main‐group metal is hard to promote because of the intrinsic lack of host d orbitals available to be combined. Herein, under the guidance of theoretical predictions, we find atom‐dispersed antimony sites (Sb−N4 moieties) can be activated to achieve high oxygen reduction reaction (ORR) activity using a functional group regulation strategy. Correspondingly, we manage to synthesize a main‐group Sb single‐atom catalysts (SACs) that comprises Sb−N4 active moieties functionalized by epoxy groups in the second microenvironment and incorporated in N‐doped graphene (Sb1/NG(O)). The electron‐rich epoxy group can adjust the electronic structure of Sb−N4 active moieties, thereby optimizing the adsorption of the intermediate. The Sb SACs are comparable to industrial Pt/C under alkaline conditions. This discovery provides new opportunities to manipulate and improve the catalytic activity of main‐group‐element electrocatalysts.

Investigation of Ni Catalyzed Oxygen Reduction Reaction with the Interdigitated Array Electrodes

With the growing concern of the energy crisis and environmental pollution, new energy storage and energy utilization methods are demanded for the sustainable development of human beings. Oxygen reduction reaction (ORR) is considered as the “bottleneck” of the energy storage and utilization, and understanding the specific reaction pathway and mechanism are essential in designing new catalysts. In this work, the non-precious metal catalyst Ni was studied towards the ORR catalytic activity utilizing the interdigitated array (IDA) electrodes for the in situ detection. IDA electrodes have high collection efficiency and are utilized for the detection of the reaction intermediate and therefore the reaction pathway. It was observed that the average electron transfer number of Ni-catalyzed ORR is about 3, and it varies with the change of applied potential and the surface state of catalyst. The H2O2 production changes between 40% and 75%, reflecting the possible reaction pathway at different status.

Dual-mode corroborative detection of miRNA-21 based on catalytic hairpin assembly reaction and oxygen reduction reaction combined strategy for the signal amplification

Here, we first combined the catalytic hairpin assembly (CHA) reaction and oxygen reduction reaction (ORR) to amplify the electrochemical signal for the determination of miRNA-21. In the presence of target microRNA-21, C-Ag+-C structure probe formed by hairpin DNA1 (H1) and Ag+ could be opened and catalytic hairpin assembly reaction could be carried out. Then the capture probe (C1) modified Fe3O4 @PDA@AuNPs could immobilize all the H1 and the typical oxygen reduction reaction AuNPs could be electrodeposited in situ in the I-T test. Besides, the released Ag+ in the solution could be also detected by fluorescence and colorimetry with the assistance of CdSe QDs. The fluorescence intensity and emission wavelength of CdSe QDs could be changed by the Ag+, which could reflect the concentration of miRNA-21. As a result, the limit of detection (LOD) was 323 aM. Besides, the constructed biosensor exhibited its good performance in the real samples demonstrating its practical application potential. This rarely dual-mode detection strategy makes the miRNA-21 detection results more accurate and reliable.

Synthesis of Fe-doped carbon hybrid composed of CNT/flake-like carbon for catalyzing oxygen reduction

Synthesis of Fe-doped carbon hybrid composed of CNT/flake-like carbon for catalyzing oxygen reduction

Impact of Carbon N-Doping and Pyridinic-N Content on the Fuel Cell Performance and Durability of Carbon-Supported Pt Nanoparticle Catalysts.

Cathode catalyst layers of proton exchange membrane fuel cells (PEMFCs) typically consist of carbon-supported platinum catalysts with varying weight ratios of proton-conducting ionomers. N-Doping of carbon support materials is proposed to enhance the performance and durability of the cathode layer under operating conditions in a PEMFC. However, a detailed understanding of the contributing N-moieties is missing. Here, we report the successful synthesis and fuel cell implementation of Pt electrocatalysts supported on N-doped carbons, with a focus on the analysis of the N-induced effect on catalyst performance and durability. A customized fluidized bed reduction reactor was used to synthesize highly monodisperse Pt nanoparticles deposited on N-doped carbons (N-C), the catalytic oxygen reduction reaction activity and stability of which matched those of state-of-the-art PEMFC catalysts. Operando high-energy X-ray diffraction experiments were conducted using a fourth generation storage ring; the light of extreme brilliance and coherence allows investigating the impact of N-doping on the degradation behavior of the Pt/N-C catalysts. Tests in liquid electrolytes were compared with tests in membrane electrode assemblies in single-cell PEMFCs. Our analysis refines earlier views on the subject of N-doped carbon catalyst supports: it provides evidence that heteroatom doping and thus the incorporation of defects into the carbon backbone do not mitigate the carbon corrosion during high-potential cycling (1-1.5 V) and, however, can promote the cell performance under usual PEMFC operating conditions (0.6-0.9 V).

Porphyrin polymer-derived single-atom Fe assisted by Fe2O3 with oxygen vacancy for efficient oxygen reduction reaction

Single-atom catalysts (SACs) have been deemed as one of the most prospective substitutes for high-efficiency oxygen reduction reaction (ORR) catalysts due to its theoretical maximum atomic utilization. However, the convenient preparation and the further improvement in activity of SACs are laborious. Herein, the N-doped porous carbon (NC) material with in site produced Fe-N4 single-atom catalytic sites (FeSA) accompanied by Fe2O3 species with abundant oxygen vacancies (Ov-Fe2O3) as co-catalytic sites (Ov-Fe2O3@FeSA@NC) is successfully obtained by using a well-designed porphyrin conjugated mesoporous polymer (CMP) consisting of iron porphyrin and metal free porphyrin units as a precursor, and followed by pyrolysis. A series of controllable experiments reveal that FeSA assisted by Ov-rich Fe2O3 render Ov-Fe2O3@FeSA@NC outstanding ORR activity in the alkaline medium with the onset and half-wave potentials (Eonset and E1/2) of 0.987 V and 0.901 V vs RHE, which significantly outperformed the electrochemical activity of FeSA@NC (Eonset = 0.962 V, E1/2 = 0.850 V) and Ov-Fe2O3@NC (Eonset = 0.913 V, E1/2 = 0.821 V) with individual FeSA and Ov-Fe2O3 active sites, respectively. This work innovatively demonstrates the importance of oxygen vacancy-assisted single-atom catalysts for oxygen reduction catalysis, and also provides guidance for the design of high-performance SACs.

Constructing Synergistic Zn‐N4 and Fe‐N4O Dual‐Sites from the COF@MOF Derived Hollow Carbon for Oxygen Reduction Reaction

Synergistic Dual-Sites for Oxygen Reduction Reaction In article number 2100225, Qing Xu, Chengbin Yu, Gaofeng Zeng, and co-workers constructed synergistic dual-sites for catalyzing oxygen reduction reaction from a core-shell hybrid of a covalent organic framework (COF) and a metal organic framework (MOF). The synergistic effect between the Fe and Zn sites made the catalysts with high activity and selectivity. This provides a new insight into developing electrocatalysis from COFs and MOFs.

Dual-metal-organic frameworks as ultrahigh-performance bifunctional electrocatalysts for oxygen reduction and oxygen evolution

At present, it is significant to research bifunctional catalysts for metal-air batteries with bargain price, excellent stability, and satisfactory activity. Herein, by density functional theory, the performance of dual-metal-organic frameworks M2-BTC (M2 = Ni2, Fe2, Co2, FeNi, CoNi, FeCo) as bifunctional electrocatalysts to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is investigated. All M2-BTC are proved to possess satisfactory thermodynamical stability. For ORR, FeNi-Ni, Ni2-BTC, Co2-BTC, and CoNi-Ni are confirmed to have high activity with corresponding overpotential of 0.40, 0.25, 0.31, and 0.28 V, respectively, which are both better than Pt(111) (ηORR = 0.45 V). For OER, Fe2-BTC, Ni2-BTC, Co2-BTC, and CoNi-Ni show excellent catalytic activity, with the overpotential of 0.42, 0.38, 0.22, and 0.31 V, respectively, which can be compared to RuO2(110) (ηOER = 0.37 V) or even better than it. According to the ORR/OER potential gap, Ni2-BTC, Co2-BTC, and CoNi-Ni are screened out to be ultrahigh-performance bifunctional electrocatalysts. The results of the highest occupied molecular orbital and the lowest unoccupied molecular orbital confirm that the metal atom is the main active site, and the O atoms attached to the active metal also participate in the reaction. Density of states analysis indicates that the different catalytic performance of M2-BTC is caused by the variety of electronic structures.

Atomically dispersed Zn-Co-N-C catalyst boosting efficient and robust oxygen reduction catalysis in acid via stabilizing Co-N bonds

Transition metal supported N-doped carbon (M-N-C) catalysts for oxygen reduction reaction (ORR) are viewed as the promising candidate to replace Pt-group metal (PGM) for proton exchange membrane fuel cells (PEMFCs). However, the stability of M-N-C is extremely challenging due to the demetalation, H2O2 attack, etc. in the strongly oxidative conditions of PEMFCs. In this study, we demonstrate the universal effect of Zn on promoting the stability of atomically dispersed M-Nx/C (M = Co, Fe, Mn) catalysts and the enhancement mechanism is unveiled for the first time. The best-performing dual-metal-site Zn-Co-N-C catalyst exhibits a high half-wave potential (E1/2) value of 0.81 V vs. reversible hydrogen electrode (RHE) in acid and outstanding durability with no activity decay after 15,000 accelerated degradation test (ADT) cycles at 60 °C, surpassing most reported Co-based PGM-free catalysts in acid media. For comparison, the Co-N-C in the absence of Zn suffers from a rapid degradation after ADT due to the demetalation and higher H2O2 yield. X-ray adsorption spectroscopy (XAS) and density functional theory (DFT) calculations suggest the more negative formation energy (by 1.2 eV) and increased charge transfer of Zn-Co dual-site structure compared to Co-N-C could strength the Co-N bonds against the demetalation and the optimized d-band center accounts for the improved ORR kinetics.

Boosting Oxygen Reduction Catalysis with Hierarchically Porous Fe-Doped Carbon by Chemical Vapor Deposition in Zn–Air Batteries

Boosting Oxygen Reduction Catalysis with Hierarchically Porous Fe-Doped Carbon by Chemical Vapor Deposition in Zn–Air Batteries