Oxygen Reduction Activity Research Articles

Enhanced oxygen reduction activity of α-MnO2 by NH3 plasma treatment

Oxygen vacancies and heteroatom doping play important role in oxygen reduction activity of metal oxides. Developing efficient modification method is one of the key issues in catalysts research. Room temperature plasma treatment, with the advantages of mild working conditions, no emissions and high efficiency, is a new catalyst modification method developed in recent years. In this work, hydrothermal synthesized α-MnO2 nanorods are treated in NH3 plasma at room temperature. In the reducing atmosphere, oxygen vacancies and N doping are achieved simultaneously on the surface. The NH3 plasma etched MnO2 demonstrate a significant enhanced oxygen reduction activity with half-wave potential of 0.84 V, limiting current density of 6.32 mA cm−2 and transferred electrons number of 3.9. The Mg–air battery with N-MnO2 display a maximum power density of 76.3 mW cm−2 as well as stable discharge performance. This work provides new ideas for preparing efficient and cost-effective method to boost the catalysts activity.

Bifunctional boron-nitrogen-containing graphite felt cathode for highly efficient treatment on dye wastewater depending on the metal-free electro-Fenton process

The heterogeneous electro-Fenton technology can settle a matter of narrow pH application range in the traditional electro-Fenton process. Direct O2 electro-reduction to •OH on the surface of metal-free catalysts can effectively solve the problem of easy leaching of metal-based catalysts under acidic conditions and improve the oxidation efficiency of H2O2. In this work, a stable bifunctional boron-nitrogen-containing catalyst was directly synthesized on the surface of graphite felt. The H2O2 yield (4.32 mg cm-2 h−1) and rhodamine B degradation rate (0.174 min−1) of boron-nitrogen-containing catalyst were significantly improved at the pH value of 7, compared with nitrogen-containing graphite felt catalyst. The catalyst had a rapid degradation ability for various dyes and actual dye wastewater, and the specific energy consumption of actual dye wastewater degradation was 4.02 kW h kg−1 COD-1 lower than that reported in literature (6.38–29.7 kW h kg−1 COD-1). DFT calculations and XPS results revealed the potential reaction mechanism. The introduction of −BCO2 group into the nitrogen-containing plane significantly enhanced the oxygen adsorption and oxygen reduction activity, and the directly formation of •OH was promoted jointly by graphite nitrogen and −BCO2 group. This work provided a new insight into the development of metal-free electro-Fenton catalyst.

Pore size modulation of cobalt-corrole-based porous organic polymers for boosted electrocatalytic oxygen reduction reaction

The highly active and selective oxygen reduction reaction (ORR) is vital to promote the performance of advanced energy conversion systems, such as fuel cells and other electrochemical devices. Porous framework materials have the capability to combine the catalytic performance of catalytic active units with their porous characteristics, making them promising oxygen reduction catalysts. However, due to the difficulty in designing and synthesizing catalytic active units, the pore size modulation of framework materials is primarily achieved by altering the linkers. We herein report the design and synthesis of three cobalt-corrole-based porous organic polymers (Co-POP-1, Co-POP-2 and Co-POP-3) with different pore sizes, which were obtained by extending 5,15-meso substituents of Co corroles. Compared to Co-POP-1 and Co-POP-2, Co-POP-3 has the largest pore size. Benefiting from the enhanced mass transfer and the highly exposed active sites, Co-POP-3 displayed remarkably boosted activity for the selective four-electron/four-proton (4e−/4 H+) ORR with a half-wave potential of E1/2 = 0.89 V versus reversible hydrogen electrode (RHE) in 0.1 M KOH solutions. This work not only presents a cobalt-corrole-based porous organic polymer catalyst with high ORR activity and selectivity but also provides a new strategy to moderate the pore size of porous framework materials.

VOx Matrix Confinement Approach to Generate Sub-3nm L10-Pt-Based Intermetallic Catalysts for Fuel Cell Cathode.

Pt-based intermetallic compounds (IMCs) are considered as a class of promising fuel cell electrocatalysts, owing to their outstanding intrinsic activity and durability. However, the synthesis of uniformly dispersed IMCs with small sizes presents a formidable challenge during the essential high-temperature annealing process. Herein, a facile and generally applicable VOx matrix confinement strategy is demonstrated for the controllable synthesis of ordered L10-PtM (M = Fe, Co, and Mn) nanoparticles, which not only enhances the dispersion of intermetallic nanocrystals, even at high loading (40 wt%), but also simplifies the oxide removal and acid-washing procedures. Taking intermetallic PtCo as an example, the as-prepared catalyst displays a high-performance oxygen reduction activity (mass activity of 1.52 A mgPt -1) and excellent stability in the membrane electrode assemblies (MEAs) (the ECSA has just 7% decay after durability test). This strategy provides an economical and scalable route for the controlled synthesis of Pt-based intermetallic catalysts, which can pave a way for the commercialization of fuel cell technologies.

Ni-Substituted Sr2FeMoO6-δ as an Electrode Material for Symmetrical and Reversible Solid-Oxide Cells.

This work develops a novel perovskite Sr2FeNi0.35Mo0.65O6-δ (SFN0.35M) simultaneously using as a fuel electrode and oxygen electrode in a reversible solid oxide cell (RSOC). SFN0.35M shows outstanding electrocatalytic activity for hydrogen oxidation, hydrogen evolution, oxygen reduction, and oxygen evolution. In situ exsolution and dissolution of Fe-Ni alloy nanoparticles in SFN0.35M is revealed. In a reducing atmosphere, SFN0.35M shows in situ exsolution of Fe-Ni alloy nanoparticles, and then the Fe-Ni alloy is reoxidized into SFN0.35M while converting into an oxidizing atmosphere. The polarization resistances of SFN0.35M electrode are 0.043 Ω cm2 in 20% O2-N2 and 0.064 Ω cm2 in H2 at 850 °C. Moreover, symmetric fuel cells using the SFN0.35M electrode achieves a maximum power density of 0.501 W cm-2 at 850 °C in H2 fuel, while the symmetric electrolysis cell has an electrolysis current density of 0.794 A cm-2 at 1.29 V in 90% H2O-10% H2 at 850 °C. It is the first time we demonstrate that the cell voltage of symmetrical cell at 0.5 A cm-2 in the fuel cell mode and -0.5 A cm-2 in the electrolysis cell mode can be fully recovered in 10 electrode alternating cycles and therefore demonstrate the possibility that SFN0.35M can be used in a fully symmetric RSOC stack with electrode alternating functions.

Geometric and electronic engineering of cobalt, manganese oxide sites in porous nitrogen-doped carbon for boosted oxygen reduction activity in microbial fuel cell

The development microbial fuel cell relies heavily on cathodic catalysts to provide excellent activity and fast electron rotor transfer rates. However, the design of such electrocatalysts is extremely challenging. Here, a strategy is proposed to regulate the electrocatalyst comprised of cobalt and manganese oxides embedded the porous nitrogen-doped carbon (Co3O4-MnO2/NC) with dominant crystal surface by geometric and electronic engineering. Experimental results and theoretical calculations show that the coordination of bimetallic oxides with N atoms induces an asymmetric distribution of charge of central metal sites, which promotes the adsorption/desorption of oxygen intermediates. This electrocatalyst exhibits excellent oxygen reduction reaction (ORR) activity, long-term stability and antitoxic tolerance. Importantly, microbial fuel cell equipped with Co3O4-MnO2/NC generates excellent performance in power density, chemical oxygen demand (COD) removal rate and coulomb efficiency. This work demonstrates the importance of geometric and electronic engineering design of bimetallic oxide to expose more dominant crystal faces to improve electrocatalytic activity in electrochemical energy conversion systems.

Precise control of platinum coordination environment on fullerene-derived catalysts for oxygen reduction reaction

The interaction between catalysts and supports is recognized as a crucial factor influencing catalytic activity and stability. However, the carbon materials, which have been widely employed as the support at present, encounter challenges including intricate composition and the difficulty of precise control. In this study, the fullerene-derived carbon materials serve as support to electrocatalysts with low platinum. Fullerene-based materials, as the only carbon material with a well-defined molecular structure, have a controllable active site structure, which can provide a reaction model for studying metal-support interactions. Four kinds of fullerene-derived catalysts such as Pt/fullerene, Pt/nitrogen-doped fullerene, Pt/sulfur-doped fullerene, and Pt/phosphorus-doped fullerene, were synthesized. Once the coordination environment of the Pt particles was controlled, thus their catalytic performance was modulated. Despite a platinum loading of only 4.2%, Pt/N-fullerene demonstrates superior oxygen reduction activity and stability compared to commercial Pt/C (20%). Density functional theory calculations show that the introduction of heteroatoms can change the surface charge distribution of fullerenes, in which N-fullerene has a more negative electrostatic potential and can effectively anchor Pt. This research establishes a foundation for understanding the catalysts-support interaction and further precise control of the coordination environment of Pt. This provides new insights for designing efficient ORR catalysts.

Oceanographic processes driving low-oxygen conditions inside Patagonian fjords

Abstract. The dissolved oxygen (DO) levels of coastal ocean waters have decreased over the last few decades in part because of the increase in surface and subsurface water temperature caused by climate change, the reduction in ocean ventilation, and the increase in stratification and eutrophication. In addition, biological and human activity in coastal zones, bays, and estuaries has contributed to the acceleration of current oxygen loss. The Patagonian fjord and channel system is one world region where low-DO water (LDOW, 30 %–60 % oxygen saturation) and hypoxia conditions (<30 % oxygen saturation, 2 mL L−1 or 89.2 µmol L−1) are observed. An in situ dataset of hydrographic and biogeochemical variables (1507 stations), collected from sporadic oceanographic cruises between 1970 and 2021, was used to evaluate the mechanisms involved in the presence of LDOW and hypoxic conditions in northern Patagonian fjords. Results denoted areas with LDOW and hypoxia coinciding with the accumulation of inorganic nutrients and the presence of salty and oxygen-poor Equatorial Subsurface Water mass. The role of biological activity in oxygen reduction was evident in the dominance of community respiration over gross primary production. This study elucidates the physical and biogeochemical processes contributing to hypoxia and LDOW in the northern Patagonian fjords, highlighting the significance of performing multidisciplinary research and combining observational and modeling work. This approach underscores the importance of a holistic understanding of the subject, encompassing both real-world observations and insights provided by modeling techniques.

Increasing Activity of Trimetallic Oxygen Reduction PtNiMo/C Catalysts Through Initial Conditioning

AbstractThis study investigates the importance of preconditioning in Pt‐alloy catalysts for oxygen–reduction reactions. Previous research indicated that slower scanning rates during preconditioning initially boost activity, but this is followed by a rapid decline. The study reveals the required number of cycles to achieve the first constant steady state activity in PtNiMo/C catalysts when using slower scanning rates during preconditioning. It also highlights the resulting activity differences. Remarkably, a catalyst preconditioned with 150 slow cycles showed an activity of approximately 1.25 mA cm−2 at 0.90 VRHE, significantly higher than one preconditioned at a fast rate (0.82 mA cm−2). Both ex–situ and in–situ analyses revealed that Pt, along with Ni, was leached during pretreatment. At slower scan rates of 20 mV s−1, the dissolved Pt redeposited as highly active, small‐sized clusters or single atoms. Fast scan rates of of 500 mV s−1, in contrast, resulted in fewer such clusters. Accelerated stress tests up to 1.10 VRHE confirmed the high stability of these clusters, demonstrating a substantial activity increase even after 24,000 cycles.

Correlating oxygen reduction activity of N, S-co-doped carbon with the structures of dopant molecules

Developing metal-free carbon electrocatalysts with atomically precise structures of hetero-doping is crucial for inventing reliable alternatives to precious metal-based catalysts. Our study reveals that the optimal active site is the edge-exposed N-neighbored carbon site in a chained N-C-C-S structure. Carbon material with N-C-C-S functional doping is controllably synthesized through polymer dehalogenation and heteroatom doping with thiomorpholine at room temperature. The resulting N/S-co-doped carbon with N-C-C-S functionalization, named N-C2-S, exhibits excellent ORR performance compared to other types of N, S-co-doped carbon, and commercial Pt/C. Typically, the N-C2-S sample shows the earliest onset potential of 0.96 V and a high half-wave potential of 0.85 V for promoting ORR. Assembled into an Al-air battery, The N-C2-S delivers an exceptional open-circuit voltage of 1.95 V and a large specific power of 128.1 mW cm2. The synthesis strategy developed in this work can potentially open up precise functionalization of synthetic carbons with heteroatoms.

Single-phase ruthenium-based oxide with dual-atoms induced bifunctional catalytic centers enables highly efficient rechargeable Zn-air batteries

Composite strategies for constructing dual-atom sites at the hetero-interface provide considerable prospects for designing efficient bifunctional oxygen catalysts. Given the insufficient interface site and the instability of the phase interface, we need to develop more efficient strategies for efficiently utilizing the dual-atom site. Here, we report a doping strategy to construct abundant dual-atom sites in single-phase oxide catalysts. Ru/Mn dual-atom bond formation enables electronic interaction between Ru and Mn, which reduces the oxidation state of Ru sites and meanwhile constructs electron-rich states of Mn sites. DFT calculation was further applied to explore the reaction mechanism. We found that Mn and Ru atoms serve as oxygen reduction and oxygen evolution reaction catalytic sites respectively to facilitate oxygen adsorption and OH* desorption. More importantly, co-adsorption of OOH* on Mn/Ru dual sites can greatly enhance oxygen reduction activity. The resulting Mn-RuO2 catalyst exhibits an ultra-low ORR/OER overpotential of just 0.65 V, substantially lower than RuO2 and MnOx. Remarkably, Mn-RuO2 also demonstrates excellent stability, with minimal ORR decay after repeated OER cycling. Rechargeable zinc-air batteries using Mn-doped RuO2 achieve super-durability for 2000 cycles with a final energy efficiency retention of 87.5 %.

Enhancing Oxygen Reduction Activity and CO2 Tolerance by a Bismuth Doping Strategy for Solid Oxide Fuel Cell Cathodes

AbstractLayered perovskite related oxides, LnBaCo2O5+δ (Ln = rare‐earth element) are potential ceramic cathodes for intermediate temperature solid oxide fuel cells. Herein, a simple way to tune the performance of NdBaCo2O5+δ (NBC) perovskite as a cathode by doping the Co‐site with bismuth cation is reported. Compared with the parent oxide, the obtained stabilized double perovskites NdBaCo2−xBixO5+δ (x = 0.1 and 0.2) show a much improved electrocatalytic activity, achieving area‐specific resistance of 0.268, 0.107 and 0.152 Ω cm2 at 700 °C in air for NBC, x = 0.1, and 0.2, respectively. Density functional theory results demonstrate that bismuth doping effectively reduces the formation energy of oxygen vacancies. Moreover, the bismuth doping of NdBaCo2−xBixO5+δ cathode is much more robust against CO2 than that of NBC cathode. This work indicates that bismuth doping in the B‐site of LnBaCo2O5+δ may be a highly attractive strategy for the future development of cathode materials.

Origin of the Oxygen Reduction Activity on Boron-Doped Fe–N–C Catalysts for Zinc–Air Battery Applications

Origin of the Oxygen Reduction Activity on Boron-Doped Fe–N–C Catalysts for Zinc–Air Battery Applications

Renewable lignin-derived heteroatom-doped porous carbon nanosheets as an efficient oxygen reduction catalyst for rechargeable zinc-air batteries

Lignin upgrading to various functional products is promising to realize high-value utilization of low-cost and renewable biomass waste, but is still in its infancy. Herein, using industry waste lignosulfonate as the biomass-based carbon source and urea as the dopant, we constructed a heteroatom-doped porous carbon nanosheet structure by a simple NaCl template-assisted pyrolytic strategy. Through the synergistic effect of the NaCl template and urea, the optimized lignin-derived porous carbon catalyst with high content of active nitrogen species and large specific surface area can be obtained. As a result, the fabricated catalysts exhibited excellent electrocatalytic oxygen reduction activity, as well as good methanol tolerance and stability, comparable to that of commercial Pt/C. Moreover, rechargeable Zn-air batteries assembled with this electrocatalyst have a peak power density of up to 150 mW cm-2 and prominent long-term cycling stability. This study offers an inexpensive and efficient way for the massive production of highly active metal-free catalysts from the plentiful, inexpensive and environmentally friendly lignin, offering a good direction for biomass waste recycling and utilization.

A stepwise thermal migration for inducing copper nanoparticles to boost oxygen reduction activity of single-atomic copper sites

Although single-atom M-N-C electrocatalysts have demonstrated their potential in metal-air batteries and fuel cells, their activity for oxygen reduction reaction (ORR) needs to be further improved. Regulating the electronic structure of M-Nx single sites to accelerate the activity and simultaneously directly identify the enhancement mechanisms is highly desirable but remains a challenge. Here we propose a stepwise thermal migration strategy to in situ introducing Cu nanoparticles (Cu-NPs) adjacent to single atoms Cu (Cu-SAs) confined into hierarchically porous carbon. The optimization of the electronic structure of the Cu-Nx site by adjacent Cu nanoparticles is confirmed by both enhanced ORR activity and theoretical calculations. The optimized CuSA-NP@NC exhibits a more positive half-wave potential (0.870 V) than CuSA@NC (0.842 V) and superior stability with an 86.6% ORR current retention after 24 hours of chronoamperometric test in alkaline electrolyte. When utilized as an air cathode in rechargeable Zn-air batteries, CuSA-NP@NC displays a high-power density of 224.1 mWcm−2 and a specific capacity of 802.0 mAh g−1. Theoretical calculations demonstrate that the introduction of Cu-NPs endows the Cu-N4 site with an enriched electron density, which optimizes the adsorption/desorption of ORR intermediates on the Cu-N4 sites. This work reports an effective way and provides insights into the ORR activity improvement of single-atom electrocatalysts.

Tailoring First Coordination Sphere of Dual‐Metal Atom Sites Boosts Oxygen Reduction and Evolution Activities

AbstractIt is important to tune the coordination configuration of dual‐atom catalyst (DAC), especially in the first coordination sphere, to render high intrinsic catalytic activities for oxygen reduction/evolution reactions (ORR/OER). Herein, a type of atomically dispersed and boron‐coordinated DAC structure, namely, FeN4B‐NiN4B dual sites, is reported. In this structure, the incorporation of boron into the first coordination sphere of FeN4/NiN4 atomic sites regulates its geometry and electronic structure by forming “Fe‐B‐N” and “Ni‐B‐N” bridges. The FeN4B‐NiN4B DAC exhibits much enhanced ORR and OER property compared to the FeN4‐NiN4 counterparts. Density functional theory calculations reveal that the boron‐induced charge transfer and asymmetric charge distributions of the central Fe/Ni atoms optimize the adsorption and desorption behavior of the ORR/OER intermediates and reduce the activation energy for the potential‐determining step. Zinc‐air batteries employing the FeN4B‐NiN4B cathode exhibit a high maximum power density (236.9 mW cm−2) and stable cyclability up to 1100 h. The result illustrates the pivotal role of the first‐coordination sphere of DACs in tuning the electrochemical energy conversion and storage activities.

Optimizing Oxygen Electrode Bifunctionality with Platinum and Nickel Nanoparticle-Decorated Nitrogen-Doped Binary Metal Oxides

Developing bifunctional oxygen electrode materials with superior activity for oxygen reduction (ORR) and oxygen evolution (OER) reactions is essential for advancing regenerative fuel cell and rechargeable metal–air battery technologies. This present work deals with the synthesis and characterization of electrocatalysts containing Pt and Ni nanoparticles supported on nitrogen-doped mixed metal oxides (Mn2O3-NiO) and the systematic evaluation of their bifunctional ORR/OER performance in an alkaline medium. These electrocatalysts have been successfully synthesized by a simple and fast microwave method. PtNi/Mn2O3-NiO-N with a binary metal oxide-to-N ratio of 1:2 demonstrated the best performance among the studied materials regarding bifunctional electrocatalytic activity (∆E = 0.96 V) and robust stability.

Carbon materials co-doped with nitrogen and sulfur for highly efficient catalytic activity in oxygen reduction and evolution

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) represent crucial steps in the functioning of fuel cells and metal-air batteries. Designing bifunctional oxygen electrode catalysts with high activity for both ORR and OER remains an immense challenge. In this study, we address this challenge by employing in-situ polymerization to design nitrogen and sulfur co-doped carbon materials (NSCs). The resulting NSC-1000–3 exhibits an onset potential of 1.03 V vs. RHE and a half-wave potential (E1/2) of approximately 0.89 V during ORR in an alkaline solution. When compared to commercial Pt/C, it demonstrates a positive shift of 60 mV in the half-wave potential. Furthermore, NSC-1000–3 displays outstanding oxygen evolution performance. At a current density of 10 mA cm−2, its performance matches that of RuO2. This material demonstrates exceptional performance in both ORR and OER, showcasing the synergistic doping effects of nitrogen and sulfur.

N-Decorated Main-Group MgAl2O4 Spinel: Unlocking Exceptional Oxygen Reduction Activity for Zn-Air Batteries.

The development of economical and efficient oxygen reduction reaction (ORR) catalysts is crucial to accelerate the widespread application rhythm of aqueous rechargeable zinc-air batteries (ZABs). Here, a strategy is reported that the modification of the binding energy for reaction intermediates by the axial N-group converts the inactive spinel MgAl2O4 into the active motif of MgAl2O4-N. It is found that the introduction of N species can effectively optimize the electronic configuration of MgAl2O4, thereby significantly reducing the adsorption strength of *OH and boosting the reaction process. This main-group MgAl2O4-N catalyst exhibits a high ORR activity in a broad pH range from acidic and alkaline environments. The aqueous ZABs assembled with MgAl2O4-N shows a peak power density of 158.5mWcm-2, the long-term cyclability over 2000h and the high stability in the temperature range from -10 to 50°C, outperforming the commercial Pt/C in terms of activity and stability. This work not only serves as a significant candidate for the robust ORR electrocatalysts of aqueous ZABs, but also paves a new route for the effective reutilization of waste Mg alloys.

Engineering Pt–S–Mo and Pd–S–Mo sites in hierarchical porous MoS2 for boosted oxygen reduction activity in microbial fuel cell

Efficient and stable electrocatalysts with low platinum content are crucial for the practical application of fuel cells. The development of Pt-based single atom catalysts (SACs) has emerged as a promising research direction. In this study, we design and prepare a SACs based on MoS2 with Pt–S–Mo and Pd–S–Mo active sites (Pd, Pt–MoS2) by successively occupying vacancies, while maintaining the individual characteristics of the active sites. The resulting Pd, Pt–MoS2 catalyst exhibits excellent electrocatalytic activity for oxygen reduction reaction (ORR), long-term stability, and resistance to common poisons (SCN−, S2−, and methanol) under neutral conditions. Meanwhile, the microbial fuel cell (MFC) equipped with Pd, Pt–MoS2 exhibits excellent performance in terms of actual electricity generation performance and sewage purification capacity with an ultrahigh power density, average chemical oxygen demand (COD) removal rate, and coulombic efficiency (CE) of 1398.6 ± 43.5 mW m−2, 96.2 ± 2.2 %, and 22.5 ± 0.5 %, respectively. This strategy will provide new insights into the development of advanced bimetallic as well as polymetallic doped vacancies of MoS2 SACs.