Oxygen Reduction Catalysis Research Articles

Transformation of Waste Agarwood Leaves into Heteroatom-Doped Microporous Carbon for Highly Active Metal-Free Catalytic Oxygen Reduction Reaction and Efficient Capacitive Energy Storage Application

Transformation of Waste Agarwood Leaves into Heteroatom-Doped Microporous Carbon for Highly Active Metal-Free Catalytic Oxygen Reduction Reaction and Efficient Capacitive Energy Storage Application

Well‐defined N3C1‐anchored Single‐Metal‐Sites for Oxygen Reduction Reaction

AbstractN‐, C‐, O‐, S‐coordinated single‐metal‐sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well‐defined such SMSs, and the fundamental comprehension has long been impeded in case‐by‐case reports using carbon materials as investigation targets. In this work, the well‐defined molecular catalysts with N3C1‐anchored SMSs, i.e., N‐confused metalloporphyrins (NCPor‐Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor‐Ms with corresponding N4‐anchored SMSs (metalloporphyrins, Por‐Ms), are synthesized for catalytic activity evaluation. Among all, NCPor‐Co reaches the top in established volcano plots. NCPor‐Co also shows the highest half‐wave potential of 0.83 V vs. RHE, which is much better than that of Por‐Co (0.77 V vs. RHE). Electron‐rich, low band gap and regulated d‐band center contribute to the high activity of NCPor‐Co. This study delves into the examination of well‐defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high‐performance asymmetric SMS catalysts.

Well-defined N3 C1 -anchored Single-Metal-Sites for Oxygen Reduction Reaction.

N-, C-, O-, S-coordinated single-metal-sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well-defined such SMSs, and the fundamental comprehension has long been impeded in case-by-case reports using carbon materials as investigation targets. In this work, the well-defined molecular catalysts with N3 C1 -anchored SMSs, i.e., N-confused metalloporphyrins (NCPor-Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor-Ms with corresponding N4 -anchored SMSs (metalloporphyrins, Por-Ms), are synthesized for catalytic activity evaluation. Among all, NCPor-Co reaches the top in established volcano plots. NCPor-Co also shows the highest half-wave potential of 0.83 V vs. RHE, which is much better than that of Por-Co (0.77 V vs. RHE). Electron-rich, low band gap and regulated d-band center contribute to the high activity of NCPor-Co. This study delves into the examination of well-defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high-performance asymmetric SMS catalysts.

Oxygen reduction catalysis by [Cu(cyclen)Cl]Cl·H2O: The relationship of selectivity to proton in nonaqueous solution and aqueous solution

The reaction of 1,4,7,10‐tetraazacyclododecane (cyclen) with CuCl2·2H2O results in a novel five‐coordinated mononuclear copper complex, [Cu(cyclen)Cl]Cl·H2O, which has been characterized using physicochemical and spectroscopic methods. This copper complex can serve as a catalyst for oxygen reduction reactions (ORRs). The selectivity for 4e−/4H+ reduction to H2O νersus 2e−/2H+ reduction to H2O2 is determined by the relationship of the pKa value of the proton donor in nonaqueous solutions. The dissociation of Cl− from [Cu(cyclen)Cl]Cl·H2O creates an empty position on the copper centre, enabling to binding of dioxygen (O2) to form Cu(II)‐superoxo intermediate, which further reacts with a strong acid as a proton donor to form H2O and with a weak acid as a proton donor to form H2O2. Moreover, the faradaic efficiency for H2O2 production increases in an aqueous environment with the increase of pH.

Design of NiCo2S4@ZnAl-LDH/TiO2@MXene synthesis as promising cathode catalyst for enhancing electrochemical performance in microbial fuel cell

In this work, a double-bimetallic compound (NiCo2S4@ZnAl-LDH/TiO2@MXene) was successfully prepared by a simple hydrothermal-coprecipitation method. NiCO2S4@ZnAl-LDH/TiO2@MXene was combined with two bimetallic compounds, NiCo2S4@ZnAl-LDH and TiO2@MXene, which formed a firm structure. This material showed superior catalytic oxygen reduction reaction (ORR) according to the large integral area and sharp slope. The maximum power density of NiCo2S4@ZnAl-LDH/TiO2@MXene-microbial fuel cell (MFC) was 565.81 mW/m2 and could be maintained for 10 d, which was 7.07 times of NiCo2S4/TiO2@ZnAl-LDH-MFC (80 mW/m2), 11.43 times of NiCo2S4@ZnAl-LDH (49.5 mW/m2), 14.15 times of TiO2@MXene (40 mW/m2), indicating the excellent electrical performance of NiCo2S4@ZnAl-LDH/TiO2@MXene. TiO2 and NiCo2S4 were introduced in ZnAl-LDH and MXene separately to avoid aggregation between layers, which provided more pathways for ions and accelerated the speed of the transportation of electrons. NiCO2S4@ZnAl-LDH/TiO2@MXene were coated tightly and firmly with the coprecipitation method which further enhanced the electrochemical performance of MFC. Therefore, this study would give a boarder horizon about the application of cathode materials of MFC.

Reduced graphene oxide-supported palladium oxide-MOx for improving the performance of air-cathode microbial fuel cells: Influence of the Sn, Ce, Zn, and Fe precursors

Over the past few decades, microbial fuel cells (MFCs) have attracted significant interest within the realm of renewable energy technologies owing to their capability to generate electricity from low-grade substrates. However, their commercialization and scaling-up are impeded by significant obstacles, including high capital costs, limited durability, and sluggish oxygen reduction reaction (ORR). Here, we demonstrate an environmentally-friendly approach for developing highly efficient electrocatalysts consisting of palladium oxide (PdO) and different transition metal oxides (i.e., tin (IV) oxide (SnO2), ceric oxide (CeO2), iron (III) oxide (Fe2O3), and zinc oxide (ZnO)) embedded within reduced graphene oxide (rGO) framework for improving the efficiency of ORR in neutral medium and MFCs. Among the as-prepared electrocatalysts, the PdO–SnO2/rGO possesses the highest ORR electrochemical catalytic activity in a neutral medium (pH ∼ 7.2) following a four-electron ORR pathway, with a current density slightly lower than that of benchmark Pt/C electrocatalyst. The assessment of MFC performance is conducted by employing activated sludge as the inoculum and glucose as the sole electron donor in the anode chamber of single-chamber, air-cathode MFCs. Consistent with electrochemical performance, the maximum power output of an MFC equipped with PdO–SnO2/rGO as an air cathode is significantly higher than other tested MFCs, reaching 84.6 ± 2.8 mW m−2, which represents ∼ 91 % of the power output of an MFC with Pt/C air cathode. Our results reveal that the incorporation of PdO into transition metal reduced graphene oxide framework has the potential to facilitate their long-term application as air cathodes in MFCs that possess easy fabrication, relatively affordable cost, and outstanding electrochemical catalytic oxygen reduction capability, for enhancing electricity generation from wastewater.

The corrosion resistant Pt5Ce–CeO2 structure provides significant oxygen reduction catalysis

Platinum-based alloy catalysts have been extensively studied in the oxygen reduction reaction (ORR) because of their excellent performance. In this study, Pt5Ce–CeO2/C composite catalysts were synthesized by polyol reduction method and high-temperature calcination method. Owing to the dual effects of the alloying effect of forming Pt5Ce intermetallic compound and the electronic effect of CeO2 modulating the electronic structure of Pt, it exhibits further improved ORR performance than the commercial Pt/C catalysts. The material possesses a 1.0 V starting potential, a 0.83 V half-wave potential, high durability, and methanol resistance. It has strong ORR catalytic activity and works well in Zn-air batteries. The experimental findings demonstrate that metal oxide and alloy structure can be combined to enhance catalyst ORR performance.

Controlled construction of core-shell structured Prussian Blue analogues towards enhanced oxygen reduction.

Metal-organic frameworks-based electrocatalysts have been developed as highly desirable and promising candidates for catalyzing oxygen reduction reaction (ORR), which, however, usually need to be prepared at elevated temperatures and may suffer from the framework collapse in water environment largely preventing its industrial application. Herein, we demonstrate a facile low-temperature ion exchange method to synthesize Mn and Fe co-loaded Prussian blue analogues possessing core-shell structured frameworks and favorable water-tolerance. Among the catalysts prepared, the optimal HMPB-2.6Mn shows a high ORR electrocatalytic performance featuring a half-wave potential of 0.86 V and zinc-air battery power density of 119 mW cm-2, as well as negligible degradation up to 60 h, which are comparable to commercial Pt/C. Such an excellent electrocatalytic performance is attributed to the special core-shell-like structure with Mn concentrated in outer shell, and the synergetic interactions between Mn and Fe, endowing HMPB-Mn with outstanding ORR activity and good stability.

Precise synthetic control of exclusive ligand effect boosts oxygen reduction catalysis

Ligand effect, induced by charge transfer between catalytic surface and substrate in core/shell structure, was widely proved to benefit Pt-catalyzed oxygen reduction reaction by tuning the position of d-band center of Pt theoretically. However, ligand effect is always convoluted by strain effect in real core/shell nanostructure; therefore, it remains experimentally unknown whether and how much the ligand effect solely contributes electrocatalytic activity improvements. Herein, we report precise synthesis of a kind of Pd3Ru1/Pt core/shell nanoplates with exclusive ligand effect for oxygen reduction reaction. Layer-by-layer growth of Pt overlayers onto Pd3Ru1 nanoplates can guarantee no lattice mismatch between core and shell because the well-designed Pd3Ru1 has the same lattice parameters as Pt. Electron transfer, due to the exclusive ligand effect, from Pd3Ru1 to Pt leads to a downshift of d-band center of Pt. The optimal Pd3Ru1/Pt1-2L nanoplates achieve excellent activity and stability for oxygen reduction reaction in alkaline/acid electrolyte.

Selective Four‐Electron Reduction of Oxygen by a Nonheme Heterobimetallic CuFe Complex

AbstractWe report herein the first nonheme CuFe oxygen reduction catalyst ([CuII(bpbp)(μ‐OAc)2FeIII]2+, CuFe−OAc), which serves as a functional model of cytochrome c oxidase and can catalyze oxygen reduction to water with a turnover frequency of 2.4×103 s−1 and selectivity of 96.0 % in the presence of Et3NH+. This performance significantly outcompetes its homobimetallic analogues (2.7 s−1 of CuCu−OAc with %H2O2 selectivity of 98.9 %, and inactive of FeFe−OAc) under the same conditions. Structure‐activity relationship studies, in combination with density functional theory calculation, show that the CuFe center efficiently mediates O−O bond cleavage via a CuII(μ‐η1 : η2‐O2)FeIII peroxo intermediate in which the peroxo ligand possesses distinctive coordinating and electronic character. Our work sheds light on the nature of Cu/Fe heterobimetallic cooperation in oxygen reduction catalysis and demonstrates the potential of this synergistic effect in the design of nonheme oxygen reduction catalysts.

Selective Four-Electron Reduction of Oxygen by a Nonheme Heterobimetallic CuFe Complex.

We report herein the first nonheme CuFe oxygen reduction catalyst ([CuII (bpbp)(μ-OAc)2 FeIII ]2+ , CuFe-OAc), which serves as a functional model of cytochrome c oxidase and can catalyze oxygen reduction to water with a turnover frequency of 2.4×103 s-1 and selectivity of 96.0 % in the presence of Et3 NH+ . This performance significantly outcompetes its homobimetallic analogues (2.7 s-1 of CuCu-OAc with %H2 O2 selectivity of 98.9 %, and inactive of FeFe-OAc) under the same conditions. Structure-activity relationship studies, in combination with density functional theory calculation, show that the CuFe center efficiently mediates O-O bond cleavage via a CuII (μ-η1 : η2 -O2 )FeIII peroxo intermediate in which the peroxo ligand possesses distinctive coordinating and electronic character. Our work sheds light on the nature of Cu/Fe heterobimetallic cooperation in oxygen reduction catalysis and demonstrates the potential of this synergistic effect in the design of nonheme oxygen reduction catalysts.

Biaxially‐Strained Phthalocyanine at Polyoxometalate@Carbon Nanotube Heterostructure Boosts Oxygen Reduction Catalysis

AbstractIron phthalocyanine (FePc) with unique FeN4 site has attracted increasing interests as a promising non‐precious catalyst. However, the plane symmetric structure endows FePc with undesired catalytic performance toward the oxygen reduction reaction (ORR). Here, we report a novel one‐dimensional heterostructured ORR catalyst by coupling FePc at polyoxometalate‐encapsulated carbon nanotubes (FePc‐{PW12}@NTs) using host‐guest chemistry. The encapsulation of polyoxometalates can induce a local tensile strain of single‐walled NTs to strengthen the interactions with FePc. Both the strain and curvature effects of {PW12}@NT scaffold tune the geometric structure and electronic localization of FeN4 centers to enhance the ORR catalytic performance. As expected, such a heterostructured FePc‐{PW12}@NT electrocatalyst exhibits prominent durability, methanol tolerance, and ORR activity with a high half‐wave potential of 0.90 V and a low Tafel slope of 30.9 mV dec−1 in alkaline medium. Besides, the assembled zinc‐air battery demonstrates an ultrahigh power density of 280 mW cm−2, excellent charge/discharge ability and long‐term stability over 500 h, outperforming that of the commercial Pt/C+IrO2 cathode. This study offers a new strategy to design novel heterostructured catalysts and opens a new avenue to regulate the electrocatalytic performance of phthalocyanine molecules.

Biaxially-Strained Phthalocyanine at Polyoxometalate@Carbon Nanotube Heterostructure Boosts Oxygen Reduction Catalysis.

Iron phthalocyanine (FePc) with unique FeN4 site has attracted increasing interests as a promising non-precious catalyst. However, the plane symmetric structure endows FePc with undesired catalytic performance toward the oxygen reduction reaction (ORR). Here, we report a novel one-dimensional heterostructured ORR catalyst by coupling FePc at polyoxometalate-encapsulated carbon nanotubes (FePc-{PW12}@NTs) using host-guest chemistry. The encapsulation of polyoxometalates can induce a local tensile strain of single-walled NTs to strengthen the interactions with FePc. Both the strain and curvature effects of {PW12}@NT scaffold tune the geometric structure and electronic localization of FeN4 centers to enhance the ORR catalytic performance. As expected, such a heterostructured FePc-{PW12}@NT electrocatalyst exhibits prominent durability, methanol tolerance, and ORR activity with a high half-wave potential of 0.90 V and a low Tafel slope of 30.9 mV dec-1 in alkaline medium. Besides, the assembled zinc-air battery demonstrates an ultrahigh power density of 280 mW cm-2, excellent charge/discharge ability and long-term stability over 500 h, outperforming that of the commercial Pt/C+IrO2 cathode. This study offers a new strategy to design novel heterostructured catalysts and opens a new avenue to regulate the electrocatalytic performance of phthalocyanine molecules.

Optimization of Fe and Co distribution on Fe-CoZn-ZIF derived polyhedral carbon via secondary adsorption for reversible catalysis of oxygen and zinc-air batteries

Bimetallic/polymetallic organic frameworks (MOFs) and their derivants have the advantages of structural adjustable, efficient charge transfer rate and intermetallic synergistic effects which can catalyze oxygen reduction reactions (ORR) and oxygen evolution reaction (OER) efficiently. However, traditional MOFs still faces limited active sites. The construction of catalysts with target active sites using binary/polymetallic MOFs is essential. Here, we prepared catalysts with bimetallic active sites highly dispersed in the interior and surface of N-doped carbon polyhedron via an inside-out (cavity confinement and secondary adsorption) approach. The prepared FeCo@FeCo-CN catalysts exhibited considerable bifunctional catalytic performance, as evidenced by the remarkable improved half-wave potential (E1/2 = 0.878 V) for ORR and the desired overpotential (368 mV) for OER as well as the small potential gap between them (ΔE = 0.720 V). Moreover, the liquid rechargeable Zinc-Air batteries based on the prepared catalyst showed high open-circuit voltage (1.506 V) and specific capacity (890.310 mA h gzn−1) with an impressive cycling stability which is apparently outperformed than Pt/C+RuO2 catalyst. The prime electrocatalytic behavior of the catalyst can be ascribed to the secondary adsorption of Fe and Co which contributes to the generation of more active sites while preventing the undesirable aggregation of metals.

Effect of Pretreatment on the Nitrogen Doped Activated Carbon Materials Activity towards Oxygen Reduction Reaction.

Nitrogen-doped activated carbons with controlled micro- and mesoporosity were obtained from wood and wastes via chemical processing using pre-treatment (pyrolysis at 500 °C and hydrothermally carbonization at 250 °C) and evaluated as oxygen reduction catalysts for further application in fuel cells. The elemental and chemical composition, structure and porosity, and types of nitrogen bonds of obtained catalyst materials were studied. The catalytic activity was evaluated in an alkaline medium using the rotating disk electrode method. It was shown that an increase in the volume of mesopores in the porous structure of a carbon catalyst promotes the diffusion of reagents and the reactions proceed more efficiently. The competitiveness of the obtained carbon materials compared to Pt/C for the reaction of catalytic oxygen reduction is shown.

(Digital Presentation) Biogenic Electrodes for Low-Temperature Solid Oxide Fuel Cells

Biogenic Electrodes for Low-Temperature Solid Oxide Fuel Cells Jyoti Bhattacharjee, Subhasis Roy* Department of Chemical Engineering, University of Calcutta, 92 A. P. C. Road, Kolkata-700009, India * Email: subhasis1093@gmail.com/srchemengg@caluniv.ac.in : Solid oxide fuel cells (SOFCs) are potential energy-generation devices. They operate at hightemperatures, typically between 800°C-1000°C, limiting their utility. The primary challengein developing these fuel cells is synthesizing strong biogenic electrodes that function at lowtemperatures, maintaining high performance. This experimental study examines how eco-friendly,facile, and novel techniques for synthesis can be used to make robust, effective, and affordableelectrodes for low-temperature recyclable SOFCs (LT-SOFC). A green approachwas implemented by using biomass waste and biochar, specifically coconut shells and ricehusks, as raw materials. The synthesis comprised the hydrothermal carbonization of biomassprecursors, such as lignocellulosic nanostructures, and carbon nanotubes under controlledconditions, followed by activation with potassium hydroxide(KOH). The resulting electrodeshad a large surface area, catalytic oxygen reduction, excellent conductivity, and sufficientelectrochemical performance. The efficacy of the biomass-derived electrodes was enhancedby employing transition metal oxides as electrocatalysts, such as nickel oxide(NiO) andcobalt oxide(Co3O4). The morphology and elemental composition of the electrode materialwere studied using the scanning electron microscope(SEM) and energy-dispersive X-rayspectroscopy(EDS). Electrochemical impedance spectroscopy(EIS)was used to examine theelectrochemical properties of cell electrolytes. Findings demonstrated that the hydrothermalstrategy led to the formation of homogeneous and porous electrode structures with highgalvanic activity. The biodegradable LT-SOFC stack achieved an optimal power density of346mW/cm2 at around 550°C, indicating a substantial increase over previous experiments.Our results have significant economic consequences for the expansion of sustainable andrenewable energy innovations in industry and nanotechnology, providing auxiliary power inautomobiles and hydrogen generation. Greenhouse gas emissions and carbon footprint can bediminished by using biomass waste streams as feedstocks, reducing the need for fossil fuels.The outcomes of this research provide important insights into the development, challenges,and future possibilities of biomass-derived electrodes, and minimal temperature electrolytesfor stable SOFCs. Keywords: Biomass-derived; carbon footprint; electrochemical efficiency; green energy; low-temperature solid oxide fuel cells; nanotubes.

Electrochemical Activation of Metabolic Enzymes in Human Liver S9 Fractions

Human liver subcellular fractions such as liver microsomes, liver cytosol fractions, or S9 fractions are widely used in in-vitro assays to predict liver metabolism. The S9 fractions are the supernatants of human liver homogenates consist of both human liver microsomes and the cytosol. Therefore, these fractions contain majority of cytochrome P450 (CYP) enzymes and soluble phase II enzymes like glucuronosyltransferases, N-acetyl transferases, sulfotransferases, and glutathione-S-transferases. Here we report the direct electrochemistry and biocatalytic features of redox active enzymes impregnated in S9 fractions. We investigated the electrochemical properties of S9 films by immobilizing them onto a high purity graphite electrode and performing cyclic voltammetry in anaerobic (Ar saturated) and aerobic (O2 saturated) conditions. The electron transfer between the S9 film and the high purity graphite electrode was observed at the formal potential of -0.48 V, with respect to Ag/AgCl reference electrode, which confirmed the activation of CYP450 reductase enzyme in the film. These films also demonstrated a catalytic oxygen reduction with a maximum current density of ~0.5 mA cm-2 at the scan rate of 0.050V/s. We investigated the CYP activity in the S9 biofilm for phase 1 metabolism using diclofenac hydroxylation as a probe reaction and could able to identify metabolic products using liquid chromatography-mass spectrometry (LC-MS) technique. Eventually, we envision to develop a platform to perform both phase I and II metabolic reactions in a single electrochemical assay.

Interface Engineering and Boron Modification of Pd-B/Pd Hetero-Metallene Synergistically Accelerate Oxygen Reduction Catalysis.

2D metallene possess high surface area and excellent electron transport capability, thus enabling efficient application in oxygen reduction reaction (ORR). However, the interface regulation and electronic structure optimization of metallene are still great challenges. Herein, Pd-B/Pd hetero-metallene is constructed by interface engineering and B modification strategies for efficient electrocatalytic ORR. The 2D configuration of Pd-B/Pd hetero-metallene exposes a large number of surface atoms and unsaturated defect sites, thus providing abundant catalytic active sites and exhibiting high electron mobility. More importantly, interface engineering and B modification synergistically optimizing the electronic configuration of the metallene system. This work not only provides an effective strategy for the rational regulation of the electronic configuration of metallene, but also offers a reference for the construction of efficient ORR catalysts.

PdM (M = Fe, Co, Ni) bimetallic nanowires enhances oxygen reduction catalysis in acid medium

PdM (M = Fe, Co, Ni) bimetallic nanowires enhances oxygen reduction catalysis in acid medium

Two-stage confinement derived small-sized highly ordered L10-PtCoZn for effective oxygen reduction catalysis in PEM fuel cells

Intermetallic ordered PtCo is effective for high oxygen reduction reaction (ORR) activity and stability. However, preparing small-sized, highly ordered PtM alloys is still challenging. Herein, we report a controlled two-stage confinement strategy, in which highly ordered PtCoZn/NC nanoparticles of 5.3 nm size were prepared in a scalable process. The contradiction between the high ordering degree with the small particle size as well as the atomic migration with the space confinement was well resolved. An outstanding PEMFC performance was achieved for L10-PtCoZn/NC with a high mass activity (MA) of 1.21 A/mgPt at 0.9 ViR-free, 80.1 % MA retention after 30 k cycles in H2-O2 operation, and a high mass-specific power density of 8.24 W mg-1Pt in H2-Air operation with a slight loss of cell voltage@0.8 A cm−2 of 28 mV after 30 k cycles. The high performance can be ascribed to the high Pt area exposure, the enhanced Pt-Co coupling, and the prevented agglomeration in the mesoporous carbon wall. Overall, this strategy may contribute to the commercialization of fuel cells.