Oxygen Reduction Catalysis Research Articles

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.

Clarifying the Origin of Ordering Effect of PtCo Intermetallic Catalysts in Catalyzing Oxygen Reduction

Pt intermetallic catalysts exhibit higher activity for oxygen reduction reaction (ORR) than the disordered counterparts, but the origin of exact effect of structural ordering has not been fully clarified yet. Herein, by comparing the PtCo catalysts with changed ordering degree but the exactly same alloying degree, we distinguish the ordering effect from alloying effect of intermetallic catalysts in catalyzing ORR; the ordering effect is identified to increase the ORR activity by ∼1.5 times. The highly ordered PtCo intermetallic catalyst is first prepared by separating the alloying and ordering stages, then the disordered counterpart with the same alloying degree is obtained by quenching the ordered catalyst at high temperatures to freeze the random atomic arrangement. Experimental and theoretical studies reveal that both alloying effect and ordering effect of intermetallic alloy catalysts intrinsically originate from the compressive strain effect, which leads to the weakened adsorbate bonding towards oxygen-containing adsorbate and thus the promoted ORR kinetics.

Hierarchical sheet-interconnected fan-shaped N/S-containing Co-based metal organic frameworks for effectively catalyzing oxygen reduction and oxygen evolution reactions

The development of cost-effective non-precious metal bifunctional catalysts has become a promising path to meet the commercialization needs of rechargeable zinc-air batteries. Herein, an effective bifunctional catalyst, hierarchical sheet-interconnected fan-shaped N/S-containing Co-based metal organic frameworks (HSFS-N/S-Co-MOFs), has been constructed using 1,2-bis(4-pyridyl)ethane and thiophene-2,5-dicarboxylic acid as dual ligands through a solvothermal approach. Additionally, several cations and anions may affect the microstructures, surface compositions, surface areas, oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of the constructed N/S-MOFs. As a result, the hierarchical sheet-interconnected fan-shaped structure and N/S dual introduction make HSFS-N/S-Co-MOFs exhibit favorable ORR and OER performance in alkaline medium. The current research provides an option to rationally construct other MOFs-based electrocatalysts.

Facilitating two-electron oxygen reduction with pyrrolic nitrogen sites for electrochemical hydrogen peroxide production

Electrocatalytic hydrogen peroxide (H2O2) production via the two-electron oxygen reduction reaction is a promising alternative to the energy-intensive and high-pollution anthraquinone oxidation process. However, developing advanced electrocatalysts with high H2O2 yield, selectivity, and durability is still challenging, because of the limited quantity and easy passivation of active sites on typical metal-containing catalysts, especially for the state-of-the-art single-atom ones. To address this, we report a graphene/mesoporous carbon composite for high-rate and high-efficiency 2e− oxygen reduction catalysis. The coordination of pyrrolic-N sites -modulates the adsorption configuration of the *OOH species to provide a kinetically favorable pathway for H2O2 production. Consequently, the H2O2 yield approaches 30 mol g−1 h−1 with a Faradaic efficiency of 80% and excellent durability, yielding a high H2O2 concentration of 7.2 g L−1. This strategy of manipulating the adsorption configuration of reactants with multiple non-metal active sites provides a strategy to design efficient and durable metal-free electrocatalyst for 2e− oxygen reduction.

Combination of Mn-Mo Oxide Nanoparticles on Carbon Nanotubes through Nitrogen Doping to Catalyze Oxygen Reduction.

An efficient and low-cost oxygen catalyst for the oxygen reduction reaction (ORR) was developed by in situ growth of Mn-Mo oxide nanoparticles on nitrogen-doped carbon nanotubes (NCNTs). Doped nitrogen effectively increases the electron conductivity of the MnMoO4@NCNT complex and the binding energy between the Mn-Mo oxide nanoparticles and carbon nanotubes (CNTs), leading to fast charge transfer and more catalytically active sites. Combining Mn and Mo with NCNTs improves the catalytic activity and promotes both electron and mass transfers, greatly enhancing the catalytic ability for ORR. As a result, MnMoO4@NCNT exhibited a comparable half-wave potential to commercial Pt/C and superior durability, demonstrating great potential for application in renewable energy conversion systems.

Atomically Dispersed FeN2P2 Motif with High Activity and Stability for Oxygen Reduction Reaction Over the Entire pH Range

AbstractThe past decade has witnessed the great potential of Fe‐based single‐atom electrocatalysis in catalyzing oxygen reduction reaction (ORR). However, it remains a grand challenge to substantially improve their intrinsic activity and long‐term stability in acidic electrolytes. Herein, we report a facile chemical vapor deposition strategy, by which high‐density Fe atoms (3.97 wt%) are coordinated with square‐planar para‐positioned nitrogen and phosphorus atoms in a hierarchical carbon framework. The as‐crafted atomically dispersed Fe catalyst (denoted Fe‐SA/PNC) manifests an outstanding activity towards ORR over the entire pH range. Specifically, the half‐wave potential of 0.92 V, 0.83 V, and 0.86 V vs. reversible hydrogen electrode (RHE) are attained in alkaline, neutral, and acidic electrolytes, respectively, representing the high performance among reported catalysts to date. Furthermore, after 30,000 durability cycles, the Fe‐SA/PNC remains to be stable with no visible performance decay when tested in 0.1 M KOH and 0.5 M H2SO4, and only a minor negative shift of 40 mV detected in 0.1 M HClO4, significantly outperforming commercial Pt/C counterpart. The coordination motif of Fe‐SA/PNC is validated by density functional theory (DFT) calculations. This work provides atomic‐level insight into improving the activity and stability of non‐noble metal ORR catalysts, opening up an avenue to craft the desired single‐atom electrocatalysts.

Atomically Dispersed FeN2 P2 Motif with High Activity and Stability for Oxygen Reduction Reaction Over the Entire pH Range.

The past decade has witnessed the great potential of Fe-based single-atom electrocatalysis in catalyzing oxygen reduction reaction (ORR). However, it remains a grand challenge to substantially improve their intrinsic activity and long-term stability in acidic electrolytes. Herein, we report a facile chemical vapor deposition strategy, by which high-density Fe atoms (3.97 wt%) are coordinated with square-planar para-positioned nitrogen and phosphorus atoms in a hierarchical carbon framework. The as-crafted atomically dispersed Fe catalyst (denoted Fe-SA/PNC) manifests an outstanding activity towards ORR over the entire pH range. Specifically, the half-wave potential of 0.92 V, 0.83 V, and 0.86 V vs. reversible hydrogen electrode (RHE) are attained in alkaline, neutral, and acidic electrolytes, respectively, representing the high performance among reported catalysts to date. Furthermore, after 30,000 durability cycles, the Fe-SA/PNC remains to be stable with no visible performance decay when tested in 0.1 M KOH and 0.5 M H2 SO4 , and only a minor negative shift of 40 mV detected in 0.1 M HClO4 , significantly outperforming commercial Pt/C counterpart. The coordination motif of Fe-SA/PNC is validated by density functional theory (DFT) calculations. This work provides atomic-level insight into improving the activity and stability of non-noble metal ORR catalysts, opening up an avenue to craft the desired single-atom electrocatalysts.

Promoting Oxygen Reduction Reaction by Inducing Out-of-plane Polarization in Metal Phthalocyanine Catalyst.

Metal phthalocyanine (MPc) materials with well-defined MN4 moiety offers a platform for catalyzing oxygen reduction reaction (ORR), while their practical performances are often limited by the insufficient O2 adsorption due to the planar MN4 nature. Here, we proposed a design (called as Gr-MG -O-MP Pc) that the metal of MPc (MP ) is axially coordinated to a single metal atom in graphene (Gr-MG ) through a bridge-bonded oxygen atom (O), introducing effective out-of-plane polarization to promote O2 adsorption on MPc. Manipulating the out-of-plane polarization charge by varying types of MP and MG (MP = Fe/Co/Ni, MG = Ti/V/Cr/Mn/Fe/Co/Ni) in the axial coordination zone of -MG -O-MP - were examined by density functional theory simulations. Among them, the catalyst of Gr-V-O-FePc stands out with the highest calculated O2 adsorption energy, which was synthesized successfully and verified by systemic X-ray absorption spectroscopy measurements. Importantly, it delivered a remarkable ORR performance with half-wave potential of 0.925V (versus RHE) and kinetic current density of 26.7mA cm-2 . This thus demonstrates a new and simple way to pursue high catalytic performance by inducing out-of-plane polarization in catalysts. This article is protected by copyright. All rights reserved.

Explosion effect directly induced hierarchical carbon nanotube electrocatalyst integrated with Fe/Co dual sites for hydrogen fuel cells

Atomically dispersed metal-site catalysts, especially those derived from high temperature calcination of zeolite-based imidazole salt framework (ZIFs), have great potential in catalyzing oxygen reduction reaction (ORR) with slow kinetics owing to their large atomic utilization and tunable coordination environment. However, ZIFs-derived carbon-based catalysts often exhibit octahedral particle morphology and thus complex post-treatment processes were usually required to modulate the pore structure of the membrane electrodes to enhance the utilization of metal-site sites in the cathode ORR of fuel cells. Herein, a highly efficient catalyst with Fe/Co dual metal sites anchored onto N-doped carbon nanotubes (CNTs) was synthesized by one-step calcination based on the explosion effect of ClO4- ion and Fe-Co bimetal coordination interaction, named FeCo-N-CNT. The introduction of ClO4- ions and Fe/Co bimetals gives the catalyst a dense reachable active site and a hierarchical porous structure. It is worth noting that the half-wave potential of the FeCo-N-CNT reached 0.9 V in an alkaline medium and showed good cyclic stability. More impressively, the FeCo-N-CNT also shows excellent ORR catalytic performance in both acid and neutral electrolytes, with a maximum power density 1.2 and 1.4 times higher than Fe-N-PC and Co-N-PC with single-metal sites in hydrogen fuel cells, respectively. This work provides a novel method for adjusting the structure of catalysts and improving the accessibility of metal-sites.

Boosting oxygen reduction catalysis by introducing Fe bridging atoms between Pt nanoparticles and N-doped graphene

Introducing heterometals into Pt/C catalyst to construct multi-metal catalyst for improving the intrinsic activity is a rational strategy which can optimize the over-strong *O adsorption of Pt nanoparticles for oxygen reduction reaction (ORR). However, the practical activity and stability of such carbon supported Pt-based bimetallic catalysts are simultaneously limited by the conductivity degradation and deactivation caused by the weaker interaction between Pt and carbon support. Herein, by taking advantage of the precise control and self-limiting reaction of atomic layer deposition, we construct a novel Pt-Fe-NG structure in which Fe atoms play the bridging role between Pt nanoparticles and the N-doped graphene by multistep deposition. Impressively, the obtained catalyst exhibits an outstanding ORR half-wave potential of 0.948 V, a total four-electron pathway and superior durability over 10,000 cycles. The mass activity of the catalyst at 0.9 V is 15 times higher than that of commercial Pt/C. Moreover, when used as the cathode catalyst of Zn-air battery, the Pt-Fe-NG performs a maximum density power of 230 mW cm-2 and excellent stability after 180 discharge–charge cycles. The experimental results and theoretical calculations indicate that Fe bridging atoms play the role of elevating the d-band center of Pt nanoparticles and enhancing the interaction between Pt nanoparticles and carbon support, which paves a pathway for constructing novel multi-metal catalysts.

Thermodynamically controllable synthesis of ZIF-8 exposing different facets and their applications in single atom catalytic oxygen reduction reactions

Thermodynamically controllable synthesis of ZIF-8 exposing different facets and their applications in single atom catalytic oxygen reduction reactions

Enhanced Oxygen Reduction Reaction Performance by Adsorbed Water on Edge Sites.

Pt-based alloy nanoparticles have broad application prospects as cathode catalyst materials for proton-exchange membrane fuel cells (PEMFCs). Optimization of the oxygen adsorption energy is crucial to boost the performance of oxygen reduction catalysis. We successfully synthesized well-dispersed Pt1.2Ni tetrahedra and obtained the Pt1.2Ni/C catalyst adopting the one-pot synthetic protocol, which exhibits superb activity and good long-term stability for oxygen reduction reaction (ORR), achieving a mass activity of 1.53 A/mgPt at 0.90 VRHE, which is 12 times higher than that of commercial Pt/C. On combining X-ray photoelectron spectroscopy and density functional theory calculations, abundant water is adsorbed stably on the Pt1.2Ni alloy surface. We find that the intense interaction between the adsorbed O atom and adsorbed water can weaken the adsorption of oxygen, contributing to the ORR performance.

Non‐planar Nest‐like [Fe2S2] Cluster Sites for Efficient Oxygen Reduction Catalysis

AbstractMetal‐nitrogen‐carbon catalysts, as promising alternative to platinum‐based catalysts for oxygen reduction reaction (ORR), are still highly expected to achieve better performance by modulating the composition and spatial structure of active site. Herein, we constructed the non‐planar nest‐like [Fe2S2] cluster sites in N‐doped carbon plane. Adjacent double Fe atoms effectively weaken the O−O bond by forming a peroxide bridge‐like adsorption configuration, and the introduction of S atoms breaks the planar coordination of Fe resulting in greater structural deformation tension, lower spin state, and downward shifted Fe d‐band center, which together facilitate the release of OH* intermediate. Hence, the non‐planar [Fe2S2] cluster catalyst, with a half‐wave potential of 0.92 V, displays superior ORR activity than that of planar [FeN4] or [Fe2N6]. This work provides insights into the co‐regulation of atomic composition and spatial configuration for efficient oxygen reduction catalysis.

Non-planar Nest-like [Fe2 S2 ] Cluster Sites for Efficient Oxygen Reduction Catalysis.

Metal-nitrogen-carbon catalysts, as promising alternative to platinum-based catalysts for oxygen reduction reaction (ORR), are still highly expected to achieve better performance by modulating the composition and spatial structure of active site. Herein, we constructed the non-planar nest-like [Fe2 S2 ] cluster sites in N-doped carbon plane. Adjacent double Fe atoms effectively weaken the O-O bond by forming a peroxide bridge-like adsorption configuration, and the introduction of S atoms breaks the planar coordination of Fe resulting in greater structural deformation tension, lower spin state, and downward shifted Fe d-band center, which together facilitate the release of OH* intermediate. Hence, the non-planar [Fe2 S2 ] cluster catalyst, with a half-wave potential of 0.92 V, displays superior ORR activity than that of planar [FeN4 ] or [Fe2 N6 ]. This work provides insights into the co-regulation of atomic composition and spatial configuration for efficient oxygen reduction catalysis.

Longitudinally Grafting of Graphene with Iron Phthalocyanine-based Porous Organic Polymer to Boost Oxygen Electroreduction.

Iron phthalocyanine-based polymers (PFePc) are attractive noble-metal-free candidates for catalyzing oxygen reduction reaction (ORR). However, the low site-exposure degree and poor electrical conductivity of bulk PFePc restricted their practical applications. Herein, laminar PFePc nanosheets covalently and longitudinally linked to graphene (3D-G-PFePc) was prepared. Such structural engineering qualifies 3D-G-PFePc with high site utilization and rapid mass transfer. Thence, 3D-G-PFePc demonstrates efficient ORR performance with a high specific activity of 69.31 μA cm-2, a high mass activity of 81.88 A g-1, and a high turnover frequency of 0.93 e s-1 site-1 at 0.90 V vs reversible hydrogen electrode in O2-saturated 0.1 M KOH, outperforming the lamellar PFePc wrapped graphene counterpart. Systematic electrochemical analyses integrating variable-frequency square wave voltammetry and in-situ scanning electrochemical microscopy further underline the rapid kinetics of 3D-G-PFePc towards ORR.

Longitudinally Grafting of Graphene with Iron Phthalocyanine‐based Porous Organic Polymer to Boost Oxygen Electroreduction

AbstractIron phthalocyanine‐based polymers (PFePc) are attractive noble‐metal‐free candidates for catalyzing oxygen reduction reaction (ORR). However, the low site‐exposure degree and poor electrical conductivity of bulk PFePc restricted their practical applications. Herein, laminar PFePc nanosheets covalently and longitudinally linked to graphene (3D‐G‐PFePc) was prepared. Such structural engineering qualifies 3D‐G‐PFePc with high site utilization and rapid mass transfer. Thence, 3D‐G‐PFePc demonstrates efficient ORR performance with a high specific activity of 69.31 μA cm−2, a high mass activity of 81.88 A g−1, and a high turnover frequency of 0.93 e s−1 site−1 at 0.90 V vs. reversible hydrogen electrode in O2‐saturated 0.1 M KOH, outperforming the lamellar PFePc wrapped graphene counterpart. Systematic electrochemical analyses integrating variable‐frequency square wave voltammetry and in situ scanning electrochemical microscopy further underline the rapid kinetics of 3D‐G‐PFePc towards ORR.

One-pot synthesis of ultrafine trimetallic PtPdCu alloy nanoparticles decorated on carbon nanotubes for bifunctional catalysis of ethanol oxidation and oxygen reduction

Bifunctional catalysts for ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) with high noble-metal utilization are highly beneficial to direct ethanol fuel cells (DEFCs). This study developed a ternary bifunctional catalyst composed of ultrafine PtPdCu alloy nanoparticles and carbon nanotubes (CNTs) support through a facile surfactant-free solvothermal route. The carboxyl terminal groups on CNTs ensure the confined growth of PtPdCu alloys (∼5 nm) and suppress Ostwald ripening of metallic active sites during electrochemical cycling. Consequently, PtPdCu/CNTs exhibits high mass activity (1.95 A mg−1) and specific activity (4.08 mA cm−2) toward EOR, which are 7.8 and 8.9 times higher, respectively, than those of commercial Pt/C. Furthermore, PtPdCu/CNTs displays superior stability toward EOR compared with its bimetallic counterparts (PtPd/CNTs and PtCu/CNTs). In addition, PtPdCu/CNTs exhibits the highest half-wave potential of 0.888 V among all electrocatalysts, indicating high ORR activity. Density functional theory calculations reveal that Pd and Cu mediate the electronic structure of Pt, leading to enhanced catalytic activity of PtPdCu/CNTs. The excellent catalytic property of PtPdCu/CNTs can also be attributed to the bifunctional effects of Pd/Cu and the interaction between metal and the carbon support. The proposed material is a contribution to the family of efficient ternary-alloy electrocatalysts for fuel cells.

Nanoreactor of Fe, N Co-Doped Hollow Carbon Spheres for Oxygen Reduction Catalysis.

A simple template strategy was applied to prepare a Fe, N co-doped hollow carbon (Fe-NHC) nanoreactor for the oxygen reduction reaction (ORR) by coating Fe nanoparticles (Fe-NPs) with polydopamine (PDA), followed by high temperature pyrolysis and acid-leaching. With this method, Fe-NPs were used as both the template and the metal precursor, so that the nanoreactors can preserve the original spherical morphology and embed Fe single atoms on the inner walls. The carbonized PDA contained abundant N content, offering an ideal coordination environment for Fe atoms. By regulating the mass ratio of Fe-NPs and PDA, an optimal sample with a carbon layer thickness of 12 nm (Fe-NHC-3) was obtained. The hollow spherical structure of the nanoreactors and the atomically dispersed Fe were verified by various physical characterizations. As a result, Fe-NHC-3 performed well in ORR tests under alkaline conditions, with high catalytic activity, durability, and methanol resistance, demonstrating that the as-fabricated materials have the potential to be applied in the cathodic catalysis of fuel cells.

Catalytic Four-Electron Reduction of Oxygen to Water by a Molecular Cobalt Complex Consisting of a Proton Exchanging Site at the Secondary Coordination Sphere

Catalytic Four-Electron Reduction of Oxygen to Water by a Molecular Cobalt Complex Consisting of a Proton Exchanging Site at the Secondary Coordination Sphere