Efficient Oxygen Reduction Electrocatalysis Research Articles

Core/shell Ni@C particle-supported N-doped carbon with hollow capsules for efficient electrocatalytic reduction of oxygen

To replace the noble metal catalysts for oxygen reduction reaction (ORR), a Ni@C-supported N-doped carbon material (Ni@C/NC) is in-situ prepared via one-step pyrolyzing the polymerizable ionic liquid of vinyl imidazole combined with Ni(NO3)2. Systemic investigations demonstrate that these nanosized Ni particles are tightly wrapped with a thin carbon layer to form the core/shell structure, meanwhile carbon capsules are synchronously yielded on the carbon matrix. As a result, both the carbon shell and the carbon capsule jointly increase the active sites of the Ni@C/NC, while the carbon shell also contributes the fast electron-transfer from Ni particle. Compared with the normal Ni-supported carbon catalyst, the Ni@C/NC shows the respectable ORR performance with the onset and half-wave potentials of 0.96 and 0.84 VRHE. After the long-term electrocatalysis (10 h), the Ni@C/NC is found to possess the great structural and electrocatalytic stabilities, which maintains 93 % of the initial current density and the well-dispersed and uniform Ni@C particles. Subsequently, a Zn-Air battery with the Ni@C/NC cathode is assembled and exhibits a peak power density of 200 mW cm−2. Therefore, the as-obtained Ni@C/NC with the high electroactivity and stability can be expected as an ideal candidate to apply in the metal-air batteries and fuel cells in the future.

Strain effect induced Pd nanoparticles decorated Pd2+-doped Co3O4 nanosheets for efficient electrocatalytic ethanol oxidation and oxygen reduction reactions

Reactive metal-support interaction (RMSI) is an effective means of inducing surface strain and charge transfer in catalysts, which further enhances electrochemical activity and modulates reaction pathways. Nevertheless, the precise synthesis of nanomaterials with tunable strain and unique morphology remains a challenge. In this work, we have synthesized Pd nanoparticles decorated Pd2+- doped Co3O4 nanosheets (Pd7.4%/Co3O4) by a NaBH4 reduction method, which exhibit excellent performance for ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR). The introduction of the Pd into the Co3O4 by the means of elemental doping and nanoparticle decoration, and the resulting lattice strain and electron redistribution are responsible for the improved performance. Meanwhile, Pd7.4%/Co3O4 has a relatively low d-band center that reduces the adsorption energy of reaction intermediates to improve reaction selectivity and eliminate EOR toxic intermediates, ultimately promoting reaction kinetics. This work demonstrates a simple and effective strategy to manipulate lattice strain and electronic coupling and provides a novel and advanced way for the development of low-cost and high-quality direct ethanol fuel cells (DEFCs) catalysts.

Formation of N‐doped Graphene and Carbon Nanoparticles Integrated Composite for Efficient Oxygen Reduction Electrocatalysis

AbstractN‐doped carbon‐based materials have been regarded as promising alternatives to Pt‐based electrocatalysts for the four‐electron (4e−) oxygen reduction reaction (ORR), which is an important electrochemical reaction for the polymer electrolyte fuel cells. Here, we report a N‐doped graphene and N‐doped carbon nanoparticles integrated composite electrocatalyst by a multi‐step acid etching plus annealing method. Despite the low N‐doping level, the material exhibits efficient 4e− ORR activity with an onset potential of 0.932 V, a half‐wave potential of 0.814 V, and a limiting current density of 5.3 mA cm−2 in 0.1 M KOH solution. We demonstrate that the promoted 4e− ORR activity is attributed to the special 2D–0D integrated structure for exposing massive active sites, the favorable porous structure facilitating the H2O transfer dynamics, and the high content of oxygen‐containing C−O−C species and the increased intrinsic carbon defects for additional active sites. A “decomposition and recrystallization” mechanism is proposed for the formation of N‐doped graphene.

Highly dispersed Zn-N, S co-doped carbon for highly efficient electrocatalytic oxygen reduction

Supportive atomic Zn electrocatalysts exhibit excellent stability for oxygen reduction reaction (ORR) due to their fully occupied d orbitals of Zn, but their catalytic activity is not satisfactory. Whereas heteroatom doping can anchor the Zn atoms to achieve higher Zn loading; and additionally serve as auxiliary sites to enhance the catalytic activity of Zn sites. Herein, we present a method for the synthesis of N, S co-doped carbon with highly dispersed Zn (named Zn-NSC). The ORR activity of the Zn-NSC catalysts is optimized by adjusting the pyrolysis temperature and the atomic structure of the dopant molecules. The optimized Zn-NSC demonstrates significantly enhanced ORR electrocatalytic activity, this is attributable to its highly co-doping of N and S heteroatoms that are adjacent to Zn atoms. Specifically, the Zn-NSC3 catalyst exhibits remarkable ORR characteristics with excellent onset voltage (0.97 V vs RHE) and half-wave potential (0.87 V vs RHE), surpassing those of Pt/C (0.97 V and 0.85 V, respectively). Additionally, the Zn-NSC3 can be utilized as efficient cathode for Al-air batteries, achieving a high power density of 119.4 mW cm−2 and satisfactory discharge stability. This work proposes an approach for synthesizing low-cost and efficient ORR electrocatalysts for Al-air battery applications.

Nitrogen-Doped Carbon Nanosheets Supported Co for Efficient and Stable Electrocatalytic Oxygen Reduction

Nitrogen-Doped Carbon Nanosheets Supported Co for Efficient and Stable Electrocatalytic Oxygen Reduction

Ordered mesoporous carbon with binary CoFe atomic species for highly efficient oxygen reduction electrocatalysis.

The exploration of powerful, efficient and precious metal-free electrocatalysts for facilitating the sluggish kinetics of the oxygen reduction reaction (ORR) is a crucial endeavor in the development and application of energy conversion and storage devices. Herein, we have rationally designed and synthesized bimetallic CoFe species consisting of CoFe nanoparticles and atomically dispersed dual atoms anchored on an ordered mesoporous carbon matrix (CoFe/NC) as highly efficient ORR electrocatalysts. The pyrolyzation temperature for CoFe/NC plays a vital role in regulating the morphology and composition of both the carbon matrix and CoFe species. The optimized CoFe/NC-750 exhibits a favorable ORR performance in 0.1 M KOH with a high half-wave potential (E1/2) of 0.87 V vs. RHE, excellent tolerance to methanol and remarkable durability (no obvious decrease in E1/2 value after 3000 cycles), all of which are superior to the performance of commercial Pt/C. Experimental measurements and density functional theory (DFT) calculations reveal that the improved ORR performance of CoFe/NC-750 is mainly attributed to the electronic structure of atomically dispersed Fe active sites modulated by the surrounding CoFe alloys and Co single atoms, which accelerates the dissociation and reduction of intermediate OH* species and promotes the ORR process.

Ni clusters immobilized on oxygen-rich siloxene nanosheets for efficient electrocatalytic oxygen reduction toward H2O2 synthesis.

Hydrogen peroxide (H2O2) electrosynthesis via the two-electron oxygen reduction reaction (2e- ORR) represents a green alternative to the energy-intensive anthraquinone process. However, the practical application of this method is limited by the lack of cost-effective and high-performance electrocatalysts. Reported here is a hybrid catalyst composed of nickel (Ni) clusters immobilized onto the surface of two-dimensional siloxene nanosheets (Ni/siloxene), which exhibits excellent efficiency and selectivity in electrocatalytic oxygen reduction to H2O2 in an alkaline medium, demonstrating a standard 2e- pathway with >95% H2O2 selectivity across a wide potential range. Experimental results disclose that the high performance of Ni/siloxene can be traced to a synergy of the Ni clusters and the oxygen-rich surface of siloxene. Density functional theory (DFT) calculations further reveal a weakened interaction between Ni/siloxene and *OOH and the consequently reduced energy barrier for the *OOH protonation toward H2O2 desorption, thus leading to a high 2e- ORR reactivity and selectivity. This work provides a valuable and practical guidance for designing high-performance 2e- ORR electrocatalysts based on the rational engineering of the metal-support interaction.

Tailoring the Chemisorption Manner of Fe d‐Band Center with La2O3 for Enhanced Oxygen Reduction in Anion Exchange Membrane Fuel Cells

AbstractEngineering the electronic configuration and intermediates adsorption behaviors of high‐performance non‐noble‐metal‐based catalysts for the sluggish oxygen reduction reaction (ORR) kinetics at the cathode is highly imperative for the development of anion exchange membrane fuel cells (AEMFCs), yet remains an enormous challenge. Herein, a rare‐earth metal oxide engineering tactic through the formation of Fe3O4/La2O3 heterostructures in N,O‐doped carbon nanospheres (Fe3O4/La2O3@N,O‐CNSs) for efficient oxygen reduction electrocatalysis is reported. The theoretical calculations reveal that the interfacial bonds formed by the La─O─Fe heterogeneous interface effectively optimize the electronic structure of the Fe d‐band center relative to the Fermi level, which results in a significant reduction of the reaction barriers of rate‐limiting steps during the ORR. The modulation in intermediates chemisorption enables Fe3O4/La2O3@N,O‐CNSs an outstanding ORR performance and improved stability, with a significantly higher half‐wave potential value (0.88 V). More impressively, this integrated catalyst delivers a remarkable power density of 148.7 mW cm−2 in practical AEMFC operating conditions, along with negligible performance degradation over 100 h using an H2‐air atmosphere, which is higher than commercial Pt/C‐coupled electrodes. The results presented here are believed to provide guidelines for fabricating high‐performance AEMFCs electrocatalysts in terms of heterointerface engineering and strong electronic coupling effect induced by rare‐earth oxides.

Ultra-fine Fe3C nanoparticles decorated in the Fe–N co-doped carbon networks with hierarchical nanoarchitectonics towards efficient oxygen reduction electrocatalysis

The iron-nitrogen co-doped carbon (Fe–N–C) materials have considered one of the oxygen reduction reaction catalysts with the best potential. Unfortunately, their insufficient intrinsic activity and low active sites result in thick cathode catalytic layers of fuel cell, which has limited discharge performance of the Fe–N–C catalysts in the fuel cells. Herein, a supramolecular assembly strategy is designed to prepare accessible Fe-Nx sites and ultra-fine Fe3C nanoparticles in porous carbon nanosheet with optimized pore structure toward oxygen reduction electrocatalysis. It is found that supramolecular assembly strategy has significantly increased the specific surface area and Fe-Nx site content, and induced the formation of highly dispersed Fe3C nanoparticles, which contributes to the high electrochemical active surface area and catalytic activity. The obtained FeNC-900-S catalyst exhibits a high half-wave potential of 0.860 V and a current density of up to 8.28 mA/cm2 (Jk at 0.85 V) in 0.1 M KOH, outperforming the those of commercial Pt/C. More importantly, when the FeNC-900-S is employed as an air cathode catalyst towards zinc-air batteries, it obtains an open-circuit voltage of 1.548 V, a power density of 188.8 mW/cm2 and a specific capacity of 790.5 mAh/g.

Trace amount Pt anchored on nitrogen-doped carbon nanoparticle with hollow capsule structure for efficient electrocatalytic oxygen reduction

The utilization of sustainable green energies requires the energy conversion devices to enhance the convenience of use and storage. The oxygen reduction reaction (ORR), as one of the necessary steps in the operation of these devices, exhibits a slow reaction kinetic rate that seriously affects energy conversion and output efficiency. Due to the low abundance and poor stability of Pt, it is essential to develop high-performance oxygen reduction catalysts with low Pt loading. In this work, a composite precursor consisting of ZIF-8 coupled with ferrocene and chloroplatinic acid was prepared, and subsequently derived to obtain nitrogen-doped carbon nanoparticles with hollow capsule morphology on the surface. These hollow capsule structure formed with the assistance of Pt and Fe significantly enhances the performance of Pt/FC@ZIF-8-C nanoparticles as the ORR electrocatalyst, exhibiting superior catalytic activity and stability compared to Pt/C at a low Pt loading (0.7 wt%). This is very important for promoting the design and preparation of Pt-based catalysts, as well as the application of energy conversion and storage devices in the field of green energy sources.

Alliance of atomic-scale/nanoscale Fe/Co active sites with hierarchically porous N-doped carbon frameworks for efficient electrocatalytic oxygen reduction

Alliance of atomic-scale/nanoscale Fe/Co active sites with hierarchically porous N-doped carbon frameworks for efficient electrocatalytic oxygen reduction

Controlling of coordination state of RuxNy clusters for efficient oxygen reduction electrocatalysis

Controlling of coordination state of RuxNy clusters for efficient oxygen reduction electrocatalysis

Universal Synthesis of Half-Metallic Diatomic Catalysts for Efficient Oxygen Reduction Electrocatalysis.

Developing efficient and low-cost noble-free metal electrocatalysts is an urgent requirement. Herein, a one-step, solid-state template-assisted method for fabricating isolated half-metallic diatomic M, Zn─N─C (M═Fe, Co, and Ni) catalysts is reported. In particular, the fabricated Fe, Zn─N─C structure exhibits superior oxygen reduction reaction capabilities with a half-wave potential of 0.867V versus RHE. The Mossbauer spectra reveal that the Fe, Zn─N─C half-metallic diatomic catalyst has a large proportion of the D2 site (ferrous iron with a medium spin state). Density functional theory (DFT) reveals that in Fe, Zn─N─C structures, the zinc sites play a unique role in accelerating the protonation process of O2 in ORR. In assembled zinc-air batteries, a maximum power density of 138mWcm-2 and a capacity of 748 mAhgzn-1 can be obtained. This work fabricates a series of efficient M, Zn─N─C diatomic electrocatalysts, and the developed solid-state reactionmethod can hopefully apply in other energy conversion and storage fields.

Efficient electrocatalytic two-electron oxygen reduction over aminophenol formaldehyde resin-derived carbon microspheres

The electrocatalytic 2-electron oxygen reduction reaction (2e-ORR) to hydrogen peroxide (H2O2) required cheap and efficient electrocatalytic materials. Herein cheap 3-aminophenol formaldehyde resin microspheres were synthesized at a large scale of about 15 g in one run. By annealing it, nitrogen-doped carbon spheres could be conveniently obtained, which was found to be efficient electrocatalyst for 2e-ORR with the highest H2O2 selectivity of about 94% at 0.4 V vs RHE. The electrolysis H2O2 production rate over N-doped carbon in 0.1 M KOH solution reached 48 mmol gcat-1h−1. Aminophenol formaldehyde resin-derived carbon provided a cheap and effective catalyst for electrocatalytic H2O2 production.

Hollow N-doped carbon spheres with anchored single-atom Fe sites for efficient electrocatalytic oxygen reduction

We anchored atomically dispersed Fe-N4 sites on hollow N-doped carbon spheres (Fe SAs/HNCSs-800) for electrocatalytic ORR; the obtained material exhibited electrocatalytic activity and stability comparable to that of commercial Pt/C, with an onset potential of 0.925 V and a half-wave potential of 0.867 V. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy results confirmed the presence of highly dispersed Fe single atoms in Fe SAs/HNCSs-800. The results of experiments and theoretical calculations show that the single-atom dispersed Fe-N4 serve as the ORR active sites, and the adjacent C defects can effectively regulate the electronic structure of Fe atoms and improve the electrocatalytic ORR activity.

Engineering carbon semi-tubes supported platinum catalyst for efficient oxygen reduction electrocatalysis

Innovation of catalyst structure is extremely important to develop the high-performance electrocatalysts for oxygen-reduction reaction (ORR). Herein, nitrogen-doped carbon semi-tube (N-CST) is used as a functional support for stabilizing the microwave-reduced Pt nanoparticles with an average size of ∼2.8nm to synthesize the semi-tubular Pt/N-CST catalyst. The contribution of interfacial Pt-N bond between N-CST support and Pt nanoparticles with electrons transfer from N-CST support to Pt nanoparticles is found by electron paramagnetic resonance (EPR) and X-ray absorption fine structure (XAFS) spectroscopy. This bridged Pt-N coordination can simultaneously help ORR electrocatalysis and promote electrochemical stability. As a result, the innovative Pt/N-CST catalyst exhibits excellent catalytic performance, realizing ORR activity and electrochemical stability superior to the commercial Pt/C catalyst. Furthermore, density functional theoretical (DFT) calculations suggest that the interfacial Pt-N-C site with unique affinity of O∗+ OH∗ can provide new active routes for the enhanced electrocatalytic ORR capacity.

Iron and nitrogen co-modified multi-walled carbon nanotubes for efficient electrocatalytic oxygen reduction

Multi-walled carbon nanotubes (MWCNTs) with one-dimensional nanostructure are an ideal support for oxygen reduction reaction (ORR) catalysts thanks to their intrinsic outstanding electrical conductivity and high specific surface area. Iron and nitrogen doping could alter the local electronic structure and therefore enhance the ORR activity of MWCNTs, but the preparation process always includes complicated growth conditions and post-treatment. Herein, an iron and nitrogen co-modified multi-walled carbon nanotubes (Fe–N-MWCNTs) with hierarchical nanostructure is engineered and synthesized via a simple two-step pyrolysis approach. Large specific surface area, low resistivity, and intensified charge density near the Fermi level synergistically endow the Fe–N-MWCNTs with outstanding ORR activity. The optimal Fe–N-MWCNTs exhibit a higher onset potential value of 0.92 V (versus RHE) and half-wave potential (E 1/2) of 0.85 V (versus RHE) in 0.1 M KOH medium, which exceeds the benchmark Pt/C electrocatalyst (E 1/2 = 0.84 V). This strategy of modifying MWCNTs support by a simple calcination process provides a feasible method to prepare cost-efficient ORR electrocatalysts.

Catalytic upcycling of waste polypropylene for gram-scale production of FeCo@N-doped carbon nanotubes toward efficient oxygen reduction electrocatalysis

Exploring novel low-cost and high-efficiency non-precious metal catalysts for use in oxygen reduction reactions (ORR) is of key importance. Based on catalytic pyrolysis of waste plastics, a facile method for preparing N-doped Fe/Co-encapsulated carbon nanotubes (FexCoy@NCNTs) was proposed. Particularly, gram-scale yield of the composite catalyst (3.87 g) was achieved in one pot with considerable atomic conversion rate of carbon (∼57.3 %) from waste polypropylene to high-quality CNTs, suggesting great potential for waste plastics valorization. The effects of Fe-to-Co ratios were studied by testing the ORR performance of each sample, indicating that as the Fe proportion increased, the ORR performance initially increased and then decreased. The Fe1Co1@NCNTs catalyst showed optimal performance which was comparable with commercial Pt/C catalyst: Particularly, an initial potential of 0.97 V vs RHE, a half-wave potential of 0.81 V vs RHE, and a limiting current density of –5.68 mA cm−2 were recorded. The encapsulated Fe and Co species in N-doped CNTs enhanced catalytic activity, while the porous carbon structure augmented the exposure of active sites. This strategy offers an auspicious platform for reusing waste plastics in the mass production of CNTs, and also provides an innovative approach for preparing low-cost, high-performance, and non-precious metal-based electrocatalysts for ORRs.

Gram-scale synthesis and unraveling the activity origin of atomically dispersed Co-N4O sites toward superior electrocatalytic oxygen reduction

Exploring highly efficient nonprecious metal-based single-atom catalysts (SACs) toward the electrocatalytic oxygen reduction reaction (ORR) is critical for the sustainable development of ORR-related energy conversion and storage systems. However, the scalable synthesis, delicate regulation of the coordination environment and molecular-level elucidation of the electrocatalytic mechanism remain challenging. Herein, we report a facile gram-scale synthesis of atomically dispersed Co sites anchored on N-doped carbon nanofibers (noted as Co-SA@N-CNFs) via a reliable predesigned phenolic resin-mediated strategy for efficient oxygen reduction electrocatalysis. The local coordination configuration of the single-atomic Co sites is proposed as the Co-N4O moiety with one O atom in the axial direction perpendicular to the Co-N4 plane. Theoretical calculations uncover that, compared with the common Co-N4 single sites, the formation of Co-N4O configuration is beneficial to reduce the reaction energy barrier, adjust the bond length between the metal sites and the intermediates, and also increase the electric conductivity. Therefore, the Co-SA@N-CNFs demonstrated distinguished ORR activity, outstanding electrochemical stability and methanol tolerance in KOH electrolyte. Furthermore, when assembled in liquid and flexible solid-state rechargeable zinc-air batteries (ZABs), the Co-SA@N-CNFs-equipped ZABs exhibited higher power densities, larger specific capacities and extraordinary cycling performance, compared with the Pt/C-based ZABs. The simple and robust methodology for the mass production of SACs and the engineered coordination environment for performance optimization inspire the future design of a wide range of SACs for energy devices.

A microwave-assisted decoration of carbon nanotubes with Fe3O4 nanoparticles for efficient electrocatalytic oxygen reduction reaction

The electrocatalytic oxygen reduction process (ORR) is one of the possible methods for producing sustainable energy, but its slow kinetics necessitates the use of inexpensive and efficient catalysts. Herein, Fe3O4 nanoparticles (Fe3O4 NPs) were loaded onto multiwall carbon nanotubes (Fe3O4@CNTs) using a single-step microwave-assisted strategy. The prepared Fe3O4@CNTs composite was characterized via multiple analytical techniques, and the results suggested a thin film of Fe3O4 NPs coating on the CNT surface, having a high specific surface area and pore volume. The prepared Fe3O4@CNTs composite exhibited a positive shift in ORR half-wave potential of 240 and 20 mV with respect to Fe3O4 and 20% Pt/C catalysts, respectively. The improved ORR activity of the Fe3O4@CNTs composite can be attributed to the synergetic interaction between CNTs and Fe3O4, which is also supported by theoretical simulations. Furthermore, the Fe3O4@CNTs composite showed superior cycling stability and remarkable methanol tolerance, proving its applicability as an ORR catalyst at a practical level. This research will aid in the development of microwave-based strategies for producing efficient ORR catalysts. It will also give a basic understanding of the relationships between composition, structure, and activity.