ORR Catalytic Performance Research Articles

Co–doped nitrogenated carbon nanotubes encapsulating CoNi alloys as bifunctional catalysts for urea-assisted rechargeable Zn-air battery

As a desirable alternative for oxygen evolution reaction (OER), urea oxidation reaction (UOR) with the effectively reduced overpotential has attracted considerable attention in pollutant degradation and rechargeable Zn-air battery (ZAB). Herein, a bifunctional electrocatalyst with CoNi alloy and Co–N dual active sites encapsulated by nitrogen-doped carbon nanotubes have been rationally designed and successfully prepared. The as-obtained catalyst CoNi/Co–NCNT displays excellent catalytic activity for oxygen reduction (ORR) and UOR with a narrow potential difference of 0.56 V. The urea-assisted rechargeable ZABs based on CoNi/Co–NCNT provide higher energy conversion efficiency (61%), 15% higher than that of conventional ZABs. In addition to verify the UOR pathway on the CoNi/Co–NCNT, DFT calculations reveal that CoNi alloy and Co–N in CoNi/Co–NCNT synergistically function as the main active sites for ORR and UOR. The excellent ORR catalytic performance and the superior energy conversion efficiency of CoNi/Co–NCNT based urea-assisted rechargeable ZAB is expected to accelerate the practical application of ZAB technology. This work paved a new way for the development of bifunctional catalysts for higher efficiency ZABs, and also provides a potential scheme for disposing urea rich wastewater.

The Asymmetrical Fe-O-Se Bonds in Fe2O(SeO3)2 Boosting Bifunctional Oxygen Electrocatalytic Performance for Zinc-Air Battery.

Zinc-air batteries (ZABs) have the advantages of high energy density and rich zinc raw materials. It is a low-cost, green and sustainable energy storage device. At present, one of the key technologies that hinder the large-scale application of ZABs is the design and fabrication oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) bifunctional catalysts with excellent performance, especially the non-platinum-based catalysts. Here N-doped carbon-coated Fe-based selenium oxide catalyst Fe2O(SeO3)2/Fe3C@NC with high performance has been fabricated by a one-step pyrolysis and then the electrochemical oxidization. The experimental results confirmed that the existence of Fe-O-Se bonds in Fe2O(SeO3)2 crystal phase of Fe2O(SeO3)2/Fe3C@NC, and the Fe-O-Se bonds could obviously enhance ORR and OER catalytic performance of Fe2O(SeO3)2/Fe3C@NC. Density functional theoretical calculations (DFT) confirmed that the Fe2O(SeO3)2 in Fe2O(SeO3)2/Fe3C@NC had a higher d-band center of Fe atom and a lower p-orbital coupling degree with its own lattice O atom than Fe2O3, which leads to Fe site of Fe2O(SeO3)2 being more likely to adsorb external oxygen intermediates. The Fe-O-Se bonds in Fe2O(SeO3)2 results in the modification of coordination environment of Fe atoms and optimizes the adsorption energy of Fe site for oxygen intermediates. Compared with Fe2O3/Fe3C@NC, the Fe2O(SeO3)2/Fe3C@NC showed the obvious enhancements of ORR/OER catalytic activities with a half-wave potential of 0.91 V for ORR in 0.1 M KOH electrolyte and a low overpotential of 345 mV for OER at 10 mA cm-2 in a 1.0 M KOH electrolyte. The peak power density and specific capacity of Fe2O(SeO3)2/Fe3C@NC-based ZABs are higher than those of Pt/C+RuO2-ZABs. The above results demonstrate that the asymmetrical Fe-O-Se bonds in Fe2O(SeO3)2 plays a key role in improving the bifunctional catalytic activities of ORR/OER for ZABs.

In situ green architecture of the 3D FeZn-N-C based electrocatalyst for efficient oxygen reduction.

We prepared a 3D FeZn-N-C based catalyst by green in situ growth of 1D Fe-N-C carbon nanotubes by introducing ferrocyanide ions on the surface of 2D exfoliated MOF-5. The 1D/2D FeZn-N-C based electrocatalyst is conducive to O2 diffusion and ionic/electron transfer, exhibiting an excellent ORR catalytic performance and a peak power density of 294 mW cm-2 for Zn-air batteries.

Improving the ORR catalytic performance of hollow porous carbon derived from F127 assembled in ethanol-hexane mixture containing Fe3+ ion

Improving the ORR catalytic performance of hollow porous carbon derived from F127 assembled in ethanol-hexane mixture containing Fe3+ ion

Surface modified FeCoZn-ZIF derived polyhedral electrocatalysts for ORR under alkaline and acidic conditions

Electrocatalysts for catalyzing oxygen reduction reactions at variable pH conditions are essential for energy conversion and storage. Herein, Fe@FeCoZn–CN electrocatalysts were prepared with internal and external doping approach. The Fe@FeCoZn–CN electrocatalyst exhibits a desirable ORR performance in both acid and alkaline electrolytes. Specifically, the half-wave potential (E1/2) of Fe@FeCoZn–CN electrocatalyst is 0.890 V which far beyond Pt/C electrocatalyst (0.839 V) in alkaline electrolyte. In addition, Fe@FeCoZn–CN electrocatalyst also exhibits improved ORR activity (E1/2 = 0.801 V) compared to Pt/C (0.797 V) electrocatalysts in acidic electrolytes. What's exciting is that the rechargeable ZABs based on Fe@FeCoZn–CN electrocatalysts exhibit an impressive performance with a favorable open-circuit potential of 1.517 V and a promising specific capacity is 833.7 mA h gzn−1, good charge/discharge cycle stability. The remarkable ORR catalytic performance of Fe@FeCoZn–CN electrocatalysts can be traced to the internal doping of metals which prevent excessive metal aggregation and surface modified which can increase the metal loading to expose more active sites.

Nanoflower-like NiCo2O4 Composite Graphene Oxide as a Bifunctional Catalyst for Zinc-Air Battery Cathode.

Developing efficient bifunctional catalysts for nonprecious metal-based oxygen reduction (ORR) and oxygen evolution (OER) is crucial to enhance the practical application of zinc-air batteries. The study harnessed electrostatic forces to anchor the nanoflower-like NiCo2O4 onto graphene oxide, mitigating the poor inherent conductivity in NiCo2O4 as a transition metal oxide and preventing excessive agglomeration of the nanoflower-like structures during catalysis. Consequently, the resulting composite, NiCo2O4-GO/C, exhibited notably superior ORR and OER catalytic performance compared to pure nanoflower-like NiCo2O4. Notably, it excelled in OER catalytic activity of the OER relative to the precious metal RuO2. As a bifunctional catalyst for ORR and OER, NiCo2O4-GO/C displayed a potential difference of 0.88 V between the ORR half-wave potential and the OER potential at 10 mA·cm-2, significantly lower than the 1.08 V observed for pure flower-like NiCo2O4 and comparable to the 0.88 V exhibited by precious metal catalysts Pt/C + RuO2. The NiCo2O4-GO/C-based zinc-air battery demonstrated a discharge capacity of 817.3 mA h·g-1, surpassing that of precious metal-based zinc-air batteries. Moreover, charge-discharge cycling tests indicated the superior stability of the NiCo2O4-GO/C-based zinc-air battery compared to its precious metal-based counterparts.

Investigating the effect of Fe–N5 configuration in the oxygen reduction reaction using N-heterocycle functionalized carbon nanotubes

The ORR catalytic performance of penta-coordinated FePc/N-CNTs was significantly influenced by the local surface structure surrounding the axial ligand on the functionalized CNTs.

Rhein/carbon nanotube derived carbon materials with quinone group for hydrogen peroxide electrosynthesis

Oxygen-doped carbon materials (OC) have been studied as the electrocatalysts of two-electron oxygen reduction reaction (2-e ORR) to synthesize H2O2 due to their low cost and high selectivity. In this study, quinone group contained OC (OC-R/CNT) were prepared using the mixture of rhein with quinone group and carbon nanotube (CNT) as the precursor via one-step pyrolysis. The RRDE test showed that the OC-R/CNT gave a H2O2 selectivity of 94 % at 0.20 V in neutral medium. During the H-cell test, the H2O2 yield of OC-R/CNT can be up to 170 mmol gcat−1 h−1 at 0 V vs. RHE and the OC-R/CNT catalyst exhibited good long-term stability and reusability. The H2O2 solution produced at 0 V vs. RHE for 1 hour showed good bactericidal properties. For comparison, the OC without quinone group (OC-G/CNT) were also prepared with glucose and CNT as the precursor under the same condition, which showed poorer 2-e ORR catalytic performance. This study not only provides a feasible method to prepare quinone group contained carbon materials but also verifies the important role of quinone group in 2-e ORR.

Preparation of 1D Porous Fe-N-C based ORR Electrocatalysts by Pyrolysis of Trace Fe-doped ZIF-8/PAN Electrospun Fibres

The development of a simple and efficient method for batch preparation of porous Fe-N-C catalysts is of great significance for it large-scale application. Electrostatic spinning is a common method that can be used to produce carbon-based catalysts on a large scale simply by increasing the number of needles. However, it is still difficult to control the pore structure and composition of the pyrolysis products of electrostatically spun fibers by modulating the composition. In this paper, highly graphitized one-dimensional Fe-N-C catalysts with a large number of open pores were prepared by pyrolysis of electrospun fibres of trace Fe-doped ZIF-8 particles with PAN. The materials were structurally and compositionally analyzed using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption-desorption test. The electrocatalytic ORR performance of the catalysts was characterized by cyclic voltammetry, linear scanning voltammetry, and rotating ring-disk electrode tests. The results show that trace Fe doping achieves a transition from closed to open pores, exposing the active sites within the pores to allow them to participate efficiently in the reaction. Fe could catalyze the formation of surface graphite structures during pyrolysis, which reduces the charge transfer resistance and indirectly increases the ORR reaction rate. The formation of highly reactive Fe-N-C and graphite-N sites, the optimization of pore structure and the enhancement of graphitization allow 5% Fe-NC to achieve excellent ORR catalytic performance beyond that of commercial 20% Pt/C.

Facile synthesis of ultrathin S-N co-doped carbon nanosheet as ORR electrocatalysts for application in sustainable zinc-air battery

The exploration of inexpensive, efficient electro-materials for oxygen reduction reactions in the field of zinc-air batteries has attracted the attention of researchers. Metal-free carbon catalysts with adulteration heteroatoms have been considered in recent years as the most promising alternative to conventional Pt-based electrocatalysts. Herein, we have researched a simple and high-performance grinding and pyrolyzing strategy for the preparation of S-N co-doped carbon nanosheets (S-N-C) with a 3D ultrathin structure that serves as resultful catalysts for ORR in zinc-air batteries. As expected, the prepared S-N-C 1000 catalysts have a super-colossal specific surface area and exhibit splendid ORR catalytic performance with half-wave potentials up to 0.858 V, which is superior to Pt/C. Furthermore, S-N-C 1000 catalysts show good stability and resistance to methanol poisoning. Additionally, the zinc-air batteries employing S-N-C 1000 as the air cathode also show excellent electrochemical performance. The power density of 164.68 mW cm−2, the cycling stability of more than 600 h at 5 mA cm−2, and the specific capacity of 830.85 mAh gZn−1 point to a possible application in zinc-air batteries. Therefore, this effective and environmentally friendly synthetic method may present a novel use for non-metallic heteroatom-doped carbon materials in zinc-air batteries.

Co–Pyridinic-N Bond Constructed at the Interface of CoxP and N-Doped Carbon to Effectively Facilitate Oxygen Reduction

The construction of bonding interfaces between cobalt-base phosphides and N-doped carbon is considered an effective means to promote ORR catalytic performance. However, the role of different nitrogen configurations in promoting the ORR performance of cobalt-base phosphides is currently unknown. Herein, the honeycomb-like CoxP@N-doped carbon catalyst was constructed to systematically investigate the effect of different nitrogen configurations on improving the catalytic performance of CoxP. Systematic experimental investigations and density functional theory (DFT) calculations indicate that the interaction of Co with pyridinic-N not only regulates the atomic Co coordination environment but also induces strong orbital hybridization between N-p orbitals and Co-d orbitals, significantly increasing the electron density on pyridinic-N sites, which greatly increases the attraction to oxygen-containing intermediates and lowers the reaction energy barrier, thus promoting the catalytic activity for ORR. Furthermore, honeycomb morphology not only reduces the internal diffusion resistance of reactants and products as well as the relative concentration of surface reactants but also exposes more accessible active sites and increases the contact area with the electrolyte, thus greatly enhancing the oxygen reduction reaction. As expected, the as-prepared catalyst exhibits ultrahigh ORR activity with a half-wave potential of 0.88 V, which is superior to that of the noble metal Pt and most previously reported non-noble metal catalysts. This study perfectly explains why cobalt-base phosphide embedded in N-doped carbon can improve its ORR catalytic performance.

First principles calculation study of single transition metal atom grafted Au25 as efficient electrocatalysts for OER and ORR

The method of grafting metal atoms by ligands can construct 'grafted single-atom catalysts' with good catalytic activity without destroying the cluster structure. In this study, the catalytic performance of Fe2+, Co2+ and Ni2+ grafted Au25(SR)18 cluster through l-cysteine ligand as bridging ligand (denoted as Au25-nCys-M, where n is the number of grafted Cys-ligand) in OER and ORR was investigated by density functional theory (DFT) simulations. A volcanic diagram between the overpotential of OER and ORR and the adsorption free energy of intermediates on Au25–nCys-M was determined, which showed that the adsorption strength of oxygenated intermediates can be adjusted by the grafting method and the number of bridging ligands, thus affecting the catalytic performance. Among three kinds of metal ions, the grafted Ni2+single atom catalysts showed excellent bi-functional OER and ORR activities. In particular, the Au25–1Cys-Ni2+ (n = 1) had the lowest overpotentials of 0.48 and 0.27 V for OER and ORR. Through in-depth analysis, we found that the spin magnetic moments of metal cations can be used as the descriptor of the catalytic performance of the grafted single atom catalyst. The excellent catalytic performance of Au25–nCys-Ni2+was originated from the smaller spin magnetic moment of Ni2+. These findings provided new idea for the preparation of nanocomposites with excellent OER and ORR catalytic performance.

Optimizing reaction intermediate adsorption by engineering the coordination structure of single-atom Fe–N5–C electrocatalysts for efficient oxygen reduction

Guided by DFT calculation results, the FeN5single-atom catalyst with asymmetric coordination is fabricated by axially anchoring FeN4species with the N atom doped on graphene and shows extraordinary ORR catalytic performance.

Kapok fiber derived biochar as an efficient electro-catalyst for H2O2 in-situ generation in an electro-Fenton system for sulfamethoxazole degradation

Developing highly efficient, low-cost, and environmental-friendly catalysts to generate hydrogen peroxide (H2O2) through two-electron oxygen reduction reaction (2e−–ORR) is very important for the electro-Fenton systems. In this work, nitrogen (N) self-doped biochar were synthesized through the carbonization of natural Kapok fiber (KF), and they were used as 2e−–ORR catalysts to generate H2O2 in electro-Fenton systems. The KF-derived biochar that carbonized at 700 °C (named as KFBC-700) exhibited the optimal 2e−–ORR catalytic performance. The pyridinic-N and COOH played key roles on O2 adsorption and reduction. The maximum H2O2 accumulated concentration of the KFBC-700 electro-Fenton system was as high as 108.5 mg/L. Sulfamethoxazole (SMX) can be completely removed through both the Fe2+ catalyzed homogeneous and the FeOCl mediated heterogeneous electron-Fenton reactions within 60 min. Moreover, the electro-Fenton systems showed an excellent stability and reusability for SMX degradation. Additionally, SMX was possibly degraded through three pathways according to the detected degradation intermediates. This paper for the first time used KF-derived biochar as 2e−-ORR catalysts of the electro-Fenton system, and obtained a prominent H2O2 in-situ generation efficiency and a high efficient SMX removal.

Electronic Perturbation of Platinum Alloy By Transition Metal-Doping Towards Improved ORR Activity and Stability

As of today, Pt-based catalysts are the predominant ORR catalysts that meet the desired activity requirements of ORR in fuel cells. However, their broader applications are still challenging due to highly sluggish ORR kinetics, limited stability and higher cost of Pt. In order to develop novel electrocatalyst materials, herein we report surface tuning of binary PtCo alloy through transition metal doping, which reveals superior ORR activity achieving a mass activity of 2.07 A mgPt -1 at 0.9 V vs. reversible hydrogen electrode (RHE) and excellent durability with minor degradation after 30000 cycles. The ternary PtCoMn@NGNS alloy prepared through facile molten salt pyrolysis reveals a strong metal-support interaction via metal-nitrogen-graphene coordination.Furthermore, Mn dopants alter the electronic structure of Pt alloy, which improves the oxygen-intermediate binding energy on the interface and suppress the Co dissolution through unique configuration, resulting in enhanced activity and durability of the catalyst. According to the DFT calculations, the surface Mn extensively adsorbs an OH, resulting in increased surface Co stability and overall ORR catalytic performance. Therefore, it is understandable that the development of ternary Pt alloy results in considerable changes in the structural and electrical characteristics of metal overlayer, which varies dramatically from monometallic surfaces.Our experimental results corroborated by theoretical calculations show that electronic perturbation of PtCo by Mn doping stabilizes the Co and causes significant strain in the Pt(111), which accounts for the increased ORR performance. The strained lattice of Pt caused by Co alloying and surface segregation of Mn both play important roles in the increased ORR activity. Similarly, the Pt3CoMn-OH configuration diminishes Co dissolution and improves overall stability. It is anticipated that such a facile preparation of high-performance electrocatalysts will advance the practical applications of ORR catalysts.Figure 1: Figure 1

FeNx nanoparticles embedded in three-dimensional N-doped carbon nanofibers as efficient oxygen reduction reaction electrocatalyst for microbial fuel cells in alkaline and neutral media

Herein, an approach is reported for the fabrication of 3D carbon nanofibers (CNFs) wrapped by carbon nanotubes (CNT) with graphitic carbon-encased FeNx nanoparticles originated from metal–organic frameworks (MOFs). It is found that Fe-FeNx@N-CNT/CNFs exhibits outstanding catalytic activity towards ORR, whose half-wave potential are 0.89 V and 0.87 V in alkaline and neutral environments, respectively, much higher than MOF-based catalysts reported so far and commercial Pt/C. When the obtained cathode catalysts are loaded in MFCs for power generation test, the experimental consequences show that the Fe-FeNx@N-CNT/CNFs cathode exhibits a supernal power density of 742.26 mW·m−2 and output current density of 3241 mA·m−2 which are comparable to Pt/C. The splendid ORR catalytic performance is mainly attributable to the three-dimensional structure of carbon nanofibers and the active sites of Fe-Nx. These result in a higher graphitization degree beneficial for electronic mobility, high specific surface area, benign mesoporous nanostructure and excellent mass transfer capability. The strategy provides a new scheme to devise and research Fe-Nx electrocatalysts with MOF-based for the conversion of clean and environment-friendly energy.

Tailoring 2-electron oxygen reduction reaction selectivity on h-BN-based single-atom catalysts from superoxide dismutase: A DFT investigation

The production of hydrogen peroxide (H2O2) plays an important role in human lives. Currently applying the two-electron oxygen reduction reaction (2e- ORR) to synthesis of H2O2 is regarded as a promising strategy to substitute the traditional anthraquinone method;however, design of efficient 2e- ORR catalysts remains difficulties. Inspired by superoxide dismutase, which can covert superoxide (•O2–) to H2O2. We design eight types of 2e- ORR catalysts in which Ni is embedded on defective boron nitride (h-BN) which coordinates with non-metal atoms (B, N, O, S) doping to imitate the active center of superoxide dismutase. Density functional theory (DFT) computations demonstrate that NiN2S2/BN has the most favorable 2e- ORR catalytic performance with the overpotential of 0.11 V. Especially, the competitive 4e- ORR pathway can be significantly suppressed, as indicated by favorable thermodynamics with more positive Gibbs free energies of O* above 3.52 eV. Besides, coordination environments change induced different adsorption behavior of O2, electron density around Ni, and work function are unveiled. Our work is expected to provide useful understanding for development of novel high-efficiency h-BN-based single-atom catalysts for 2e- ORR.

Investigations on the ORR Catalytic Performance Attenuation of a 1D Fe Single-Atom Catalyst during the Discharge Process

Investigations on the ORR Catalytic Performance Attenuation of a 1D Fe Single-Atom Catalyst during the Discharge Process

Efficient synthesis of Pt3Co/NC alloy catalysts with enhanced durability and activity for the oxygen reduction reaction

Lack of catalytic performance, short life, and high cost are three main problems related to JM-Pt/C catalysts for proton exchange membrane fuel cells. The introduction of cheap transition metals improves catalytic performance while significantly reducing the cost of the catalysts. Here, we report the synthesis of Pt3Co/NC alloy catalysts via coating and pyrolysis treatment. The agglomeration of nanoparticles during the high-temperature alloying process is significantly inhibited by coating with PANI. Remarkably, the obtained Pt3Co/NC alloy catalysts exhibit excellent ORR catalytic performance and structural stability in 0.1 mol/L HClO4. After 30,000 potential cycles, the mass activity and area-specific activity of Pt3Co/NC alloy catalysts are 1.949 and 3.936 times higher, respectively, than that of JM-Pt/C with negligible performance loss. The strong metal-support interaction between N and Pt and the Pt-rich surface restrict the dissolution of Pt and Co, resulting in excellent stability. This synthesis approach provides an effective way to develop active and stable Pt alloy catalysts.

Synthesis of one-dimensional vanadium-doped CoS/Co9S8 heterojunctions as bifunctional electrocatalysts for zinc-air battery

Cobalt-based electrocatalysts have been considered promising materials for the oxygen evolution reaction (OER). Herein, we now report the synthesis of vanadium-doped CoS/Co9S8 heterostructures embedded on carbon nanorods (V-CoS/Co9S8@CNR), which was realized through one-step sulfurization of Zeolitic Imidazolate Framework-67 (ZIF-67) grown on V2O5 nanorods (V2O5@ZIF-67). The results of experiment and theoretical calculation verified that because of the vanadium dopant and the coupled nanointerface that can expedite the synergistic effect of Co9S8 and CoS, the obtained V-CoS/Co9S8@CNR showed an excellent OER catalytic performance (269 mV@10 mA/cm2) and comparable ORR catalytic performance. The assembled rechargeable Zn-air batteries displayed a superior performance as well as high charging–discharging cycling stability (>200 h) with a slight increase in the voltage gap.