Electrocatalytic Oxygen Reduction Research Articles

Engineering bimetallic cluster architectures: harnessing unique “remote synergy effect” between Mn and Y for enhanced electrocatalytic oxygen reduction reaction

Engineering bimetallic cluster architectures: harnessing unique “remote synergy effect” between Mn and Y for enhanced electrocatalytic oxygen reduction reaction

First principle studies of oxygen reduction reaction on boron doped X-graphene nanoflakes (X = N, P and S) electrocatalysts

Heteroatoms in boron doped X-graphene nanoflakes (X = N, P and S) generate active site on the surface of catalysts; make it interesting to explore for electrocatalytic oxygen reduction reaction (ORR) which is vital for fuel cell applications. Comparative ORR processes on three different boron doped X-graphene nanoflakes (X = N, P and S) electrocatalysts in acidic medium is explored in this study using the density functional theory. The conceptual analysis of structure, energy profile, NBO, FMO and DOS plots is presented. Our results revealed that boron doped P-graphene nanoflakes has excellent catalytic performance and favors the ORR the most.

Guinier–Preston Zones Featuring PtCu Nanocrystals: Coherency Strain Fields Reshaping the Band Structure for Oxygen Reduction Electrocatalysis

Guinier–Preston Zones Featuring PtCu Nanocrystals: Coherency Strain Fields Reshaping the Band Structure for Oxygen Reduction Electrocatalysis

Two-Dimensional Covalent Organic Frameworks with Carbazole-Embedded Frameworks Facilitate Photocatalytic and Electrocatalytic Processes

Catalytic technologies are pivotal in enhancing energy efficiency, promoting clean energy production, and reducing energy consumption in the chemical industry. The pursuit of novel catalysts for renewable energy is a long-term goal for researchers. In this work, we synthesized three two-dimensional covalent organic frameworks (COFs) featuring electron-rich carbazole-based architectures and evaluated their catalytic performance in photocatalytic organic reactions and electrocatalytic oxygen reduction reactions (ORRs). Pyrene-functionalized COF, termed as FCTD-TAPy, demonstrated excellent photocatalytic performance for amino oxidation coupling and showed a remarkable preference for substrates with electron-withdrawing groups (up to >99% Conv. and >99% Sel). Furthermore, FCTD-TAPy favored a four-electron transfer pathway during the ORR and exhibited favorable reaction kinetics (51.07 mV/dec) and a high turnover frequency (0.011 s−1). In contrast, the ORR of benzothiadiazole-based FCTD-TABT favored a two-electron transfer pathway, which exhibited a maximum double-layer capacitance of 14.26 mF cm−2, a Tafel slope of 53.01 mV/dec, and a hydrogen peroxide generation rate of 70.3 mmol g−1 h−1. This work underscores the potential of carbazole-based COFs as advanced catalytic materials and offers new insights into the design of metal-free COFs for enhanced catalytic performance.

Host-guest-induced electronic state triggers two-electron oxygen reduction electrocatalysis

Supramolecular polymers possess great potential in catalysis owing to their distinctive molecular recognition and dynamic crosslinking features. However, investigating supramolecular electrocatalysts with high efficiency in oxygen reduction reaction to hydrogen peroxide (ORHP) remains an unexplored frontier. Herein, we present organic polymers for ORHP by introducing cyclodextrin-containing noncovalent building blocks, affording these supramolecules with abundant dynamic bonds. The electronic states and reaction kinetics are further well-modulated via a host-guest strategy, resulting in appropriate regional electron binding force and controllable chemical activity. Notably, integrating supramolecular units into phenyl group-containing model covalent polymer achieves a production rate of 9.14 mol g−1cat h−1, with 98.01% Faraday efficiency, surpassing most reported metal-free electrocatalysts. Moreover, the dynamic bonds in supramolecular catalysts can effectively regulate the binding ability of oxygen intermediates, leading to high reactivity and selectivity for the 2e− pathway. Supported by theory calculation and in situ experiment, C atoms (site–1) adjacent to the –C = N (N) group are potential active sites. This work pioneers host-guest strategy and provides inspiring ideas for the ORHP process.

“One‐Stone, Two‐Birds”: Zinc‐Rich Metal–Organic Frameworks as Precursors for High‐Entropy Zn‐Air Battery Electrocatalysts with Hierarchical Pore Structures

AbstractThe active sites of inexpensive transition metal electrocatalysts are sparse and singular, thus high‐entropy alloys composed of non‐precious metals have attracted considerable attention due to their multi‐component synergistic effects. However, the facile synthesis of high‐entropy alloy composites remains a challenge. Herein, we report a “one‐stone, two‐birds” method utilizing zinc (Zn)‐rich metal–organic frameworks as precursors, by virtue of the low boiling point of Zn (907 °C) and its high volatility in alloys, high‐entropy alloy carbon nanocomposite with a layered pore structure was ultimately synthesized. The experimental results demonstrate that the volatilization of zinc can prevent metal agglomeration and contribute to the formation of uniformly dispersed high‐entropy alloy nanoparticles at slower pyrolysis and cooling rates. Simultaneously, the volatilization of Zn plays a crucial role in creating the hierarchically porous structure. Compared to the zinc‐free HEA/NC‐1, the HEA/NC‐5 derived from the precursor containing 0.8 Zn exhibit massive micropores and mesopores. The resulting nanocomposites represent a synergistic effect between highly dispersed metal catalytic centers and hierarchical adsorption sites, thus achieving excellent electrocatalytic oxygen reduction performance with low catalyst loading compared to commercial Pt/C. This convenient zinc‐rich precursor method can be extended to the production of more high‐entropy alloys and various application fields.

"One-Stone, Two-Birds": Zinc-Rich Metal-Organic Frameworks as Precursors for High-Entropy Zn-Air Battery Electrocatalysts with Hierarchical Pore Structures.

The active sites of inexpensive transition metal electrocatalysts are sparse and singular, thus high-entropy alloys composed of non-precious metals have attracted considerable attention due to their multi-component synergistic effects. However, the facile synthesis of high-entropy alloy composites remains a challenge. Herein, we report a "one-stone, two-birds" method utilizing zinc (Zn)-rich metal-organic frameworks as precursors, by virtue of the low boiling point of Zn (907 °C) and its high volatility in alloys, high-entropy alloy carbon nanocomposite with a layered pore structure was ultimately synthesized. The experimental results demonstrate that the volatilization of zinc can prevent metal agglomeration and contribute to the formation of uniformly dispersed high-entropy alloy nanoparticles at slower pyrolysis and cooling rates. Simultaneously, the volatilization of Zn plays a crucial role in creating the hierarchically porous structure. Compared to the zinc-free HEA/NC-1, the HEA/NC-5 derived from the precursor containing 0.8 Zn exhibit massive micropores and mesopores. The resulting nanocomposites represent a synergistic effect between highly dispersed metal catalytic centers and hierarchical adsorption sites, thus achieving excellent electrocatalytic oxygen reduction performance with low catalyst loading compared to commercial Pt/C. This convenient zinc-rich precursor method can be extended to the production of more high-entropy alloys and various application fields.

Empowering Tri-Functional Palladium's Catalytic Activity and Durability in Electrocatalytic Formic Acid Oxidation Reaction via Innovative Self-Caging and Alloying Strategies.

Direct formic acid fuel cells (DFAFCs) stand out for portable electronic devices owing to their ease of handling, abundant fuel availability, and high theoretical open circuit potential. However, the practical application of DFAFCs is hindered by the unsatisfactory performance of electrocatalysts for the sluggish anodic formic acid oxidation reaction (FAOR). Palladium (Pd) based nanomaterials have shown promise for FAOR due to their highly selective reaction mechanism, but maintaining high electrocatalytic durability remains challenging. In this study, a novel Pd-based electrocatalyst (UiO-Pd-E) is reported with exceptional durability and activity for FAOR, which can be attributed to the Pd nanoparticles encapsulated within a carbon framework where concurrent chemical alloying of Pd and Zr occurs. Further, the UiO-Pd-E demonstrates noteworthy multifunctionality in various electrochemical reactions including electrocatalytic ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) in addition to the FAOR, highlighting its practical potentials.

Improving Active Site Local Proton Transfer in Porous Organic Polymers for Boosted Oxygen Electrocatalysis.

Improving proton transfer is vital for electrocatalysis with porous materials. Although several strategies are reported to assist proton transfer in channels, few studies are dedicated to improving proton transfer at the local environments of active sites in porous materials. Herein, we report on new Co-corrole-based porous organic polymers (POPs) with improved proton transfer for electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). By tuning the pore sizes and installing proton relays at Co corrole sites, we designed and synthesized POP-2-OH with improved proton transfer both in channels and at local Co active sites. This POP shows remarkable activity for both electrocatalytic ORR with E1/2=0.91 V vs RHE and OER with η10=255 mV. Therefore, this work is significant to present a strategy to improve active site local proton transfer in porous materials and highlight the key role of such structural functionalization in boosting oxygen electrocatalysis.

DFT modeling of the oxygen electroreduction reaction on SiN3-doped carbon nanotubes

The thermodynamic features and mechanism of the electrocatalytic oxygen reduction reaction were studied using the revPBE0-D3(BJ)/Def2-TZVP method on the example of (6,6)-armchair carbon nanotube doped with a tricoordinated silicon atom and nitrogen atoms of pyridinic and graphitic nature. Irreversible oxidation of the silicon center as a result of the formation of stable oxygen-containing adsorbates was shown. It was found that Si-poisoned structures are capable of participating in the catalysis of the target reaction along two- and four-electron routes at high overpotentials. For a nanotube doped simultaneously with pyridinic and graphitic nitrogens the potential possibility of eliminating the silicon atom from the catalyst composition in the form of orthosilicic acid and the participation of a silicon-free nitrogen-doped framework in the oxygen electroreduction reaction, for which the stage of tautomerization of pyridin-2(1H)-one to pyridin-2-ol is the limiting step was shown.

Boosting electrocatalytic oxygen reduction of Fe-Co polyphthalocyanine via the synergy of metal component optimization and axial ligand modification

Conjugated metal polyphthalocyanine (MPPc) organic skeletons, a kind of novel porous materials containing inherent M−N4 highly active sites, are of great significance for oxygen reduction reaction (ORR). Herein, bimetallic Fe-Co phthalocyanine covalent polymers (denoted as FeCoPPc) were prepared as ORR electrocatalysts through a solvothermal process and subsequent oxidation treatment. Meanwhile, the effect of axial oxygen-containing ligands of metal centers on the catalytic kinetic processes was also investigated. Benefiting from the highly exposed bimetal active sites and the finely designed ligand structure, FeCoPPc with optimized Fe/Co ratio and ClO3− coordination (Fe0.9Co0.1PPc-ClO3) displayed an outstanding ORR electrocatalytic activity and superior durability compared to 20 % Pt/C, manifested by an onset potential of 0.986 V vs. reversible hydrogen electrode (RHE) and a half-wave potential of 0.923 V vs. RHE in a 0.1 M KOH solution. This work may guide the rational design of high-performance electrocatalysts to regulate the catalytic activity.

Pt-decorated binary transition metal oxides (MnO-NiO, MnO-TiO2) for enhanced electrocatalysis of oxygen reduction and borohydride oxidation

Integrating transition metal oxides with precious metals is a strategic approach to designing cost-effective electrocatalysts with enhanced stability. Herein, platinum (Pt) nanoparticles (NPs) were prepared by microwave irradiation and anchored onto MnO and two binary metal oxides, MnO-NiO and MnO-TiO2, obtained by solid-state dispersion. Voltammetric and electrochemical impedance spectroscopy techniques evaluated their performance for oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) in alkaline media. Tafel slope and the number of exchanged electrons, n, were determined to compare the three electrocatalysts’ performance for fuel cell applications. Pt/MnO-NiO revealed a Tafel slope of 177 mV dec–1 for ORR and an n value of ca. 4 and 3 e- for ORR and BOR, respectively. These findings demonstrate that Pt NPs supported on binary metal oxide supports, particularly Pt/MnO-NiO, are promising electrocatalysts for ORR and BOR in alkaline media, thus recommending their use in direct borohydride fuel cells.

Nitrogen-doped carbon embedded with heterostructured Co3Fe7-Co5.47N nanoalloys for electrocatalytic oxygen reduction reaction in zinc-air battery

The oxygen reduction reaction (ORR) is the cathodic process in zinc-air batteries, but its sluggish kinetics significantly limit the energy conversion efficiency of these batteries. Therefore, developing high-performance ORR electrocatalysts is essential to support the advancement of zinc-air battery technology. Herein, a nitrogen-doped carbon embedded with heterostructured Co3Fe7-Co5.47N nanoalloys (FeCo@NC-900) was fabricated, and its electrocatalytic ORR activity and stability of FeCo@NC-900 were investigated in alkaline media. The FeCo@NC-900 catalyst exhibited a half-wave potential of 0.84 V, a Tafel slope of 76.06 mV·dec−1, and an electron transfer number (n) of approximately 3.83 for ORR. A rechargeable zinc-air battery was assembled using FeCo@NC-900 as the air cathode, achieving an open-circuit voltage of 1.435 V and a maximum power density of 81 mW cm−2, along with good cycling stability.

In Situ Construction of Highly Dispersed Pd on Cobalt Nanoparticle on Hollow Functional Cubic Graphene by Double Framework for ORR.

Developing advanced functional carbon materials is essential for electrocatalysis, caused by their vast merits for boosting many key energy conversion reactions. Herein, the covalent organic frameworks (COFs) is utilized on metal-organic frameworks (MOFs) as the template, under the controllable metal atoms thermal migration process successfully in situ constructs Pd-Co alloy nanoparticles on hollow cubic graphene. The electrocatalytic oxygen reduction reaction (ORR) evaluation showed excellent performances with a half-wave potential of 0.866V, and a limited current density of 4.975mA cm-2, that superior to the commercial Pt/C and Co nanoparticles. The contrast experiments and X-ray absorption spectrum demonstrated the aggregated electrons at highly dispersed Pd atoms on Co nanoparticle that promoted the main activities. This work not only enlightens the novel carbon materials designing strategies but also suggests heterogeneous electrocatalysis.

Regulating Fe Intermediate Spin States via FeN4‐Cl‐Ti Structure for Enhanced Oxygen Reduction

AbstractModulating the spin states of FeN4 moieties is critical for enhancing the electrocatalytic oxygen reduction reaction (ORR). In this study, Ti4N3Clx and Ti4N3Ox MXenes are synthesized and functionalized with iron phthalocyanine (FePc) to form model catalysts with well‐defined FeN4‐Cl‐Ti and FeN4‐O‐Ti structures, respectively. The FeN4‐Cl‐Ti structure, formed within the Ti4N3Clx/FePc composite, enables precise modulation of FeN4 spin states from low to intermediate spin, significantly enhancing ORR performance. In contrast, the FeN4‐O‐Ti structure in Ti4N3Ox/FePc shows less effective spin state modulation, leading to comparatively lower ORR activity. Compared to FePc and Ti4N3Ox/FePc, Ti4N3Clx/FePc demonstrates superior electrochemical performance, with an ORR half‐wave potential of +0.91 V versus RHE and doubled power densities in Zn–air batteries (214.5 mW cm−2). Theoretical studies confirm that the intermediate spin states induced by the weak‐field ligand‐modified FeN4‐Cl‐Ti structure in Ti4N3Clx/FePc facilitate electron filling in the antibonding orbital composed of Fe 3dz2 and O2 π* orbitals, greatly enhancing O₂ activation and ORR activity. These findings underscore the superior catalytic properties of FeN4‐Cl‐Ti compared to FeN4‐O‐Ti, advancing the understanding of spin state‐related catalytic mechanisms and guiding the design of high‐performance ORR catalysts.

Atomically dispersed Co-based species containing electron withdrawing groups for electrocatalytic oxygen reduction reactions.

Single-atom-based catalysts are a promising catalytic system with advantages of molecular catalysts and conductive supports. In this work, a new hybrid material (CoF/NG) is produced using a low-temperature reaction between an organometallic complex (Co(C5HF6O2)2) (CoF) and N-doped reduced graphene oxide (NG). CoF contains electron-withdrawing CF3 groups in the ligand around a Co atom. Microscopic and chemical characterization studies reveal that Co-based species are coordinated to N sites of NG and molecularly dispersed on the surface of NG. The CoF/NG hybrid shows improved electrocatalytic properties, such as onset (0.91 V) and half-wave (0.80 V) potentials, for the electrochemical oxygen reduction reaction (ORR) relative to the NG material. Control experiments reveal that Co-(N)graphene acts as a major active species for ORR. CoF/NG shows moderate cycling durability and microscopy measurements of CoF/NG-after-cycle indicate the formation of nanoparticles after electrocatalytic measurements. All experimental data support that the incorporation of Co-based organometallic species containing electron-withdrawing groups around the metal center onto the graphene-based networks improves the electrocatalytic ORR performance but diminishes the electrocatalytic stability of the active species.

Modulating the Bader Charge Transfer in Single p‐Block Atoms Doped Pd Metallene for Enhanced Oxygen Reduction Electrocatalysis

AbstractMetallene is considered as an emerging family of electrocatalysts due to its atomically layered structure and unique surface stress. Here we propose a strategy to modulate the Bader charge transfer (BCT) between Pd surface and oxygenated intermediates via p‐d electronic interaction by introducing single‐atom p‐block metal (M=In, Sn, Pb, Bi) into Pd metallene nanosheets towards efficient oxygen reduction reaction (ORR). X‐ray absorption and photoelectron spectroscopy suggests that doping p‐block metals could facilitate electron transfer to Pd sites and thus downshift the d‐band center of Pd and weaken the adsorption energy of O intermediates. Among them, the developed Bi−Pd metallene shows extraordinarily high ORR mass activity of 11.34 A mgPd−1 and 0.86 A mgPd−1 at 0.9 V and 0.95 V in alkaline solution, respectively, representing the best Pd‐based ORR electrocatalysts ever reported. In the cathode of a Zinc‐air battery, Bi−Pd metallene could achieve an open‐circuit voltage of 1.546 V and keep stable for 760 h at 10 mA cm−2. Theoretical calculations suggest that the BCT between Pd surface and *OO intermediates greatly affects the bond length between them (dPd‐*OO) and Bi doping could appropriately reduce the amount of BCT and stretch the dPd‐*OO, thus enhancing the ORR activity.

Ultrasmall Fe‐Nanoclusters‐Anchored Carbon Polyhedrons Interconnected with Carbon Nanotubes for High‐Performance Zinc‐Air Batteries

The catalytic activity of metal catalyst is closely related to its particle size. Yet, the size effect in electrocatalytic oxygen reduction reaction (ORR), an important reaction for metal‐air batteries and fuel cells, has not been clearly studied. Herein, a two‐step anchoring method is utilized to control the Fe catalyst in forms of nanoparticles (NPs), ultrasmall nanoclusters (NCTs), and isolated atoms as well as stabilized and dispersed by carbon polyhedrons interconnected with carbon nanotubes (CNTs). The uniformly distributed Fe NCTs displays superior ORR performance compared with Fe NPs, isolated Fe atoms, and commercial Pt/C. The brilliant ORR activity of Fe NCTs is a result of its unique electron structure and abundant edge and corner active sites. Due to the porous structure of carbon polyhedrons and high electron conductivity of CNTs, Fe NCTs also delivers an excellent discharge performance in zinc‐air battery with a peak power density of 213.3 mW cm−2 and long‐term stability. In these findings, a new strategy for the design of metal NCTs catalysts applied in various catalytic reactions is opened up.

Electrocatalytic oxygen reduction at non-metalated and pyrolysis free hypercrosslinked polymers

Oxygen reduction is one of the core steps of non-emissive zero carbon energy conversion. Therefore, enhancement of its sluggish kinetics is extremely important. Very recently researchers focused on oxygen electrocatalysis at porous polymers. Here we applied the non-metalated and pyrolysis free hypercrosslinked polymers with high specific surface area and abundant active sites. Electrode modified with the copolymer prepared from the twisted triphenylbenzene and N containing triphenyl amine exhibits electrocatalytic ORR in alkaline medium. Tafel slope value (0.067 V dec−1) indicates the efficient electrocatalytic activity and fast reaction kinetics. The lack of H2O2 product detected by scanning electrochemical microscopy suggests 4-electron path. The electrocatalytic activity of electrodes modified with hypercrosslinked polymers prepared from single monomers is also seen.

Regulating the evolution of interfacial species via B, N-codoped Pt sites for oxygen reduction electrocatalysis

The sluggish kinetics of the oxygen reduction reaction (ORR) poses significant limitations to the widespread application of the ORR in advanced energy systems. Here, we present a composite catalyst consisting of Pt nanoparticles immobilized on 3D B, N-doped graphene oxide (Pt/GO-BCN). Through X-ray absorption fine structure spectroscopy and synchrotron radiation infrared spectroscopy analyses, we discovered that the codoping of B and N significantly regulates the electronic structure of graphene and enhances the interaction between Pt nanoparticles and the supports. The electronic state-optimized 3D support promotes the uniform distribution of Pt nanoparticles with small size, forming a low-resistance interfacial environment to accelerate the cleavage of the *OOH species during the reaction process. The ORR activity and selectivity of Pt/GO-BCN significantly surpass those of commercial Pt/C catalysts, and excellent durability under long-term operation is achieved. These results provide a new avenue for the design of advanced Pt-based catalysts.