ORR Catalysts Research Articles

Humidity-Induced Degradation Mapping of Pt3Co ORR Catalyst for PEFC by In-Operando Electrochemistry and Ex Situ SAXS.

Understanding the degradation mechanisms of Pt-alloy catalysts is crucial for enhancing their durability. This study investigates the impact of relative humidity on Pt and Pt3Co catalysts using potential-cycling-based accelerated stress tests. Two conditions are investigated: 100% relative humidity on both sides, and a gradient with 30% at the anode and over 100% at the cathode. Pt3Co demonstrates sensitivity, with 77% performance loss and reductions in electrocatalyst surface area. Results demonstrate a 30% decrease in potential loss for Pt catalysts and a 77% increase for Pt3Co catalysts, indicating significant performance degradation in high humidity conditions, with Pt3Co exhibiting greater sensitivity. Measurements of electrochemically active surface area reinforce these findings. Resistance analysis using electrochemical impedance spectroscopy using equivalent circuit modeling reveals a threefold increase in Pt3Co MEAs' cathode charge transfer resistance and mass transport resistance during accelerated stress tests. Local current distribution analysis highlights differences between Pt catalyst and Pt3Co, with the latter displaying dealloying effects. Small-angle X-ray scattering reveals changes in particle and cluster sizes, indicating structural changes. Scanning electron microscopy highlights catalyst and membrane thickness variations, suggesting heterogeneity in Pt3Co. Under humidity gradients, Ostwald ripening plays a significant role in altering the catalyst's Pt3Co structure and subsequently impacting its performance.

Building Cobalt-Nickel Diatomic Sites as Oxygenophilic ORR Catalyst with Strong Cl--Corrosion Resistance for Seawater Batteries.

The seawater battery (SWB) holds great potential as the next-generation energy supply system for marine electrical equipment. However, its efficiency and durability are hindered by low oxygen concentration and harmful Cl- adsorption and corrosion in seawater. Herein, a host-guest strategy is developed to fabricate diatomic catalysts with adjacent Co and Ni sites on nitrogen-doped carbon (CoNi-DAC), where Co and Ni atoms are each coordinated to three nitrogen atoms. Theoretical calculations and in situ characterization reveal that the synchronized reduction of Co and Ni valence states enhances ORR kinetics by optimizing the O2 adsorption energy barrier, facilitating direct O─O bond cleavage and preventing *OOH intermediate formation. This electronic modulation enhances oxygenophilicity and Cl- corrosion resistance. The Co/Ni diatomic sites synergistically improve ORR catalytic activity, achieving a half-wave potential (E1/2) of 0.79V and exceptional long-term durability of nearly 700 h in natural seawater. The assembled SWB with CoNi-DAC coated carbon brush electrode attains a peak power density of 3.3W L-1. This work offers valuable insights into the design and development of advanced ORR electrocatalysts for natural seawater environments.

Atomically Dispersed High-Active Site Density Copper Electrocatalyst for the Reduction of Oxygen

Enlarging the M-Nx active-site density is an effective route to enhance the ORR performance of M-N-C catalysts. In this work, a single-atom catalyst Cu–N@Cu–N–C with enlarged Cu–N4 active site density was prepared by the second doping and pyrolysis (SDP) of Cu–N–C derived from Cu-doped zeolite imidazole frameworks. The half-wave potentials of Cu–N@Cu–N–C were measured as 0.85 V in alkaline electrolyte and 0.75 V in acidic media, which was 50 mV and 60 mV higher than that of Cu–N–C, respectively. N2 adsorption–desorption isotherm curves and corresponding pore distribution analysis were used to verify the successful filling of additional Cu and N in micropores of Cu–N–C after SDP. The obvious increase in Cu contents for Cu–N@Cu–N–C (1.92 wt%) compared with Cu–N–C (0.88 wt%) tested by ICP demonstrated the successful doping of Cu into Cu–N–C. XAFS analysis confirmed the presence of Cu–N4 single-atom active centers in Cu–N@Cu–N–C. The N 1 s high-resolution XPS results proved a great increase in Cu–N4 contents from 13.15% for Cu–N–C to 18.36% for Cu–N@Cu–N–C. The enhanced ORR performance of Cu–N@Cu–N–C was attributed to the enlargement of Cu–N4 active site density, providing an effective route for the preparation of efficient and low-cost ORR catalysts.

Strong metal-support interaction induced by oxygen vacancies to enhance the activity and durability of Pt/TiO2/ hollow carbon nanospheres ORR catalyst

For the commercial Pt-loaded carbon ORR catalysts used in proton exchange membrane fuel cells (PEMFC), carbon support corrosion, along with the migration and aggregation of Pt nanoparticles (NPs) due to the weak interaction between Pt NPs and carbon, leads to a drastic reduction in both electrocatalytic activity and stability. Hence, exploring active and steady supports is crucial to restrain the activity loss and stabilize Pt catalysts. In this work, a composite support consisting of hollow carbon nanospheres (HC) and TiO2 NPs with abundant oxygen vacancies (OV) loaded with Pt NPs (PTHC-H) was designed and synthesized. Experiment results show that PTHC-H exhibits superior activity and stability compared to PTHC-N (TiO2 with lower OV content) and commercial Pt/C catalyst. Specifically, PTHC-H delivers a half-wave potential of 0.883V versus reversible hydrogen electrode. And its mass activity and half-wave potential decrease by only 15.96% and 7mV, respectively, after 10,000 cycles of accelerated durability testing. The excellent activity and stability are ascribed to the enhanced metal-support interaction induced by OV, which can optimize the Pt d-band center and suppresses the migration and aggregation of Pt NPs. This work may be favorable for designing efficient and durable anti-corrosion nano catalysts.

Magnetic field-enhanced two-electron oxygen reduction reaction using CeMnCo nanoparticles supported on different carbonaceous matrices

The current study illustrates the successful synthesis of Ce1.0Mn0.9Co0.1 nanoparticles, characterized through XRD, EPR, magnetization curves, and TEM/HRTEM/EDX analyses. These nanoparticles were then loaded into the carbon Vulcan XC72 and the carbon Printex L6 matrices in varying amounts (1, 3, 5, and 10 % w/w) via wet impregnation method to fabricate electrocatalysts for the 2-electron ORR. Before experimentation, the material was characterized via XPS and contact angle measurements. The electrochemical results produced significant findings, indicating that the electrocatalysts with the nanostructures modifying both carbon blacks notably augmented currents in rotating ring-disk electrode measurements, signifying enhanced selectivity for H2O2 production. Moreover, our research underscored the significant impact of Magnetic Field-Enhanced Electrochemistry, employing a constant magnetic field strength of 2000 Oe, on 2-electron ORR experiments. Particularly noteworthy were the observed results surpassing the ones without the magnetic field, demonstrating heightened currents and improved selectivity for H2O2 production (more than 90 %) facilitated by CeMnCo nanoparticles. These significant findings in electrocatalytic efficiency have practical implications, suggesting the potential for developing more efficient and selective catalysts for the 2-electron ORR.

First principles study of V2CT2-based MXenes materials in oxygen reduction and oxygen evolution reactions

The development of bifunctional ORR/OER electrocatalysts with low cost, high activity and sustainable cycle plays an important role in improving the performance of new green energy storage and conversion devices to alleviate the energy crisis and environmental pollution. As a graphene-like two-dimensional inorganic layered compound with unique electrochemistry, MXenes materials have attracted more and more attention in the field of electrocatalytic applications. In this paper, based on the first-principles calculation method based on density functional theory (DFT) and quantum mechanics, an effective scheme for designing efficient ORR/OER bifunctional electrocatalysts by introducing Pd/Pt single atoms to regulate the electronic structure of V2CT2 (T = O, F) is proposed. Firstly, we discussed the stability of the designed series of single-atom catalysts by calculating the formation energy, binding energy and molecular dynamics simulation. Secondly, by comparing the theoretical overpotentials of these single-atom catalysts for ORR and OER, we found that among the designed SACs, V2CO2-Pd, V2CF2-Pd and V2CO2-VO-Pt are catalysts with good bifunctional catalytic activity for ORR/OER. Our work provides some guidance for the application of MXenes materials in the field of electrocatalysis.

Effect of Annealing Time on Various PtNi/C Binary Alloy Catalysts for ORR in PEFCs

Polymer electrolyte fuel cells (PEFCs) are used in automotive power supplies due to their advantages of low environmental impact and high energy conversion efficiency. However, Pt used for electrocatalysts is expensive and its activity and durability are problematic. In this study, the PtNi/C catalysts were prepared with different annealing times and the oxygen reduction reaction activity was evaluated. The linear sweep voltammograms and current-voltage curves showed that the PtNi/C catalysts annealing time for 60 min performed better than the commercial catalyst. This would be attributed to the internal alloying of Ni and better electronic structure due to the longer annealing time.

Effect of Porous and Highly N,O-Doped Amorphous Carbon Materials with Defects Generated by KOH Etching on the Stability of ORR Catalysts

Effect of Porous and Highly N,O-Doped Amorphous Carbon Materials with Defects Generated by KOH Etching on the Stability of ORR Catalysts

Metal Doped Nanocages and Metal Doped Nanotubes as Effective Catalysts for ORR and OER

Metal Doped Nanocages and Metal Doped Nanotubes as Effective Catalysts for ORR and OER

Simplified Ftacv Model to Quantify the Electrochemically Active Sitedensity in PGM-Free ORR Catalysts

The development of platinum group metal-free catalysts is considered the most prominent path for reducing thecost of low-temperature fuel cells (LTFC). Despite the great advancement in the field, its further progress iscurrently limited by the ability to understand and mitigate the catalysts’ degradation mechanisms, which up torecent years was limited by the lack of activity descriptors. Recent work showed that this could be solved usingFourier-transformed alternating current voltammetry that enables to deconvolute Faradaic currents arising fromthe redox reaction of the active sites from the capacitive currents, and by that accurately measure the electrochemicallyactive site density of these catalysts in situ fuel cells. However, the analysis of the results can becomplex, requiring simulation software for accurate parameter extraction. Herein, a simplified analysis ofFourier-transformed alternating current voltammetry is presented. This was done by mapping the influence ofvarious variables, such as resistivity, capacitance, and thermodynamic and kinetic dispersion, on the accuracy ofelectrochemically active site density measurements. Under specific, yet realistic, operating conditions, a singleequation with the peak current of the 5th harmonic as the only variable can be used to quantify electrochemicallyactive site density with high accuracy. This approach was demonstrated using molecular catalysts, iron phthalocyanine,as a model molecule, and a commercial, heat-treated catalyst.

Self-templated formation of ZnNC microtube with high oxygen reduction reaction overpotential for Zn-based catalyst

The synthesis of hollow morphologies without employing templates and addressing the high overpotential of the oxygen reduction reaction in Zn-N4-C-based materials poses a significant challenge. In this study, we present a straightforward yet robust approach based on a self-templated metal-organic framework (MOF-based) to synthesize ZnNC microtubes and explore the reason behind its high oxygen reduction (ORR) overpotential through density functional theory (DFT) calculation. ZnNC microtubes, benefiting from the abundant Zn-N4 active sites, hierarchical porosity, and a reasonable degree of graphitization, exhibited superior ORR activity and methanol tolerance compared to the traditional precious Pt/C catalyst. On the other hand, DFT calculation shows that Zn exhibits a d10 electronic configuration and diamagnetic nature in Zn-N4 moieties confirmed by the partial density of state (PDOS), hence the main reason behind the high ORR overpotential. This study provides a novel roadmap for further engineering efforts to achieve an ideal ORR catalyst in Zn-based materials.

Electrochemical Evaluation of Penta‐Coordinated Fe Phthalocyanine During the Oxygen Reduction Reaction in Various Acidic Solutions

AbstractIron phthalocyanine (FePc) was penta‐coordinated with pyridine ligand (Py) grafted on carbon nanotube (CNT), to form (FePc‐Py‐CNT). The complex was studied as a catalyst for the oxygen reduction reaction ORR in seven different supporting electrolytes: OH− (0.1 M), OH− (1 M), NO3− (1 M), HSO4− (1 M), ClO4− (1 M), Br− (1 M), Cl− (1 M), to unveil anion‐poisoning effects and mechanism. Through cyclic voltammetry and polarization curves in N2 and O2 saturated atmospheres, thermodynamic and kinetic data were acquired. In acid media, the formal potential Fe(III)/(II) (E0’Fe(III)/(II)) of the complex is biased to more negative potentials by the anion presence. Similar effects were observed for the onset potential (Eonset) during polarization curves for the ORR. When the ORR was performed in the presence of either ClO4−, or HSO4−, anions, Tafel analysis showed different values depending if were derived from the low or from the high overpotential regions, revealing an inner‐sphere electron transfer mechanism (ISET). The Tafel values derived from measurements in the presence of Cl− and Br− anions do not change when extracted at low or at high overpotentials evidencing an outer‐sphere reaction mechanism (OSET). Gibbs free energies were derived from poisoning tests confirming the ISET and OSET mechanisms. The poisoning effect is responsible for the immediate loss of performance for these catalysts during the ORR in acidic media.

Perovskite Type Lanthanum Oxide and Graphene Oxide (LaFeO3-GO) Composite as (Low Overpotential) ORR Catalyst for Low and High Temperature Fuel Cells

Due to depletion of fossil fuel and their environmental effect, renewable resources are the prime interest in which fuel cell technology competes with fossil fuels but their ORR at cathode restrict its efficiency. Perovskite type orthorhombic structure of LaFeO3 incorporated GO has ability to use as catalyst in low and high temperature fuel cells having non-agglomerated particles in nanometers range (20- 100), high temperature stability, low overpotential of about 0.6V, ECSA of about 13.22 m2g-1 and current density of about 0.012 mAcm-1. Results open further research directions in supercapacitors, batteries, biological fuel cells, and applications which requires high temperature stability.

Rapid Synthesis and Microenvironment Optimization of Hierarchical Porous Fe─N─C Catalysts for Enhanced ORR in Microbial Fuel Cells.

Here, an approach to produce a hierarchical porous Fe-N-C@TABOH catalyst with densely accessible high intrinsic active FeNx sites is proposed. The method involves a single-step pyrolysis of Zn/Fe-zeolitic imidazolate framework (Zn/Fe-ZIF-H) with tetrabutylammonium hydroxide (TABOH) micelles, which is obtained by utilizing TABOH as a structural template and electronic mediator at room temperature for a brief duration of 16min. Notably, the yield of Zn/Fe-ZIF-H is 3.5 times that of Zn/Fe-ZIF-N prepared by conventional method. Results indicate that in addition to expediting synthesis and increasing yield of the Zn/Fe-ZIF-H, the TABOH induces a hierarchical porous structure and fosters the formation of more and higher intrinsic active FeNx moieties in Fex-N-C@TABOH, showing that TABOH is a multifunctional template. Crucially, the increased mesoporosity/external surface area and optimized microenvironment of Fe-N-C@TABOH significantly enhance ORR activity by facilitating the formation of high intrinsic active FeNx sites, increasing accessible FeNx sites, and reducing mass transfer resistance. Through structure tailoring and microenvironment optimization, the resulting Fe-N-C@TABOH exhibits superior ORR performance. DFT calculation further validates that the synergistic effect of these two factors leads to low ORR barrier and optimized *OH adsorption energy. This study underscores the importance of structure and electronic engineering in the development of highly active ORR catalysts.

Confined Pt and M (M = Fe, Co) nanoparticles on NC with ultralow Pt loading for oxygen reduction reaction

In this work, we have prepared Pt and M nanoparticles on nitrogen-doped carbon catalysts (Pt&M/NC, M = Fe, Co) with an ultralow Pt loading (<3 wt%) from room reduction of Pt and 3d transition metals by sodium borohydride on NC, where NC is firstly from pyrolysis of carbon black together with melamine. In Pt&M/NC (M = Fe, Co), Pt and 3d transition metals are in the individual nanoparticles with the size < 2 nm, where M is conducive to create the spatial confinement effect to anchor Pt nanoparticles. Meanwhile, Pt&M/NC (M = Fe, Co) has more internal defects than those of Pt/NC and M/NC. Owing to the synergistic effect of Pt and M together with NC, electrochemical results show that Pt&Co/NC has the ORR peak potential and half wave potential of 0.863 and 0.840 V vs. RHE, respectively, where they are 0.848 and 0.827 V vs. RHE for Pt&Fe/NC, more positive than that of Pt/NC. The average electron transfer number of Pt&M/NC (M = Fe, Co) is more than 3.8, close to the four-electron transfer way. This work provides a new method to reduce Pt use for ORR catalysts.

Stable Pentagonal Layered Palladium Diselenide Enables Rapid Electrosynthesis of Hydrogen Peroxide.

Electrosynthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e- ORR) is promising for various practical applications, such as wastewater treatment. However, few electrocatalysts are active and selective for 2e- ORR yet are also resistant to catalyst leaching under realistic operating conditions. Here, a joint experimental and computational study reveals active and stable 2e- ORR catalysis in neutral media over layered PdSe2 with a unique pentagonal puckered ring structure type. Computations predict active and selective 2e- ORR on the basal plane and edge of PdSe2, but with distinct kinetic behaviors. Electrochemical measurements of hydrothermally synthesized PdSe2 nanoplates show a higher 2e- ORR activity than other Pd-Se compounds (Pd4Se and Pd17Se15). PdSe2 on a gas diffusion electrode can rapidly accumulate H2O2 in buffered neutral solution under a high current density. The electrochemical stability of PdSe2 is further confirmed by long device operational stability, elemental analysis of the catalyst and electrolyte, and synchrotron X-ray absorption spectroscopy. This work establishes a new efficient and stable 2e- ORR catalyst at practical current densities and opens catalyst designs utilizing the unique layered pentagonal structure motif.

Tailoring the high-density active sites via metal-coordinated ionic liquid encapsulated trimetallic core-shell MOF-derived catalysts for superior ORR in flexible Al-air batteries

The attainment of practicality in flexible Al-air batteries is impeded by the need for efficient air cathodes. To address this challenge, we systematically engineered the trimetallic (ZnCoFe)NC catalyst with a unique morphology of nitrogen-doped carbon nanotubes (NCNTs) on the 3D polyhedral structure (IL-ZnCoFe@CNT/NC) as an effective cathode. The augmented growth of NCNT facilitated by the metal-coordinated ionic liquid enhances both the specific surface area and the electrochemically active surface area (ECSA). As a result, IL-ZnCoFe@CNT/NC material exhibits a higher onset (1.0 V vs RHE) and half-wave potential (E1/2 = 0.89 V vs. RHE) as well as low Tafel slope (61 mV/dec) and surpassed the bare MOF-derived catalysts and Pt/C. E1/2 decreased by only 7 mV after the stability test describes the durability and fast reaction kinetics in the ORR. Upon testing on flexible Al-air with IL-ZnCoFe@CNT/NC cathode catalysts, it exhibited an OCV of 1.49 V and a peak power density of 34.7 mW cm−2 with 1.3 times higher power performance than the commercial Pt/C along with 3 times longevity than bare catalysts. Additionally, the Density-functional theory (DFT) calculations provide rational evidence that the IL-ZnCoFe@CNT/NC catalyst has an upshifted d-band center, which, in turn, enhances the adsorption of reaction intermediates, making the catalyst highly promising towards ORR.

Theoretical screening of corrole-based covalent organic framework metal single-atom catalysts for ORR and OER

Corrole-based covalent organic frameworks (COFs) are newly developing porous crystalline materials in the catalysis field due to their thermal stability, and ease of being functionalized by high-valent metal at the corrole center. In this work, based on the monolayer TPAPC-COF (m-TPAPC-COF), a series of stable metal corrole-based 2D monolayer SACs M1@TPAPC-COFs (M = Fe, Co, Ni, Cu, Ru, Rh, Os, Ir, Pt, Au) have been obtained by screening using density functional theory (DFT) calculations. As O2 can be adsorbed and activated on M1@TPAPC-COFs (M = Fe, Co, Ru, Rh, Os, Ir), we predicted two types of non-noble metal corrole-based COFs SACs, one is a bifunctional SAC Fe1@TPAPC-COF with high electrocatalytic activity for ORR/OER and the other is a Co1@TPAPC-COF with high electrocatalytic activity for OER, respectively. This work demonstrates that corrole-based COF is a promising 2D material for constructing high-performance SACs for the ORR and OER.

Efficient ORR catalyst: porous activated carbon prepared from water hyacinth with high N content

Efficient ORR catalyst: porous activated carbon prepared from water hyacinth with high N content

Design and assembly of ZIF@PPy-derived hierarchical structure CeCo-NxCC electrocatalyst towards oxygen reduction reaction

The research of high-performance catalysts for ORR is always a great challenge in the field of zinc-air batteries (ZABs) applications. Herein, a near-regular dodecahedral ZIF-67-derived nitrogen-doped carbon material (CeCo-NxCC-700) with abundant hollow nanospheres on the surface is successfully constructed by introducing Ce ions to replace part of the Co ions and polymerizing pyrrole on the surface of the polyhedrons. PPy-coating is beneficial to improving the electrochemical stability and increasing the number of Co-Nx active sites, especially the pyrrole N and pyridine N sites. Ce-doping adjusts the charge density around the active sites. Meanwhile, the pyrolysis at 700 °C during the preparation process does not cause the structural collapse of CeCo-NxCC. Based on their decent ORR/OER performance, ZABs have been further assembled with CeCo-NxCC-700, which exhibit a high specific capacity of 815.4 mAh·g (Zn)−1 and cycling stability of more than 80 h, indicating a great application potentiality in ZABs manufacturing.