Efficient Oxygen Reduction Reaction Research Articles

Main Group SnN4O Single Sites with Optimized Charge Distribution for Boosting the Oxygen Reduction Reaction.

Transition metal single-atom catalysts (SACs) have been regarded as possible alternatives to platinum-based materials due to their satisfactory performance of the oxygen reduction reaction (ORR). By contrast, main-group metal elements are rarely studied due to their unfavorable surface and electronic states. Herein, a main-group Sn-based SAC with penta-coordinated and asymmetric first-shell ligands is reported as an efficient and robust ORR catalyst. The introduction of the vertical oxygen atom breaks the symmetric charge balance, modulating the binding strength to oxygen intermediates and decreasing the energy barrier for the ORR process. As expected, the prepared Sn SAC exhibits outstanding ORR activity with a high half-wave potential of 0.912 V (vs RHE) and an excellent mass activity of 13.1 A mgSn-1 at 0.850 V (vs RHE), which surpasses that of commercial Pt/C and most reported transition-metal-based SACs. Additionally, the reported Sn SAC shows excellent ORR stability due to the strong interaction between Sn sites and the carbon support with oxygen atom as the bridge. The excellent ORR performance of Sn SAC was also proven by both liquid- and solid-state zinc-air battery (ZAB) measurements, indicating its great potential in practical applications.

Thermodynamics of Proton-Coupled Electron Transfer at Tricopper μ-Oxo/Hydroxo/Aqua Complexes.

Multicopper oxidases (MCOs) utilize a tricopper active site to reduce dioxygen to water through 4H+ 4e- proton-coupled electron transfer (PCET). Understanding the thermodynamics of PCET at a tricopper cluster is essential for elucidating how MCOs harness the oxidative power of O2 while mitigating oxidative damage. In this study, we determined the O-H bond dissociation free energies (BDFEs) and pKa values of a series of tricopper hydroxo and tricopper aqua complexes as synthetic models of the tricopper site in MCOs. Tricopper intermediates on the path of alternating electron and proton transfer (ET-PT-ET-PT-ET) have modest BDFE(O-H) values in the range of 53.0-57.1 kcal/mol. In contrast, those not on the path of ET-PT-ET-PT-ET display much higher (78.1 kcal/mol) or lower (44.7 kcal/mol) BDFE(O-H) values. Additionally, the pKa of bridging OH and OH2 motifs increase by 8-16 pKa units per oxidation state. The same oxidation state changes have a lesser impact on the pKa of N-H motif in the secondary coordination sphere, with an increase of ca. 5 pKa units per oxidation state. The steeper pKa increase of the tricopper center promotes proton transfer from the secondary coordination sphere. Overall, our study shed light on the PCET pathway least prone to decomposition, elucidating why tricopper centers are an optimal choice for promoting efficient oxygen reduction reaction.

Coordination-environment regulation of atomic Co-Mn dual-sites for efficient oxygen reduction reaction

Coordination-environment regulation of atomic Co-Mn dual-sites for efficient oxygen reduction reaction

Electronic Structure Engineering of Pt-Ni Alloy NPs by Coupling of Gold Single Atoms on N-Doped Carbon for Highly Efficient Oxygen Reduction Reaction and Hydrogen Evolution Reaction.

Improving the catalytic activity and durability of platinum-based alloy catalysts remains a formidable challenge in the context of renewable energy electrolysis applications. Herein, a facile and rapid photochemical deposition strategy for the synthesis of gold single atoms (Au SAs) anchored on N-doped carbon is presented. These Au SAs serve as a charge redistribution support for Pt-Ni alloy nanoparticles (PtNiNPs/AuSA-NDC), creating an extended electron-donating interface with Pt-Ni alloy sites. Consequently, the PtNiNPs/AuSA-NDC hybrid catalyst manifests exceptional catalytic performance and durability in both the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) under acidic conditions. Specifically, in ORR, it exhibits a half-wave potential (0.92V vs RHE), with a mass activity 20.4 times superior to Pt/C at 0.9V. In HER, PtNiNPs/AuSA-NDC demonstrates a notably reduced overpotential of 19.1mV vs RHE at 10mAcm-2 and a mass activity 38 times higher than Pt/C (at 0.25mV). Furthermore, this hybrid catalyst displays outstanding durability, with only an 8.0mV decay observed for ORR and a 6.9mV decay for HER after 10000 cycles. Theoretical calculations provide insight into the mechanism, demonstrating that isolated Au sites effectively modulate the electronic structure of Pt-Ni alloy sites, facilitating intermediate adsorption and enhancing reaction kinetics.

Carbon‐Embedded Pt Alloy Cluster Catalysts for Proton Exchange Membrane Fuel Cells

AbstractMinimizing the use of platinum (Pt) in proton exchange membrane fuel cells (PEMFCs) is crucial for expanding the PEMFC market. The most straightforward approach would be to reduce the size of Pt particles. However, small Pt clusters, particularly those <2 nm in size, typically exhibit reduced activity for the oxygen reduction reaction (ORR) due to the overly strong adsorption of oxygen intermediates. Additionally, these small Pt clusters tend to degrade more quickly, resulting in lower durability. In this study, carbon‐embedded Pt alloy cluster catalysts (PtFe, PtCo, PtNi) that demonstrate high activity and durability in the PEMFC cathode are presented. Density functional theory calculations indicate that carbon atoms stably adsorb onto the Fe sites of PtFe clusters, making the neighboring Pt sites active for ORR with an optimal adsorption strength for oxygen intermediates. This research can pave the way for developing durable and efficient ORR catalysts while significantly reducing Pt usage in PEMFCs.

Two-Dimensional Leafy Fe/N-Doped Carbon Nanomaterials Derived from Vitamin C-Modified ZIF-L for Efficient Oxygen Reduction Reaction

Two-Dimensional Leafy Fe/N-Doped Carbon Nanomaterials Derived from Vitamin C-Modified ZIF-L for Efficient Oxygen Reduction Reaction

Single-atom Fe catalysts with pyrrolic-type FeN4 sites for efficient oxygen reduction reaction: Identifying the roles of different N species

Developing electrocatalysts with efficient cathode oxygen reduction reaction (ORR), for example, iron-based single-atom catalysts (Fe-SACs), has been deemed necessary to accelerate the commercialisation process of zinc (Zn)–air batteries. Nevertheless, determining how various nitrogen species and active metal centres coordinate on an atomic scale remains unclear and inadequately explained. Herein, we demonstrate a soft-template-aided technique using Fe-containing molecules (e.g. iron phthalocyanine [FePc], Fe-1,10-phenanthroline [Fe-Phen] and Fe-glucose) to enhance the performance of Fe-SACs in terms of ORR. In this technique, FePc molecules can be converted into atomically dispersed pyrrolic-type iron–nitrogen (FeN4) sites during a pyrolytic process. The resultant catalyst exhibits excellent ORR activity (half-wave potential = 0.90 V) in alkaline medium and standing battery performance when used in Zn–air batteries (peak power density = 197.3 mW cm−2 and specific capacity = 796.2 mAh g−1). As per the findings from control experiments and characterisation studies, electron transfer between the support and the active Fe centre amplifies the ORR performance. Theoretical calculations substantiate that Fe sites coordinated with pyrrolic N atoms govern the electronic configuration of the catalysis, reducing the free energy absorption of reaction intermediates and thus increasing its intrinsic ORR capability. Herein, we aim to offer a fresh perspective on the relation between coordination environments and catalytic activity in ORR catalysts.

Resonant structure substrate anchors Pt to form ordered alloys for efficient oxygen reduction reaction

Platinum-based ordered alloys have excellent catalytic performance for the cathodic oxygen reduction reaction (ORR) in fuel cells. However, these alloys exhibit a lower degree of ordering and larger crystal grains after heat treatment. Herein, a series of cyanamide group molecules (cyanamide, dicyandiamide, melamine) was employed as substrates to modify Pt-based alloys by promoting the binding between metal ions, leading to the preparation of ∼ 4 nm PtM (M = Co, Fe, Ni) ordered alloys after heat treatment. Among them, the PtCo ordered alloy prepared using hydrolyzed cyanamide with a unique resonance structure exhibits a high degree of order (93.1 %), and its mass activity of 0.915 A mgPt-1 at 0.9 V is superior to that of Pt/C. The theoretically calculated adsorption energies of these alloys demonstrate that the resonance structure of the cyanamide substrate is beneficial for alloy formation, thereby facilitating ordered alloy synthesis.

Well-dispersed Pt/Nb2O5 on zeolitic imidazolate framework derived nitrogen-doped carbon for efficient oxygen reduction reaction

In this work, an advanced hybrid material was constructed by incorporating niobium pentoxide (Nb2O5) nanocrystals with nitrogen-doped carbon (NC) derived from ZIF-8 dodecahedrons, serving as a support, referred to as Nb2O5/NC. Pt nanocrystals were dispersed onto Nb2O5/NC using a simple impregnation reduction method. The obtained Pt/Nb2O5/NC electrocatalyst showed high oxygen reduction reaction (ORR) activity due to three-phase mutual contacting structure with well-dispersed Pt and Nb2O5 NPs. In addition, the conductive NC benefits electron transfer, while the induced Nb2O5 can regulate the electronic structure of Pt element and anchor Pt nanocrystals, thereby enhancing the ORR activity and stability. The half-wave potential (E 1/2) for Pt/Nb2O5/NC is 0.886 V, which is higher than that of Pt/NC (E 1/2 = 0.826 V). The stability examinations demonstrated that Pt/Nb2O5/NC exhibited higher electrocatalytic durability than Pt/NC. Our work provides a new direction for synthesis and structural design of precious metal/oxides hybrid electrocatalysts.

Tailoring Zirconia Supported Intermetallic Platinum Alloy via Reactive Metal-Support Interactions for High-Performing Fuel Cells.

Developing efficient and anti-corrosive oxygen reduction reaction (ORR) catalysts is of great importance for the applications of proton exchange membrane fuel cells (PEMFCs). Herein, we report a novel approach to prepare metal oxides-supported intermetallic Pt alloy nanoparticles (NPs) via the reactive metal-support interaction (RMSI) as ORR catalysts, using Ni-doped cubic ZrO2 (Ni/ZrO2) supported L10-PtNi NPs as a proof of concept. Benefiting from the Ni migration during RMSI, the oxygen vacancy concentration in the support is increased, leading to an electron enrichment of Pt. The optimal L10-PtNi-Ni/ZrO2-RMSI catalyst achieves remarkably low mass activity (MA) loss (17.8%) after 400,000 accelerated durability test cycles in a half-cell and exceptional PEMFC performance (MA = 0.76 A mgPt-1at 0.9 V, peak power density = 1.52/0.92 W cm-2in H2-O2/-air, and 18.4% MA decayafter 30,000 cycles), representing the best reported Pt-based ORR catalysts without carbon supports. Density functional theory (DFT) calculations reveal that L10-PtNi-Ni/ZrO2-RMSI requires a lower energetic barrier for ORR than L10-PtNi-Ni/ZrO2 (direct loading), which is ascribed to a decreased Bader charge transfer between Pt and *OH, and the improved stability of L10-PtNi-Ni/ZrO2-RMSI compared to L10-PtNi-C can be contributed to the increased adhesion energy and Ni vacancy formation energy within the PtNi alloy.

Construction of Cu Single‐Atom Catalysts by Taking Spatial‐Confinement and Chemical‐Anchoring Effect of Hyperbranched Phthalocyanine Copper for Efficient Oxygen Reduction Reaction

AbstractAtomically dispersed nonprecious metal‐based catalysts have been considered as the most promising alternatives to Pt‐based catalysts since their excellent catalytic activities and almost 100 % atom utilization in oxygen reduction reaction. However, the agglomeration of metal atoms is unavoidable during pyrolysis process, thus leads to the decrease of electrocatalytic performance. Herein, hyperbranched phthalocyanine copper (HCuPc) wrapping nano‐silica is synthesized via in situ polymerization and served as precursor for preparing atomically dispersed Cu−N−C electrocatalysts. Owing to the confinement effect of chemical‐anchoring and spatial‐hindrance, the migration and agglomeration of Cu atoms are restricted in carbonization process. The aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray photoelectron spectroscopy (XPS) are performed to confirm the atomically dispersed of as‐synthesized catalyst, which is labelled as HCu−N−C/SiO2. In addition, the HCu−N−C/SiO2 possess superior ORR electrocatalytic activities with a half‐wave potential of 0.874 V vs RHE and a limiting current density of 5.7 mA cm−2. The zinc‐air batteries assembled with HCu−N−C/SiO2 catalyst exhibit a high specific capacity of 789 mAh g−1 as well as a maximum discharge power density of 176 mW cm−2. This work proves that hyperbranched phthalocyanine structure could be a useful confined framework to the fabrication of singles‐atom catalysts.

Theoretical designs of ORR/OER single‐atom catalysts TM@Ti2CT2 (T = O, S, Cl)

AbstractDriven by the goal of establishing a fossil‐fuel‐free and nuclear‐power‐free economy based on renewable energy, metal‐air batteries are regarded as promising energy conversion and storage devices. Developing efficient oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional electrocatalysts for the air electrode of metal‐air batteries is becoming increasingly important. In this work, 36 transition metal (TM) single‐atom catalysts are designed based on MXenes Ti2CT2 with different surface terminal atoms (T = O, S, Cl), and their ORR/OER catalytic activity and stability are evaluated by the density functional theory. Ni@Ti2CO2, Pd@Ti2CS2, and Co@Ti2CCl2 are found to exhibit good catalytic activity with ORR/OER overpotentials of .54 V/.62 V, .59 V/.29 V, .44 V/.40 V. The aggregation behavior of three catalysts is estimated by comparing the average binding energy of one, two, three, and four TM atoms anchored on Ti2CT2. This work cannot only provide a theoretical guide to develop bifunctional single‐atom catalysts, but also help us understand the effect of terminal atoms on the electronic structures and catalytic activity of TM@Ti2CT2.

Platinum-alloy Materials for highly efficient oxygen reduction reaction in fuel cell

Platinum-alloy Materials for highly efficient oxygen reduction reaction in fuel cell

S-doped NiCo layered double hydroxides enable efficient and durable methanol oxidation and oxygen reduction reactions for Zn-methanol-air batteries

The employment of alcohol oxidation reactions (AORs) is thermodynamically more favorable to replace the anodic oxygen evolution reaction (OER) in rechargeable Zn-air batteries (ZABs). As a representative AOR-coupled ZAB, Zn-methanol-air battery (ZMAB) gratifyingly delivers a lower charge voltage, higher energy efficiency, longer cycle life and more valuable charge product in comparison with the traditional ZAB. For such emerging ZMABs, it is imperative to explore efficient, stable and cost-effective bifunctional electrocatalysts for both methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). Herein, sulfur-doped NiCo layered double hydroxides (termed NiCo-LDH@SOH) are fabricated by a room-temperature surface sulfurization route. Remarkably, the NiCo-LDH@SOH heterostructure catalyst achieves a superb bifunctional activity for MOR and ORR, performing a low potential gap ΔE between the Ej10 for MOR and the half-wave potential E1/2 for ORR of only 0.596 V, far surpassing that (0.790 V) for Pt/C-IrO2 benchmark catalyst. The electronic interactions between S2− and transition metal ions significantly accelerate the charge transfer process and generate highly efficient Ni3+ and Co2+ active sites on NiCo-LDH@SOH, which account for the exceptional MOR and ORR performance, respectively. Thanks to the favorable replacement of OER with MOR and the excellent MOR/ORR bifunctional activity of NiCo-LDH@SOH, the ZMAB can output a comparable discharge power density (140 mW cm−2) to the traditional ZAB counterpart (149 mW cm−2), but a much lower charge voltage than the latter. In consequence, the ZMAB demonstrates an extraordinary long-term cyclability of 2880 cycles for 480 h (20 days) with almost no degradation, which is more than 5 times longer than that of the traditional ZAB.

One-Pot Etching Pyrolysis to Defect-Rich Carbon Nanosheets to Construct Multiheteroatom-Coordinated Iron Sites for Efficient Oxygen Reduction.

Constructing multiheteroatom coordination structure in carbonaceous substrates demonstrates an effective method to accelerate the oxygen reduction reaction (ORR) of supported single-atom catalyst. Herein, the novel etching route assisted by potassium thiocyanate (KCNS) is developed to convert metal-organic framework to 2D defect-rich porous N,S-co-doped carbon nanosheets for anchoring atomically dispersed iron sites as the high-performance ORR catalysts (Fe-SACs). The well-designed KCNS-assisted etching route can generate spatial confinement template to direct the carbon nanosheet formation, etching condition to form defect-rich structure, and additional sulfur atoms to coordinate iron species. Spectral and microscopy analysis reveals that the iron element in Fe-SACs is highly isolated on carbon nanosheet and anchored by nitrogen and sulfur atoms in unsymmetrical Fe-S1N3 structure. The optimized Fe-SACs with large specific surface area could show remarkable alkaline ORR performances with a high half-wave potential of 0.920 V versus RHE and excellent durability. The rechargeable zinc-air battery assembled with Fe-SACs air electrodes delivers a large power density of 350 mW cm-2 and a stable voltage platform during charge and discharge over more than 1300 h. This work proposes a novel strategy for the preparation of single-atom catalysts with multiheteroatom coordination structure and highly exposed active sites for efficient ORR.

Mn-modulated Co–N–C oxygen electrocatalysts for robust and temperature-adaptative zinc-air batteries

Flexible zinc-air batteries (FZABs) are featured with safety and high theoretical capacity and become one of the ideal energy supply devices for flexible electronics. However, the lack of cost-effective electrocatalysts remains a major obstacle to their commercialization. Herein, we synthesized a porous dodecahedral nitrogen-doped carbon (NC) material with Co and Mn bimetallic co-embedding (CoxMn1−x@NC) as a highly efficient oxygen reduction reaction (ORR) catalyst for ZABs. The incorporation of Mn effectively modulates the electronic structure of Co sites, which may lead to optimized energetics with oxygen-containing intermediates thereby significantly enhancing catalytic performance. Notably, the optimized Co4Mn1@NC catalyst exhibits superior E1/2 (0.86 V) and jL (limiting current density, 5.96 mA cm−2) compared to Pt/C and other recent reports. Moreover, aqueous ZAB using Co4Mn1@NC as a cathodic catalyst demonstrates a high peak power density of 163.9 mW cm−2 and maintains stable charging and discharging for over 650 h. Furthermore, FZAB based on Co4Mn1@NC can steadily operate within the temperature range of −10 to 40 °C, demonstrating the potential for practical applications in complex climatic conditions.

Synthesis of NbC@C(Nx) nanoparticles using DC arc discharge plasma for highly efficient oxygen reduction reaction

Development of the low-cost, high-efficiency, and durable non-precious metal electrocatalysts for cathodic oxygen reduction reaction (ORR) is of vital importance for fuel cells and metal-air batteries. Herein, the carbon-coated NbC nanoparticles (NbC@C NPs) were prepared using DC arc discharge plasma under a methane atmosphere. Then, the nitrogen-doping was conducted by heat treatment, resulting in nitrogen-doped carbon-coated NbC nanoparticles (NbC@C(Nx) NPs). Benefiting from the merit of unique core-shell structure and best synergy between the nitrogen-doped carbon shell and the NbC core, the obtained highest nitrogen-doped NbC@C(N1.36) NPs showed an onset potential (Eonset) of 0.89 V (vs. RHE) and a half-wave potential (E1/2) of 0.79 V, which are comparable to those of commercial Pt/C (20 wt%) (Eonset = 0.90 V, E1/2 = 0.80 V), and its diffusion-limited current density (JL) of 5.99 mA·cm−2 is even higher than that of commercial Pt/C (5.43 mA·cm−2). Moreover, it exhibited a remarkable long-term durability and impressive methanol resistance than Pt/C catalyst. In addition, the real-time optical emission spectrum (OES) analysis of arc plasma shows that the electron temperature (Te) is 7562.9 K in local thermal equilibrium (LTE) plasma. Therefore, the use of the DC arc discharge plasma method opens a fast and simple way to develop cost-effective and highly efficient non-precious metal catalysts for ORR.

Multiscale Regulation of Ordered PtCu Intermetallic Electrocatalyst for Highly Durable Oxygen Reduction Reaction.

Transforming the Pt-M alloy into an ordered intermetallic is an effective strategy to improve the electrocatalytic activity and stability toward the oxygen reduction reaction (ORR). However, the synthesis of nanosized intermetallics remains challenging. Herein, we report an efficient ORR electrocatalyst, consisting of a monodisperse nanosized PtCu intermetallic on hollow mesoporous carbon spheres (HMCS). As predicted by theoretical calculations, PtCu intermetallics exhibit beneficial electronic structure, with a low theoretical overpotential of 0.33 V and enhanced Cu stability. Resulting from the multiscale modulation of catalyst structure, the O-PtCu/HMCS catalyst delivers a high mass activity of 2.73 A cm-2Pt at 0.9 V and remarkable stability. Identical location transmission electron microscopy (IL-TEM) investigations demonstrate that the rate of carbon corrosion is alleviated on HMCS, which contributes to the long-term durability. This work provides a promising design strategy for an ORR electrocatalyst, and the IL-TEM investigations offer new perspectives for the performance enhancement mechanism.

A facile synthesis of iron single-atom electrocatalyst for high-performing oxygen reduction reaction and remarkable rechargeable zinc-air battery

Iron-based single-atom catalysts (SACs) are considered to the most promising catalysts to replace Pt for efficient oxygen reduction reaction (ORR). However, the precise synthesis of high-performance SACs and the understanding of their ORR origin remain challenging. In this work, microporous nitrogen-doped carbon with abundant and accessible atomically dispersed N-coordinated Fe sites (Fe-N-C) is prepared by molecular-confined coupling pyrolysis strategy. The Fe-N-C exhibits excellent ORR activities in acid (E1/2 of 0.78 V vs. RHE) and alkaline (E1/2 of 0.91 V vs. RHE) electrolytes. When integrated into a rechargeable aqueous Zinc-air battery (ZAB), both large specific capacity (770 mAh g−1) and high peak power density (240 mW cm−2) are achieved. Remarkably, the as-prepared ZAB presents amazing charge-discharge cycle performance of 1600 h at the large current density, which is 52.5 times of that using Pt/C+RuO2. Furthermore, all-solid-state ZAB delivers ultra-robust cycling stability even under bending. This work may advance a critical step towards the design of rational and controlled preparation of remarkable and ultra-stable catalysts.

An improvement on the electrocatalytic performance of ZIF-67 by in situ self-growing CNTs on surface

Efficient and robust oxygen reduction reaction (ORR) catalysts are essential for the development of high-performance anion-exchange membrane fuel cells (AEMFC). To enhance the electrochemical performance of metal–organic frameworks of cobalt-based zeolite imidazolium skeleton (ZIF-67), this study reported a novel ZIF-67-4@CNT by in situ growing carbon nanotubes (CNTs) on the surface of ZIF-67 via a mild two-step pyrolysis/oxidation treatment. The electrochemical results showed that the as-prepared ZIF-67-4@CNT after CTAB modification exhibited excellent catalytic activity with good stability, with Eonset, E1/2, and Ilimit, respectively were 0.98 V (versus RHE), 0.87 V (versus RHE) and 6.04 mA cm−2@1600 rpm, and a current retention rate of about 94.21% after polarized at 0.80 V for 10 000 s, which were all superior to that of the commercial 20 wt% Pt/C. The excellent ORR catalytic performance was mainly attributed to the large amount of the in situ growing CNTs on the surface, encapsulated with a wide range of valence states of metallic cobalt.