Oxygen Reduction Catalysts Research Articles

Enhanced electrochemical oxygen reduction reaction on “C–O–Si” bonds in Si-doped graphene-like carbon

The use of heteroatom-doped carbon materials as non-precious metal catalysts for oxygen reduction reactions has attracted much attention from researchers. This paper presents the synthesis of two-dimensional Si-doped graphene-like materials (Si-GLC) featuring “C–O–Si” bonds through an in-situ doping method. Since the electronegativity of the Si (1.90) is much smaller than that of C (2.55) and O (3.44), the formation of the “C–O–Si” bond causes Si to lose a large number of electrons and become positively charged. This increases the adsorption of electronegative oxygen, thereby improving the activity of oxygen reduction reactions. The adsorption energy of oxygen molecules on Si-GLC was calculated to be −3.57 eV using density functional theory, much lower than on GLC (−2.18 eV). This suggests that Si doping enhances the adsorption of oxygen molecules by graphene-like materials, which is crucial for improving the performance of oxygen reduction reaction. Si-GLC displayed a half-wave potential of 0.80 V (vs. RHE) and a diffusion-limited current density of 5.81 mA cm−2 in 0.1 M KOH solution, demonstrating excellent catalytic activity for oxygen reduction reaction. It also exhibits good stability and tolerance to methanol crossover effect. In-situ doping creates “C–O–Si” bonds, modulating charge density and providing a strategy for high-performance oxygen reduction catalysts.

Laser ablation-induced convenient fabrication of surfactant-free platinum nanospheres with clean surface structures for enhanced electrocatalytic methanol oxidation

Platinum (Pt) is the most promising catalyst for hydrogen oxidation and oxygen reduction. However, the residual surface-stabilizing agents capped on Pt-based nanomaterials via traditional chemical approaches will significantly reduce their catalytic activity. Herein, a new one-step strategy for the facile synthesis of surfactant-free Pt nanospheres with clean surface structures is developed by laser ablation of Pt target in distilled water. The distinctive advantage is that the pure water-dispersed Pt nanospheres can be obtained without any extra purification procedures, and the obtained catalyst exhibits enhanced electrocatalytic activity compared with Pt nanospheres capped with polyvinyl pyrrolidone or cetyl trimethyl ammonium bromide, which are most regular stabilizers or surfactants in traditional nanoparticles synthesis method. Importantly, the mass-normalized cyclic voltammetry (CV) curves for the methanol oxidation reaction show that the measured value of peak current is nearly 610 and 1050 times higher than that of Pt/PVP and Pt/CTAB samples. Moreover,the chronoamperometric (CA) measurements reveals that the steady-state current density is about 1.28 mA/cm2, while which of Pt/PVP and Pt/CTAB are 1.07 and 0.017 μA/cm2, respectively. It is no doubt that the application of laser beam as an environmental friendly tool for sculpting pure functional metal-based nanomaterials is a breakthrough in the additive problems that arise from standard chemical fabrication.

Facile growth of a heteroepitaxial layer on perovskite oxide surfaces for active and durable fuel cell cathodes

Polycrystalline perovskite oxide particles are promising candidates for cathode materials in solid oxide fuel cells. However, their limited activity and stability pose significant challenges for practical applications. In this study, we demonstrate a novel approach to achieve both high activity and durability in a PrBaCo2O5+δ catalyst through a simple epitaxial layer growth strategy. We found that an amorphous precursor of the highly durable catalyst SmBa0.5Ca0.5CoCuO5+δ can spontaneously adhere to the surface of PrBaCo2O5+δ particles. Upon heat treatment, it grows along the perovskite lattice, forming a heteroepitaxial layer with just a few atomic layers thickness. This heterostructure enhances the operational stability of PrBaCo2O5+δ transforming a 78% decrease over 100 h into a 7% increase. After 100 h, the power output density of the cell with the modified sample is more than 500% higher than that of unmodified PrBaCo2O5+δ. This work presents a new strategy for fabricating heteroepitaxial layers on polycrystalline ceramic catalysts and introduces a pioneering approach for developing high-performance oxygen reduction catalysts and related materials.

Density Functional Theory Study on Screening and Key Metrics for Non-metallic Oxygen Reduction Catalysts.

This study systematically investigates the oxygen reduction reaction (ORR) catalytic activity of graphene doped with various non-metallic impurities. The non-metal elements include boron (B), silicon (Si), nitrogen (N), phosphorus (P), arsenic (As), oxygen (O), sulfur (S), selenium (Se), tellurium (Te), fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). We found that adsorbates tend to adsorb on positively charged impurity atoms. We identified several substrates with good catalytic activity, all of which have an ORR overpotential of around 0.6 V. We further verified the thermodynamic stability of these substrates and found them to be very stable. We summarized the optimal adsorption energies for ORR intermediates O2H, O, and OH to be -1.9, -3.4, and -2.4 eV, respectively, and validated their reasonableness. Finally, we used simple linear functions to fit the relationship between the adsorption energies of O2H, O, and OH and the charge and magnetic moment of the adsorption site atoms. This model can roughly predict the ORR catalytic activity of doped graphene, facilitating the faster screening of excellent ORR catalysts.

Biochar from residues of anaerobic digestion and its application as electrocatalyst in Zn–air batteries

BackgroundBiochar, the product obtained by pyrolysis of biomass, is a new eco-friendly material with excellent properties and many promising applications. Among them it can be used as cathode in Zn-air batteries with very satisfactory results MethodsThe residue was obtained by anaerobic digestion of a mixture of corn silage (10%), malt (10%), and cattle manure (80%), aiming to biogas production. It was first freeze–dried and then it was subjected to pyrolysis up to 800oC. Significant findingsThe biochar was physicochemically characterized. It has moderate specific surface area, sufficient sp2/sp3 ratio and metal and non–metal surface chemical species. The biochar demonstrated satisfactory electrocatalytic performance, both as oxygen reduction and oxygen evolution catalyst. When applied as electrocatalyst in Zn–air batteries it reached an open–circuit potential of 1.45 V, a short–circuit current density of 200 mA cm–2 and maximum power density of around 62 mW cm–2. Its energy density was 927 Wh kg–1, (at 20 mA), and 518 Wh kg–1 (at 100 mA). In a charge–discharge mode at 10 mA, the potential varied between 1.35 and 1.90 V. These data, show that the waste biomass can be used as inexpensive material for Zn–air batteries and offers a useful approach to combine waste management with energy storage.

Modulating the Local Coordination Environment of M‐Nx Single‐Atom Site for Enhanced Electrocatalytic Oxygen Reduction

AbstractEfficient, durable, and economical oxygen reduction catalysts are key for practical applications such as fuel cells and metal–air batteries. Single atom catalysts (SACs) have attracted sustained and widespread attention owing to their unique electronic properties and exceptional atomic utilization, positioning them as promising electrocatalysts in energy conversion and storage. However, the symmetric charge distribution of the metal site in the symmetric M‐N4 configuration of SACs is not conducive to electron transfer and transport in electrocatalytic reactions, resulting in a low adsorption energy for oxygen reduction reaction (ORR) related species (*OH, *O, and *OOH), which severely limits the intrinsic activity of the electrocatalysts. To overcome this limitation and improve the activity and durability, heteroatom doping can effectively modulate the local coordination environment (LCE) of the metal atom, including the coordinating atoms, coordination shells and coordination number. These modifications have significantly improved the performance of carbon supported SACs with M‐N4 configuration in the ORR. Based on this, a thorough summary of the major progress made in recent years in adjusting the LCE of SACs through doping with heteroatoms is provided and a perspective on the future development is offered here.

Coordination engineering of B/N-doped graphene with phosphorus-transition metal diatomic catalysts for enhanced oxygen bifunctionality electrocatalysis

The design of highly active and cost-effective bifunctional catalysts for oxygen evolution (OER) and oxygen reduction (ORR) reactions is critical for advancing energy storage and conversion, yet significant challenges remain. Inspired by the efficient bifunctionality of graphene-based single-atom and diatomic catalysts in OER/ORR, we designed 42 structural of TMPX4@graphene (X = B, N; TM = V-Pt) and A-BN, and assessed their OER and ORR catalytic performance using density functional theory (DFT). The sum of overpotentials (ηsum = ηOER + ηORR) was identified as an effective descriptor for predicting the bifunctional catalytic properties of the TMPX4@graphene system. The transferred electron count and d-orbital occupation of Co atoms were identified as key sources of catalytic activity in OER and ORR, as determined through Bader charge analysis and partial density of states (PDOS). Finally, constant potential method (CPM) calculations showed that CoPB4@graphene exhibits excellent catalytic activity under alkaline conditions, with ORR and OER overpotentials of 0.86 V and 1.38 V, respectively. This study highlights the importance of rationally designing the local coordination environment by regulating boron content to enhance catalytic activity. It further provides insights into the rational design of stable and efficient catalysts by considering electrode potential and pH effects in electrocatalytic systems.

Confined pyrolysis synthesis of N-doped carbon-supported FePr nanoparticles for efficient oxygen reduction based on 3d–4f orbital coupling

To meet the growing demand for new energy storage and conversion technologies, there is an urgent need to prepare highly efficient, economical and durable oxygen reduction catalysts that can replace those based on precious. Herein, N-doped porous carbon supported FePr nanoparticles (FePr/NC) were prepared by confined adsorption and pyrolysis. The characterizations and electrocatalytic properties of the FePr/NC were investigated in details. The prepared FePr/NC catalyst showed excellent oxygen reduction reaction (ORR) catalytic performance with a half-wave potential (E1/2) of 0.87 V in a 0.1 M KOH solution, outperforming commercial Pt/C catalyst (E1/2 = 0.82 V) under the identical conditions. Besides, its onset potential (Eonset) was up to 1.002 V, exceeding the Pt/C (Eonset = 0.92 V). Moreover, the E1/2 only exhibited a negative shift of 7 mV after 2000 cycles, reflecting its significant stability. To understand their exceptional preference for the ORR, the electronic structure of Fe influenced by the doped Pr and the synergistic effect of the FePr nanoparticles with N-doped carbon were investigated. The coupling of Fe's 3d orbitals with Pr's 4 f orbitals in the FePr significantly enhanced the electrocatalytic activity. This work provides a promising strategy for preparation of high-quality transition metal-based carbon catalysts for green energy devices.

Bimetallic CoZn-MOF nanosheets derived two dimensional Co single-atom catalysts for efficient oxygen reduction

Two-dimensional (2D) materials have gained significant attention as ideal templates for constructing single-atom catalysts (SACs), which maximizes the exposure of active sites and ensures uniform dispersion of metal atoms. Herein, a novel two-dimensional (2D) CoZn-MOF nanosheet was synthesized, which was used as a precursor to construct a N-doped carbon catalyst modified with Co single atoms (Co SAs-NC). During the calcination process, the nitrogen atoms in ligands were converted into a N-doped carbon matrix, effectively anchoring Co ions and generating uniformly distributed Co-Nx active sites. Co SAs-NC exhibited superior ORR performance compared to Pt/C, with a half-wave potential of 0.886 V. Additionally, zinc-air batteries (ZABs) based on Co SAs-NC exhibit a peak power density of 134 mW cm−2, significantly exceeding that of Pt/C (89 mW cm−2). The completion of this work will provide new insights into developing efficient 2D carbon-based non-precious metal ORR catalysts.

N,S‐Doped Zeolite‐Templated Carbon Like Supported NixFeySz as an Efficient Bifunctional Catalyst for Rechargeable Zinc Air Batteries

AbstractA still unexplored class of heterostructured bifunctional catalysts for oxygen evolution (OER) and reduction (ORR) reactions is investigated: Ni−Fe sulfides deposited onto a N,S‐co‐doped zeolite‐templated carbon (ZTC) substrate achieved upon the impregnation of a ZTC with thiourea and Ni and Fe precursors (Ni/Fe atomic ratio of 1). By heat‐treating the impregnated ZTC substrate at 700 °C under N2 atmosphere the efficient bifunctional catalyst is generated. A difference of only 0.76 V is measured between the potential required to drive an OER current density of 10 mA cm−2 and the ORR half‐wave potential. Using electrochemical measurements and physico‐chemical characterizations, it is evidenced that OER activity results from the presence of a sulfide containing both Fe and Ni whereas the ORR activity originates from the N,S‐doped ZTC substrate. The selectivity of the ORR process is improved through the presence of sulfide phases. Compared to more conventional carbon substrate such as N,S‐co‐doped reduced graphene oxide, high specific surface area ZTC favors high ORR performances. The functional ZTC material was further successfully implemented as bifunctional air electrode in a coin‐type Zn‐air battery.

Polymerized Phthalocyanine Manganese/Graphene Composites for Single-Atom Oxygen Reduction Catalysts

Polymerized Phthalocyanine Manganese/Graphene Composites for Single-Atom Oxygen Reduction Catalysts

Nitrogen-doped porous carbon nanosheets derived from furfural residue as an oxygen reduction catalyst

The complex pore structure of porous carbon plays a pivotal role in determining the catalytic activity of catalysts involved in the oxygen reduction reaction (ORR), and template methods have emerged as the gold standard in the fabrication of porous carbon. This study describes the preparation of a series of carbon materials that use furfural residue and urea as carbon and nitrogen sources, respectively, in conjunction with KOH as an activating agent through a template method. The prepared catalysts have a large specific surface area and an abundance of micro/mesoporous structures, both of which facilitate ion transport and promote active site exposure. Notably, the sample with a carbon-to-nitrogen mass ratio of 1:4 (FR/C-4) exhibits an exceptionally high specific surface area (2190 m2 g−1) along with an impressive array of pore structures. Compared with commercial Pt/C, FR/C-4 demonstrates superior ORR catalytic activity with a half-wave potential (E1/2) of 0.88 V. Furthermore, FR/C-4 demonstrates remarkable stability and methanol tolerance in alkaline electrolytes, indicating its potential for a wide range of applications, such as fuel cells and metalair batteries.

Molten Salt-Assisted Synthesis of Ferric Oxide/M-N-C Nanosheet Electrocatalysts for Efficient Oxygen Reduction Reaction.

Efficient, stable, and low-cost oxygen reduction catalysts are the key to the large-scale application of metal-air batteries. Herein, high-dispersive Fe2O3 nanoparticles (NPs) with abundant oxygen vacancies uniformly are anchored on lignin-derived metal-nitrogen-carbon (M-N-C) hierarchical porous nanosheets as efficient oxygen reduction reaction (ORR) catalysts (Fe2O3/M-N-C, M═Cu, Mn, W, Mo) based on a general and economical KCl molten salt-assisted method. The combination of Fe with the highly electronegative O induces charge redistribution through the Fe-O-M structure, thereby reducing the adsorption energy of oxygen-containing substances. The coupling effect of Fe2O3 NPs with M-N-C expedites the catalytic activity toward ORR by promoting proton generation on Fe2O3 and transfer to M-N-C. Experimental and theoretical calculation further revealed the remarkable electronic structure evolution of the metal site during the ORR process, where the emission density and local magnetic moment of the metal atoms change continuously throughout their reaction. The unique layered porous structure and highly active M-N4 sites resulted in the excellent ORR activity of Fe2O3/Cu-N-C with the onset potential of 0.977V, which is superior to Pt/C. This study offers a feasible strategy for the preparation of non-noble metal catalysts and provides a new comprehension of the catalytic mechanism of M-N-C catalysts.

Synthesis of coralline Cu-HHTP conductive MOF as an efficient oxygen reduction catalyst to enhance the power generation of the microbial fuel cell

Synthesis of coralline Cu-HHTP conductive MOF as an efficient oxygen reduction catalyst to enhance the power generation of the microbial fuel cell

Boosting the bifunctional catalytic activity of Co3O4 on silver and nickel substrates for the alkaline oxygen evolution and reduction reactions

Developing an efficient bifunctional catalyst for oxygen reduction (ORR) and evolution reactions (OER) is a crucial step for the wide commercialization of alkaline water electrolyzers. However, a proper assessment and comparison of various catalysts is still challenging due to the different catalyst substrates and loadings. In this work, Co3O4 spinel nanoparticles (NPs) were investigated as a bifunctional catalyst at different substrates of glassy carbon or Ag bulk substrate or Ni particles and with different loadings. For Co3O4 (800 µg cm-2)/Ag electrode, not only the overpotential for ORR was 50 mV lower than the bare Ag electrode, but also the OER overpotential was 40 mV lower than the sole Co3O4. Besides, less than 1% peroxide intermediate was detected during ORR using the rotating ring disc electrode (RRDE) method, suggesting a 4-electron O2 reduction. Tafel slopes of 70 and 60 mV dec‑1 at Co3O4/Ag were obtained for ORR and OER, respectively. The improved bifunctional activity could be attributed to a synergistic effect between Co3O4 and the Ag support. For the loading effect, it is revealed that the number of accessible sites of Ag surface decreases with increasing the Co3O4 loading, as evaluated from lead-underpotential deposition measurements. Interestingly, after running ORR/OER cycles, the surface area increased by 4–6 times. This surface roughening was also confirmed by SEM and EDX. The study was extended to Co3O4+Ni mixed catalyst to validate the effect of the support on this induced synergism. Hence, this work provides a simple route for designing potential effective catalytic interfaces and contributes to unravelling the influence of the substrate and loading on the catalyst activity for water electrolyzers.

Nanoparticles of CoFeZn Supported on N-Doped Carbon as Bifunctional Catalysts for Oxygen Reduction and Oxygen Evolution

Nanoparticles of CoFeZn Supported on N-Doped Carbon as Bifunctional Catalysts for Oxygen Reduction and Oxygen Evolution

Asymmetric Microenvironment Tailoring Strategies of Atomically Dispersed Dual-Site Catalysts for Oxygen Reduction and CO2 Reduction Reactions.

Dual-atom catalysts (DACs) with atomically dispersed dual-sites, as an extension of single-atom catalysts (SACs), have recently become a new hot topic in heterogeneous catalysis due to their maximized atom efficiency and dual-site diverse synergy, because the synergistic diversity of dual-sites achieved by asymmetric microenvironment tailoring can efficiently boost the catalytic activity by optimizing the electronic structure of DACs. Here, this work first summarizes the frequently-used experimental synthesis and characterization methods of DACs. Then, four synergistic catalytic mechanisms (cascade mechanism, assistance mechanism, co-adsorption mechanism and bifunction mechanism) and four key modulating methods (active site asymmetric strategy, transverse/axial-modification engineering, distance engineering and strain engineering) are elaborated comprehensively. The emphasis is placed on the effects of asymmetric microenvironment of DACs on oxygen/carbon dioxide reduction reaction. Finally, some perspectives and outlooks are also addressed. In short, the review summarizes a useful asymmetric microenvironment tailoring strategy to speed up synthesis of high-performance electrocatalysts for different reactions.

ZIF-8-derived carbon substrates embedded with atomically dispersed FeN2O2 active sites as bifunctional catalysts for electrochemical carbon dioxide and oxygen reduction

Transition metal assemblies on nitrogen-containing carbon substrates have promising applications as bifunctional electrocatalysts for electrochemical carbon dioxide reduction reaction (CO2RR) and oxygen reduction reaction (ORR). In this study, ZIF-8 with a rhombic dodecahedral morphology was grown from zinc nitrate and 2-methylimidazole feedstock. Then, a nitrogen-containing carbon substrate with a pore structure was formed after the release of Zn through high-temperature calcination. During the calcination process at 700°C, Fe atoms were physically adsorbed on the nitrogen-containing carbon substrate and ligated with N/O to form FeN2O2 reactive sites. For CO2RR, FeN2O2/NC exhibited excellent catalytic properties for converting CO2 to CO, achieving a high Faraday efficiency of 95.5 % at −0.7 V. Under alkaline conditions, it demonstrated ORR performance (E1/2 = 0.83 V) comparable with that of Pt/C (E1/2 = 0.82 V). This study not only presents an energy-efficient method for CO2RR but also provides new insights into highly active catalysts for ORR.

One-pot synthesis of supported PtCox bifunctional catalysts for oxygen reduction and hydrogen evolution reactions

Hydrogen fuel cells and water electrolyzers hold significant potential for net zero emission and climate change mitigation, but their practical applications are limited by the use of the precious-metal platinum as catalysts. In this study, a one-pot method is developed for the synthesis of PtCox alloys supported on hybrid carbon materials, and it is found that the developed catalysts with reduced Pt loading can act as excellent bifunctional catalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Morphology and composition characterizations indicate uniform dispersion and adjustable composition of PtCox alloys with the particle size of ∼3 nm on the carbon support. Among them, Pt3Co/C achieves the highest ORR performance with a high mass activity of 179.23 A/g and a specific activity of 3.15 A/m2 in acidic condition, and an extremely low overpotential of 47.6 mV at 10 mA/cm2 in alkaline media as a HER catalyst. This study presents a cost-effective approach for the development of high performance PtCox/C catalysts, and confirms their potential application in hydrogen energy technologies.

Functional Ni/MnO2 heterostructure electrocatalysts based on self-sacrifice-induced LDHs anchored on nanofibers for microbial fuel cells

Designing cost-effective, highly active oxygen reduction catalysts for high-power-density microbial fuel cells (MFCs) is a significant challenge. To address this, this study uniformly dispersed layered double hydroxides (LDHs) on nanofiber surfaces, and subsequently utilized the self-sacrifice method of zeolite imidazole frameworks (ZIFs) to synthesize LDH/ZIF@CNFs bimetallic heterostructure with precise lattice matching. Experimental results collectively verified that LDH/ZIF@CNFs-12 exhibits an onset potential of -0.087 V, surpassing Pt/C (-0.098 V). Impressively, MFC equipped with LDH/ZIF@CNFs-12 achieves a high power density of 939.05 mW/cm2, surpassing Pt/C (859.74 mW/cm2). The excellent electrocatalytic performance of this catalyst originates from the rich active sites exposed in the LDHs core during the MOFs-assisted synthesis process, and the synergistic catalysis achieved by the formation of heterojunctions. In addition, 3D nanofibers uniformly disperse active sites and reduce large band gaps. This work unveils a new perspective for cost-effective, eco-friendly, and sustainable catalysts suitable for MFCs.