Electrocatalysts For Oxygen Reduction Reaction Research Articles

Engineering peripheral S-doped atomic Fe-N4 in defect-rich porous carbon nanoshells for durable oxygen reduction reaction and Zn-air batteries

Iron-nitrogen-carbon (Fe-N-C) single-atom materials have emerged as the most promising catalysts for the oxygen reduction reaction (ORR), which yet suffers from inadequate stability arising from the attack of ·OH and HO2· radicals generated by H2O2. In this study, density functional theory (DFT) calculations reveal that the presence of peripheral S atoms can regulate the electronic structure of the Fe center and suppress the formation of H2O2 to enhance the catalyst's durability. Thereafter, atomic Fe-N4 with peripheral S doping is intricately engineered in defect-rich porous carbon nanoshells (Fe-NS-C) through an adsorption-pyrolysis method. The incorporation of S not only optimizes the coordination microenvironment of Fe-N4 but also induces a larger specific surface area and richer defects. The Fe-NS-C catalyst displays remarkable ORR performance, featuring a half-wave potential (E1/2) of 0.90 V. Its low H2O2 yield (below 1.1 %) and excellent stability (10 mV day in E1/2 after 10,000 cycles) further underscore the superiority of Fe-NS-C. When employed as the cathode for Zn-air battery, Fe-NS-C achieves an impressive peak power density of 230.1 mW cm−2 and stable charge/discharge potentials over an extended duration of 150 h. This study presents an effective strategy for engineering efficient and durable single-atom electrocatalysts for ORR and Zn-air batteries.

Spin Manipulation of Heterogeneous Molecular Electrocatalysts by an Integrated Magnetic Field for Efficient Oxygen Redox Reactions.

Understanding the spin-dependent activity of nitrogen-coordinated single metal atom (M-N-C) electrocatalysts for oxygen reduction and evolution reactions (ORR and OER) remains challenging due to the lack of structure-defined catalysts and effective spin manipulation tools. Herein, both challenges using a magnetic field integrated heterogeneous molecular electrocatalyst prepared by anchoring cobalt phthalocyanine (CoPc) deposited carbon black on polymer-protected magnet nanoparticles, are addressed. The built-in magnetic field can shift the Co center from low- to high-spin (HS) state without atomic structure modification, affording one-order higher turnover frequency, a 50% increased H2O2 selectivity for ORR, and a ≈4000% magnetocurrent enhancement for OER. This catalyst can significantly minimize magnet usage, enabling safe and continuous production of a pure H2O2 solution for 100 h from a 100 cm2 electrolyzer. The new strategy demonstrated here also applies to other metal phthalocyanine-based catalysts, offering a universal platform for studying spin-related electrochemical processes.

Aminotriazine derived N-doped mesoporous carbon with a tunable nitrogen content and their improved oxygen reduction reaction performance.

The electrocatalytic activity of carbon materials is highly dependent on the controlled modulation of their composition and porosity. Herein, mesoporous N-doped carbon with different amounts of nitrogen was synthesized through a unique strategy of using a high nitrogen containing CN precursor, 3-amino 1,2,4 triazine (3-ATZ) which is generally used for the preparation of carbon nitrides, integrated with the combination of a templating method and high temperature treatment. The nitrogen content and the graphitisation of the prepared materials were finely tuned with the simple adjustment of the carbonisation temperature (800-1100 °C). The optimised sample as an electrocatalyst for oxygen reduction reaction (ORR) exhibited an onset potential of 0.87 V vs. RHE with a current density of 5.1 mA cm-2 and a high kinetic current density (Jk) of 33.1 mA cm-2 at 0.55 V vs. RHE. The characterisation results of the prepared materials indicated that pyridinic and graphitic nitrogen in the carbon framework promoted ORR activity with improved four-electron selectivity and excellent methanol tolerance and stability. DFT calculations demonstrated that the structural and planar defects in the N-doped carbon regulated the surface electronic properties of the electrocatalyst, leading to a reduction in the energy barrier for the ORR activity. This strategy has the potential to unlock a platform for designing a series of catalysts for electrochemical applications.

Earth-Abundant Divalent Cation High-Entropy Spinel Ferrites as Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions

Earth-Abundant Divalent Cation High-Entropy Spinel Ferrites as Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions

N, S co-doped carbon nanotubes loaded with Cu nanoclusters for efficient oxygen reduction reaction.

Developing highly superior precious-metal-free electrocatalysts for oxygen reduction reaction (ORR) are challenging and great significance. In this study, it is reported that an efficient ORR catalysts with N and S co-doped carbon nanotubes anchored to copper (Cu) nanoclusters by mechanical grinding and high temperature heat treatment. The obtained Cu-S1-N-C electrocatalysts exhibited a high ORR performance with an onset potential (Eonest) of 0.989 V and a half-wave potential (E1/2) of 0.905 V (vs. RHE) in alkaline electrolyte, which was superior to that of commercial Pt/C catalyst. In contrast to N doping alone, the defect structures and active species of the catalysts were optimized by precise modulation of S-atom doping, and moreover, the introduction of S-atoms provided more thiophene-sulfur active sites. This study provides an innovative idea for designing excellent ORR catalysts.

Modulating Spin of Atomic Manganese Center for High-Performance Oxygen Reduction Reaction.

Single atom catalysts (SACs) are promising non-precious catalysts for oxygen reduction reaction (ORR). Unfortunately, the ORR SACs usually suffer from unsatisfactory activity and in particular poor stability. Herein, we report atomically dispersed manganese (Mn) embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for ORR in alkaline electrolyte, realizing a half-wave potential (E1/2) of 0.883 V vs. reversible hydrogen electrode (RHE) with negligible activity degradation after 40,000 cyclic voltammetry (CV) cycles in 0.1 M KOH. Introducing sulfur (S) to form Mn-S coordination changes the spin state of single Mn atom from high-spin to low-spin, which effectively optimizes the oxygen intermediates adsorption over the single Mn atomic sites and thus greatly improves the ORR activity.

Inclusion Strategy for Constructing S/N Orbital Hybridization-Regulated sp3/sp2 Carbon toward Boost Electrocatalysis.

Metal-free carbon-based electrocatalysts have gained significant attention in the field of zinc-air batteries (ZABs) due to their affordability, good conductivity and chemical stability. However, unmodified carbon materials typically fall short in adsorbing and activating the substrates and intermediates involved in oxygen reduction reactions (ORR). Here, a metal-free carbon-based electrocatalyst with S atom p orbital hybrid modified N-sp3/sp2 carbon structure (C/NS) were prepared by cyclodextrins inclusion. The catalyst demonstrates impressive ORR activity (E1/2=0.885 V vs. RHE) and robust ZABs performance with a power density of 171.3 mW cm-2 and a specific capacity of 781.2 mAh g-1. Density functional theory (DFT) calculation reveals that S atom effectively regulates the charge distribution and p-band center of active site carbon atom in the N-sp3/sp2 carbon structure. This modification prompts the adsorption and dissociation of O2 and intermediates, resulting in higher reactive activity. This work provides a valuable and practical strategy for preparing cost-effective metal-free carbon-based electrocatalysts for ORR with high performance.

Modulating Spin of Atomic Manganese Center for High‐Performance Oxygen Reduction Reaction

Single atom catalysts (SACs) are promising non‐precious catalysts for oxygen reduction reaction (ORR). Unfortunately, the ORR SACs usually suffer from unsatisfactory activity and in particular poor stability. Herein, we report atomically dispersed manganese (Mn) embedded on nitrogen and sulfur co‐doped graphene as an efficient and robust electrocatalyst for ORR in alkaline electrolyte, realizing a half‐wave potential (E1/2) of 0.883 V vs. reversible hydrogen electrode (RHE) with negligible activity degradation after 40,000 cyclic voltammetry (CV) cycles in 0.1 M KOH. Introducing sulfur (S) to form Mn‐S coordination changes the spin state of single Mn atom from high‐spin to low‐spin, which effectively optimizes the oxygen intermediates adsorption over the single Mn atomic sites and thus greatly improves the ORR activity.

Pt Nanoparticles Electrochemically Deposited onto Heteroatom-Doped Graphene Supports as Electrocatalysts for ORR in Acid Media

Platinum nanoparticles (PtNPs) are attached to different single heteroatom-doped (N, S, P, and B) and dual heteroatom-doped (N, B and N, P) graphene nanosheets via electrochemical deposition using the chronoamperometric method, which allowed for strong attachment of the PtNPs onto the support surface. The effect of the support material on the electrocatalytic activity of the PtNPs on the oxygen reduction reaction (ORR) in acidic media is examined. The PtNPs supported on boron-doped graphene exhibit the highest specific activity (1.26 mA cm−2), and the PtNPs supported on nitrogen and boron dual heteroatom-doped graphene exhibit the highest mass activity (0.70 A mg−1) at 0.9 V vs reversible hydrogen electrode. The kinetics of the ORR vary significantly depending on the dopants, thus concluding that the heteroatom doping of the graphene support material affects the electrocatalytic activity of PtNPs toward the ORR.

Enhanced durability of Pd/CeO2-C via metal-support interaction for oxygen reduction reaction.

It is a challenge to improve the long-term durability of Pd-based electrocatalysts for oxygen reduction reaction (ORR) in fuel cells. Herein, Pd/CeO2-C-T (T= 800 °C, 900 °C and 1000 °C) hybrid catalysts with metal-support interaction are prepared from Ce-based metal organic framework precursor. Abundant tiny CeO2nanoclusters are produced to form nanorod structures with uniformly distributed carbon through a calcination process. Meanwhile, both carbon and CeO2nanoclusters have good contact with the following deposited surfactant-free Pd nanoclusters. Benefited from the large specific surface area, good conductivity and structure integrity, Pd/CeO2-C-900 exhibits the best electrocatalytic ORR performance: onset potential of 0.968 V and half-wave potential of 0.857 V, outperforming those obtained on Pd/C counterpart. In addition, the half-wave potential only shifts 7 mV after 6000 cycles of accelerated durability testing, demonstrating robust durability.

Ternary ordered L10-Pt-Co-Fe intermetallics for efficient ORR catalysis through dissociation pathway

Developing efficient and durable Pt-based electrocatalysts for oxygen reduction reaction (ORR) is critical for the practical application of fuel cells but still remains challenge at present. Here we successfully synthesized a series of ternary L10-PtCoxFe1-x (x=0.33, 0.50 and 0.67) intermetallic nanoparticles (NPs) supported on reduced graphene oxide for ORR catalysis. L10-PtCo0.50Fe0.50 exhibits the highest mass activity (MA) of 0.93 A mg−1Pt at 0.9 V (1.82 times the corresponding binary L10-PtCo intermetallics) and minimal activity loss (24.73 % loss in MA) after 30,000 potential cycles. By Density Functional Theory calculations, the excellent performance of ternary L10-PtCo0.50Fe0.50 can be ascribed to: (1) more efficient electronic structure regulation caused by dual-element driven electron transfer, which leads to more electron accumulation on Pt and weakens the over-binding of oxygen-containing species, (2) the unique two-center bridge pattern of O2 adsorption over Pt-Fe site leads to ORR proceeding via. the dissociative mechanism, avoiding the formation of OOH*.

N-doped carbon confined ternary Pt2NiCo intermetallics for efficient oxygen reduction reaction

Developing high performance electrocatalysts for the cathodic oxygen reduction reaction (ORR) is essential for the widespread application of fuel cells. Herein, a promising Pt2NiCo atomic ordered ternary intermetallic compound with N-doped carbon layer coating (o-Pt2NiCo@NC) has been synthesized via a facile method and applied in acidic ORR. The confinement effect provided by the carbon layer not only inhibits the agglomeration and sintering of intermetallic nanoparticles during high temperature process but also provides adequate protection for the nanoparticles, mitigating the aggregation, detachment and poisoning of nanoparticles during the electrochemical process. As a result, the o-Pt2NiCo@NC demonstrates a mass activity (MA) and specific activity (SA) of 0.65 A/mgPt and 1.41 mA/cmPt2 in 0.1 mol/L HClO4, respectively. In addition, after 30,000 potential cycles from 0.6 V to 1.0 V, the MA of o-Pt2NiCo@NC shows much lower decrease than the disordered Pt2NiCo alloy and Pt/C. Even cycling at high potential cycles of 1.5 V for 10,000 cycles, the MA still retains ∼70%, demonstrating superior long-term durability. Furthermore, the o-Pt2NiCo@NC also exhibits strong tolerance to CO, SOx, and POx molecules in toxicity tolerance tests. The strategy in this work provides a novel insight for the development of ORR catalysts with high catalytic activity, durability and toxicity tolerance.

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 nitrogen 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 −0.7V. Under alkaline conditions, it demonstrated ORR performance (E1/2 = 0.83V) comparable with that of Pt/C (E1/2 = 0.82V). This study not only presents an energy-efficient method for CO2RR but also provides new insights into highly active catalysts for ORR.

LaCo0.2Fe0.8O3 perovskites doped with natural Ca2+ as bifunctional electrocatalysts for oxygen evolution and reduction reactions.

Perovskite oxides are promising electrocatalysts for various energy applications due to their exceptional catalytic activity, flexible architecture, and low cost. In this study, LCFO was doped with different ratios of Ca2+ from eggshells, resulting in dual-purpose electrocatalysts for oxygen reduction and evolution processes. The nanoparticles were characterized using various techniques, including Brunauer-Emmett-Teller analysis and XRD. Results clarified the relative surface area and roughness, increasing with Ca2+ doping. LCFO also demonstrated highly magnetic properties, improved charge transfer, catalytic activity, and long-term durability. The results demonstrated the perovskite's cost-effectiveness as a bifunctional electrocatalyst, and the role of Ca2+ in enhancing its properties. La0.6Ca0.4Co0.2Fe0.8O3(LCCFO-0.4) showed higher magnetic properties (M s = 13.36 emu g-1 and M r = 2.54 emu g-1). The LCFO sample showed a current density of 5.13 mA cm-2 and 3 mA cm-2 for OER and ORR respectively, at E onset 1.7 V and 0.57 V (vs. RHE). The LCFO electrochemical active surface area is 0.033 cm2.

Factors influencing the stability of Pt-based ORR electrocatalysts in HT-PEMFCs: A theoretical investigation

Electrocatalyst stability is a key parameter for commercializing high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Here, we used density functional theory (DFT) to investigate the stability of Pt-based electrocatalysts by calculating the binding energy (ΔEb) of surface Pt atoms under working conditions. Our results show that Pt(111) is more stable than Pt(100) and Pt(110) under vacuum conditions. Stress hurts the stability of Pt(111), regardless of compressive or tensile stress. Most of the transition metals alloyed with Pt improve the stability of Pt(111), especially PtV, PtY, and PtTa, which increase the ΔEb by 0.60–0.70 eV (ΔΔEb). However, the stability of Pt is significantly destroyed under the working conditions of oxygen reduction reaction (ORR). The specific adsorption of ORR intermediates and electrolyte ions decreases the ΔEb of Pt(111) by 0.35–0.95 eV, and the effect of PO43-* is more significant. Furthermore, when the electric field of the electrochemical double layer is coupled with PO43-* specific adsorption, ΔΔEb further increases to 1.12 eV. Our results highlight the importance of the intrinsic ΔEb and the working conditions for the stability of Pt-based electrocatalysts. This work provides important guidelines for the design of stable ORR electrocatalysts for HT-PEMFCs.

On the Stability of an Atomically‐Dispersed Fe−N−C ORR Catalyst: An In Situ XAS Study in a PEMFC

AbstractThe stability of Fe−N−C oxygen reduction reaction (ORR) electrocatalysts has been considered a primary challenge for their practical application in proton exchange membrane fuel cells (PEMFCs). While several studies have attempted to reveal the possible degradation mechanism of Fe−N−C ORR catalysts, there are few research results reporting on their stability as well as the possible Fe species formed under different voltages in real PEMFC operation. In this work, we employ in‐situ X‐ray absorption near‐edge structure (XANES) to monitor the active‐site degradation byproducts of an atomically dispersed Fe−N−C ORR catalyst under a H2/O2‐operating PEMFC at 90 % relative humidity and 80 °C. For this, stability tests were carried out at two constant cell voltages, namely 0.4 and at 0.8 V. Even though the ORR activity of the Fe−N−C catalyst decreased significantly and was almost identical at the end of the tests for the two voltages employed, the analysis of the XANES recorded under H2/N2 configuration at 0.6 and 0.9 V within the stability test suggests that two different degradation mechanisms occur. They are demetalation of iron cations followed by their precipitation into Fe oxides upon operation at 0.8 V, versus a chemical carbon oxidation close to the active sites, likely triggered by reactive oxygen species (ROS) originated from the H2O2 formation, during the operation at 0.4 V.

Strain engineering of CoSA[sbnd]N[sbnd]C catalyst toward enhancing the oxygen reduction reaction activity

Developing efficient and cost-effective platinum-group metal-free (PGMF) catalysts for the oxygen reduction reaction (ORR) is crucial for energy conversion and storage devices. Among these catalysts, metal-nitrogen-carbon (MNC) materials, particularly cobalt single-atom catalysts (CoSANC), show promise as ORR electrocatalysts. However, their ORR activity is often hindered by strong hydroxyl (OH) adsorption on the Co sites. While the impact of strain engineering on MNC electrocatalysts has been minimally explored, recent studies suggest its potential to enhance catalytic performance and optimize intrinsic activity in traditional bulk catalysts. In this context, we investigate the effect of surface strain on CoSANC for ORR activity and correlate substrate-strain-induced geometric distortions with catalytic activity using experimental and theoretical methods. The findings suggest that the d-band center gap of spin states (Δεd) may be a preferred descriptor for predicting strain-dependent ORR performance in MNC catalysts. Leveraging CoSANC moiety placed on a substrate with an average size of 1.0 μm, we achieve performance comparable to that of commercial Pt/C catalysts when used as a cathode catalyst in zinc-air batteries. This investigation unveils the structure–function relationship of MNC electrocatalysts regarding strain engineering and provides valuable insights for future ORR activity design and enhancement.

Metallated graphynes as a bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions: A DFT study

Metallated graphynes as a bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions: A DFT study

Constructing Dual-Phase Co9S8-CoMo2S4 Heterostructure as an Efficient Trifunctional Electrocatalyst for Oxygen Reduction, Oxygen Evolution and Hydrogen Evolution Reactions.

Designing robust, efficient and inexpensive trifunctional electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is significant for rechargeable zinc-air batteries and water-splitting devices. To this end, constructing heterogenous structures based on transition metals stands out as an effective strategy. Herein, a dual-phase Co9S8-CoMo2S4 heterostructure grown on porous N, S-codoped carbon substrate (Co9S8-CoMo2S4/NSC) via a one-pot synthesis is investigated as the trifunctional ORR/OER/HER electrocatalyst. The optimized Co9S8-CoMo2S4/NSC2 exhibits that ORR has a half-wave potential of 0.86 V (vs. RHE) and the overpotentials at 10 mA cm-2 for OER and HER are 280 and 89 mV, respectively, superior to most transition-metal based trifunctional electrocatalysts reported to date. The Co9S8-CoMo2S4/NSC2-based zinc-air battery (ZAB) has a high open-circuit voltage (1.41 V), large capacity (804 mA h g-1) and highly stable cyclability (97 h at 10 mA cm-2). In addition, the prepared Co9S8-CoMo2S4/NSC2-based ZAB in series can self-drive the corresponding water electrolyzer. The dual-phase Co9S8-CoMo2S4 heterostructure provides not only multi-type active sites to drive the ORR, OER and HER, but also high-speed charge transfer channels between two phases to improve the synergistic effect and reaction kinetics.

Oxygen-enriched Fe-N-C electrocatalyst for efficient oxygen reduction reaction

The cathode's oxygen reduction reaction (ORR) plays a crucial role in a variety of fuel cells. Developing affordable and efficient non-precious electrocatalysts for the ORR poses a major hurdle in the realm of electrochemical energy technologies. This work presents a transition metal-based catalyst, Fe-ONC, in which Fe is loaded in an oxygen-enriched nitrogen-doped carbon (NC) material. Oxygen enrichment of the catalyst was achieved by a pre-oxidation strategy. The XPS analysis reveals that Fe-ONC exhibits a higher abundance of oxidized species. The Fe of Fe-ONC exists in the form of Fe3O4 particles and Fe-Nx, respectively, which are uniformly distributed in the NC. The even spread of iron sites and the plentiful presence of oxygen-rich species are key factors in the superior ORR efficiency of Fe-ONC. Fe-ONC's half-wave potential (E1/2) in an alkaline environment (0.1 M KOH) stands at 0.891 V, markedly surpassing the standard commercial Pt/C value (0.840 V). Additionally, Fe-ONC demonstrated enhanced longevity and resistance to ethanol in comparison to commercially available Pt/C. Fe-ONC's outstanding efficacy highlights its potential as an alternative to precious metal catalysts. The document outlines a plan for creating ORR catalytic materials that are sustainable, economical, and efficient.