Oxygen Reduction Reaction Catalysis Research Articles

Longitudinally Grafting of Graphene with Iron Phthalocyanine‐based Porous Organic Polymer to Boost Oxygen Electroreduction

AbstractIron phthalocyanine‐based polymers (PFePc) are attractive noble‐metal‐free candidates for catalyzing oxygen reduction reaction (ORR). However, the low site‐exposure degree and poor electrical conductivity of bulk PFePc restricted their practical applications. Herein, laminar PFePc nanosheets covalently and longitudinally linked to graphene (3D‐G‐PFePc) was prepared. Such structural engineering qualifies 3D‐G‐PFePc with high site utilization and rapid mass transfer. Thence, 3D‐G‐PFePc demonstrates efficient ORR performance with a high specific activity of 69.31 μA cm−2, a high mass activity of 81.88 A g−1, and a high turnover frequency of 0.93 e s−1 site−1 at 0.90 V vs. reversible hydrogen electrode in O2‐saturated 0.1 M KOH, outperforming the lamellar PFePc wrapped graphene counterpart. Systematic electrochemical analyses integrating variable‐frequency square wave voltammetry and in situ scanning electrochemical microscopy further underline the rapid kinetics of 3D‐G‐PFePc towards ORR.

Stabilizing Fe in intermetallic L10-PtAuFe nanoparticles with strong Au-Fe bond to boost oxygen reduction reaction activity and durability

The intrinsic reactivity of PtM alloys during the catalysis of oxygen reduction reactions (ORRs) under acidic conditions is deactivated by the unavoidable leaching of cocatalyst M. Herein, we propose an unprecedented “Au-stabilized strategy” to stabilize the Fe atoms in L10-PtAuFe via a strong Au-Fe bond. Simultaneously, the introduction of Au atoms regulates the Pt atomic electronic structure and increases resistance to Pt atomic oxidation, which is beneficial to further boost ORR activity and stability. As a result, the as-obtained L10-PtAuFe exhibits minimal loss of mass activity after accelerated durability tests and is far superior to L10-PtFe and commercial Pt/C. In addition, L10-PtAuFe shows fantastic ORR activity, with a 7.3-fold improvement in mass activity and a 4.5-fold increase in specific activity compared to that of commercial Pt/C. This novel Au-stabilized strategy provides a new avenue to stabilize the M atoms in L10-PtM alloys and further enhance their ORR activity and stability.

Identification and Understanding of Active Sites of Non‐Noble Iron‐Nitrogen‐Carbon Catalysts for Oxygen Reduction Electrocatalysis

Non‐noble iron‐nitrogen‐carbon (Fe‐N‐C) catalysts have been explored as one type of the most promising alternatives of precious platinum (Pt) in catalyzing the oxygen reduction reaction (ORR). However, their catalytic ORR activity and stability still cannot meet the requirement of practical applications. Active sites in such catalysts are the key factors determining the catalytic performance. This review gives a critical overview on identification and understanding of active sties of non‐pyrolytic and pyrolytic Fe‐N‐C catalysts in terms of design strategies, synthesis, characterization, functional mechanisms and performance validation. The diversity and complexity of active sites that greatly dominate the progress of Fe‐N‐C catalysts include Fe‐containing sites (Fe‐based nanoparticles and single‐atom Fe‐species) and metal‐free sites (heteroatoms doping and defects). Meanwhile, synergistic effects are also discussed in this review with emphasis on the interaction among multiple active sites. Although substantial endeavors have been devoted to develop the efficient Fe‐N‐C catalysts, some challenges still remain. To facilitate further research on Fe‐N‐C catalysts toward practical applications, some research perspectives are prospected in the aspects of innovative synthesis methods, active‐sites modulation strategies, high‐resolution ex situ/in situ/operando characterization techniques, theoretical calculations, and so on. This review may provide a guideline for identifying and understanding active‐sites for developing high‐performance Fe‐N‐C catalysts.

Boosted Oxygen Reduction Reaction Activity by Ordering Cations in the A-Site of a Perovskite Catalyst

As concerns related to climate change continue to grow, there has been an increasing number of studies on materials that can enhance the efficiency of energy conversion/storage systems. Since the oxygen reduction reaction (ORR) is considered as a rate-determining reaction for the O2 conversion system, it is essential to develop an efficient electrocatalyst that enables greater ORR activity. Perovskite has been explored as a promising electrocatalyst due to its excellent ORR activity at high and room temperatures. Recently, unique perovskite structures that can contain high oxygen vacancy ratios, such as brownmillerite, Ruddlesden–Popper, and layered perovskite, have been studied for exhibiting high ORR performance. However, few studies have dealt with the electrochemical properties of perovskite, which has different structures but the same cation stoichiometry, to know the exact effect of a specific structure. In this study, we synthesized two materials with different structures (cubic structure perovskite and layered structure perovskite) but with the same cation stoichiometry. The layered structure rather than the cubic structure showed cation ordering in the A-site of the perovskite structure with an enhanced oxygen vacancy ratio. As a result, the layered structure exhibits superior electrochemical performance than the cubic structure at high and room temperatures by a factor of ca. 2.7 at 500 °C in fuel cell mode, and ca. 5.5% decrease in overpotential (η) at −3 mA cm–2 for ORR catalysis. Moreover, perovskite hybridized with nitrogen doped reduced graphene oxide (N-rGO) could compensate for the intrinsic shortcoming of perovskite oxide and exert a catalytic synergy (27% decrease in η).

Effects of support material and electrolyte on a triphenylamine substituted cobalt porphyrin catalytic oxygen reduction reaction

The interfacial charge transfer conditions are crucial for understanding the catalytic mechanism and thus developing high performing electrocatalysts. To justify the effects of support material and electrolyte on metalloporphyrin catalytic oxygen reduction reaction (ORR), we synthesize a symmetric triphenylamine (TPA) substituted cobalt porphyrin, nominated as s-TPA-CoP, and select carbon black and multi-walled carbon nanotubes as the supports to fabricate composite catalysts. The ORR performances are measured in both acidic and alkaline solutions. While the support material affects negligibly on reduction potentials, the stronger π-π stacking in s-TPA-CoP/CNT, as revealed by X-ray photoelectron spectroscopy measurements, leads to greater limiting current densities and larger electron transfer numbers as compared to s-TPA-CoP/XC in either electrolyte. Both composites perform better ORR activity but poorer 4-electron selectivity in base than in acid, whose origins are discussed from the aspects of interfacial charge states and inner- / outer-sphere electron transfer mechanisms. Strikingly, s-TPA-CoP/CNT exhibits an electron transfer number of 3.8 in acid, demonstrating the privilege of TPA as the substitution on monometallic cobalt porphyrins in chasing 4-electron transfer oxygen reduction.

Metalloporphyrin doped macroporous ZIF-8 metal-organic framework derived M-Nx carbon material for oxygen reduction reactions

The development of effective transition metal oxygen reduction reaction (ORR) catalysts performing well in alkaline environments remains challenging. In this study, ordered macroporous ZIF-8 @C supports were prepared via carbonization using polystyrene microspheres as templates, and transition metal oxygen reduction catalysts (M-Nx/OMC; M = Fe, Co, and Mn) were prepared by loading metalloporphyrins and carbonization. Among the catalysts prepared, Fe-Nx/OMC exhibited excellent electrocatalytic activity under alkaline conditions, the half-wave (0.911 V) and initial (0.960 V) potentials are 80 and 60 mV higher than that of Pt/C respectively. In addition, the specific capacity of the zinc–air battery (ZAB) catalyzed by Fe-Nx/OMC reached 751 mAh g−1, which is 84 mAh g−1 higher than that of the ZAB catalyzed by Pt/C. The superior catalytic ORR activity is attributed to the hierarchical porous structure, which may have more exposed active centers in the carbon materials and improved mass-transfer efficiency. This study offers a new method for preparing high-performance carbon-based metal–organic framework electrocatalysts.

Molecular Insights into the Structure-Activity Relationship in Cobalt Porphyrin Catalyzed Oxygen Reduction Reaction

Molecular Insights into the Structure-Activity Relationship in Cobalt Porphyrin Catalyzed Oxygen Reduction Reaction

Synthesis of Platinum Nanocrystals Dispersed on Nitrogen-Doped Hierarchically Porous Carbon with Enhanced Oxygen Reduction Reaction Activity and Durability.

Platinum-based catalysts are widely used for efficient catalysis of the acidic oxygen reduction reaction (ORR). However, the agglomeration and leaching of metallic Pt nanoparticles limit the catalytic activity and durability of the catalysts and restrict their large-scale commercialization. Therefore, this study aimed to achieve a uniform distribution and strong anchoring of Pt nanoparticles on a carbon support and improve the ORR activity and durability of proton-exchange membrane fuel cells. Herein, we report on the facile one-pot synthesis of a novel ORR catalyst using metal-nitrogen-carbon (M-N-C) bonding, which is formed in situ during the ion exchange and pyrolysis processes. An ion-exchange resin was used as the carbon source containing R-N+(CH3)3 groups, which coordinate with PtCl62- to form nanosized Pt clusters confined within the macroporous framework. After pyrolysis, strong M-N-C bonds were formed, thereby preventing the leaching and aggregation of Pt nanoparticles. The as-synthesized Pt supported on the N-doped hierarchically porous carbon catalyst (Pt/NHPC-800) showed high specific activity (0.3 mA cm-2) and mass activity (0.165 A mgPt-1), which are approximately 2.7 and 1.5 times higher than those of commercial Pt/C, respectively. The electrochemical surface area of Pt/NHPC-800 remained unchanged (~1% loss) after an accelerated durability test of 10,000 cycles. The mass activity loss after ADT of Pt/NHPC-800 was 18%, which is considerably lower than that of commercial Pt/C (43%). Thus, a novel ORR catalyst with highly accessible and homogeneously dispersed Pt-N-C sites, high activity, and durability was successfully prepared via one-pot synthesis. This facile and scalable synthesis strategy for high-efficiency catalysts guides the further synthesis of commercially available ORR catalysts.

Carboxyl induced ultrahigh defects and boron/nitrogen active centers in cobalt-embedded hierarchically porous carbon nanofibers: The stable oxygen reduction reaction catalysis in acid

Transition metal-nitrogen-carbon (MNC) type catalysts have been considered a promising alternative to noble metals for oxygen reduction reaction (ORR) electrocatalysis. Nevertheless, poor stabilities of MNC catalysts in acidic solutions limit their commercialization. In this study, we design and synthesize novel three-dimensional (3D) cobalt (Co) nanoparticles encapsulated in ultrahigh content of boron (B) and nitrogen (N) -doped hierarchically porous carbon nanofibers (denoted as Co@BN-PCNFs) by carbonizing the 3D acetic acid/cobalt nitrate/4-hydroxybenzeneboronic acid/polyvinylpyrrolidone precursor networks woven using electrospinning method under a nitrogen atmosphere. The optimal Co@BN-PCNFs-900 catalyst has abundant micro/mesopores and numerous topological defects and exhibits the largest surface area. Under the synergistic effect of oxygen-containing acetic acid molecules and the electrospinning technology, 5.87 at.% of B and 5.91 at.% of N atoms were doped into carbon nanofibers. Specifically, B/N electrocatalytic active centers (including BC3, pyridinic-N/CoNC, pyrrolic-N, and graphitic-N) of approximately 8.70 at.% were successfully introduced into the skeletons of Co@BN-PCNFs-900. In 0.1 M KOH, the ORR onset potential (Eonset) and half-wave potential (E1/2) of Co@BN-PCNFs-900 were ∼ 64 and ∼ 63 mV, respectively, more positive than those of 20 wt% Pt/C. Additionally, in 0.5 M H2SO4, the ORR Eonset and E1/2 values of Co@BN-PCNFs-900 were only ∼ 11 and ∼ 7 mV, respectively, more negative than those of 20 wt% Pt/C. As the 3D hierarchically porous architectures, topological carbon edges, BC3, and partial NC/CoNC are relatively stable, the Co@BN-PCNFs-900 exhibits excellent stability toward ORR catalysis in both acidic and basic media. These favorable properties of Co@BN-PCNFs-900 nanofibers make them the best non-noble metal-based carbonaceous electrocatalysts for ORR in acidic electrolytes.

Facile Preparation of Cobalt Nanoparticles Encapsulated Nitrogen-Doped Carbon Sponge for Efficient Oxygen Reduction Reaction.

The facile preparation of non-noble metal nanoparticle loaded carbon nanomaterials is promising for efficient oxygen reduction reaction (ORR) electrocatalysis. Herein, a facile preparation strategy is proposed to prepare nitrogen-doped carbon sponge loaded with fine cobalt nanoparticles by the direct pyrolysis of the cobalt ions adsorbed polymeric precursor. The polymeric sponge precursor with continuous framework and high porosity is formed by the self-assembly of a poly(amic acid). Taking advantage of the negatively charged surface and porous structure, cobalt ions can be efficiently adsorbed into the polymeric sponge. After pyrolysis, fine cobalt nanoparticles covered by carbon layers are formed, while the sponge-like structure of the precursor is also well-preserved in order to give cobalt nanoparticles loaded nitrogen-doped carbon sponges (Co/CoO@NCS) with a high loading content of 44%. The Co/CoO@NCS exhibits promising catalytic activity toward ORR with a half-wave potential of 0.830 V and a limiting current density of 4.71 mA cm-2. Overall, we propose a facile polymer self-assembly strategy to encapsulate transition metal nanoparticles with high loading content on a nitrogen-doped carbon sponge for efficient ORR catalysis.

Electrochemically Quantifying Oxygen Reduction Selectivity in Nonaqueous Electrolytes

Understanding the factors that govern the selectivity of the oxygen reduction reaction (ORR) has motivated the study of ORR in nonaqueous media, in which the proton donor can be controlled and molecular catalysts can be solubilized. Rotating ring-disc electrode (RRDE) voltammetry is a powerful method for quantifying ORR selectivity but requires that the ring electrode catalyze H2O2 oxidation at transport-limited rates. While the potentials and ring materials required to satisfy this requirement have been examined for aqueous electrolytes, they have not been systematically investigated for nonaqueous electrolytes despite the growing use of RRDE in these media. Herein, we report that conventional Pt ring electrodes and typical RRDE protocols for nonaqueous media do not give rise to mass-transport-limited H2O2 oxidation kinetics. Instead, H2O2 oxidation is strongly activation-controlled on Pt surfaces with kinetics that depend on the electrolyte and solvent. We identify Au as a superior catalyst for nonaqueous H2O2 oxidation and show that transport-limited H2O2 oxidation can be accessed on high-surface-area Au rings under certain electrolyte conditions. Additionally, we develop a protocol for calibrating and correcting for sluggish H2O2 oxidation kinetics. We show that these two methods provide improved estimates of H2O2 selectivity for ORR catalysis in certain nonaqueous electrolytes.

Metal organic polymers with dual catalytic sites for oxygen reduction and oxygen evolution reactions

AbstractMetal–organic frameworks and covalent organic frameworks have been widely employed in electrochemical catalysis owing to their designable skeletons, controllable porosities, and well‐defined catalytic centers. However, the poor chemical stability and low electron conductivity limited their activity, and single‐functional sites in these frameworks hindered them to show multifunctional roles in catalytic systems. Herein, we have constructed novel metal organic polymers (Co‐HAT‐CN and Ni‐HAT‐CN) with dual catalytic centers (metal–N4 and metal–N2) to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). By using different metal centers, the catalytic activity and selectivity were well‐tuned. Among them, Co‐HAT‐CN catalyzed the ORR in a 4e− pathway, with a half‐wave potential of 0.8 V versus RHE, while the Ni‐HAT‐CN catalyze ORR in a 2e− pathway with H2O2 selectivity over 90%. Moreover, the Co‐HAT‐CN delivered an overpotential of 350 mV at 10 mA cm−2 with a corresponding Tafel slope of 24 mV dec−1 for OER in a 1.0 M KOH aqueous solution. The experimental results revealed that the activities toward ORR were due to the M–N4 sites in the frameworks, and both M–N4 and M–N2 sites contributed to the OER. This work gives us a new platform to construct bifunctional catalysts.

Modulation of electronic states in bimetallic-doped nitrogen-carbon based nanoparticles for enhanced oxygen reduction kinetics

Controlling tire local electronic structure of active ingredients to improve the adsorption-desorption characteristics of oxygen-containing intermediates over the electrochemical liquid-solid interfaces is a critical challenge in the field of oxygen reduction reaction (ORR) catalysis. Here, we offer a simple approach for modulating the electronic states of metal nanocrystals by bimetal co-doping into carbon-nitrogen substrate, allowing us to modulate the electronic structure of catalytic ao five centers. To test our strategy, we designed a typical bimetallic nanoparticle catalyst (FeCo NP/NC) to flexibly alter the reaction kinetics of ORR. Our results from synchrotron X- ray absorption spectroscopy and X-ray photoelectron spectroscopy showed that the co-doping of iron and cobalt could optimize the intrinsic charge distribution of Fe-Co NP/NC catalyst, promoting the oxygen reduction kinetics and ultimately achieving remarkable ORR activity. Consequently, the carefully designed Fe-Co NP/NC exhibits an ultra-high kinetic current density at the operating voltage (71.94 mA/cm2 at 0.80 V), and the half-wave potential achieves 0.915 V, which is obviously better than that of the corresponding controls including Fe NP/NC, Co NP/NC. Our findings provide a unique perspective for optimizing the electronic structure of active centers to achieve higher ORR catalytic activity and faster kinetics.

Tuning NiCo2O4 bifunctionality with nitrogen-doped graphene nanoribbons in oxygen electrocatalysis for zinc-air battery application

• Composites thermally prepared from NiCo 2 O 4 and nitrogen-doped graphene nanoribbons; • Tuning the NiCo 2 O 4 and N-doped graphene ratio tailors the bifunctional activity for ORR and OER; • NiCo 2 O 4 /GNRN-based catalysts as efficient bifunctional catalysts for air electrode of ZAB; • Presence of GNRN proved to be crucial for enhancing the catalysts bifunctionality. One of the major barriers to the widespread use and commercialization of zinc-air batteries (ZAB) is the use of inefficient and expensive bifunctional materials for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysis on the air electrode. Herein, we propose a highly durable ORR/OER bifunctional catalyst, which was thermally prepared using NiCo 2 O 4 blended with nitrogen-doped graphene nanoribbons (GNRN). We evaluated the activity and electrochemical stability of catalysts with different ratios of NiCo 2 O 4 and GNRN as well as the role of each component in the electrocatalytic process to find the most efficient catalyst for both ORR and OER. ORR results revealed that the NiCo 2 O 4 (80):GNRN(20) and NiCo 2 O 4 (90):GNRN(10) novel catalysts exhibited a half-wave potential of ca. 0.79 V RHE in a 4-electron pathway and were practically unaffected by the presence of methanol. With regard to OER, the unblended NiCo 2 O 4 catalyst exhibited the lowest potential required to reach 10 mA cm −2 (1.60 V RHE ), followed by NiCo 2 O 4 (90):GNRN(10) (1.62 V RHE ), and NiCo 2 O 4 (80):GNRN(20) (1.68 V RHE ); however, the presence of tuned amount of N-doped graphene proved to be crucial for enhancing charge transfer, stability, and the ORR/OER bifunctionality of catalysts. After applying NiCo 2 O 4 /GNRN materials and commercial Pt-Ru/C as catalysts in ZAB, the results showed that NiCo 2 O 4 (80):GNRN(20) and NiCo 2 O 4 (90):GNRN(10) exhibited maximum power densities of 78 and 69 mW cm -2 , respectively; these values were quite similar to that obtained for Pt-Ru/C (81 mW cm -2 ). The specific capacity for Pt-Ru/C-based ZAB was 707 mAh g Zn -1 , while both NiCo 2 O 4 /GNRN-based ZABs showed 702 mAh g Zn -1 (86% of the theoretical capacity). Moreover, long-term operation tests involving high current densities and charge-discharge ZAB cycling revealed that NiCo 2 O 4 /GNRN catalysts are clearly more suitable for use at ZAB air electrode than Pt-Ru/C and are as efficient as other non-precious metal catalysts of similar kind which have been reported in the literature.

Nitrogen-intercalated Pd metallene nanoribbons with optimized electronic structure for oxygen reduction catalysis.

Herein, we propose nitrogen (N)-intercalated Pd metallene nanoribbons (N-Pd MNRs), which exhibit favorable and stable oxygen reduction reaction (ORR) performance in alkaline media. The ultrathin configuration of the N-Pd MNRs exposes more atoms, thus acting as active sites. More importantly, N intercalation triggers electronic interaction between Pd and N to establish Pd-N bonds and induces lattice strain, which optimizes the electronic structure of the metallene nanoribbons, thereby modulating the binding strength between the intermediates and active sites. This work offers new insights into the rational design of N intercalated metallene nanoribbons for efficient ORR catalysis.

A cobalt corrole with a biologically relevant imidazolium pendant for boosted electrocatalytic oxygen reduction

Developing electrocatalysts with high activity and selectivity for the oxygen reduction reaction (ORR) has attracted increasing interest in the past decades. The many imidazole residues located at the active site of cytochrome c oxidases (CcOs) play crucial roles in facilitating the selective reduction of dioxygen to water. As inspired by nature, we herein reported on the synthesis of [Formula: see text] corrole 1 hanged with a biologically relevant imidazolium group and its electrocatalytic ORR features in both acidic and alkaline solutions. Complex 1 is more active and selective than its imidazolium-free analogue for electrocatalytic four-electron ORR. Importantly, 1 displayed ORR activities with the half-wave potentials at [Formula: see text] = 0.65 V versus RHE in 0.5 M [Formula: see text] solution and at [Formula: see text] = 0.81 V versus RHE in 0.1 M KOH solution. This work presents a strategy to simultaneously improve catalytic ORR activity and selectivity by hanging a cationic imidazolium unit over molecular catalytic sites.

电化学溶出法尺寸可控合成铜基氧还原反应催化剂: 从纳米粒子到原子团簇和单原子

Size-controllable synthesis of non-noble metal particles ranging from nanometer to subnanometer and atomic level is of great significance for demonstrating the size effects of metallic catalysts towards oxygen reduction reaction (ORR) catalysis. Herein, we propose an electrochemical leaching strategy for the top-down synthesis of Cu nanoparticles (NPs), atomic clusters (ACs) and single atoms (SAs) on sulfur-doped reduced graphene oxide (SrGO). Within this strategy, Cu NPs (about 8 nm) were electrodeposited and subsequently controllably downsized to ACs (about 2 nm) and SAs (<1 nm) via a stripping voltammetry method by adjusting the termination potential. The effective control in the size of active Cu species allowed us to conveniently investigate the size effect of Cu on ORR in multiscale. Single-atom Cu exhibited good ORR performance with a half-wave potential of 0.86 V and an electron transfer number of 3.98, as well as a long-term stability, much superior to other larger Cu particles. Our findings open a new avenue for top-down synthesis of metal particles with desirable sizes, which will effectively benefit the future design of size-controlled ORR electrocatalysts.

Evidence of Sulfur Non-Innocence in [CoII (dithiacyclam)]2+ -Mediated Catalytic Oxygen Reduction Reactions.

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]2+ (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S2 N2 -cyclam)]2+ (2; S2 N2 -cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the CoII centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2.

Beweis von Schwefel‐non‐Innocence in [CoII(Dithiacyclam)]2+‐vermittelten, katalytischen Sauerstoff‐Reduktions‐Reaktionen

AbstractIn vielen Metallenzymen sind Schwefel‐enthaltende Liganden an Elektronen‐Transfer‐Reaktionen beteiligt. In dem hier diskutierten biomimetischen Ansatz wird der Einfluss einer Schwefelkoordination auf eine Kobalt‐katalysierte Sauerstoff‐Reduktionsreaktion (ORR) demonstriert. Ein Vergleich des ORR‐Vermögens eines vierfach Stickstoff‐koordinierten [Co(Cyclam]2+‐Komplexes (1; Cyclam=1,5,8,11‐Tetraaza‐cyclotetradecan) und dessen Schwefel‐Analogons [Co(S2N2‐Cyclam)]2+(2; S2N2‐Cyclam=1,8‐Dithia‐5,11‐diazacyclotetradecan) zeigt verbesserte katalytische Eigenschaften mit dem in die Ligandensphäre am Kobalt eingeführten Chalkogen. Isolierung und Charakterisierung der Intermediate, die sich im Zuge der Sauerstoffaktivierung an den Kobalt(II)‐Zentren von1und2bilden, identifizieren eine Beteiligung des Schwefels am O2‐Reduktionsprozess als entscheidenden Faktor für die verbesserten Eigenschaften von2bei der katalytischen ORR.

Recent Advances on Heteroatom-Doped Porous Carbon—Based Electrocatalysts for Oxygen Reduction Reaction

Polymer electrolyte membrane fuel cells are considered one of the alternatives to fossil energy sources. The slow kinetics of the oxygen reduction reaction (ORR) at the cathode and the high price of Pt-based catalysts remain one of the key challenges for the commercial viability of proton exchange membrane fuel cells. However, their high cost and susceptibility to poisoning severely limit their use for large-scale commercial applications in fuel cells. Heteroatom-doped porous carbon has attracted extensive attention from scientists due to its advantages such as high specific surface area and the properties conferred by heteroatom doping. On the one hand, we discuss a variety of current methods for the preparation of heteroatom-doped porous carbons, including the template method and the activation method. On the other hand, we discuss the application of heteroatom-doped porous carbon in Pt catalysts, transition metal catalysts and metal-free catalysts. Finally, we also present the pre-existing and challenges of heteroatoms in ORR catalysis, which will drive the development of ORR catalysts.