Electrocatalysts For Oxygen Reduction Reaction Research Articles

Built‐In Electric Fields and Interfacial Electron Modulation: Enhancement of Oxygen Reduction Reaction in Alkaline Seawater

AbstractThe development of an electrocatalyst for oxygen reduction reaction (ORR) in a seawater electrolyte is the key to realizing the utilization of marine resources and application of Zn–air batteries (ZABs). Exploring the adsorption and desorption behavior of oxygen can guide the design of catalysts fundamentally and improve the catalytic performance. On this basis, WC and Co on nitrogen‐doped carbon (WC‐Co@NC) with an interfacial built‐in electric field (BEF) is designed as an ORR catalyst. The theoretical calculation certifies that the BEF of W─C─Co connections promote charge separation and directional migration, thus realizing the oxygen adsorption equilibrium and speeding up the process of ORR. These give WC‐Co@NC a high half‐wave potential of 0.872 V, and the alkaline seawater‐based ZAB with WC‐Co@NC as the air cathode has a peak power density of 188.8 mW cm−2 and excellent stability. This work can provide a basis for the rational design of the cathode of alkaline seawater‐based ZAB, and can also give a new direction for the utilization of seawater resources.

Stability of Carbon Supported Silver Electrocatalysts for Alkaline Oxygen Reduction and Evolution Reactions.

Ag-based electrocatalysts are promising candidates to catalyze the sluggish oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFC) and oxygen evolution reaction (OER) in unitized regenerative fuel cells. However, to be competitive with existing technologies, the AEMFC with Ag electrocatalyst must demonstrate superior performance and long-term durability. The latter implies that the catalyst must be stable, withstanding harsh oxidizing conditions. Moreover, since Ag is typically supported by carbon, the strict stability requirements extend to the whole Ag/C catalyst. In this work, Ag supported on Vulcan carbon (Ag/VC) and mesoporous carbon (Ag/MC) materials is synthesized, and their electrochemical stability is studied using a family of complementary techniques. We first employ an online scanning flow cell combined with inductively coupled plasma mass spectrometry (SFC-ICP-MS) to estimate the kinetic dissolution stability window of Ag. Strong correlations between voltammetric features and the dissolution processes are discovered. Very high silver dissolution during the OER renders this material impractical for regenerative fuel cell applications. To address Ag stability during AEMFC load cycles, accelerated stress tests (ASTs) in O2-saturated solutions are carried out in rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) setups. Besides tracking the ORR performance evolution, an ex situ long-term Ag dissolution study is performed. Moreover, morphological changes in the catalyst/support are tracked by identical-location transmission electron microscopy (RDE-IL-TEM). Voltammetry analysis before and after AST reveals a smaller change in ORR activity for Ag/MC, confirming its higher stability. RRDE results reveal a higher increase in the H2O2 yield for Ag/VC after the ASTs. The RDE-IL-TEM measurements demonstrate different degradation processes that can explain the changes in the long term performance. The results in this work point out that the stability of carbon-supported Ag catalysts depends strongly on the morphology of the Ag nanoparticles, which, in turn, can be tuned depending on the chosen carbon support and synthesis method.

Sustainable Synthesis of Metal-Doped Lignin-Derived Electrospun Carbon Fibers for the Development of ORR Electrocatalysts.

The aim of this work is to establish the Oxygen Reduction Reaction (ORR) activity of self-standing electrospun carbon fiber catalysts obtained from different metallic salt/lignin solutions. Through a single-step electrospinning technique, freestanding carbon fiber (CF) electrodes embedded with various metal nanoparticles (Co, Fe, Pt, and Pd), with 8-16 wt% loadings, were prepared using organosolv lignin as the initial material. These fibers were formed from a solution of lignin and ethanol, into which the metallic salt precursors were introduced, without additives or the use of toxic reagents. The resulting non-woven cloths were thermostabilized in air and then carbonized at 900 °C. The presence of metals led to varying degrees of porosity development during carbonization, improving the accessibility of the electrolyte to active sites. The obtained Pt and Pd metal-loaded carbon fibers showed high nanoparticle dispersion. The performance of the electrocatalyst for the oxygen reduction reaction was assessed in alkaline and acidic electrolytes and compared to establish which metals were the most suitable for producing carbon fibers with the highest electrocatalytic activity. In accordance with their superior dispersion and balanced pore size distribution, the carbon fibers loaded with 8 wt% palladium showed the best ORR activity, with onset potentials of 0.97 and 0.95 V in alkaline and acid media, respectively. In addition, this electrocatalyst exhibits good stability and selectivity for the four-electron energy pathway while using lower metal loadings compared to commercial catalysts.

PGM-free carbon-based catalysts for the electrocatalytic oxygen reduction reaction: active sites and activity enhancement

Exploring high-activity, low-cost platinum group metal-free (PGM-free) oxygen reduction reaction (ORR) electrocatalysts to replace precious metal Pt is critical for large-scale fuel cell applications. Owing to their wide source, controllable composition, low price, and excellent performance, the PGM-free carbon-based electrocatalysts have attracted great interest in academia and are expected to be an ideal replacement for precious metal electrocatalysts. In this review, we mainly focus on PGM-free carbon-based electrocatalysts and first introduce the ORR mechanisms and the active site classification of PGM-free carbon-based electrocatalysts. Then, we propose four strategies to enhance the ORR activity of electrocatalysts from the active site perspective based on the relationship between the structure and function of active sites. Finally, we present the current challenges and prospects for developing ORR electrocatalysts exhibiting high performance and stability.

Directly assembling initial metal–organic framework and covalent organic polymer toward bifunctional oxygen electrocatalysts for Zn-air flow battery

Developing highly efficient bifunctional oxygen electrocatalysts is important but still remains a challenge for Zn-air flow battery. Metal-organic frameworks (MOFs) and covalent organic polymers (COPs) materials have emerged as promising alternatives to the benchmark precious metal electrocatalysts due to their designable and controllable structures at the atomic level. However, their catalytic performances are limited by the conductivity and catalytic activity using initial materials. Moreover, these materials are generally developed either as single oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalysts. Herein, we utilize the π-π stacking effect to directly assemble initial nanosheet FeNi-MOF and iron phthalocyanine rich COP hybrid materials toward the highly efficient bifunctional electrocatalysts via pyrolysis-free strategy. The carbon black is added to the composite as support to limit the stacking of composites and increase the conductivity. The obtained catalyst, named as NSFeNi@COPFe-C, exhibits superior catalytic performance with an ORR onset potential of 0.99 V (vs. reversible hydrogen electrode: RHE), half-wave potential of 0.9 V (vs. RHE), and the OER potential of 1.65 V at 10 mA cm−2 in alkaline electrolyte. The assembled zinc-air flow battery with NSFeNi@COPFe-C as the bifunctional oxygen electrocatalyst shows a discharge power up to 115 mW cm−2 and a long-term stability.

Recent Advances in Non‐Precious Metal Single‐Atom Electrocatalysts for Oxygen Reduction Reaction in Low‐Temperature Polymer‐Electrolyte Fuel Cells

AbstractFuel cells have emerged as a promising clean electrochemical energy technology with a great potential in various sectors, including transportation and power generation. However, the high cost and scarcity of the noble metals currently used to synthesise electrocatalysts for low‐temperature fuel cells has hindered their widespread commercialisation. In recent decades, the development of non‐precious metal electrocatalysts for the cathodic oxygen reduction reaction (ORR) have gained significant attention. Among those, electrocatalysts with atomically dispersed active sites, referred to as single‐atom catalysts (SACs), are gaining more interest. Nanocarbon materials containing single transition metal atoms coordinated to nitrogen atoms are active electrocatalysts for the ORR in both acidic and alkaline conditions and thus have a great promise to be utilised as non‐precious metal cathode electrocatalysts in low‐temperature fuel cells. This review article provides an overview of the recent advancements in the utilisation of transition metal‐based SACs in proton exchange membrane fuel cells (PEMFCs) and anion exchange membrane fuel cells (AEMFCs). We highlight the main strategies and synthetic approaches for tailoring the properties of SACs to enhance their ORR activity and durability. Based on the already achieved results, it is evident that SACs indeed could be suitable for the cathode of the low‐temperature fuel cells.

Electrochemically Reduced Graphene Oxide Supported Palladium-Cobalt Alloy Nanoparticles as Highly Efficient Electrocatalyst for Oxygen Reduction Reaction

Pd-Co alloy nanoparticles were synthesized on electrochemically reduced graphene oxide (ErGO) for electrocatalytic oxygen reduction reaction (ORR) in alkaline media. The morphological structure, chemical composition, and crystallinity of the afforded ErGO/Pd-Co catalyst were examined by various techniques, including transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. The Pd-Co alloy nanoparticles were evenly distributed on the ErGO sheet and had a narrow size distribution, with an average particle size of 4.25 nm. The ORR activity of the as-prepared ErGO/Pd-Co alloy catalyst was evaluated by cyclic voltammetry, linear sweep voltammetry, rotating disk electrode, and rotating ring disk electrode techniques in an alkaline electrolyte. The ErGO/Pd-Co catalyst exhibits a very high electrocatalytic activity in ORR with the mass activity more than 2.0 times of the commercial 20% Pt/C due to the synergistic catalytic effect of both ErGO and Pd-Co nanoparticles. Electrocatalytic kinetics investigation shows that, the ORR on the ErGO/Pd-Co catalyst proceeds through four electrons transferred mechanism with negligible amount of peroxide species. Moreover, the ErGO/Pd-Co shows an excellent methanol tolerance than the commercial 20% Pt/C.

Lead and Nitrogen Co-Doped Multi-Walled Carbon Nanotube Electrocatalyst for Oxygen Reduction Reaction

The electrocatalysis of oxygen reduction reaction (ORR) on lead and nitrogen co-doped multi-walled carbon nanotube (Pb/N/MWCNT) composite catalyst has been investigated in the neutral, acidic and alkaline media. The mixture of lead phthalocyanine (PbPc) and MWCNTs was pyrolysed in nitrogen atmosphere to achieve co-doping of lead and nitrogen. The successful co-doping as well as formation of Pb nanoparticles were confirmed with the use of various physical and surface characterisation methods such as scanning and transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction analysis. This work brings forth the electrocatalytic effect of Pb and nitrogen co-doping of carbon by a detailed electrochemical analysis using rotating disk electrode (RDE) method. The Pb and nitrogen co-doped MWCNT material demonstrate a reasonable electrocatalytic ORR activity in acidic, neutral and alkaline media. The results indicate great potential of Pb to be employed in electrocatalyst design as co-doping agent to achieve superior cathode catalysts for microbial, proton and anion exchange membrane fuel cells.

Validating Electrochemical Active Surface Area Determination of Nanostructured Electrodes: Surface Oxide Reduction on AuPd Nanoparticles

Accurate normalization of electrochemical active surface area (ECSA) of nanostructured catalysts and nanoparticles is of utmost importance for catalyst activity determination and comparability. AuxPdy nanoparticles are a highly interesting example, as electrocatalysts for selective oxygen reduction reaction and alcohol oxidation. Most techniques used today for ECSA determination lack accurate validation for nanostructured electrodes and instead rely on reference values determined for macroelectrodes. This includes ECSA determination for AuxPdy nanoparticles, most commonly done by potentiodynamic surface oxide reduction. Here we suggest a versatile approach to validate different ECSA determination techniques for nanoparticle-modified or nanostructured electrodes, using surface oxide reduction of AuxPdy as an illustrative example. Combining this with volume determination by anodic stripping, we electrochemically estimate the NP diameter, which serves as an indication of the accuracy of the obtained ECSA values. Showcasing this for different nanoparticle compositions, we provide experimental conditions for determining AuxPdy nanoparticle ECSA using surface oxide reduction and compare those to parameters reported for macroelectrodes. The approach we introduce herein can be readily applied to a number of different alloy systems, thus, providing a widely applicable approach to determine electrochemical surface areas and validate the transferability of existing macroelectrode characterization techniques to nanostructured or nanoparticle-modified electrodes.

Interfacial engineering-induced Janus heterostructures with enhanced electronic regulation for efficient oxygen electrocatalysis in rechargeable Zn-air batteries

Construction of efficient non-noble metal electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are extremely important for zinc-air batteries (ZABs). Herein, a novel Janus heterostructure, coupling CeO2 with bimetallic metal sulfides (ZnCoS) with precise heterointerfaces, was designed through an interfacial engineering-induced strategy. Benefiting from the interfacial synergistic effect, the asymmetric Janus heterostructure of CeO2/ZnCoS (J−CeO2/ZCS) exhibits satisfactory ORR and OER activity, in terms of E1/2 of 0.87 V for ORR and overpotential of 290 mV for OER. Theoretical calculation further demonstrates that the heterointerface effectively modulates the electronic structure and charge redistribution, thus improving redox reactivity of active sites and the absorption/desorption of reaction intermediates. When the J-CeO2/ZCS applied in liquid and flexible ZABs as air cathodes, the devices deliver excellent power density and cycling stability. This Janus structure of composite catalysts affords a new opportunity for designing efficient oxygen electrocatalysts with heterostructures.

Pt-free graphene oxide-hydrogen membrane fuel cells (GOHMFCs)

High-performance conventional proton exchange membrane fuel cells (PEMFCs) typically rely on expensive Pt/C as the catalyst for the hydrogen oxidation reaction (HOR) at the anode and the oxygen reduction reaction (ORR) at the cathode, which suffers from CO poisoning. As a result, there is a surging interest in developing precious metal-free electrocatalysts in fuel cells and metal-air batteries. A promising candidate is graphene, a one-atom-thick monolayer with a 2-dimensional (2-D) hexagonal honeycomb lattice of carbon, which offers an ideal replacement opportunity as an electrocatalyst for the ORR due to its high catalytic activity and tolerance against poisoning. In this study, nitrogen-doped reduced graphene oxide (N-rGO), a low-cost and precious metal-free electrocatalyst for ORR, are synthesized using a hydrothermal method using a low-cost industrial material ammonium formate (NH4HCO2) as both the reductant agent and nitrogen source. Here, we have confirmed the successful formation of N-rGO and reduced graphene oxide (rGO) through a series of analyses on the microstructure, molecular bonding, nanometric composition, and surface chemistry of the materials and their ORR activity. By integrating a membrane electrode assembly (MEA) with MPTS-modified graphene oxide (GO) composite electrolyte (MGC-50), which contains a 50 wt% ratio of (3-mercaptopropyl)trimethoxysilane (MPTS) and GO, we have developed a safe and scalable method for Pt/C-free electrocatalyst application in graphene oxide-hydrogen membrane fuel cells (GOHMFCs). The best performing catalyst (N-rGO-AA@180) exhibited the maximum power density (MPD) of 17.57 mW/cm2 with a load current density (LCD) of 87.50 mA/cm2, significantly better than those of rGO@300, which has an MPD of 5.70 mW/cm2 with an LCD of 23.90 mA/cm2, both measured at 40 °C.

Cu-Alginate/Graphene Aerogels Derived Electrocatalyst for Oxygen Reduction Reaction

In this work, the Cu-alginate/graphene aerogels were prepared by using alginate, graphene and copper chloride as precursors by a freeze-drying process. Finally, N-doped carbon aerogels supported by Cu nanoparticles (NPs) (Cu/N-CAs) were obtained through annealing in the NH3 atmosphere. The morphology, microstructures, specific surface area, and pore size distribution were studied by SEM, XRD, and BET analysis. The results showed that a significant amount of Cu NPs were uniformly disseminated on the aerogels’ surface, and the catalysts’ specific surface area reached 141 m2/g. Electrochemical tests revealed good catalytic capabilities for the oxygen reduction reaction (ORR) of the as-obtained Cu/N-CAs. Compared to the commercial 20%Pt/C, the Cu/N-CAs exhibited comparable catalytic performance, superior catalytic stability and methanol resistance. The transfer of 3.94 electrons indicated that the Cu/N-CAs were undergoing a four-electron (4e-) ORR process.

Recent Progress in Using Mesoporous Carbon Materials as Catalyst Support for Proton Exchange Membrane Fuel Cells.

Developing durable oxygen reduction reaction (ORR) electrocatalysts is essential to step up the large-scale applications of proton exchange membrane fuel cells (PEMFCs). Traditional ORR electrocatalysts provide satisfactory activity, yet their poor durability limits the long-term applications of PEMFCs. Porous carbon used as catalyst support in Pt/C is vulnerable to oxidation under high potential conditions, leading to Pt nanoparticle dissolution and carbon corrosion. Thus, integrating Pt nanoparticles into highly graphitic mesoporous carbons could provide long-term stability. This Perspective seeks to reframe the existing approaches to employing Pt alloys and mesoporous carbon-integrated ORR electrocatalysts to improve the activity and stability of PEMFCs. The unusual porous structure of mesoporous carbons promotes oxygen transport, and graphitization provides balanced stability. Furthermore, the synergistic effect between Pt alloys and heteroatom doping in mesoporous carbons not only provides a great anchoring surface for catalyst nanoparticles but also improves the intrinsic activity. Furthermore, the addition of Pt alloys into mesoporous carbon optimizes the available surface area and creates an effective electron transfer channel, reducing the mass transport resistance. The long-term goals for fuel-cell-powered cars, especially those designed for heavy-duty use, are well aligned with the results shown when this hybrid material is used in PEMFCs to improve performance and durability.

Boosting the oxygen bifunctional activity on cobalt nanocrystals/RGO with extended durability

Nanoengineering effective bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a major challenge in improving the performance of electrochemical energy conversion devices. In this study, we present a simple synthesis route for producing Co-Nx crystals that are effectively arranged on reduced graphene oxide layers (Co–N/RGO) through mechanochemical treatment. The Co–N/RGO catalyst performs well as a bifunctional oxygen electrocatalyst. Specifically, the Co–N/RGO-700 has an earlier ORR onset (0.91 V) and a half-wave potential (0.79 V) with a higher kinetic current density of 6.6 mA cm−2 than Pt/C, as well as a lower overpotential (430 mV) and Tafel slope (115 mV dec−1) for the OER. These results demonstrate outstanding performance compared to reported Co-based catalysts. Theoretical modeling and experimental results explore the Co–N/RGO active sites, as well as the vital role of electronic structure, abundant N content, and surface defects, confirming it as a potential electrode material for energy conversion applications.

Lattice-Strained Metallic Aerogels as Efficient and Anti-Poisoning Electrocatalysts for Oxygen Reduction Reaction.

Lattice strain engineering optimizes the interaction between the catalytic surface and adsorbed molecules. This is done by adjusting the electron and geometric structure of the metal site to achieve high electrochemical performance, but, to date, it has been rarely reported on anti-poisoned oxygen reduction reaction (ORR). Herein, lattice-strained Pd@PdBiCo quasi core-shell metallic aerogels (MAs) were designed by "one-pot and two-step" method for anti-poisoned ORR. Pd@PdBiCo MAs/C maintain their original activity (1.034 A mgPd -1 ) in electrolytes with CH3 OH and CO at 0.85 V vs. reversible hydrogen electrode (RHE), outperforming the commercial Pd/C (0.156 A mgPd -1 ), Pd MAs/C (0.351 A mgPd -1 ), and PdBiCo MAs/C (0.227 A mgPd -1 ). Moreover, Pd@PdBiCo MAs/C also show high stability and anti-poisoning with negligible activity decay after 8000 cycles in 0.1 m KOH+0.3 m CH3 OH. These results of X-ray photoelectron spectroscopy, CO stripping, and diffuses reflectance FTIR spectroscopy reveal that the tensile strain and strong interaction between different elements of Pd@PdBiCo MAs/C effectively optimize the electronic structure to promote O2 adsorption and activation, while suppressing CH3 OH oxidation and CO adsorption, leading to high ORR activity and anti-poisoning property. This work inspires the rational design of MAs in fuel cells and beyond.

Potential-driven instability effect of carbon supports for Pt/C electrocatalysts

Proton exchange membrane fuel cell (PEMFC) technology is a crucial approach of achieving clean and efficient power generation. However, prior to its full commercialization, several pressing issues must be addressed, especially the dissolution/degradation of Pt-based electrocatalysts for the cathode oxygen reduction reaction (ORR). This degradation significantly reduces the electrocatalytic activity of the catalysts. In this work, the impact of solid carbon support (Vulcan XC-72 R) and porous carbon support (Ketjenblack EC-300) on the degradation process of Pt/C electrocatalysts was investigated. By utilizing various triangular-wave voltage cycles in accelerated durability testing (ADT) protocols, the experimental findings suggest that a lower upper potential limit (UPL) in ADT tends to promote Pt diffusion and further aggregation, while a higher UPL exacerbates the electrochemical dissolution of Pt. Furthermore, the results indicate that Ketjenblack is more proficient than Vulcan XC-72 R in facilitating Pt redeposition after dissolution, which helps to minimize the loss of Pt under standardized rotating disk-electrode (RDE) aqueous electrolyte ADT conditions.

Catalysis Sans Catalyst Loss: The Origins of Prolonged Stability of Graphene-Metal-Graphene Sandwich Architecture for Oxygen Reduction Reactions.

Over the past decades, the design of active catalysts has been the subject of intense research efforts. However, there has been significantly less deliberate emphasis on rationally designing a catalyst system with a prolonged stability. A major obstacle comes from the ambiguity behind how catalyst degrades. Several degradation mechanisms are proposed in literature, but with a lack of systematic studies, the causal relations between degradation and those proposed mechanisms remain ambiguous. Here, a systematic study of a catalyst system comprising of small particles and single atoms of Pt sandwiched between graphene layers, GR/Pt/GR, is studied to unravel the degradation mechanism of the studied electrocatalyst for oxygen reduction reaction(ORR). Catalyst suffers from atomic dissolution under ORR harsh acidic and oxidizing operation voltages. Single atoms trapped in point defects within the top graphene layer on their way hopping through toward the surface of GR/Pt/GR architecture. Trapping mechanism renders individual Pt atoms as single atom catalyst sites catalyzing ORR for thousands of cycles before washed away in the electrolyte. The GR/Pt/GR catalysts also compare favorably to state-of-the-art commercial Pt/C catalysts and demonstrates a rational design of a hybrid nanoarchitecture with a prolonged stability for thousands of operation cycles.

Surfactant-assisted Fe-anchored and N-doped ultrathin graphene nanosheets for enhanced electrocatalytic oxygen reduction

Exploration of tremendous electrocatalysts for oxygen reduction reaction (ORR) as promising alternatives is urgent in various electrochemical applications. As a result, one catalyst of homogeneously dispersed Fe, N sites anchored on two-dimensional (2D) ultrathin graphene nanosheets (Fe-N@C) is rationally designed and synthesized via a surfactant-assisted pyrolysis approach. Water-soluble F127 surfactant facilitates the uniform dispersion of Fe and restrains the aggregation of Fe-based particles during pyrolysis treatment, which promotes the formation of plentiful FeNx species. The 2D ultrathin structure is beneficial to expose more FeNx and make the most use of these active sites. Therefore, the developed Fe-N@C catalyst demonstrates enhanced catalytic properties in alkaline media with an approximate 4e− pathway and more positive half-wave potential (E1/2, 0.85 V), which is plus 0.04 V than commercial 20 % Pt/C catalyst. Besides, the target catalyst also exhibits superb poison resistance and long-term stability. This work presents a practical direction for the fabrication of other high-efficient catalysts and a new insight into ORR.

Pyrazine-linked Iron-coordinated Tetrapyrrole Conjugated Organic Polymer Catalyst with Spatially Proximate Donor-Acceptor Pairs for Oxygen Reduction in Fuel Cells.

Nitrogen-coordinated iron (Fe-N4 ) materials represent the most promising non-noble electrocatalysts for the cathodic oxygen reduction reaction (ORR) of fuel cells. However, molecular-level structure design of Fe-N4 electrocatalyst remains a great challenge. In this study, we develop a novel Fe-N4 conjugated organic polymer (COP) electrocatalyst, which allows for precise design of the Fe-N4 structure, leading to unprecedented ORR performance. At the molecular level, we have successfully organized spatially proximate iron-pyrrole/pyrazine (FePr/Pz) pairs into fully conjugated polymer networks, which in turn endows FePr sites with firmly covalent-bonded matrix, strong d-π electron coupling and highly dense distribution. The resulting pyrazine-linked iron-coordinated tetrapyrrole (Pz-FeTPr) COP electrocatalyst exhibits superior performance compared to most ORR electrocatalysts, with a half-wave potential of 0.933 V and negligible activity decay after 40,000 cycles. When used as the cathode electrocatalyst in a hydroxide exchange membrane fuel cell, the Pz-FeTPr COP achieves a peak power density of ≈210 mW cm-2 . We anticipate the COP based Fe-N4 catalyst design could be an effective strategy to develop high-performance catalyst for facilitating the progress of fuel cells.

Pyrazine‐linked Iron‐coordinated Tetrapyrrole Conjugated Organic Polymer Catalyst with Spatially Proximate Donor‐Acceptor Pairs for Oxygen Reduction in Fuel Cells

AbstractNitrogen‐coordinated iron (Fe−N4) materials represent the most promising non‐noble electrocatalysts for the cathodic oxygen reduction reaction (ORR) of fuel cells. However, molecular‐level structure design of Fe−N4 electrocatalyst remains a great challenge. In this study, we develop a novel Fe−N4 conjugated organic polymer (COP) electrocatalyst, which allows for precise design of the Fe−N4 structure, leading to unprecedented ORR performance. At the molecular level, we have successfully organized spatially proximate iron‐pyrrole/pyrazine (FePr/Pz) pairs into fully conjugated polymer networks, which in turn endows FePr sites with firmly covalent‐bonded matrix, strong d‐π electron coupling and highly dense distribution. The resulting pyrazine‐linked iron‐coordinated tetrapyrrole (Pz−FeTPr) COP electrocatalyst exhibits superior performance compared to most ORR electrocatalysts, with a half‐wave potential of 0.933 V and negligible activity decay after 40,000 cycles. When used as the cathode electrocatalyst in a hydroxide exchange membrane fuel cell, the Pz−FeTPr COP achieves a peak power density of ≈210 mW cm−2. We anticipate the COP based Fe−N4 catalyst design could be an effective strategy to develop high‐performance catalyst for facilitating the progress of fuel cells.