High-performance Oxygen Reduction Reaction Catalysts Research Articles

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

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

Encapsulated cementite enhances catalytic performance of carbon nanotubes for oxygen reduction reaction

Nonprecious-metal-based materials show great potential to be highly efficient catalysts for oxygen reduction reaction (ORR). There is still room for improvement in the performances of nonprecious-metal-based catalysts for ORR. In this paper, we investigated the catalytic performances of N-doped carbon nanotubes (CNTs) with encapsulated cementite (Fe3C@CNT) for ORR. The encapsulation structure was confirmed by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses. The catalytic performances of Fe3C@CNT for ORR were investigated by cyclic voltammetry, linear sweep voltammetry, Tafel analysis, rotating disk electrode, and rotating ring-disk electrode tests. The results showed that both the onset potential and half-wave potential of Fe3C@CNT-catalyzed ORR were 60 mV higher than those of 20 wt% Pt/C catalyst. Fe3C@CNT catalyzed ORR mainly happened through a four-electron pathway. The long-time running stability of the Fe3C@CNT was also superior to that of the 20 wt% Pt/C catalyst. The eutectic layers between the CNTs and cementite enhanced the electron transfer from the inner-layer CNT to the surface-layer N-doped CNT. Calculations revealed that the iron and carbon in the cementite were in positive and negative electronic states, respectively. The encapsulated cementite promoted the formation of equipotential circles on the surface-layer CNT, which greatly enhanced the catalytic performance of the Fe3C@CNT for ORR. N-doped CNTs with encapsulated cementite show great potential to be high-performance catalysts for ORR.

Fe-N-C Oxygen Reduction Catalysts Via Chemical Vapor Deposition in Fluidized Bed Reactor

Metal nitrogen carbon catalysts (MNC) are an attractive substitute for platinum-based catalysts in the oxygen reduction reaction (ORR) in PEM fuel cells. However, state-of-the-art MNC catalysts still suffer from low activity and instability. Li et al. [1] demonstrated the use of zinc imidazolate frameworks (ZIF-8) in chemical vapor deposition (CVD) to form active sites without unwanted particle formation or additional treatment steps. In this method, gaseous iron chloride exchanges the zinc in the precatalyst to form active sites.In this work, we introduce a vertical fluidized bed reactor (FBR) for high-scale synthesis of FeNC via CVD, allowing for uniform dispersion of the precatalyst and better zinc-iron exchange. Furthermore, we investigated the influence of differently sized ZIF-8 on the CVD and the formation of the FeNC catalyst.The final catalysts were characterized for their electrochemical activity in a rotating ring disc setup, their site density via CO-chemisorption, and their respective turnover frequency. The physicochemical characterization includes the analysis of surface area and pore structure via nitrogen physisorption, SEM, and TEM, as well as surface structure and compositional analysis via elemental analysis, ICP-OES, and XPS.The exchange of Zn was in the range of 90%, resulting in an iron content of 3.8 wt% with only the formation of desired Fe-Nx active sites. STEM-EDX imaging shows an even distribution of iron and nitrogen in the catalyst, with mean particle sizes of 110 nm. In rotating disc electrode experiments with 0.5 M sulfuric acid, mass activities of 0.23 A/g at 0.9 V vs RHE were achieved.Commercially nano-scaled ZIF-8 with mean particle sizes of 500 nm, synthesized particles with mean sizes of 110 nm were tested, compared to the commercial ZIF-8 Basolite Z1200 with mean particle sizes of 4.9 µm. We could show improved activity in RRDE of the nano-scaled ZIF-8 materials compared to the macro-scaled Basolite.Applying this highly scalable synthesis method for MNC catalysts could be a viable way to achieve high-performance catalysts for ORR.[1] Li Jiao, Jingkun Li, Lynne Larochelle Richard, Qiang Sun, Thomas Stracensky, et al.. Chemical vapour deposition of Fe–N–C oxygen reduction catalysts with full utilization of dense Fe–N4 sites. Nature Materials, 2021, 20, pp.1385-1391.

Nitrogen-doped carbon/graphitic CQDs composites with 98.8% microporosity as a highly stable electrocatalyst for oxygen reduction

Designing micropore-rich carbon materials with large specific surface area (SSA) as a carbon-based oxygen reduction reaction (ORR) electrocatalyst is still frontier but remains challenging in catalysis of zinc-air batteries. Here we propose a new strategy for synthesis of nitrogen atoms co-doped carbon sheets and carbon quantum dots (N-C@CQDs) with an SSA of 1485.3 m2 g−1 and 98.8 % micro-porosity from α-cellulose via using a complex salt (ZnCl2-NH4Cl) with low eutectic point (179 °C) as a pore regulator and K2FeO4 as a graphitization catalyst, which can serve as an active and stable carbon-based ORR electrocatalyst. The role of K2FeO4 not only promotes graphitization but also oxidizes the large-sized graphitic carbon particles into a huge amount of uniformly distributed CQDs. This catalyst has exhibited a comparable ORR activity and superior stability to the Pt/C, but a Zn-air battery assembled with the former has delivered a higher peak power density (214 mW cm−2) and a larger gravimetric energy density (ED) of (959 Wh kgZn-1), especially in which it also displays an outstanding catalytic durability with 98.7 % ED retention during a ∼110 h continuous discharge. This work provides a new pathway for design of high-performance carbon-based ORR catalysts in various energy devices.

Shape and composition evolution of Pt and Pt3M nanocrystals under HCl chemical etching

Controlling the shape and composition of Pt-based nanocrystals is essential to improve electrocatalytic performance. In this work, we have carefully investigated the evolution process of morphology and composition for Pt and Pt3M (M = Ni, Co) nanocrystals by hydrochloric acid (HCl) etching. As a result, only Pt3Ni nanocrystals successfully formed unsaturated step-like atoms on the surface and then constructed high-index facets (HIFs), while Pt and Pt3Co preserved a good octahedron shape. Density functional theory (DFT) calculation suggests that Cl− ions can be tightly adsorbed on the surface of Pt3Ni rather than other nanocrystals, which hinders the deposition of newly-reduced atoms and thus regulating the surface morphology. Besides, the etching of surface transitional metals further accelerates the formation of HIFs. Boosted by the active sites on the surface, HCl-Pt-Ni exhibited a ∼10.8 and ∼11.3 times higher oxygen reduction reaction (ORR) mass and specific activities than commercial Pt/C catalyst, and possessed a good durability after 10,000 cycles test. This work gives a deep insight into the design of high-performance Pt-based ORR catalysts.

Use of biogenic silver nanoparticles on the cathode to improve bioelectricity production in microbial fuel cells.

To date, research on microbial fuel cells (MFCs) has. focused on the production of cost-effective, high-performance electrodes and catalysts. The present study focuses on the synthesis of silver nanoparticles (AgNPs) by Pseudomonas sp. and evaluates their role as an oxygen reduction reaction (ORR) catalyst in an MFC. Biogenic AgNPs were synthesized from Pseudomonas aeruginosa via facile hydrothermal synthesis. The physiochemical characterization of the biogenic AgNPs was conducted via scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-visible spectrum analysis. SEM micrographs showed a spherical cluster of AgNPs of 20-100nm in size. The oxygen reduction reaction (ORR) ability of the biogenic AgNPs was studied using cyclic voltammetry (CV). The oxygen reduction peaks were observed at 0.43V, 0.42V, 0.410V, and 0.39V. Different concentrations of biogenic AgNPs (0.25-1.0mg/cm2) were used as ORR catalysts at the cathode in the MFC. A steady increase in the power production was observed with increasing concentrations of biogenic AgNPs. Biogenic AgNPs loaded with 1.0mg/cm2 exhibited the highest power density (PDmax) of 4.70W/m3, which was approximately 26.30% higher than the PDmax of the sample loaded with 0.25mg/cm2. The highest COD removal and Coulombic efficiency (CE) were also observed in biogenic AgNPs loaded with 1.0mg/cm2 (83.8% and 11.7%, respectively). However, the opposite trend was observed in the internal resistance of the MFC. The lowest internal resistance was observed in a 1.0mg/cm2 loading (87Ω), which is attributed to the high oxygen reduction kinetics at the surface of the cathode by the biogenic AgNPs. The results of this study conclude that biogenic AgNPs are a cost-effective, high-performance ORR catalyst in MFCs.

Mn-Doped Zn Metal-Organic Framework-Derived Porous N-Doped Carbon Composite as a High-Performance Nonprecious Electrocatalyst for Oxygen Reduction and Aqueous/Flexible Zinc-Air Batteries.

Developing low-cost, efficient, and stable oxygen reduction reaction (ORR) electrocatalysts is crucial for the commercialization of energy conversion devices such as metal-air batteries. In this study, we report a Mn-doped Zn metal-organic framework-derived porous N-doped carbon composite (30-ZnMn-NC) as a high-performance ORR catalyst. 30-ZnMn-NC exhibits excellent electrocatalytic activity, demonstrating a kinetic current density of 9.58 mA cm-2 (0.8 V) and a half-wave potential of 0.83 V, surpassing the benchmark Pt/C and most of the recently reported non-noble metal-based catalysts. Moreover, the assembled zinc-air battery with 30-ZnMn-NC demonstrates high peak power densities of 207 and 66.3 mW cm-2 in liquid and flexible batteries, respectively, highlighting its potential for practical applications. The excellent electrocatalytic activity of 30-ZnMn-NC is attributed to its unique porous structure, the strong electronic interaction between metal Zn/Mn and adjacent N-doped carbon, as well as the bimetallic Mn/Zn-N active sites, which synergistically promote faster reaction kinetics. This work offers a controllable design strategy for efficient electrocatalysts with porous structures and bimetallic active sites, which can significantly enhance the performance of energy conversion devices.

Electron-Donors/Acceptors Interaction Enhancing Electrocatalytic Activity of Metal Organic Polymers for Oxygen Reduction.

Catalysts with metal-Nx sites have long been considered as effective electrocatalysts for oxygen reduction reaction (ORR), yet the accurate structure-property correlations of these active sites remain debatable. Report here is a proof-of-concept method to construct 1,4,8,11-tetraaza[14]annulene (TAA)-based polymer nanocomposites with well-managed electronic microenvironment via electron-donors/acceptors interaction of altering electron-withdrawing β-site substituents. DFT calculation proves the optimal -Cl substituted catalyst (CoTAA-Cl@GR) tailored the key OH* intermediate interaction with Co-N4 sites under the d-orbital regulation, hence reaching the top of ORR performance with excellent turnover frequency (0.49 e s-1 site-1). The combination of in-situ scanning electrochemical microscopy and variable-frequency square wave voltammetry techniques contribute the great ORR kinetics of CoTAA-Cl@GR to the relatively high accessible site density (7.71×1019 site g-1) and fast electron outbound propagation mechanism. This work provides theoretical guidance for rational design of high-performance catalysts for ORR and beyond.

Use of Fe-H3BTC and GO Compounds To Prepare N/Fe-Doped Carbon for a High-Performance Oxygen Reduction Reaction Catalyst.

Zinc-air batteries (ZABs), as a new type of energy storage and conversion device, have received lots of attention due to their high energy density and low cost. The electrode material is a key factor for improving the performance of ZABs. Here, a facile strategy for the fabrication of N-rich porous carbon is reported. H3BTC and GO are selected as carbon precursors, histidine and Fe(NO3)3 are used as ligands, and urea is used as a N source and template. After the conventional drying of the complex and following carbonization process, serial N-doped carbon materials are prepared. The composition and structure of the material are characterized, and the effect of the ligand is studied. The hierarchical porous structure facilitates the full exposition of N and trace of Fe active sites and benefits the transportation of electrolytes, thus improving the oxygen reduction reaction (ORR). The ORR performances show that the porous carbon has a positive initial and half-wave potential, good limiting current density, a near four-electron transfer process, and better methanol resistance and durability. The assembled ZAB exhibits high specific capacity (880.4 mAh gZn-1), excellent open-circuit voltage (1.54 V), and superior cycling stability, which further provides the significant potential for its application.

P-Block-metal bismuth-based electrocatalysts featuring tunable selectivity for high-performance oxygen reduction reaction

•The discovery of p-block-metal bismuth-based ORR electrocatalysts is reported •The metallic Bi nanoparticles exhibit outstanding activity for H2O2 production •The single-atomic-site Bi catalysts give excellent performance for 4e− ORR •DFT calculations explain the origin of the high performance of Bi-based ORR catalysts For oxygen reduction reaction (ORR), replacing the conventional electrocatalysts based on platinum-group metals (PGMs) with alternatives based on non-noble metals is vital for the large-scale applications of green energy conversion and chemical synthesis. Here, we report the discovery of ORR catalysts based on the p-block-metal bismuth (Bi); the selectivity in ORR pathways could be controlled by tailoring the size of Bi. Specifically, the metallic Bi nanoparticles gave a high selectivity (>96%) for 2e− ORR, an ultra-high kinetic current density (3.8 mA·cm−2 at 0.65 V), and an excellent stability; in contrast, the single-atomic-site Bi catalysts gave a good selectivity for 4e− ORR and a corresponding half-wave potential of 0.875 V, approaching that of the best-known Fe/NC catalysts. This work presents new high-performance ORR catalysts based on the p-block-metal Bi, in contrast to the intensively studied d-block transition metals, and thus would provide new perspectives for developing PGM-free ORR catalysts. For oxygen reduction reaction (ORR), replacing the conventional electrocatalysts based on platinum-group metals (PGMs) with alternatives based on non-noble metals is vital for the large-scale applications of green energy conversion and chemical synthesis. Here, we report the discovery of ORR catalysts based on the p-block-metal bismuth (Bi); the selectivity in ORR pathways could be controlled by tailoring the size of Bi. Specifically, the metallic Bi nanoparticles gave a high selectivity (>96%) for 2e− ORR, an ultra-high kinetic current density (3.8 mA·cm−2 at 0.65 V), and an excellent stability; in contrast, the single-atomic-site Bi catalysts gave a good selectivity for 4e− ORR and a corresponding half-wave potential of 0.875 V, approaching that of the best-known Fe/NC catalysts. This work presents new high-performance ORR catalysts based on the p-block-metal Bi, in contrast to the intensively studied d-block transition metals, and thus would provide new perspectives for developing PGM-free ORR catalysts.

Amorphous low-coordinated cobalt sulphide nanosheet electrode for electrochemically synthesizing hydrogen peroxide in acid media

This study investigates in-depth the local atomic environment-property relationship of amorphous low-coordination catalysts toward the 2e− oxygen reduction reaction (ORR). Here, an ethanol-assisted slow nucleation strategy was adopted to flexibly regulate the intrinsic activity of CoSx nanostructures for efficient 2e− ORR by oriented control the coordination number of Co. When Co and S form Co-S4 coordination structures, the CuNW@CoS4 exhibits an ultra-low overpotential (0.018 V) with 93 % H2O2 selectivity, and 91 % Faraday efficiency in acidic media at 0.1 VRHE. Furthermore, thus produced H2O2 satisfies in-situ organic pollutants degradation by electro-Fenton. XAS and DFT calculations unveil the S-induced forming of abundant low-coordinated Co atoms as active sites in Co-S4, validating that a favorable d-band energy level of Co center can weaken the OOH* adsorption for accelerating the H2O2 production kinetics. This work is anticipated to enlighten the rational design of high-performance ORR catalysts for practically feasible H2O2 electrosynthesis toward wastewater remediation.

Progress and Perspective for In Situ Studies of Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells.

Proton exchange membrane fuel cell (PEMFC) is one of the most promising energy conversion devices with high efficiency and zero emission. However, oxygen reduction reaction (ORR) at the cathode is still the dominant limiting factor for the practical development of PEMFC due to its sluggish kinetics and the vulnerability of ORR catalysts under harsh operating conditions. Thus, the development of high-performance ORR catalysts is essential and requires a better understanding of the underlying ORR mechanism and the failure mechanisms of ORR catalysts with in situ characterization techniques. This review starts with the introduction of in situ techniques that have been used in the research of the ORR processes, including the principle of the techniques, the design of the in situ cells, and the application of the techniques. Then the in situ studies of the ORR mechanism as well as the failure mechanisms of ORR catalysts in terms of Pt nanoparticle degradation, Pt oxidation, and poisoning by air contaminants are elaborated. Furthermore, the development of high-performance ORR catalysts with high activity, anti-oxidation ability, and toxic-resistance guided by the aforementioned mechanisms and other in situ studies are outlined. Finally, the prospects and challenges for in situ studies of ORR in the future are proposed.

First-Principles Study on Pt-Based Sub-Nanocluster Carbon-Metal Hybrid Catalysts for the Oxygen Reduction Reaction

Recently, the polymer electrolyte membrane fuel cell (PEMFC) has been drawing huge attention as an eco-friendly energy conversion device which can replace an internal combustion engine without environmental contaminant such as CO2 and NOx. However, the use of expensive noble metal catalysts such as Pt is essential for the cathode because the oxygen reduction reaction (ORR) at cathode are kinetically much slower than the hydrogen oxidation at anode. For this reason, many of researchers have vigorously worked on the development of Pt-based alloy catalysts such as Pt-Co and Pt-Ni alloys to reduce noble metal usage, but there are still limitations in catalytic activity and durability for the commercialization. Herein, to overcome the limitations, we developed Pt-based carbon-metal hybrid catalyst showing high performance for ORR using density functional theory (DFT) calculation. The slab model of Pt-based carbon-metal hybrid catalyst was constructed by Pt sub-nanocluster supported on graphite with graphene-shaped carbon shell on top of the Pt sub-nanocluster. The most stable geometry of the hybrid catalyst was determined by the formation energy, and the ORR mechanism on surface of hybrid catalyst as well as electrochemical activity was investigated. As a result of investigation, we confirmed that the oxygen reduction occurs on active graphene-shaped carbon shell sites. On pure Pt sub-nanocluster hybrid catalyst, once the hydrogen superoxide (OOH) is adsorbed on carbon shell surface after the oxygen adsorption and protonation, the hydrogen peroxide (H2O2) is preferentially formed at higher onset potential than that of four-electron O2 reduction, which the final product is water (H2O). However, the formation of hydrogen peroxide in PEMFC should be avoided owing to creation of radical, resultant degradation of membrane and low energy conversion efficiency. Surprisingly, we identified that the hydrogen peroxide formed on pure Pt sub-nanocluster hybrid catalyst can be decomposed into OH and H2O with low energy barrier, whose value is much lower than desorption energy of produced hydrogen peroxide, so that subsequent reduction reaction can occur. When this four-electron ORR via hydrogen peroxide decomposition takes place, the ORR activity is improved compared to Pt(111) catalyst, where the onset potential of pure Pt sub-nanocluster hybrid catalyst presents is higher than that of Pt(111). Moreover, we introduced Pt-based alloy sub-nanocluster to reduce Pt usage further. The Pt-based alloy sub-nanocluster hybrid catalyst also exhibited increased ORR activity. For Pt-based alloy sub-nanocluster hybrid catalyst, we carried out analysis of density of state and figured out that the more orbital overlap between carbon shell and sub-nanocluster is generated, the higher catalytic activity is shown due to enrichment of electrons on carbon shell surface. We expect this work can help understanding the mechanism of activity improvement of carbon metal hybrid catalyst, suggesting promising way to design high-performance ORR catalyst with low Pt loadings.

Co-Doped Zeolite-GO Nanocomposite as a High-Performance ORR Catalyst for Sustainable Bioelectricity Generation in Air-Cathode Single-Chambered Microbial Fuel Cells.

High-performance cobalt (Co) nanoparticles supported on a zeolite-graphene oxide (1:2) matrix (catalyst Z2) are synthesized through a facile reduction method. In multipoint Brunauer-Emmett-Teller (MBET) surface area analysis, catalyst Z2 demonstrates a higher surface area compared with other synthesized catalysts, indicating the presence of a larger number of catalytic active sites, and supports outstanding ORR performance due to an improved electron-transfer rate and a higher number of redox-active sites. Furthermore, it is observed that catalyst Z2 is an excellent electrocatalytic material due to its low charge-transfer resistance and higher oxygen reduction reaction (ORR) activity. Herein, the electrocatalytic investigation suggests that catalyst Z2 at a potential of 483 mV and a reduction current of -0.382 mA displays a higher electrocatalytic performance and higher stability toward ORR compared with other synthesized catalysts and even the standard Pt/C catalyst. Also, when catalyst Z2 is applied as an air-cathode ORR electrocatalyst for a single-chambered microbial fuel cell (SC-MFC), the SC-MFC coated with catalyst Z2 generates the maximum power density of 416.78 mW/m2, which is 306% higher than that of SC-MFC coated with Pt/C (102.67 mW/m2). In fact, the longer stability and electronic conductivity have contributed to an outstanding ORR activity of the nanocomposite due to its porous surface morphology and the presence of the functional groups in the zeolite-GO support matrix. In brief, Co (cobalt) nanoparticles doped on a zeolite-GO (1:2) support matrix are promising cathode electrocatalysts in the practical application of MFCs and other related devices.

A hierarchically ordered porous Fe, N, S tri-doped carbon electrocatalyst with densely accessible Fe-Nx active sites and uniform sulfur-doping for efficient oxygen reduction reaction

Doping FeNC catalysts with heteroatoms has been widely recognized as a most promising way to improve the electrocatalytic activity to achieve the replacement of Pt-based electrocatalysts for efficient oxygen reduction reaction (ORR). However, it is still a challenge to combine delicate control of the catalyst structure with heteroatom-doping to achieve optimal electrocatalytic efficiency. Herein, a strategy of combining chemical vapor deposition (CVD) with dual-template cooperative pyrolysis was rationally designed to synthesize the novel electrocatalyst with densely isolated single Fe atoms scattered on hierarchically ordered porous N and S codoped carbon (ISA-Fe/HOPNSC). The three-dimensional hierarchically ordered interconnected macro/mesoporous structure and uniform sulfur-doping make ISA-Fe/HOPNSC exhibit superb ORR performance in both alkaline and acidic electrolytes with a positive half-wave potential (0.920 V in 0.1 M KOH and 0.795 V in 0.5 M H2SO4) as well as outstanding methanol tolerance and long-time stability. As cathode catalyst in Zn-air battery, ISA-Fe/HOPNSC also provides much better maximum power density (210.7 mW cm−2) and specific capacity (796.7 mAh gZn−1) than those of Pt/C (112.6 mW cm−2 and 712.6 mAh gZn−1). Remarkably, the synthesis strategy in this work proposes myriad opportunities for combining delicate control of the catalyst structure with heteroatom doping to synthesize high-performance ORR catalysts.

Realizing Efficient Catalytic Performance and High Selectivity for Oxygen Reduction Reaction on a 2D Ni2SbTe2 Monolayer.

One of the immediate challenges for the large-scale commercialization of hydrogen-based fuel cells is to develop cost-effective electrocatalysts to enable cathodic oxygen reduction reaction (ORR). Herein, we focus on the potential of the two-dimensional (2D) ternary chalcogenide Ni2SbTe2 monolayer as a high-performance electrocatalyst for the ORR using density function theory. Our computed results reveal that there are an obvious hybridization and electron transfer between the O 2p and Te 5p orbitals, which can activate the adsorbed oxygen and trigger the whole ORR process, with an overpotential as low as 0.33 V. In addition, the adsorption capacity of the monolayer surface for oxygen molecules can be effectively enhanced by doping with Fe or Co atoms. The Ni2SbTe2 monolayers doped with Fe or Co atoms not only maintain their original excellent ORR catalytic activity but also improve selectivity toward the four-electron (4e) reduction pathway. We highly anticipate that this work can provide excellent candidates and new ideas for designing low-cost and high-performance ORR catalysts to replace noble metal Pt-based catalysts in fuel cells.

Ultrafine platinum nanoparticles supported on N,S-codoped porous carbon nanofibers as efficient multifunctional materials for noticeable oxygen reduction reaction and water splitting performance.

The design of highly active, stable and durable platinum-based electrocatalysts towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and hydrogen adsorption has a high and urgent demand in fuel cells, water splitting and hydrogen storage. Herein, ultrafine platinum nanoparticles (Pt NPs) supported on N,S-codoped porous carbon nanofibers (Pt–N,S-pCNFs) hybrids were prepared through the electrospinning method coupled with hydrothermal and carbonation processes. The ultrafine Pt NPs are sufficiently dispersed and loaded on pCNFs and codoped with N and S, which can improve oxygen adsorption, afford more active sites, and greatly enhance electron mobility. The Pt–N,S-pCNFs hybrid achieves excellent activity and stability for ORR with ∼70 mV positive shift of onset potential compared to the commercial Pt/C-20 wt% electrocatalyst. The long-term catalytic durability with 89.5% current retention after a 10 000 s test indicates its remarkable ORR behavior. Pt–N,S-pCNFs also exhibits excellent HER and OER performance, and can be used as an efficient catalyst for water splitting. In addition, Pt–N,S-pCNFs exhibits an excellent hydrogen storage capacity of 0.76 wt% at 20 °C and 10 MPa. This work provides novel design strategies for the development of multifunctional materials as high-performance ORR catalysts, water splitting electrocatalysts and hydrogen storage materials.

A Durable Platinum Group Metal-Free Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells

A Durable Platinum Group Metal-free Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells Hanguang Zhang, Hoon T. Chung, Ulises Martinez, Edward F. Holby, and Piotr Zelenay Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Performance of platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), especially high-temperature metal-nitrogen-carbon (M-N-C) materials, has improved a lot in the last two decades,1, 2 however, their durability continues to present a big challenge. PGM-free catalysts typically suffer a 40-80% activity loss during the first 100 hours of operation in the low-temperature fuel cell cathode, which is way short of the 8,000-hour lifetime target for PEFCs.3, 4 Significant improvements to PGM-free catalyst performance durability are thus required before they can be considered for practical PEFCs.In this presentation, we will introduce a ‘dual-zone’ approach to high-temperature synthesis of PGM-free catalysts, which results in modifications to the catalyst surface and, ultimately, in very significant improvements to their durability. In H2-air fuel cell testing, the ‘dual-zone’ fuel cell catalyst has shown a minimal performance loss during up to 80,000 voltage cycles using standardized PGM-free durability test protocol developed in ElectroCat consortium and approved by DOE. The catalyst has also retained 70% of its initial activity in a 600-hour constant-voltage fuel cell test at 0.70 V.We will report fuel cell performance data in the first part of this presentation, followed by discussion of possible origins of the much improved performance durability imparted by the ‘dual-zone’ approach. Acknowledgement This research was supported by the U.S. DOE, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). References Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science 2011, 332, 443-447.Chung, H. T.; Cullen, D. A.; Higgins, D.; Sneed, B. T.; Holby, E. F.; More, K. L.; Zelenay, P., Direct atomic-level insight into the active sites of a high-performance PGM-free ORR catalyst. Science 2017, 357, 479-484.Shao, Y.; Dodelet, J.-P.; Wu, G.; Zelenay, P., PGM-Free Cathode Catalysts for PEM Fuel Cells: A Mini-Review on Stability Challenges. Mater. 2019, 31, 1807615.U.S. DRIVE Fuel Cell Technical Team Roadmap; Department of Energy, US, 2017.

Effect of Different Iron Sources onIn-SituGrowth of Zeolitic Imidazolate Frameworks-8: For Efficient Oxygen Reduction Electrocatalysts

Transition metal and nitrogen co-doped carbon-based catalysts (TM-N-C) have become the most promising catalysts for Pt/C due to their wide range of sources, low cost, high catalytic activity, excellent stability and strong resistance to poisoning, especially Fe-N-C metal-organic frameworks (MOFs), which are some of the most promising precursors for the preparation of Fe-N-C catalysts due to their inherent properties, such as their highly ordered three-dimensional framework structure, controlled porosity, and tuneable chemistry. Based on these, in this paper, different iron sources were added to synthesis a sort of zeolitic imidazole frameworks (ZIF-8). Then the imidazole salt in ZIF-8 was rearranged into high N-doped carbon by high-temperature pyrolysis to prepare the Fe-N-C catalyst. We studied the physical characteristics of the catalysts by different iron sources and their effects on the catalytic properties of the oxygen reduction reaction (ORR). From the point of morphology, various iron sources have a positive influence on maintaining the morphology of ZIF-8 polyhedron. Fe-N/C-Fe(NO₃)₃ has the same anion as zinc nitrate, and can maintain a polyhedral morphology after high-temperature calcination. It had the highest ORR catalytic activity compared to the other four catalyst materials, which proved that there is a certain relationship between morphology and performance. This paper will provide a useful reference and new models for the development of high-performance ORR catalysts without precious metals.

Enhanced oxygen reduction upon Ag/Fe co-doped UiO-66-NH2-derived porous carbon as bacteriostatic catalysts in microbial fuel cells

As a promising energy storage/conversion technology, the microbial fuel cell (MFC) is generally restricted by the biofouling on the cathode and the sluggish kinetics of oxygen reduction reaction (ORR). Consequently, developing bacteriostatic and high-performance ORR catalysts is critical for the large-scale application of MFC. Herein, we prepare an electrocatalyst of porous octahedral zirconium-based metal organic framework (MOF) UiO-66-NH2 with dispersed Ag and Fe3C nanoparticles (Ag/Fe–N–C) through a facile impregnation and pyrolysis method for an efficient alkaline and neutral ORR. Systematic experimental results demonstrate that the synergistic effect of Ag and Fe can optimize the d-band center of catalyst to boost the interfacial charge transfer, thus resulting in an increased ORR kinetics. As expected, the catalyst with Ag/Fe–N–C-2:1 exhibits outstanding onset potential (1.01 V vs. RHE) and half-wave potential (0.58 V vs. RHE) in neutral electrolyte, which is comparable to Pt/C catalyst. Meanwhile, Ag/Fe–N–C-2:1 indicates obvious antibacterial activity, inhibiting the biofouling on the cathode surface. The MFC with the Ag/Fe–N–C-2:1 as the cathode catalyst can achieve a maximum power density of 1261.1 ± 24 mW m−3, outperforms the MFC with Pt/C (1087.5 ± 14 mW m−3). In summary, Ag/Fe–N–C-2:1 composite can serve as a feasible alternative cathode catalyst for MFC.