Catalytic Activity For Oxygen Reduction Research Articles

Atomic-scale mechanistic study of oxygen reduction mechanism for B-site doped Pr(Ba,Sr)Co2O5+δ by density functional theory calculations

Pr(Ba,Sr)Co2O5+δ is a promising cathode material for solid oxide fuel cell (SOFC) due to its high oxygen ion transport capability and oxygen reduction activity. Density functional theory (DFT) calculations were performed to elucidate the oxygen reduction mechanism of B-site doped Pr(Ba,Sr)(Co,M)2O5+δ (M = Fe, Ni, Cu, and Zn) materials. First, we investigated the formation of O vacancies. The results indicate that Cu and Zn doping facilitate O vacancy formation, resulting in lower O vacancy formation energies. Furthermore, the interaction between oxygen and the (0 0 1) surfaces of B-site doped Pr(Ba,Sr)(Co,M)2O5+δ has been comprehensively discussed, involving both perfect and defective surfaces. The results demonstrate that the presence of O vacancies enhances the catalytic activity for oxygen reduction, by reducing the energy required for O2 dissociation. Zn-doped Pr(Ba,Sr)(Co,M)2O5+δ exhibits a low O vacancy formation energy, resulting in a stable adsorption configuration upon oxygen dissociation, indicating its potential as a cathode material for SOFC.

Promoting electrocatalytic activity of single-phase semiconductor Y3Fe5O12 (YIG) dual-functional cathode/electrolyte for ceramic fuel cells

To construct hybrid functions of electrolyte and cathode materials has improved fuel cell power output and structural stability at low operational temperatures as a novel approach in ceramics fuel cells (CFC) research. We found that semiconductor material Y3Fe5O12 possesses dual-functions of electrolyte and cathode, which has been systematically studied on the ion transport, oxygen kinetics, redox reaction, and electrochemical performance. The sintering temperature strongly affects the YIG, resulting in weak metal oxygen (M-O) bonds, more active sites and enrich oxygen vacancies, which provide both an active surfaces towards oxygen reduction and high oxide ion conductivity. The hybrid functional YIG exhibits good peak power output of 423 mW/cm2 (as an electrolyte) and 531 mW/cm2 (as an cathode) at 540 °C, respectively. Moreover, YIG displays outstanding oxygen reduction reaction (ORR) and catalytic activity during the electrochemical measurements. This work may offer a novel strategy for developing hybrid functions for ceramic fuel cells to enable low operational temperatures.

(Invited) Challenges with Ceria Diffusion Barrier Layer

Sr-doped perovskite has been the most commonly used oxygen electrode material for solid oxide cells due to their high conductivity and catalytic activity for oxygen reduction and oxygen evolution reactions. Direct contact of the electrode material with the doped zirconia electrolyte leads to formation of resistive Sr- and La-zirconate phases during cell fabrication and long-term operation leads to performance loss. A doped ceria barrier layer is applied between the electrolyte and the oxygen electrode to avoid the reactions that form the resistive phase. The ceria layer is applied using a variety of processes and screen printing is the preferred method as the oxygen electrode also uses the same fabrication option. The barrier layer is sintered at high temperature to target a thin, dense layer. The barrier layer sintering temperature needs to balance good resulting density without any reaction with the electrolyte. The ceria-zirconia solid solution is more resistive than the end members. Thus, it is accepted to limit the sintering temperature which results in a porous barrier layer.OxEon stacks tested for several thousand hours were post-test analyzed at the Pacific Northwest National Laboratory using an array of electron microscopes, and Sr migration to the zirconia interface through pores and discontinuity in the barrier layer was confirmed. The use of Sr-free electrode composition between the barrier layer and the Sr-containing electrode layer did not prevent Sr migration to the electrolyte interface when discontinuities are present in the barrier layer.In addition, the dopant in ceria, samaria in this case, also migrates into zirconia during long-term operation while as fabricated cells do not show migration of samaria.Investigations are ongoing to improve the density of the barrier layer without deleterious interdiffusion during fabrication.

The interplay between surface area and sulfur doping of carbon support on Pt NPs nucleation and growth: A synergistic enhancement of catalytic activity for oxygen reduction

Metal–carbon interaction plays a fundamental role in tuning the electrocatalytic behavior of metal nanoparticles (NP). The aim of this study is to emphasize the effective synergy between sulfur doping and the porous structure of the carbon support on the Pt NPs morphology and dimension. Thiophenic-like defects exert a metal-support interaction that affects Pt NPs nucleation and growth and their catalytic activity versus the oxygen reduction reaction (ORR), which makes them promising candidates for the cathode side of PEMFC. Pt NPs defectivity, size, and size dispersion were asserted by using synchrotron wide-angle X-ray total scattering and advanced data analysis. The analyses confirm a mutual correlation between the carbon surface area and the density of sulfur groups with the Pt-specific surface area and with their electrocatalytic properties. The catalytic activity for ORR reaches its peak when a balance is struck between the mesoporosity and the sulfur functionalization of the carbon support.

Construction of Warped Graphitic Layers from Fullerene Soot and Study of Their Catalytic Oxygen Reduction Activity

Construction of Warped Graphitic Layers from Fullerene Soot and Study of Their Catalytic Oxygen Reduction Activity

Ca2Fe2O5 and Ca2Co2O5 based composite cathode for IT-SOFC application

Solid Oxide Fuel Cells at intermediate operating temperatures require high catalytic activity and compatibility of cathode material with electrolyte to reduce interfacial polarisation losses. In the present work, Brownmillerite structured composite based on Ca2Fe2O5 and Ca2Co2O5 [CFO-CCO] was studied for its cathodic properties. The Mixed Ionic and Electronic conducting (MIEC) properties of this composite material improves the Oxygen Reduction Reaction (ORR), catalytic activity and interfacial polarisation resistance. The structural, morphological and elemental analysis of the composite was carried out by XRD, BET, XPS, SEM and EDX. Electrical studies revealed that the Composite Cathode [CFO-CCO] has better ionic conductivity and sufficient electronic conductivity at 800 °C. Impedance analysis of Half-cell[CFO-CCO/SDC] and Symmetric-cell [CFO-CCO/SDC/CFO-CCO] at 800 °C shows the Area Specific Resistance (ASR) of 10.45 Ω cm2 and 1.14 Ω cm2 respectively. Performance of full cell [NiO-SDC/SDC/CFO-CCO] with Samarium doped Ceria (SDC) as electrolyte yields a power density of 160 mW/cm2. Electrochemical Impedance spectroscopy (EIS) measured at open circuit voltage (OCV) shows lower polarisation loss but higher ohmic loss due to the thicker electrolyte. The CFO-CCO composite material shows promising results, attributed to its microstructure and mixed conducting properties, enabling application for Intermediate Temperature solid oxide fuel cells (SOFCs).

Well‐defined N3C1‐anchored Single‐Metal‐Sites for Oxygen Reduction Reaction

AbstractN‐, C‐, O‐, S‐coordinated single‐metal‐sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well‐defined such SMSs, and the fundamental comprehension has long been impeded in case‐by‐case reports using carbon materials as investigation targets. In this work, the well‐defined molecular catalysts with N3C1‐anchored SMSs, i.e., N‐confused metalloporphyrins (NCPor‐Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor‐Ms with corresponding N4‐anchored SMSs (metalloporphyrins, Por‐Ms), are synthesized for catalytic activity evaluation. Among all, NCPor‐Co reaches the top in established volcano plots. NCPor‐Co also shows the highest half‐wave potential of 0.83 V vs. RHE, which is much better than that of Por‐Co (0.77 V vs. RHE). Electron‐rich, low band gap and regulated d‐band center contribute to the high activity of NCPor‐Co. This study delves into the examination of well‐defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high‐performance asymmetric SMS catalysts.

Well-defined N3 C1 -anchored Single-Metal-Sites for Oxygen Reduction Reaction.

N-, C-, O-, S-coordinated single-metal-sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well-defined such SMSs, and the fundamental comprehension has long been impeded in case-by-case reports using carbon materials as investigation targets. In this work, the well-defined molecular catalysts with N3 C1 -anchored SMSs, i.e., N-confused metalloporphyrins (NCPor-Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor-Ms with corresponding N4 -anchored SMSs (metalloporphyrins, Por-Ms), are synthesized for catalytic activity evaluation. Among all, NCPor-Co reaches the top in established volcano plots. NCPor-Co also shows the highest half-wave potential of 0.83 V vs. RHE, which is much better than that of Por-Co (0.77 V vs. RHE). Electron-rich, low band gap and regulated d-band center contribute to the high activity of NCPor-Co. This study delves into the examination of well-defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high-performance asymmetric SMS catalysts.

Zinc Anodes with Electrodeposited Ionomer Protection Layer for Rechargeable Zinc-Air Batteries

Metal air batteries are assembled from a metal anode and a porous cathode in a suitable electrolyte. They combine the design of fuel cells and conventional batteries and have been demonstrated to have large theoretical energy densities higher compared to devices based on Li-ion chemistry, due to the ability to use air at the cathode and to exchange two electrons per zinc atom. ZAB represent a safe, environmentally benign, affordable and simple way to store and deliver electrical energy for a wide variety of devices. However, research efforts are necessary to increase the efficiency of rechargeable ZAB and mitigate obnoxious occurrences that decrease the number of charge-discharge cycles such as zinc dendrite formation, cathode degradation and alkaline electrolyte carbonation.The protection of zinc metal anodes in zinc-air batteries (ZAB) is an efficient way to reduce corrosion and Zn dendrite formation and improve cyclability and overall battery efficiency. The extent of improvement depends on the type and thickness of the protective layer.In this work, we explore an advanced coating of the zinc anode by anion-conducting poly(N-vinylbenzyl, N,N,N trimethylammonium) chloride (PVBTMA) that is electropolymerized directly on the zinc metal. The Zn deposition in presence of quaternary ammonium salts and polyelectrolytes was recently studied to improve the cyclability. The major advances foreseen by this approach are excellent qualities of the metal/ionomer interface, due to the in-situ deposition process, improving the corrosion protection and the selective anion permeability; furthermore, the chosen ionomer presents a high stiffness and strength to resist the formation of zinc dendrites, due to the stiff polystyrene backbone. Moreover, the presence of a polyelectrolyte separator facilitates device miniaturization. The zinc anode protection layer was observed by optical microscopy and scanning electron microscopy (Figure : SEM micrographs of Zn pellet with PVBTMA layer: a) from 0.01 M precursor solution, b) and c) from 0.1 M precursor solution) .and the wettability of the ionomer-coated zinc surface was investigated by contact angle measurements.The resulting ZAB battery with PVBTMA anode coating is analyzed in terms of cyclability in alkaline electrolyte and solid-state configuration using a Whatman paper separator.The goal is to pair metal-free electrode materials with appreciable catalytic activity for oxygen reduction and evolution with a zinc anode that has a protection layer against dendrite formation to maximize efficiency. Figure 1

Activation of ferrocene-based coordination compounds for oxygen evolution and the application in zinc-air battery

Rational reconstruction of oxygen evolution reaction (OER) pre-catalysts and the performance index is crucial but still challenging. Herein, a coordination compound composed by ferrocenedicarboxylic acid and Co2+ was prepared, which was then treated by NaBH4 solution for the rational reconstruction. The electrochemical activation of the treated product results in the generation of oxyhydroxides with unique microstructure acting as the catalytic active phase, which exhibits excellent electrocatalytic activity with a low overpotential of 256 mV for 10 mA cm−2 towards OER and a half-wave potential of 0.69 V (vs RHE) for oxygen reduction (ORR). Ru species was then loaded on the treated product to further improve the catalytic activity for oxygen reduction. The annealed product (Ru-CoFe/C) presents a core-shell structure with carbon layer on the surface. The product presents an increased half-wave potential of 0.744 V (vs RHE) for ORR with the OER/ORR overpotential gap of 0.776 V for 10 and 1 mA cm−2, respectively, showing the bifunctional catalytic activity. Ru species with small size improves the catalytic activity for ORR; the carbon shell provides the high stability. A Zn-air battery was then fabricated with the Ru-CoFe/C catalyst, which delivers a high power density of 88 mW cm−2 and a large specific capacity of 709 mAh g−1, as well as an excellent cycling stability over 65 h, surpassing commercial Pt/C + RuO2 based counterpart, demonstrating its feasibility in the field of renewable electronic devices. This work affords valuable guidelines for the application of ferrocene-based materials in OER and for the exploring of advanced bifunctional ORR/OER catalysts in rational construction of high-quality Zn-air batteries.

Boosting activity on copper functionalized biomass graphene by coupling nanocrystalline Nb2O5 as impressive rate capability for supercapacitor and outstanding catalytic activity for oxygen reduction

A novel and hierarchical porous but cross-linked copper-doped biomass graphene (Cu@HPBG) combined with Nb2O5 (denoted as Nb2O5/Cu@HPBG) is successfully fabricated on a large-scale using fig peels as biomass carbon and copper as the graphitization catalyst. During the synthesis process, basic copper carbonate serves dual functions of pore-forming agent, as well as homogeneous copper provider, and NH3 is employed as a defect-forming agent and N dopant. Owing to the porous hierarchical structure increased availability of contact interface and pseudo capacitance active sites provided by copper and Nb2O5, the assembled asymmetrical supercapacitor (ASC) employing Nb2O5/Cu@HPBG as positive electrode and HPBG as negative electrode can not only widen the stability window range of 0～1.9 V, but also deliver a maximum gravimetric energy density of 82.8 W h kg−1 at the power density of 950.0 W kg−1 and maintain a remarkable cycling stability of 97.1% after 15,000 cycles. Impressively, due to the synergistic enhancement of Cu@HPBG and Nb2O5, the resulting Nb2O5/Cu@HPBG hybrid displays more positive half wave potential (∼0.85 V) and a long-life stability than Pt/C electrode toward oxygen reduction reaction (ORR). Our research provides a feasible strategy to fabricate renewable biomass graphene electroactive composites for large-scale supercapacitor electrodes and efficient ORR catalysts toward energy applications.

Iron-Decorated Nitrogen/Boron co-Doped Reduced Graphene Oxide Aerogel for Neutral Rechargeable Zn-Air Batteries

Zn-air batteries (ZABs) with neutral electrolytes offer a significantly longer lifespan and better recyclability than alkaline ones. However, low-performance bifunctional catalytic activities for oxygen reduction or evolution reaction (i.e., ORR/OER) in neutral electrolytes still hamper their development. Here, we report iron nanoparticle-decorated nitrogen/boron co-doped reduced graphene oxide aerogel (Fe-NBrGO) with distinguished ORR/OER activity, enabling its application in neutral rechargeable ZABs. Taking advantage of the formation of 3D porous structure of graphene aerogel, N/B-moieties active sites, and Fe-containing active sites, Fe-NBrGO exhibits high ORR onset potential (1.074 and 0.817 V) and adequate OER overpotential (476 and 615 mV) in alkaline and neutral electrolytes, respectively. Fe-NBrGO enables the production of a neutral-ZAB with 34 mW cm−2 in peak power density and remains stable for a 284 h (~852 cycles) cycling test. This research highlights the rational design of highly active oxygen catalysts for the widespread implementation of new energy storage technologies.

Modeling Anion Poisoning during Oxygen Reduction on Pt Near-Surface Alloys

Electrolyte effects play an important role in the activity of the oxygen reduction reaction (ORR) of Pt-based electrodes. Herein, we combine a computational model and rotating disk electrode measurements to investigate the effects from phosphate anion poisoning for the ORR on well-defined extended Pt surfaces. We construct a model including the poisoning effect from phosphate species on Pt(111) and Cu/Pt(111) based on density functional theory simulations. By varying the subsurface Cu content of the Cu/Pt(111) alloy, we tune the *OH binding energies on the surface by means of ligand effects, and as a result, we tune the ORR activity. We have investigated the effect of adsorbed phosphate species at low overpotentials when tuning *OH binding energies. Our results display a direct scaling relationship between adsorbed *OH and phosphate species. From the model, we observe how the three-fold binding sites of phosphate anions limit the packing of poisoning phosphate on the surface, thus allowing for *OH adsorption even when poisoned. Our work shows that, regardless of surface site blockage from phosphate, the trend in the catalytic oxygen reduction activity is predominantly governed by the *OH binding.

Isometric Covalent Triazine Framework-Derived Porous Carbons as Metal-Free Electrocatalysts for the Oxygen Reduction Reaction.

Covalent triazine frameworks (CTFs) and their derivative N-doped carbons have attracted much attention for application in energy conversion and storage. However, previous studies have mainly focused on developing new building blocks and optimizing synthetic conditions. The use of isometric building blocks to control the porous structure and to fundamentally understand structure-property relationships have rarely been reported. In this work, two isometric building blocks are used to produce isometric CTFs with controllable pore geometries. The as-prepared CTF with nonplanar hexagonal rings demonstrates higher surface area, larger pore volume, and richer N content than the planar CTF. After pyrolysis, nonplanar porous CTF-derived N-doped carbons exhibit admirable catalytic activity for oxygen reduction in alkaline media (half-wave potential: 0.86 V; Tafel slope: 65 mV dec-1 ), owing to their larger pore volume and the abundance of pyridinic and graphitic N species. When assembled into a zinc-air battery, the as-made electrocatalysts show high capacities of up to 651 mAh g-1 and excellent durability.

Valorization of biomass furfural residue: Nitrogen-doped porous carbon towards electrocatalytic reaction

Catalysts made of non-noble metal for electrocatalytic reaction such as oxygen reduction with low cost, abundant resources, high stability, and excellent performance play a key role in promoting large-scale commercial application of fuel cells. In this work, industrial residue from biomass-based furfural production was selected and processed as carbon source to prepare a series of catalysts with excellent oxygen reduction reaction (ORR) catalytic performance. The processed furfural residue (FR) consisted mainly cellulose fiber and lignin particles in micro/nanoscale with size (length, width, and diameter) well-described by a lognormal distribution. The FR material followed a two-stage thermal decomposition process. The prepared FR carbon (FRC) material demonstrated high oxygen reduction catalytic activity and stability in oxygen saturated electrolyte (0.1 mol/L KOH). Its catalytic activity reached more than 90% of that of commercial platinum-carbon catalysts, showing its high application potential in fuel cell cathode.

The simple construction of rice-husk-derived carbon catalyst for oxygen reduction reaction by the synergism of iron and nitrogen co-doping

A rice-husk-derived carbon electrocatalyst (RHFeN) with oxygen reduction catalytic activity are obtained by the synergism of iron and nitrogen co-doping.

Bifunctional P-Containing RuO2 Catalysts Prepared from Surplus Ru Co-Ordination Complexes and Applied to Zn/Air Batteries.

An innovative synthetic route that involves the thermal treatment of selected Ru co-ordination complexes was used to prepare RuO2-based materials with catalytic activity for oxygen reduction (ORR) and oxygen evolution (OER) reactions. Extensive characterization confirmed the presence of Ru metal and RuP3O9 in the materials, with an improved electrocatalytic performance obtained from calcinated [(RuCl2(PPh3)3]. A mechanistic approach for the obtention of such singular blends and for the synergetic contribution of these three species to electrocatalysis is suggested. Catalysts added to carbon-based electrodes were also tested in all-solid and flooded alkaline Zn/air batteries. The former displayed a specific discharge capacity of 10.5 A h g-1 at 250 mA g-1 and a power density of 4.4 kW kg-1 cm-2. Besides, more than 800 discharge/charge cycles were reached in the flooded alkaline Zn/air battery.

Enhanced oxygen reduction reaction of LaSrCoO4–Ce0.9Mn0.1O2 composite cathode for solid oxide fuel cells

The development of high-performance cathodes with low polarization resistance and good tolerance to CO2 are important issues for solid oxide fuel cells (SOFC). In this work, we synthesized LaSrCoO4–Ce0.9Mn0.1O2 (LSCO4-CMO) composite cathode materials by the citric acid-nitrate method. The composite cathode sintered at 950 °C for 4 h shows large porous morphology and superior electrochemical activity of oxygen reduction reaction (ORR). Electrochemical properties analysis suggests that LSCO4-35 wt% CMO (L-35C) exhibits the lowest polarization resistance (Rp) at 800 °C and the value of Rp is 0.14 Ω cm2 which is far lower than that of pure LSCO4 (0.77 Ω cm2). It is found that the LSCO4-CMO has unique microstructure and more active sites for ORR. Moreover, the doping of CMO offers more oxygen ions transport channels as the concentration of oxygen vacancies increases. The study of the effect of oxygen partial pressure on Rp reveals that as the temperature rises, the rate of dissociation of oxygen molecules is significantly accelerated, indicating that the charge transfer of oxygen atoms becomes the main rate-limiting step. A high oxygen reduction catalytic activity and excellent CO2 tolerance were demonstrated in L-35C by O2-TPD and CO2-TPD tests, making LSCO4-CMO a potential candidate for SOFC cathode.

Ternary Synergism of Heterogeneous M1N4‐C‐M2N4‐C‐M3N4Single‐Atom Sites to Manipulate the Electrocatalytic Pathway for Zn‐Air Battery and Water Splitting

AbstractTernary metal catalysts hold great promise in complementary functionality and synergistic interplay, which are promising for combined reactions involving multi‐intermediates. However, simultaneously downscaling all three metal species into single‐atom level still remains challenge. Herein, a universal metal encapsulation‐segregation‐overlay strategy is designed to realize the fabrication of heterogeneous M1N4‐C‐M2N4‐C‐M3N4ternary single‐atoms (TSAs)‐based catalysts, with well‐defined configuration and threefold enhancement of single‐atom loading (IrPtCu TSAs, up to 21.24 wt%). Taking non‐precious‐metallic CoN4‐C‐NiN4‐C‐FeN4TSAs for instance, the integration of triple‐decker single‐atoms affords strong electronic reciprocity, with interbedded Ni donating electrons for both Fe and Co, thereby simultaneously enhancing the catalytic activity for oxygen reduction, oxygen evolution, and hydrogen evolution through a “site‐selective master‐servant” mechanism. Thanks to the mutually assisted tri‐functionality, the CoN4‐C‐NiN4‐C‐FeN4TSAs‐electrode takes on alternatating master/servant roles to enable outstanding recyclability for energy devices. This work breaks the obstructions in synthesis and fundamental study of TSAs, providing insights into atomic material design for complicated catalytic reactions.

Inner-pore reduction nucleation of palladium nanoparticles in highly conductive wurster-type covalent organic frameworks for efficient oxygen reduction electrocatalysis

Covalent organic frameworks (COFs) have emerged as a class of promising supports for electrocatalysis because of their advantages including good crystallinity, highly ordered pores, and structural diversity. However, their poor conductivity represents the main obstruction to their practical application. Here, we reported a novel synthesis strategy for synergistically endowing a triphenylamine-based COFs with improved electrical conductivity and excellent catalytic activity for oxygen reduction, via the in-situ redox deposition and confined growth of palladium nanoparticles inside the porous structure of COFs using reductive triphenylamine frameworks as reducing agent; meanwhile, the triphenylamine unit was oxidized to radical cation structure and affords radical cation COFs with conductivity as high as 3.2*10−1 S m−1. Such a uniform confine palladium nanoparticle on highly conductive COFs makes it an efficient electrocatalyst for four-electron oxygen reduction reaction (4e-ORR), showing excellent activities and fast kinetics with a remarkable half-wave potential (E1/2) of 0.865 V and an ultralow Tafel slope of 39.7 mV dec−1 in alkaline media even in the absence of extra commercial conductive fillers. The generality of this strategy was proved by preparing the different metal and metal alloy nanoparticles supported on COFs (Au@COF, Pt@COF, AuPd@COF, AgPd@COF, and PtPd@COF) using reductive triphenylamine frameworks as reducing agent. This work not only provides a facile strategy for the fabrication of highly conductive COF supported ORR electrocatalysts, but also sheds new light on the practical application of Zn-air battery.