Oxygen Reduction In Alkaline Media Research Articles

Efficient and durable oxygen reduction in alkaline media by doping heteroatomic boron into FeSA-NC catalyst

Despite extensive research has been conducted on atomic dispersion catalysts for various reactions, altering the electronic structure of the central metal to enhance electrochemical reactivity remains a challenging task. Herein, the electrochemical reactivity was considerably enhanced by introducing heteroatomic B to adjust the d-band of single Fe center. In specific, the obtained FeSA-BNC catalyst demonstrated an outstanding ORR performance (E1/2 = 0.87 V) and exhibited greater long-term durability in alkaline media compared to Pt/C. The performance of FeSA-BNC in Zn–air battery was also higher than that of Pt/C. According to theoretical calculations, a downward shift in the d-band center of Fe was induced by introducing B, thereby improving the desorption of intermediates and facilitating the oxygen reduction reaction (ORR).

Synergistic effects of fluorine and nitrogen dopants in fluorine/nitrogen-coordinated iron-co-doped carbon catalysts for enhanced oxygen reduction in alkaline media

The expensiveness of oxygen reduction reaction (ORR) catalyst materials especially Pt has hindered the commercialization of next-generation energy conversion devices including metal–air batteries and polymer electrolyte membrane fuel cells. Fe–N–C has drawn attention as a nonprecious metal catalyst owing to its high but commercially unsatisfactory ORR performance; nevertheless, additional heteroatom co-doping could help augment its ORR activity. Here we report nitrogen/fluorine-coordinated iron-co-doped carbon (Fe@NFC) catalysts with improved ORR performance in alkaline media. The annealing temperature affects the nitrogen/fluorine doping and functional group formation, as ascertained by an analysis of control samples annealed at various temperatures. To assess the synergy between the doped fluorine and nitrogen-coordinated iron, we compare the catalyst annealed at 700 °C (Fe@NFC700) with control samples containing different heteroatom dopants but annealed at 700 °C (Fe@NC, Fe@FC). Fe@NFC700 shows improved ORR kinetics and onset potential than those of Fe@NC and commercial Pt/C, respectively, in alkaline media.

Computationally screening non-precious single atom catalysts for oxygen reduction in alkaline media

The performance of single-atom catalysts (SACs) containing Sc, Ti, V, Mn, Fe, Ni, Cu, and Pt on N-doped carbon (NC) as possible cathodes in advanced chlor-alkali electrolysis has been investigated by means of density functional theory (DFT) with the aim of finding candidates to improve the sluggish kinetics of the oxygen reduction reaction (ORR). A plausible mechanism is proposed for the ORR that allows making use of the computational hydrogen electrode (CHE) approach in this environment, and suitable models have been used to estimate the free-energy changes corresponding to the elementary reaction steps. The performance of the different catalysts has been analyzed in terms of the electrochemical-step symmetry index (ESSI) and Gmax descriptors. From these descriptors, the Cu-containing SAC is predicted to exhibit the highest catalytic activity which is consistent with a theoretical overpotential of 0.71 V, indicating that this type of catalysts in oxygen depolarized cathodes (ODCs) may overcome the limitations of the high cost and low abundance of Pt and other precious metals.

Machine learning enabled exploration of multicomponent metal oxides for catalyzing oxygen reduction in alkaline media

Machine learning can map and predict the oxygen reduction reaction performance of multicomponent metal oxides in alkaline media.

Microwave-assisted synthesis of N/S-doped CNC/SnO2 nanocomposite as a promising catalyst for oxygen reduction in alkaline media

In this study, we report an all-green approach for the synthesis of novel catalysts for oxygen reduction reaction (ORR) via a simple two-step procedure. In particular, conductive cellulose nanocrystals (CNCs) were obtained via pyrolysis, and a successive microwave-assisted hydrothermal process was employed to activate the carbon lattice by introducing sulfur (S) and nitrogen (N) dopants, and to decorate the surface with tin oxide (SnO2) nanocrystals.The successful synthesis of N/S-doped CNC/SnO2 nanocomposite was confirmed by X-ray Photoelectron Spectroscopy analysis, Energy Dispersive X-ray microanalysis, X-ray Diffraction and Field Emission Scanning Electron Microscopy. The synergistic effects of the dopants and SnO2 nanocrystals in modifying the catalytic performance were proved by various electrochemical characterizations. Particularly, the nanocomposite material reaches remarkable catalytic performance towards the ORR, close to the Pt/C benchmark, in alkaline environment, showing promising potential to be implemented in alkaline fuel cell and metal-air battery applications.

Surface engineered PdNFe3 intermetallic electrocatalyst for boosting oxygen reduction in alkaline media

Surface engineering has been identified as an effective way to maximize the utilization of noble atoms and facilitate the oxygen reduction reaction. However, a cost-effective and highly durable platform for tailoring the electrocatalytic activity, is still absent. Herein, we demonstrate a new and promising catalytic material of antiperovskite-typed PdNFe3 and construct a high performance PdNFe3 @Pd catalyst with atomic layers of strained Pd shell. The PdNFe3 @Pd/C catalyst presents a high mass activity (MA) of 1.14 A mg−1Pd at 0.9 V, which is 9 and 6 times higher than those of the Pt/C and Pd/C, respectively. More importantly, the excellent performance of PdNFe3 @Pd/C was also verified in anion-exchange membrane fuel cells and rechargeable Zn−air batteries. Density functional theory calculations reveal that the strain effect aroused by the lattice mismatch between PdNFe3 core and Pd shell contributes to the enhanced ORR performance by optimizing the binding strength of oxygen intermediates on Pd.

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.

Tunning the Activity of Silver Alloy Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Media

A bottleneck to achieve efficient and stable electrocatalysts for Anion Exchange Membrane Fuel Cells (AEMFCs) is the relatively slow kinetics of the oxygen reduction reaction (ORR) taking place at the cathode. The rather mild alkaline conditions in the AEMFC enable the utilization of various PGM-free catalysts, which brings up new possibilities of finding abundant and inexpensive electrocatalysts without compromising the power density. From theory and previous experiments, it is known that Au and Ag bind oxygen weakly, whereas other transition metals (e.g., Pd, Cu, Fe, Ni) bind strongly to oxygenated species1. Therefore, a suitable geometric arrangement between Ag, an abundant metal with relatively high specific activity, and other metals may give rise to optimum binding of oxygen and thus a high activity. A good strategy to improve the activity of Ag-based catalysts could be a rational design of alloys that can enhance the intrinsic activity of Ag by both ensemble and electronic effects2–4. The former is based on the combination of active sites that facilitate the initial oxygen binding together with Ag active sites that help desorb hydroxide anions, whereas the latter is induced by the alloying metal (which binds oxygenated species strongly) on the electronic structure of the overlaying Ag that tunes its binding to oxygen5. Herein, we report the fabrication and characterization of Ag thin-films alloyed with Pd, Ni, Cu and Mo as a tool to investigate the ORR reaction in terms of ensemble and electronic effects and thus relate alloy composition and geometric arrangement with ORR activity. Ag thin-film model catalysts are fabricated by means of physical vapor deposition methods (PVD) with high control over the amount of material deposited. By varying alloy composition and evaluating electrochemical activity and stability, together with detailed physical characterization, the degree and extent of electronic effects are elucidated. In the same way, sputtering of the same amount of Ag on thin-films of different metals evidences the role of the alloying metal on tuning the activity of Ag through an adjustment of its d-band that changes the binding of oxygenated species, as well as through an ensemble effect that provides active sites for the first elementary steps of the reaction. These results provide insights for more tailored design of electrocatalysts in alkaline media by shedding new light on the mechanisms through which the ORR kinetics are improved in alkaline media. Nørskov, J. K. et al. Origin of the overpotential for oxygen reduction at a fuel-cell cathode. J. Phys. Chem. B 108, 17886–17892 (2004).Betancourt, L. E. et al. Enhancing ORR Performance of Bimetallic PdAg Electrocatalysts by Designing Interactions between Pd and Ag. ACS Appl. Energy Mater. 3, 2342–2349 (2020).Slanac, D. A., Hardin, W. G., Johnston, K. P. & Stevenson, K. J. Atomic ensemble and electronic effects in Ag-rich AgPd nanoalloy catalysts for oxygen reduction in alkaline media. J. Am. Chem. Soc. 134, 9812–9819 (2012).Zamora Zeledón, J. A. et al. Tuning the electronic structure of Ag-Pd alloys to enhance performance for alkaline oxygen reduction. Nat. Commun. 12, 1–9 (2021).Stamenkovic, V. et al. Changing the Activity of Electrocatalysts for Oxygen Reduction by Tuning the Surface Electronic Structure. Angew. Chemie 118, 2963–2967 (2006).

Core-shell and heterostructured silver-nickel nanocatalysts fabricated by γ-radiation induced synthesis for oxygen reduction in alkaline media.

To reach commercial viability for fuel cells, one needs to develop active and robust Pt-free electrocatalysts. Silver has great potential to replace Pt as the catalyst for the oxygen reduction reaction (ORR) in alkaline media due to its low cost and superior stability. However, its catalytic activity needs to be improved. One possible solution is to fabricate bimetallic nanostructures, which demonstrate a bifunctional enhancement in the electrochemical performance. Here, two types of bimetallic silver-nickel nanocatalysts, core-shells (Ag@NiO) and heterostructures (Ag/Ni), are fabricated using γ-radiation induced synthesis. The Ag@NiO nanoparticles consist of an amorphous, NiO layer as a shell and a facetted crystalline Ag particle as a core. Meanwhile, the Ag/Ni heterostructures comprise Ag particles decorated with Ni/Ni(oxy-hydro)-oxide clusters. Both materials demonstrate similar and increased alkaline ORR activity as compared to monometallic catalysts. It was revealed that the enhanced catalytic activity of the core-shells is mainly attributed to the electronic ligand effect. While in the Ag/Ni heterostructures, a lattice mismatch between the Ni-based clusters and Ag implies a significant lattice strain, which, in turn, is responsible for the increased activity of the catalyst. Also, the Ag/Ni samples exhibit good stability under operating conditions due to the existence of stable Ni3+ compounds on the surface.

Gold nanobipyramids doped with Au/Pd alloyed nanoclusters for high efficiency ethanol electrooxidation.

Plasmonic metal nanostructures are of great interest due to their excellent physicochemical properties and promising applications in a wide range of technical fields. Among metal nanostructures, bimetallic nanostructures with desired morphologies, such as core–shell, uniform alloy and surface decoration, are of great interest due to their improved properties and superior synergetic effects. In this paper, Au/Pd nanoclusters were deposited on the surface of gold nanobipyramids (AuBPs) into a core–shell nanostructure (AuBP@AuxPd1−x) through a reductive co-precipitation method. The AuBP@AuxPd1−x nanostructure integrates effectively the advantages of plasmonic AuBPs and catalytic Pd ultrafine nanoclusters, as well as the stable Au/Pd alloy shell. The AuBP@AuxPd1−x nanostructure exhibits superior electrocatalytic activity and durability for oxygen reduction in alkaline media owing to the synergistic effect between the AuBP core and Au/Pd shell. Furthermore, the shell thickness of AuBP@AuxPd1−x nanostructures can be adjusted by varying the amount of precursor. Overall, the catalytic activity of bimetallic Au/Pd catalysts is likely to be governed by a complex interplay of contributions from the particle size and shape.

(Invited) Design and Synthesis of Nano-Porous / Nano-Structured Electrochemical Interfaces with Application in the Fuel Cell Catalysis

The drive toward efficient and durable fuel cells is founded on the design, synthesis, characterization, and testing of a variety of catalysts that in most cases include either Pt or Pd or a combination of both. Given the high cost and scarcity of these metals it is essential to either find a cost-effective alternative or to minimize as much as possible the amount of Pt / Pd in developed catalysts of interest. The route of amount minimization has been firstly approached by synthesizing catalysts in the form of nanoparticles. Nanoparticles are undoubtedly superior to other type of materials applicable in catalysis with their large surface area to volume ratio and unique physical and chemical properties. At the same time, they are also associated with some drawbacks like material loss during synthesis, surface contamination that is difficult to deal with, mechanical disconnection from the carrier electrode, and / or aggregation in time of exploitation. Such unwanted developments lead to a rapid reduction of the electrochemically active surface area (ECSA) and thus, to loss of activity and poor durability.A way to address these drawbacks is to employ electrochemical approaches for synthesizing the catalytically active layer directly on the carrier electrode. Such approach would not only provide for better adhesion and contamination free surface but would also enable a complete control over the amount of the deposited material along with its surface structure and composition thus reducing the overall synthetic cost. The electrochemical means normally include electrodeposition of a binary / ternary alloy layer with controlled thickness and elemental composition followed by a selective oxidative dissolution (de-alloying) of the less / least noble metal to create a continuous nanoporous film with tunable pore and ligament size in the single-digit nanometer range (1-4). Finally, as-synthesized film may either be employed directly as catalyst (3-7) or be subjected to an additional surface functionalization for boosting its activity and/or durability (1, 2, 8-10).This talk will introduce the use of electrochemical means in the design and synthesis of continuous nanoporous alloy catalysts based on Pt-(1, 9), Pd-(7, 10), and Au-(2, 6) with application in small organic molecule oxidation, oxygen reduction in alkaline media, and nitrate electroreduction reactions, respectively. The discussed synthetic approaches will include bulk alloy electrodeposition, electrochemical de-alloying, and electrochemical atomic layer deposition for sub-monolayer to a few layers surface functionalization. The presentation of each catalyst will include electrochemical and ultra-high vacuum-based characterization, followed by standard performance tests of the activity and durability of said catalysts in the respective applications. Finally, aspects of the catalysts’ performance along with hypothesized mechanistic views will be critically discussed in comparison with other nanoparticulate and/or nanostructured counterpart catalysts in the literature. References D. A. McCurry, M. Kamundi, M. Fayette, F. Wafula and N. Dimitrov, Acs Appl Mater Inter, 3, 4459 (2011).Y. Xie and N. Dimitrov, Acs Omega, 3, 17676 (2018).Y. Xie and N. Dimitrov, Appl Catal B-Environ, 263, 118366 (2020).Y. Xie, Y. Yang, D. A. Muller, H. D. Abruna, N. Dimitrov and J. Y. Fang, Acs Catal, 10, 9967 (2020).Y. Xie, C. Li, S. A. Razek, J. Y. Fang and N. Dimitrov, Chemelectrochem, 7, 569 (2020).H. Yang, J. X. Xia, L. Bromberg, N. Dimitrov and M. S. Whittingham, J Solid State Electr, 21, 463 (2017).Y. Xie, C. Li, E. Castillo, J. Fang and N. Dimitrov, Electrochimica Acta, 138306 (2021).L. Bromberg, M. Fayette, B. Martens, Z. P. Luo, Y. Wang, D. Xu, J. Zhang, J. Fang and N. Dimitrov, Electrocatalysis, 4, 24 (2013).J. X. Xia, I. Achari, S. Ambrozik and N. Dimitrov, Mater Res Bull, 85, 1 (2017).I. Achari and N. Dimitrov, Electrochem, 1, 4 (2020).

Reduced graphene oxide-wrapped α-Mn2O3/α-MnO2 nanowires for electrocatalytic oxygen reduction in alkaline medium

Reduced graphene oxide-wrapped α-Mn2O3/α-MnO2 nanowires for electrocatalytic oxygen reduction in alkaline medium

Synthesis and Characterizations of PdNi Carbon Supported Nanomaterials: Studies of Electrocatalytic Activity for Oxygen Reduction in Alkaline Medium.

Electrocatalytic materials offer numerous benefits due to their wide range of applications. In this study, a polyol technique was used to synthesize PdNi nanoparticles (NPs) with different percent atomic compositions (Pd = 50 to 90%) to explore their catalytic efficiency. The produced nanoparticles were characterized using X-ray diffraction (XRD) and electrochemical investigations. According to XRD measurements, the synthesized NPs were crystalline in nature, with crystallite sizes of about 2 nm. The electrochemical properties of the synthesized NPs were studied in alkaline solution through a rotating ring-disk electrode (RRDE) technique of cyclic voltammetry. The PdNi nanoparticles supported on carbon (PdNi/C) were used as electrocatalysts and their activity and stability were compared with the homemade Pd/C and Pt/C. In alkaline solution, PdNi/C electrocatalysts showed improved oxygen reduction catalytic activity over benchmark Pd/C and Pt/C electrocatalysts in all composition ratios. Furthermore, stability experiments revealed that PdNi 50:50 is more stable in alkaline solution than pure Pd and other PdNi compositions.

Nanoporous Pd-Cu thin films as highly active and durable catalysts for oxygen reduction in alkaline media

A facile electrochemical etching approach was developed and implemented to enhance the electrocatalytic performance of Pd-Cu films for oxygen reduction reaction (ORR) in alkaline media. The nanoporous (np) Pd-Cu was synthesized through electrochemical de-alloying of pre-deposited Pd-Cu films. Scanning electron microscopy (SEM) with energy dispersive spectroscopy was employed to confirm the residual amount of Cu in the np structure. The accordingly prepared np catalysts showed excellent ORR activity up to 1.11 A/mgPd at a potential of 0.9 V vs. RHE which is around 22-times and 6.2-times higher than that of a plain Pd film and commercial Pd/C catalyst, respectively. The ORR activity enhancement is attributed to the unique porous structure, large Pd surface area, and modified electronic structure of Pd with residual Cu as confirmed by the SEM, hydrogen underpotential deposition, and CO stripping characterizations. The np Pd-Cu catalyst also showed excellent durability which is manifested by a negligible decrease in the half-wave potential (4 mV negative shift) after 10,000 potential cycles in alkaline media. These findings provide insights into the rational design of an electrocatalyst's structure utilizing an electrochemical de-alloying method to achieve high atomic utilization and improved catalytic performance.

Synthesis, characterization and electrocatalytic properties of bimetallic sulfides CoS/MnS/N-C for oxygen reduction in alkaline media

Synthesis, characterization and oxygen reduction reaction (ORR) catalytic properties of bimetallic sulfides CoS/MnS/N-C catalyst was discussed. The catalyst was derived from a typical Co based zeolitic imidazolate framework (ZIF-67) and manganese aminoporphyrin. 5,15-Bis(4-aminophenyl)-10,20-bis(4-bromophenyl) porphyrin manganese oxoacetate loaded with ZIF-67 forms a porphyrin loaded ZIF-67. This product was then calcined at 800ˆ∘C and vulcanized with thioacetamide to obtain the bimetallic sulfide product CoS/MnS/N-C. The structure of CoS/MnS/N-C was further characterized by XRD, XPS, FESEM and HRTEM spectra which indicated a novel porous and hollow sphere structure. The electrocatalytic properties of the bimetallic material as well as its parent porphyrin and ZIF-67 were also compared in alkaline condition (0.1 M KOH) with a rotating disk electrode. The prepared catalyst CoS/MnS/N-C exhibits a higher catalytic performance than its precursors (PorMnOAc, ZIF-67 and PorMnOAc loaded ZIF-67) with almost four electron transfers under this condition.

Palladium Nanobelts with Expanded Lattice Spacing for Electrochemical Oxygen Reduction in Alkaline Media

Pd has been considered as a promising catalyst for the electrochemical oxygen reduction reaction (ORR) in an alkaline environment. However, the strategies and fundamental understanding for improvin...

Electrocatalytic activity enhancement of N,P-doped carbon nanosheets derived from polymerizable ionic liquids

A facile preparation method was developed to obtain two-dimensional (2D) metal-free N, P-co-doped carbon nanosheets with sp2/sp3 interface derived from polymerizable ionic liquids (PIL) and ammonium nitrate (NH4NO3), exhibiting better electrocatalytic activity than that of the commercial Pt/C toward oxygen reduction reaction (ORR). The introduction of NH4NO3 can benefit the formation of carbon nanosheets structure and hierarchical porous structure due to decomposition and carbonization of polymer and gases emission resulting from ammonia nitrate, which can be confirmed by the SEM, TEM and BET results. The sp3 carbon and doping effect of heteroatoms of N, P can be investigated with the XPS, Raman and NEXAFS spectroscopy. The present work developed a facile method to prepare heteroatom-co-doped carbon as metal-free catalyst toward ORR with superior catalytic performance. Two-dimensional carbon nanosheets doped with N, P atoms can be successfully prepared via pyrolysis process of the polymerizable ionic liquids ([Hvim]DHP) and NH4NO3, demonstrating superior electrocatalytic performance toward oxygen reduction in alkaline media.

High Compositional Dependence of Activity of Platinum–Dysprosium Alloys for Oxygen Reduction in Alkaline Media: Experimental and Theoretical Study

High Compositional Dependence of Activity of Platinum–Dysprosium Alloys for Oxygen Reduction in Alkaline Media: Experimental and Theoretical Study

Fe-N-C electrocatalysts in the oxygen and nitrogen cycles in alkaline media: the role of iron carbide.

Fe-N-C electrocatalysts hold a great promise for Pt-free energy conversion, driving the electrocatalysis of oxygen reduction and evolution, oxidation of nitrogen fuels, and reduction of N2, CO2, and NOx. Nevertheless, the catalytic role of iron carbide, a component of nearly every pyrolytic Fe-N-C material, is at the focus of a heated controversy. We now resolve the debate by examining a broad range of Fe3C sites, spanning across many typical size distributions and carbon environments. Removing Fe3C selectively by a non-oxidizing acid reveals its inactivity towards two representative reactions in alkaline media, oxygen reduction and hydrazine oxidation. The activity is assigned to other pre-existing sites, most probably Fe-Nx. DFT calculations prove that the Fe3C surface binds O and N intermediates too strongly to be catalytic. By settling the argument on the catalytic role of Fe3C in alkaline electrocatalysis, we hope to spur innovation in this critical field.

High Compositional Dependence of Activity of Platinum–Dysprosium Alloys for Oxygen Reduction in Alkaline Media: Experimental and Theoretical Study

High Compositional Dependence of Activity of Platinum–Dysprosium Alloys for Oxygen Reduction in Alkaline Media: Experimental and Theoretical Study