Cathodic Oxygen Reduction Reaction Research Articles

Non-noble metals as activity sites for ORR catalysts in proton exchange membrane fuel cells (PEMFCs)

Proton exchange membrane fuel cells (PEMFCs) have great potential to become the next generation green energy technique, but its application is limited by the slow kinetics of the cathode oxygen reduction reaction (ORR) in acidic medium.

Synthesis and electrochemical oxygen reduction reaction activities of palladium-based intermetallic nano-electrocatalysts

Changing the atomic structure of a material to alter its characteristics is a key and powerful technique in materials research. Electrocatalytic applications are a growing field for structurally long range ordered materials. Similar electrocatalysts with a disordered structure, however, are unable to perform as well as those with an ordered structure because of the specific functionalities that may be achieved by the ordered structure. There has been a lot of interest in using highly active and stable ordered intermetallics as electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs). Electrocatalysts based on palladium have lately emerged as one of the most promising classes for the oxygen reduction reaction (ORR) in alkaline media because of their superior ORR activity and durability at lower prices than platinum. As electrocatalysts for fuel cells, palladium-based intermetallic nano-electrocatalysts (Pd-INECs) have gained a lot of interest in recent years. Pd-INECs have exceptional catalytic activity and great stability due to their well-defined composition and predictable control over structural, geometric, and electronic effects. In this short article, we will briefly go through the current state of knowledge on Pd-INECs for cathodic ORR in fuel cells. The first step is a brief review of the synthetic ways in which Pd-INECs with a predetermined stoichiometry and a well-defined atomic structure will be discussed. We also emphasized the use of Pd-INECs in electrochemical ORR operations as a second part of the review. Methods are comprehensively reviewed for enhancing the electrocatalytic activity of Pd-INECs. Finally, suggestions for future research directions and current difficulties are made.

Metal-free carbon semi-tubes for oxygen reduction electrocatalysis

New carbon morphologies are desirable in the development of high-performance carbon-based electrocatalysts for cathodic oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells. In this work, a carbon semi-tube (CST) is successfully constructed by polymerizing m-phenylenediamine (mPDA) using surfactant-assembled micelles as a soft template. After pyrolysis, the CST morphology is retained in the formed N-doped CST (N-CST) catalyst. This mPDA-induced catalyst can provide rich micropores, high N-content, and good conductivity, imbuing it with superior catalytic ORR activity, stability, and methanol tolerance to the commercial Pt/C catalyst. By using such a metal-free N-CST as a cathode catalyst, an alkaline polymer electrolyte fuel cell exhibits a maximum power density of about 200 mW cm−2. Furthermore, density functional theory (DFT) calculations suggest that high curvature can be greatly conducive to the excellent catalytic ORR activity by the induced strong OOH∗ adsorption on active sites through a strong dipole-electric field interaction.

Unveiling the inter-molecular charge transfer mechanism of N-doped graphene/carbon nanotubes heterostructure toward oxygen reduction process for Zn-air battery

Heteroatom-doped carbon-based materials have been deemed as highly efficient electrocatalysts for cathodic oxygen reduction reaction (ORR) in the sustainable energy conversion technologies. However, the limited active sites caused by the aggregation of carbon layers ineluctably hinder the mass transfer, thereby generating insufficient ORR performance. Herein, we offer a rational and facile method to manufacture a hybrid heterostructure of N-doped graphene and carbon nanotubes at the pyrolysis temperature of 900 °C (N-G/CNTs-900), which exhibits a better ORR activity than most of reported carbon-based ORR electrocatalysts, and comparable to that of Pt/C. Thus-fabricated N-G/CNTs-900 features hierarchically porous architecture, high specific surface area, abundant defects, and high active N content, and what’s more, it also affords active sites for oxygen activation and subsequent 4e− reduction processes due to the hetero-interlayer charge transfer and the electron accumulations of the carbon atoms on the surface layer by theoretical calculations. Compared with commercial Pt/C, N-G/CNTs-900-based Zn-air battery presents a higher peak power density (133.60 mW/cm2) and a larger specific capacity (707 mAh/gZn). This work provides a novel idea to design the high-efficiency and long-term durability ORR catalyst, which is benefit for boosting the commercial applications of metal-free carbon-based materials in the renewable energy conversion devices.

Secondary reduction strategy synthesis of Pt–Co nanoparticle catalysts towards boosting the activity of proton exchange membrane fuel cells

Based on the volcanic relationship between catalytic activity and key adsorption energies, Pt–Co alloy materials have been widely studied as cathode oxygen reduction reaction (ORR) catalysts in proton exchange membrane fuel cells (PEMFCs) due to their higher active surface area and adjustable D-band energy levels compared to Pt/C. However, how to balance the alloying degree and ORR performance of Pt–Co catalyst remains a great challenge. Herein, we first synthesized a well-dispersed Pt/Co/C precursor by using a mild dimethylamine borane (DMAB) as the reducing agent. The precursor was calcined at high temperature under H2/Ar mixed gas by a secondary reduction strategy to obtain an ordered Pt3Co intermetallic compound nanoparticle catalyst with a high degree of alloying. The optimization of electronic structure due to Pt–Co alloying and the strong metal-carrier interaction ensure the high kinetic activity of the cell membrane electrode. Additionally, the high degree of graphitization increases the electrical conductivity during the reaction. As a result, the activity and stability of the catalyst were significantly improved, with a half-wave potential as high as 0.87 V, which decreased by only 20 mV after 10000 potential cycles. Single-cell tests further validate the high intrinsic activity of the ordered Pt3Co catalyst with mass activity up to 0.67 A mgpt−1, exceeding the United States Department of Energy (US DOE) standard (0.44 A mgpt−1), and a rated power of 5.93 W mgpt−1.

Sulfur-Doped rGO Aerogel Enables the Anchoring of 1T/2H MoS2 for Durable Oxygen Reduction Reaction Catalyst Support.

Durability is crucial for the long-term application of cathode oxygen reduction reaction (ORR) catalysts in fuel cells. In this work, sulfur was successfully doped into reduced graphene oxide (rGO) aerogels to achieve the formation of 1T/2H hybrid phase MoS2 , obtaining MoS2 @S-rGO-300 composite ORR catalyst support. After loading ultrafine Pt nanoparticles, Pt/MoS2 @S-rGO-300 showed not only an enhanced ORR activity, but also a significantly improved stability after 10000 cycles. The mass activity retention for Pt/MoS2 @S-rGO-300 after cycles reached 89.94 %, while that of Pt/rGO was only 37.44 %. Density functional theory calculations revealed that the enlarged binding energy between Pt atoms and MoS2 @S-rGO-300 led to the prevention of Pt agglomeration as well as Ostwald ripening.

Mixed-Dimensional Pt-Ni Alloy Polyhedral Nanochains as Bifunctional Electrocatalysts for Direct Methanol Fuel Cells.

Pt nanocatalysts play a critical role in direct methanol fuel cells (DMFCs) due to their appropriate adsorption/desorption energy, yet suffer from an unbalanced relationship between size-dependent activity and stability. Herein, mixed-dimensional Pt-Ni alloy polyhedral nanochains (Pt-Ni PNCs) with an ordered assembly of a nanopolyhedra-nanowire-nanopolyhedra architecture are fabricated as bifunctional electrocatalysts for DMFCs, effectively alleviating the size effect. The Pt-Ni PNCs exhibit 7.23 times higher mass activity for the anodic methanol oxidation reaction (MOR) than that of commercial Pt/C. In situ Fourier transform infrared spectroscopy and CO stripping measurements demonstrate the prominent stability of the Pt-Ni PNCs to resist CO poisoning. For the cathodic oxygen reduction reaction (ORR), a positive half-wave potential exceeding Pt/C is achieved by the Pt-Ni PNCs, and it can be well maintained for 10000 cycles with negligible activity decay. The designed nanostructure can alleviate the agglomeration and dissolution problems of 0D small-sized Pt-Ni alloy nanocrystals and enrich surface atom steps and active facets of 1D chain-like nanostructures. This work provides a proposed strategy to improve the catalytic performance of Pt-based nanocatalysts by constructing novel interfacial relationships in mixed dimensions to alleviate the imbalance between catalytic activity and catalytic stability caused by size effects.

A novel and durable oxygen reduction reaction catalyst with enhanced bio-energy generation in microbial fuel cells based on Ag/Ag2WO4@f-MWCNTs

• Ag/Ag 2 WO 4 @f-MWCNTs was fabricated with a scalable, high efficiency, energy-saving, and time-saving strategy. • Ag/Ag 2 WO 4 @f-MWCNTs catalyst enriches oxygen diffusion and facilitates oxygen reduction reaction in MFCs. • The Ag/Ag 2 WO 4 @f-MWCNTs catalyst indicates high cathodic oxygen reduction reaction rate with 4e – pathway. • The Ag/Ag 2 WO 4 @f-MWCNTs has the potential to be an alternative to Pt/C-based oxygen reduction reaction catalysts. • The usage of this catalyst can substantially improves power production and enables broader applications of MFCs. Microbial fuel cell, as a promising technology, utilizes microorganisms to break down and oxidize the organic matter for harvesting energy. Progress in creating specific compositional functionalities of electrodes that are catalytically active, durable, cost-effective, and energy-recovery efficient is exclusively challenging for microbial fuel cell operation because of its bio-compatibility requirement. The electrodes composition impresses the oxidation-reduction reaction and electron charge-discharge rates. This study explores the use of silver/silver tungstate supported on different kinds of carbon materials, as cathode material for microbial fuel cells. The as-prepared catalysts were synthesized by a simple, environment-friendly, and self-developed surfactant-less method. Among proposed catalysts, the Ag/Ag 2 WO 4 @f-MWCNTs upgraded the oxygen reduction reaction to a four-electron pathway. As well, the optimal catalyst Ag/Ag 2 WO 4 @f-MWCNTs, exhibited excellent oxygen reduction reaction performance activity and stability with onset potential of -0.037 V and kinetic current density of 17.66 mA cm −2 compared with other synthesized catalysts and even the standard Pt/C catalyst. Owing to the more active sites, larger surface, and faster charge transfer, the microbial fuel cell equipped Ag/Ag 2 WO 4 @f-MWCNTs device delivered a high power density and current density of 0.965 W m –2 and 6.43 A m –2 , respectively. Consequently, Ag/Ag 2 WO 4 @f-MWCNTs is an effective catalyst that has the potential to be an alternative to Pt/C-based oxygen reduction reaction catalysts. The usage of this Ag/Ag 2 WO 4 @f-MWCNTs catalyst can therefore substantially improves power production and enable broader applications of microbial fuel cells for renewable electricity generation using waste materials.

Enhanced reaction kinetics of BCFZY-GDC-PrOx composite cathode for low-temperature solid oxide fuel cells

Solid oxide fuel cells function as promising power generation devices in the 21 century, but the lack of effective active cathodes at a low-temperature hinders their practical applications. In this study, BaCo0.4Fe0.4Zr0.1Y0.1O3-σ-Ce0.8Gd0.2O1.9 (BCFZY-GDC) composite cathode with infiltration of PrOx nanoparticles is systematically investigated. It is found that not only the composite cathodes demonstrate excellent phase compatibility, but also their reaction kinetics toward oxygen reduction reactions is substantially improved. Simultaneously, when the amount of the PrOx nanoparticles is about 18 mg/cm2, the Rp value of the resultant cathode reaches the minimum, and the value is about 0.082 Ω·cm2 at the operating temperature of 600 °C, which is only 25.3% of that of the cathode without PrOx. Furthermore, at operating temperatures of 700 °C, 650 °C, and 600 °C, the single-cell's power densities with the configuration of Ni-YSZ/YSZ/GDC/Pr18 (PrOx in BCFZY-GDC cathode is 18 mg/cm2) can reach about 1.55, 1.02, 0.56 W cm−2 under H2 atmosphere, and 1.22, 0.78, 0.39 W cm−2 under 20%CH3OH-80%N2 atmosphere, respectively, which is among the top high values based on the commercially available Ni-YSZ anode-supported single cells. The mechanism investigation further verifies that the enhanced reaction kinetics can be attributed to the improved surface exchange and ion transfer at the cathode's oxygen reduction reactions.

Iron carbide and iron phosphide embedded N-doped porous carbon derived from biomass as oxygen reduction reaction catalyst for microbial fuel cell

The splendid activity of oxygen reduction reaction (ORR) catalyst can greatly promote the power generation of air cathode microbial fuel cell (AC-MFC). Here, benefiting from the rich P element in radish, Fe3C and Fe2P incorporated N-doped porous carbon (Fe3C/Fe2P@NC-N4Fe2) are prepared with the assistance of NH4Cl through carbothermal reduction method without adding P resources. As expected, Fe3C/Fe2P@NC-N4Fe2 possesses excellent ORR performance, in which Fe3C and Fe2P furnish abundant ORR active sites and the porous structure in N-doped carbon matrix can facilitate mass transfer. Moreover, the AC-MFC assembled with Fe3C/Fe2P@NC-N4Fe2 as cathodic ORR catalyst exhibits superior power output performance with the maximum power density of 948.9 mW m−2, which is 1.03 times of that of 20 wt% Pt/C catalyst. Therefore, Fe3C/Fe2P@NC-N4Fe2 should be a viable ORR catalyst to replace Pt/C catalyst in the application in AC-MFC.

A Review of One‐Dimensional Nanomaterials as Electrode Materials for Oxygen Reduction Reaction Electrocatalysis

AbstractIn fuel cells, the generally low oxygen reduction reactions (ORR) rate at the cathode is a major factor limiting the overall performance of fuel cell, so the development of high‐performance, stable and inexpensive ORR electrocatalysts is a major researching direction. Nano‐electrocatalysts, especially one‐dimensional (1D) electrocatalysts, exhibit good catalytic behavior in fuel cell reactions due to their unique anisotropic structure, large specific surface area, high elasticity and excellent stability. To date, many advanced 1D electrocatalysts have been reported for optimizing the cathode ORR of fuel cells. Therefore, a comprehensive review of the structural design of 1D nano‐electrocatalysts and a systematic analysis of their enhanced performance still need further summarized and concluded. In this review, we firstly introduce the main synthetic methods of 1D electrocatalysts, and then discuss the recent advances and advantages of different structured 1D electrocatalysts involving nanofibers, nanotubes, nanorods, nanochains, nanowires, nanobelts, nanoneedles, nanowhiskers, and coaxial nanocables. In addition, we also introduce 1D electrocatalysts while highlighting advanced strategies and preparation methods for these different structured 1D electrocatalysts to improve ORR performance. Finally, we prospect the future development of 1D ORR electrocatalysts.

Applications of Nanomaterials in Microbial Fuel Cells: A Review.

Microbial fuel cells (MFCs) are an environmentally friendly technology and a source of renewable energy. It is used to generate electrical energy from organic waste using bacteria, which is an effective technology in wastewater treatment. The anode and the cathode electrodes and proton exchange membranes (PEM) are important components affecting the performance and operation of MFC. Conventional materials used in the manufacture of electrodes and membranes are insufficient to improve the efficiency of MFC. The use of nanomaterials in the manufacture of the anode had a prominent effect in improving the performance in terms of increasing the surface area, increasing the transfer of electrons from the anode to the cathode, biocompatibility, and biofilm formation and improving the oxidation reactions of organic waste using bacteria. The use of nanomaterials in the manufacture of the cathode also showed the improvement of cathode reactions or oxygen reduction reactions (ORR). The PEM has a prominent role in separating the anode and the cathode in the MFC, transferring protons from the anode chamber to the cathode chamber while preventing the transfer of oxygen. Nanomaterials have been used in the manufacture of membrane components, which led to improving the chemical and physical properties of the membranes and increasing the transfer rates of protons, thus improving the performance and efficiency of MFC in generating electrical energy and improving wastewater treatment.

Fe3C decorated, N-doped porous carbon as cost-effective and efficient catalyst for oxygen reduction reaction

The catalytic activity, stability and methanol tolerance for alkali oxygen reduction reaction (ORR) of cathode are pivotal metrics determining the actual performance of methanol fuel-cell. Carbonaceous materials with heteroelement doping and guest catalytic component hybriding are promising ways to improve the above metrics for ORR and simultaneously reduce the cost, therefore hold bright prospect in the industrialization of fuel-cell. Herein, a Fe3C decorated, N doped hierarchically porous carbon, denoted as SP-N1-Z0.6/F0.5, was designed as cathodic ORR catalyst by pyrolytic carbonization, N-doping, Fe3C decoration and etching of a easily-available shaddock peel (SP) precursor. Benefitted by the synergy of N dopant and Fe3C hybriding, the typical SP-N1-Z0.6/F0.5 catalyst demonstrated ORR peak potential of 0.874 V and peak current density of −2.60 mA cm−2 for alkali ORR. In addition, the ORR catalytic activity hardly changed undergoes 5000 cycles of linear sweep voltammetries (LSVs), and fine methanol tolerance could also be ensured. All of these metrics are superior to the benchmark Pt/C catalyst, showing the potential of Fe3C incorporate and N doped carbonaceous catalyst in alkali ORR.

Cu-Nx active sites derived from copper phthalocyanine in porous carbon promoting oxygen reduction reaction

Transition metal-nitrogen-carbon materials have been reported to be a promising candidate for cathodic oxygen reduction reaction in fuel cell and metal air battery. In this paper, a copper and nitrogen co-doped carbon catalyst (Cu/PC) was designed and successfully synthesized through hydrothermal method and two high temperature calcinations process. The new designed Cu/PC catalyst exhibited a superior catalytic activity with the half-wave potential and limited diffusion current density of 0.847 V and 5.52 mA cm−2, respectively. Mechanisms insight from electrochemical experiments and density functional calculations revealed that the Cu-Nx active sites on the surface of porous carbon and large pore volume played key roles on the excellent electrochemical performance. The results reported in this work provide a new perspective for the design of transition metal catalysts and lay a solid foundation for the related mechanism studies.

Defective nanomaterials for electrocatalysis oxygen reduction reaction.

The difficulties in O2 molecule adsorption/activation, the cleavage of the O-O bond, and the desorption of the reaction intermediates at the surface of the electrodes make the cathodic oxygen reduction reaction (ORR) for fuel cells show extremely sluggish kinetics. Thus, it is important to the exploitation of highly active and stable electrocatalysts for the ORR to promote the performance and commercialization of fuel cells. Many studies have found that the defects affect the electron and the geometrical structure of the catalyst. The catalytic performance is enhanced by constructing defects to optimize the adsorption energy of substrates or intermediates. Unfortunately, still many issues are poorly recognized, such as the effect of defects (types, contents, and locations) in catalytic performance is unclear, and the catalytic mechanism of defective nanomaterials is lacking. In this review, the defective electrocatalysts divided into noble and non-noble metals for the ORR are highlighted and summarized. With the assistance of experimental results and theoretical calculations, the structure-activity relationships between defect engineering and catalytic performance have been clarified. Finally, after a deeper understanding of defect engineering, a rational design for efficient and robust ORR catalysts for PEMFCs is further guided.

Annealing-temperature-dependent relation between alloying degree, particle size, and fuel cell performance of PtCo catalysts

Pt-M (M is typically 3d transition metal) alloy nanoparticles as the state-of-the-art electrocatalysts exhibit superior activity for the sluggish cathodic oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells (PEMFCs). The specific activity (SA) of Pt-M alloy catalysts is strongly correlative to their surface compressive strains that are majorly dependent on the M type and content. In order to promote the alloying of Pt with M to improve the SA, a high-temperature annealing is normally inevitable, which however accelerates the metal sintering resulting in larger particles and lowers electrochemical surface areas (ECSAs) as well as the high-current–density PEMFCs performance. Herein, we systematically studied the ORR/PEMFCs performance of a family of PtCo catalysts with varied alloying degree and particle size, which were prepared at different annealing temperatures ranging from 400 to 1000 °C. We found the annealing-temperature-dependent trade-off relation between the alloying-degree-dependent SA and particle-size-dependent ECSA. The optimal PtCo catalyst was thus achieved at a medium annealing temperature of 600 °C, showing a high mass activity (MA) of 1.04 A mg−1 and a large rated power density of 1.07 W cm−2 with a low Pt loading of 0.1 mgPt cm−2.

Non-Noble Metal Catalysts in Cathodic Oxygen Reduction Reaction of Proton Exchange Membrane Fuel Cells: Recent Advances.

The oxygen reduction reaction (ORR) is one of the crucial energy conversion reactions in proton exchange membrane fuel cells (PEMFCs). Low price and remarkable catalyst performance are very important for the cathode ORR of PEMFCs. Among the various explored ORR catalysts, non-noble metals (transition metal: Fe, Co, Mn, etc.) and N co-doped C (M–N–C) ORR catalysts have drawn increasing attention due to the abundance of these resources and their low price. In this paper, the recent advances of single-atom catalysts (SACs) and double-atom catalysts (DACs) in the cathode ORR of PEMFCs is reviewed systematically, with emphasis on the synthesis methods and ORR performance of the catalysts. Finally, challenges and prospects are provided for further advancing non-noble metal catalysts in PEMFCs.

Robust and highly conductive Ti4O7/MXene nanocomposites as high-performance and long cyclic stability oxygen reduction electrocatalysts

Electrocatalysts play an important role in the cathodic Oxygen Reduction Reaction (ORR) of fuel cells. Because of the high cost, poor cycle stability and methanol tolerance, the commercial Pt/C catalysts have been seriously restricted during large-scale application and development in electrochemical devices. The development of non-noble metal ORR catalysts is one of the effective ways to achieve fuel cell cost reduction and performance improvement at the same time. In this work, Ti4O7/MXene nanocomposites were synthesized through hydrothermal followed by carbothermal reduction reactions. Such catalysts exhibit large electrochemical active surface area (ECSA = 215.74 cm2) and excellent ORR catalytic activity in alkaline media. The initial potential and half-wave potential were confirmed to be 0.91 V and 0.72 V with the electron transfer number of 3.3. In addition, the Ti4O7/MXene catalysts have better cyclic stability and methanol tolerance than commercial Pt/C catalyst. This study provides a new idea and method for the innovative preparation of MXene-based composite electrocatalysts.

Electrochemistry of Sulfides: Process and Environmental Aspects

One of the main sources of non-ferrous and precious metals is sulfide ores. This paper presents a review of the existing literature on the electrochemical properties of some of the most common industrial sulfides, such as pentlandite, chalcopyrite, sphalerite, galena, pyrrhotite, pyrite, etc. The study results of the surface redox transformations of minerals, galvanic effect, cathodic oxygen reduction reaction on the surface of sulfides are presented. The electrochemical properties of sulfide minerals are manifested both in the industrial processes of flotation and hydrometallurgy and in the natural geological setting or during the storage of sulfide-containing mining, mineral processing, and metallurgical industry waste.

Double-Faced Atomic-Level Engineering of Hollow Carbon Nanofibers as Free-Standing Bifunctional Oxygen Electrocatalysts for Flexible Zn-Air Battery.

Flexible solid-state zinc-air batteries (ZABs) with low cost, excellent safety, and high energy density has been considered as one of ideal power sources for portable and wearable electronic devices, while their practical applications are still hindered by the kinetically sluggish cathodic oxygen reduction and oxygen evolution reactions (ORR/OER). Herein, a Janus-structured flexible free-standing bifunctional oxygen electrocatalyst, with OER-active O, N co-coordinated Ni single atoms and ORR-active Co3O4@Co1-xS nanosheet arrays being separately integrated at the inner and outer walls of flexible hollow carbon nanofibers (Ni-SAs/HCNFs/Co-NAs), is reported. Benefiting from the sophisticated topological structure and atomic-level-designed chemical compositions, Ni-SAs/HCNFs/Co-NAs exhibits outstanding bifunctional catalytic activity with the ΔE index of 0.65 V, representing the current state-of-the-art flexible free-standing bifunctional ORR/OER electrocatalyst. Impressively, the Ni-SAs/HCNFs/Co-NAs-based liquid ZAB show a high open-circuit potential (1.45 V), high capacity (808 mAh g-1 Zn), and extremely long life (over 200 h at 10 mA cm-2), and the assembled flexible all-solid-state ZABs have excellent cycle stability (over 80 h). This work provides an efficient strategy for developing high-performance bifunctional ORR/OER electrocatalysts for commercial applications.