Oxygen Reduction Reaction Behavior Research Articles

Low platinum loading electrocatalyst supported on a carrier derived from carbon dots doped ZIF-67 for the ORR and zinc-air batteries.

The development of economical and efficient platinum-based catalysts for the oxygen reduction reaction (ORR) is considered the most promising strategy for the widespread application of clean energy conversion devices. Herein, Co nanoparticles encapsulated in N-doped carbon carriers, CoCN(CDs-X), were constructed by pyrolyzing carbon dots (CDs) doped ZIF-67 and further used to anchor Pt to prepare low Pt loading catalysts, PtCoCN(CDs-X). The introduction of CDs not only improves the conductivity for efficient electron transfer, but also regulates the interaction between Pt and the CoCN(CDs-X) support and alleviates the oxidation of Pt. The optimized PtCoCN(CDs-0.10) displays decent ORR behavior with onset and half-wave potentials of 0.95 V and 0.83 V, respectively, in alkaline media and superior catalytic stability and methanol tolerance. While employing PtCoCN(CDs-0.10) as a cathode catalyst for an as-assembled zinc-air battery (ZAB), it delivers an excellent power density of 194.2 mW cm-2 and exceptional operation stability, which is indicated by a voltage efficiency loss of only 7.7% after a long cycle life of 100 h, demonstrating its great potential applications.

Electrochemical Hydrogen Peroxide Production on Single Atoms and Atomic Clusters

The electrochemical oxygen reduction reaction (ORR) involving the transfer of two electrons (2-electron ORR) offers a sustainable alternative for the production of hydrogen peroxide (H2O2) on-site. Minimizing the use of expensive noble metal catalysts and maximizing their atomic utilization can be achieved by reducing the size of the catalysts. While previous studies have primarily focused on the relationship between particle size and oxygen reduction activity in the 4-electron ORR using Pt-based catalysts, less attention has been paid to the 2-electron ORR for H2O2 production. In this study, we prepared a series of size-controlled Pd clusters and investigated the oxygen reduction in acidic conditions to understand the relationship between cluster size and catalytic performance. Our results showed that larger Pd clusters favored the 4-electron ORR and the production of H2O, while smaller clusters favored the 2-electron ORR and the production of H2O2. To estimate the contribution of single atoms in the catalysts to their performance, we introduced CO. Using in-situ attenuated total reflection-surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS), we observed a range of CO vibrational signatures that correlated with specific ORR behaviors depending on the particle/cluster size.

Towards superior metal phthalocyanine catalysts for electrochemical oxygen reduction: A comprehensive screening under experimental conditions

Metal phthalocyanines (MPcs) represent a promising class of single-atom catalysts with diverse structures, high thermal stability, and versatile chemical properties. In this work, we have computationally screened nineteen MPcs (metal M = V–Zn, Mo–Ag, and W–Pt ordered based on the atomic number) to assess their suitability as electrochemical oxygen reduction reaction (ORR) catalysts, with consideration of a broad range of experimental conditions, including the oxygen adsorption, temperature effects, partial pressure, solvation effects, pH effects, and demetallation decomposition. Using density functional theory calculations based on the hybrid functional, we find that the ORR behaviors on these MPcs fall into three categories, which are characterized by their distinct oxygen adsorption ability. We correctly predict the experimental ORR performance trend of common MPcs and forecast Rh−, Ir−, Ru−, and MnPc as the four most effective ORR catalysts, outperforming the state-of-the-art FePc in terms of catalytic activity and stability. This study highlights the crucial role of oxygen adsorption, predicts superior MPcs for ORR electrocatalysis, and offers detailed guidance on the optimal working conditions.

Iron single Atom–Iron nanoparticles dual-deposited nitrogen-doped graphene hybrid as an innovative catalyst to enhance the oxygen reduction reaction

The fabrication of an effective electrocatalyst for cathodic oxygen reduction reaction (ORR) is important to enhance the performance of fuel cell applications. Here, we prepared a novel hybrid material based on the combination of iron single atoms–small iron nanoparticles homogeneously distributed on the surface of nitrogen-doped graphene nanosheets (FeSA-FeNPs/NG). The achieved FeSA–FeNPs/NG material exhibited high catalytic ORR behaviors with high positive values of +0.94 V and +0.81 V for onset potential and half-wave potential, respectively, as well as the remarkable stability with 90% retention of initial current over an operation period of 15 000 s), superior to commercial Pt/C in 0.1 M KOH medium. In addition, the material favored a four-electron reaction pathway along with good methanol crossover tolerance towards ORR. The outstanding catalytic performance could be attributed to the formation of a unique microporous nanoarchitecture owning large specific surface area of 103.63 m2 g−1 and high conductivity, which create rich active sites and fast charge transfer ability, thus effectively accelerating the adsorption and catalyzation processes to convert oxygen reactant to product during ORR. These findings suggest a novel route for the synthesis of potential catalysts exhibiting excellent efficiency and cost effectiveness for fuel cell industries.

Core-shell Fe/Fe3C heterostructure@carbon layers anchored on N-doped porous carbon for boosting oxygen reduction reaction

It is still challenging but crucial to plumb non-noble metal-based oxygen reduction reaction (ORR) catalysts with comparable or better performance than benchmark Pt/C catalysts. Herein, we proffer an unconventional core-shell-structured iron-based heterostructure electrocatalyst constructed by a Fe/Fe3C heterostructure nanoparticle core wrapped by a graphitic shell embedded on a conductive N-doped mesoporous graphite skeleton (Fe/Fe3C@NC) via facile pyrolysis of MIL-53(Fe) (MIL = Matérial Institute Lavoisier) and melamine. The Fe/Fe3C@NC catalyst delivers more positive half-wave potential (E1/2) of 0.86 V and a low Tafel slope of 56 mV dec−1 for ORR, outpacing the benchmark Pt/C catalyst, and it also shows remarkable long-term durability and excellent methanol tolerance. The marvelous ORR behaviors can be attributed to its distinctive morphologic structure: the heterostructure can enhance intrinsic ORR activity; the core-shell nanostructure can enhance ORR activities through unique electron transfer between iron species and their conductive carbon shells, which can also act as protective barriers to ensure long-term stability; the high-content pyridinic-N doping can be used as additional active centers; and the abundant mesopores facilitate the diffusion of electrolyte, which can further upgrade ORR activities. This study proffers a strategy to design and fabricate non-noble catalysts with well-designed nanoarchitecture and high catalytic activity.

Insight into oxygen reduction activity and pathway on pure titanium using scanning electrochemical microscopy and theoretical calculations

HypothesisUnlike noble metals, the oxygen reduction reaction (ORR) behavior on Ti is more complicated due to its spontaneously formed oxide film. This film results in sluggish ORR kinetics and tends to be reduced within ORR potential region, causing the weak and multi-reaction coupled current. Though Ti is being used in chemical and biological fields, its ORR research is still underexplored. ExperimentsWe innovatively employed the modified reactive tip generation-substrate collection (RTG/SC) mode of scanning electrochemical microscopy (SECM) with high efficiency of 97.2 % to quantitatively study the effects of film characteristics, solution environment (pH, anion, dissolved oxygen), and applied potential on the ORR activity and selectivity of Ti. Then, density functional theory (DFT) and molecular dynamics (MD) analyses were employed to elucidate its ORR behavior. FindingsOn highly reduced Ti, film properties dominate ORR behavior with promoted 4e– selectivity. Rapid film regeneration in alkaline/O2-saturated conditions inhibits ORR activity. Besides, ORR is sensitive to anion species in neutral solutions while showing enhanced 4e– reduction in alkaline media. All the improved 4e– selectivities originate from the hydrogen bond/electrostatic stabilization effect, while the decayed ORR activity by Cl– arises from the suppressed O2 adsorption. This work provides theoretical support and possible guidance for ORR research on oxide-covered metals.

Atomic Scaled Depth Correlation to the Oxygen Reduction Reaction Performance of Single Atom Ni Alloy to the NiO2 Supported Pd Nanocrystal.

This study demonstrates the intercalation of single-atom Ni (NiSA ) substantially reduces the reaction activity of Ni oxide supported Pd nanoparticle (NiO2 /Pd) in the oxygen reduction reaction (ORR). The results indicate the transition states kinetically consolidate the adsorption energy for the chemisorbed O and OH species on the ORR activity. Notably, the NiO2 /Ni1 /Pd performs the optimum ORR behavior with the lowest barrier of 0.49eV and moderate second-step barrier of 0.30eV consequently confirming its utmost ORR performance. Through the stepwise cross-level demonstrations, a structure-Eads -ΔE correspondence for the proposed NiO2 /Nin /Pd systems is established. Most importantly, such a correspondence reveals that the electronic structure of heterogeneous catalysts can be significantly differed by the segregation of atomic clusters in different dimensions and locations. Besides, the doping-depth effect exploration of the NiSA in the NiO2 /Pd structure intrinsically elucidates that the Ni atom doping in the subsurface induces the most fruitful NiSA /PdML synergy combining the electronic and strain effects to optimize the ORR, whereas this desired synergy diminishes at high Pd coverages. Overall, the results not only rationalize the variation in the redox properties but most importantly provides a precision evaluation of the process window for optimizing the configuration and composition of bimetallic catalysts in practical experiments.

Understanding the growth N–Fe3C from assembly of carbon-coated iron nanoparticles on rGO as efficient oxygen reduction electrocatalysts

The oxygen reduction reaction (ORR) is an essential reaction in metal-air battery systems. However, the traditional noble metal Pt-based catalysts for ORR limit the commercial applications of air battery systems due to their high price, low abundance and poor tolerance. In recent studies, nitrogen–doped transition metal carbides have shown promise as an alternative to traditional noble metal catalysts. In this paper, the thermal cracking and calcination method was used to successfully obtain the growth N-doped carbon coated iron carbide nanoparticles (Fe3C@NC/rGOx NP) from assembly of carbon-coated iron oxide Nano-crystals on rGO (Fe3O4@NC/rGOx NCs). Transmission electron and scanning electron microscopy of the fabricated specimens indicated the presence of many carbon shells and pores in the etched samples. The electrochemical test results of the fabricated specimens suggested that the Fe3C@NC/rGO 100 NP annealed at 800 °C exhibited a better ORR behavior than that of Pt/C in a basic electrolyte.

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.

An improved Stӧber method towards iron and nitrogen co-doped porous carbon spheres for oxygen reduction reaction in alkaline media

The significant progress of non-precious metal cathodic electrocatalytic materials is impressive in electrochemical energy conversion application. Here, iron and nitrogen co-doped porous carbon spheres (Fe/N-PCS) have been designed via 3-aminophenol/formaldehyde (APF) resin spheres as carbon precursor, ferric nitrate as iron source, colloidal silica as template and tetramethylguanidine as catalyst by the improved Stöber method. Fe/N-PCS possesses uniform spherical morphology, abundant mesoporous shape and high surface area and exhibits higher oxygen reduction reaction (ORR) electrocatalytic activity (E1/2, 0.838 V vs. RHE) compared with the Pt/C (E1/2, 0.827 V vs. RHE) in alkaline media. In addition, the methanol tolerance and catalytic stability of Fe/N-PCS are greater than commercial Pt/C catalyst. The outstanding ORR behavior of Fe/N-PCS mainly benefits from the iron and nitrogen elements synergistic effect, pyridinic N and the spherical porous structure enabling plenty of active sites exposed. This method is prospective for preparation of highly efficient cathodic ORR electrocatalyst.

A dual ligand coordination strategy for synthesizing drum-like Co, N co-doped porous carbon electrocatalyst towards superior oxygen reduction and zinc-air batteries

We herein propose a dual ligand coordination strategy for deriving puissant non-noble metal electrocatalysts to substitute valuable platinum (Pt)-based materials toward oxygen reduction reaction (ORR), a key reaction in metal-air batteries and fuel cells. In brief, cobalt ions are firstly double-coordinated with proportionate 2-methylimidazole (2-MeIm) and benzimidazole (BIm) to obtain drum-like zeolitic imidazolate frameworks (D-ZIFs), which are then carbonized to output the final Co, N co-doped porous carbon (Co–N–PCD) catalyst inheriting the drum-like morphology of D-ZIFs. The Co–N–PCD is featured by mesopores and exhibits superb electrocatalytic behavior for ORR. Impressively, the half-wave potential of Co–N–PCD catalysts is 0.886 V with finer methanol-tolerance and stability than those of commercial Pt/C. Additionally, a zinc-air battery assembled from the Co–N–PCD displays an open-circuit voltage of 1.413 V, comparable to that of commercial Pt/C (1.455 V), suggesting the potentials of Co–N–PCD in practical energy conversion devices.

Co2P embedded in nitrogen-doped carbon nanoframework derived from Co-based metal-organic framework as efficient oxygen reduction reaction electrocatalyst for enhanced performance of activated carbon air-cathode microbial fuel cell

• The MPD of optimized MFC was 2001 ± 48 mW m −2 , 123% higher than that of control. • The electronic interaction between embedded Co 2 P and N -C improved ORR activity. • Co 2 PNC-NF electrocatalyst exhibited a desired four-electron pathway for ORR. • The double Co site of 001 face of Co 2 P could boost the cracking of OOH* group. A kind of Co 2 P embedded in nitrogen-doped carbon nanoframework (Co 2 PNC-NF) synthesized from directly carbonized Co-based metal-organic framework (ZIF-67) combined with phosphorus was utilized in the microbial fuel cell (MFC) to modify the active carbon air-cathode for the first time. Various techniques involving XRD, FESEM, TEM/EDS, BET and XPS were used to characterize the microstructure, morphology and surface chemical composition belonging to as-synthesized Co 2 PNC-NF. The electrochemical measurements revealed that the active carbon cathode modified by Co 2 PNC-NF got reduced resistance and optimized catalytic behavior in oxygen reduction reaction (ORR) process. The optimized MFC had a high maximum power density reaching 2001 mW m −2 , increasing by 123% compared with the bare active carbon cathode MFC. This result showed that combination between transition-metals phosphide and heteroatom-doped carbon matrices was beneficial to the improvement of MFC performance. Moreover, density functional theory calculations indicated that the special structure of double Co site of 001 face of Co 2 P can accelerate the ORR by boosting the cracking of OOH* group. Therefore, the Co 2 PNC-NF could be applied as an economical and efficient electrocatalyst in MFC to replace noble metal catalyst.

Theory-Driven Design of Electrocatalysts for the Two-Electron Oxygen Reduction Reaction Based on Dispersed Metal Phthalocyanines

Theory-Driven Design of Electrocatalysts for the Two-Electron Oxygen Reduction Reaction Based on Dispersed Metal Phthalocyanines

Importance of the hydrogen evolution reaction in magnesium chloride solutions on stainless steel

Cathodic kinetics in magnesium chloride (MgCl2) solutions were investigated on platinum (Pt) and stainless steel 304 L (SS304 L). Density, viscosity, and dissolved oxygen concentration for MgCl2 solutions were also measured. A 2-electron transfer for oxygen reduction reaction (ORR) on Pt was determined using a rotating disk electrode. SS304 L displayed non-Levich behavior for ORR and, due to ORR suppression and buffering of near surface pH by Mg-species precipitation, the primary cathodic reaction was the hydrogen evolution reaction (HER) in saturated MgCl2. Furthermore, non-carbonate precipitates were found to be kinetically favored. Implications of HER are discussed through atmospheric corrosion and stress corrosion cracking.

A facile preparation of nitrogen-doped porous carbons from renewable as efficient catalysts for oxygen reduction reaction

Developing cost-effective and high active catalysts for the oxygen reduction reaction (ORR) is vital for the application of fuel cells. In this work, nitrogen-doped porous carbon nanosheets(N-PC) derived from biomass waste soybean residue were prepared by a facile combining method of solid state grinding and pyrolysing, using g-C3N4 as both nitrogen source and sacrificial template. The benefit of this facile process is that neither a designated template nor a chemical activating agent is required. The influence of g-C3N4 level on the structure and ORR behavior of the resulting N-PC was systematically investigated by means of spectroscopy (XPS), surface area analysis (BET), electron microscopy (TEM, SEM) et al., and electrochemical experiments. The optimized sample possesses appropriate defect structure, high BET surface area and pore volume (483 ​m2 ​g−1 and 1.57 ​cm3 ​g−1), and high N content (6.04 ​at.%), and exhibits decent activity and methanol tolerance in ORR process. Its superior stability versus the commercial Pt/C is also evidenced by almost 50% higher in chronoamperometric current response after 3600 ​s testing duration. This work supplies a simple and economical route to synthesize superior electrocatalyst for ORR on the basis of biomass waste.

Highly Durable Pt-Based Catalyst Supported on Carbon Derived from Tamarind Seeds for Oxygen Reduction Reaction in PEM Fuel Cell

In the process of developing an excellent active and stable Pt/C electrocatalyst for oxygen reduction reaction in fuel cells, metals are supported on heteroatom doped mesoporous carbon derived from natural resources. In this context, tamarind seeds are utilized to derive high surface area porous carbon for N heteroatom doping and followed by Pt deposition for oxygen reduction reaction (ORR) catalyst. The synthesis process involves optimization of temperature, N-content in the catalyst followed by Pt deposition by virtue of their electrochemical ORR behavior. The Pt/N-TC-1000 catalyst exhibits an outstanding activity and stability towards ORR even after 20,000 potential cycles. This is credited to the existence of N heteroatom in the matrix of carbon, where N acts as the linker between Pt and TC-1000 to avail the Pt-N and N-C chemical bonds in the Pt/N-TC-1000 catalyst. A peak power density of 800 mW cm−2 is attained while evaluating the catalyst performance in a H2-O2 polymer electrolyte membrane fuel cell (PEMFC), at 70 °C and ambient pressure. The Pt/N-TC-1000 catalyst outpaces the commercial Pt/C with reference to fuel cell performance and stability. This is attributed to the high porous and corrosion resistive carbon support in combination with the strong Pt–N–C chemical bonds.

A rotating disk electrode study on catalytic activity of iron(II) phthalocyanine-modified electrodes for oxygen reduction in acidic media

Catalytic activity of monometric metal macrocycles for oxygen reduction reaction (ORR) was investigated using rotating disk electrode voltammetry in acidic media. Iron(II) phthalocyanines (FePc) and cobalt(II) tetraphenylporphyrins (CoTPP) were immobilized on Au surfaces through molecular wires with different terminal groups of pyridine and isocyanide. The measured ORR behavior of FePc was largely influenced by the axial ligand while CoTPP promoted only the two-electron reaction regardless of the axial ligand. The FePc immobilized with pyridine was easily detached from the surface under the ORR condition, and was able to promote the four-electron reaction only under the high overpotential application. The FePc with isocyanide was more stable with the activity for the four-electron reaction, due to stronger electron donation to Fe central ions.

Electronic and Physical Property Manipulations: Recent Achievements towards Heterogeneous Carbon‐based Catalysts for Oxygen Reduction Reaction

AbstractHeterogeneous carbon‐based oxygen reduction reaction (ORR) catalysts with distinctive properties afford new exciting opportunities of low‐cost processing, address critical issues in real‐world applications and strengthen economic competitiveness of catalytic process. This minireview is mainly centered on the recent achievements of new and interesting design concepts of carbon‐based ORR catalysts, especially focusing on the electronic structure manipulations of both metal‐free heteroatom doped‐carbons and M−N−C catalysts. Effect of other key physical factors including density and dispersity of active sites, pore structure and conductivity on ORR behavior and accordingly nichetargeting synthetic strategies will be also illustrated. In the end, a brief illumination of challenges and future research directions for heterogeneous carbon‐based ORR catalysts will be provided.

Contrasting Oxygen Reduction Reactions on Zero- and One-Dimensional Defects of MoS2 for Versatile Applications.

Oxygen reduction reaction (ORR) is a key microscopic process in many electrochemical applications of materials, where the requirements of their ORR performances may vary strikingly, for example, during the uses of MoS2 as an electrocatalyst and anticorrosion/lubricating coating in aqueous/humid environments, ORR should be activated and inhibited, respectively. To reveal a complete ORR profile of MoS2, using first-principles calculations, we examine the stabilities of various possible zero-dimensional point defects on the surface and one-dimensional edge defects and comprehensively explore the ORR activities on pristine MoS2 surface and those defects in acid/alkaline solutions. It is found that the ORRs on the pristine surface and surfaces with point defects always require large overpotentials (>1.0 V), indicating a defect-immune resistance of the planar MoS2 surface against the ORR. However, the ORR overpotentials on edge defects can reach as low as 0.66 V, corresponding to a relatively high activity close to that of the prototypical catalyst Pt (overpotential ∼0.45 V). Such contrasting ORR behaviors of point and edge defects are also understood in depth by analyzing the underlying thermodynamic and electronic-structure mechanisms. This work not only quantitatively explains the performances of MoS2 in both galvanic corrosion and electrochemical catalysis but also provides a useful structure-ORR map that can facilitate adapting the realistic MoS2 to versatile electrochemical applications.

Hydrothermal synthesis of nitrogen, sulfur co-doped graphene and its high performance in supercapacitor and oxygen reduction reaction

This study reports the preparation of nitrogen and sulfur co-doped graphene by hydrothermal synthesis using methionine as doping agent and GO as precursor. The structure, morphology, mechanical property and surface chemistry of the as-prepared co-doped graphene were investigated though XRD, N2 adsorption-desorption, SEM, XPS, dynamic mechanical analyzer and Raman characterizations. The material was tested for supercapacitive and oxygen reduction reaction behaviors. It was found that the obtained co-doped sample NS-Gm05 with 3D porous structure and the highest specific surface area (260 m2 g−1) exhibited good mechanical properties, excellent capacitive performance and ORR performance. When used as free-standing electrode in supercapacitor, the specific capacitance of NS-Gm05 reached 431 F g−1 at 0.5 A g−1, which might be due to its highest specific surface area and the pseudocapacitance that N and S provided. Furthermore, the better ORR activity of the as-prepared samples can be attributed to its high specific surface area and heteroatom doping contents.