Efficient Electrocatalyst For Oxygen Reduction Reaction Research Articles

Nitrogen-rich holey graphene for efficient oxygen reduction reaction

Nitrogen (N)-doped porous carbon materials have attracted tremendous attention as low-cost and highly-efficient electrocatalysts for oxygen reduction reaction (ORR). In this study, holey graphene with a high edge pyridinic N-doping (43.0% in 5.1 at.% N, N-hG) has been prepared via a modified two-step synthetic method, involving the annealing in air at 430 °C to create holes, followed by N-doping in Ar/NH3 atmosphere at 850 °C. The resultant N-hG was demonstrated to possess a high specific surface area (1170.05 m2 g−1), outstanding ORR performance (E1/2 = 0.833 V, Eonset = 0.91 V) close to those of Pt/C catalyst in alkaline electrolyte, and a better long-term stability and methanol tolerance than Pt/C. The outstanding performance was attributed to the high specific surface area with abundant exposed active sites as well as the high edge N-content and large number of holes rich with the edge defects to ensure high catalytic activities. Furthermore, a mechanistic understanding of the hole formation in graphene lattice and subsequent edge N-doping was obtained, which could be used to guide the design and development of various new low-cost, highly efficient carbon electrocatalysts for ORR and beyond.

Atomically dispersed hierarchically ordered porous Fe–N–C electrocatalyst for high performance electrocatalytic oxygen reduction in Zn-Air battery

Rational design and synthesis of non-precious metal electrocatalysts for highly efficient oxygen reduction reaction (ORR) is urgently required. Recently, single atom catalysts (SACs) have sparked intense interests due to their maximum atom utilization efficiency and excellent properties in electrocatalysis. Herein, we reported an efficient ORR electrocatalyst with atomically dispersed FeN4 sites anchored on 3D hierarchically ordered microporous-mesoporous-macroporous nitrogen doped carbon (3DOM Fe–N–C). Owing to the synergism of highly dispersed FeN4 active sites and 3D hierarchically ordered porous architecture, 3DOM Fe–N–C-900, which was obtained via pyrolysis of ferrocene-encapsulated macro-microporous ZIF-8 precursor at 900 °C, exhibited an outstanding ORR activity in both alkaline (E1/2 of 0.875 V) and acid mediums (E1/2 of 0.784 V), as well as superior stability (only changed 2 mV after 10,000 cycles in alkaline medium). Moreover, 3DOM Fe–N–C-900 as ORR catalyst in zinc-air battery achieved a high power density of 235 mW cm−2 and a high specific capacity of 768.3 mAh g−1, exceeding that driven by Pt/C. Our results revealed that the 3D hierarchically porous architecture of electrocatalysts could facilitate mass transport and increase the accessibility of active sites, thus optimizing their performances in ORR. This work well demonstrated the importance of rationally engineering porous structure of the catalyst for highly efficient ORR.

Silver Decorated Reduced Graphene Oxide as Electrocatalyst for Zinc–Air Batteries

Due to their low cost and very high energy density, zinc–air batteries (ZABs) exhibit high potential for various energy applications. The electrochemical performance of the air-cathode has a decisive impact on the discharge performance of ZABs because the sluggish oxygen reduction reaction (ORR) kinetics increase the overpotential of the air-cathode and hence the performance of ZABs. In this work, reduced graphene oxide decorated with silver nanoparticles (AgNP/rGO) is synthesized using simultaneous reduction of graphene oxide and silver ions. Different amounts of silver loading are examined for the synthesis of AgNP/rGO. The synthesized AgNP/rGO samples are analyzed using a rotating disk electrode in order to investigate ORR activity. Then, the synthesized AgNP/rGO electrocatalyst is applied on a tubular designed zinc–air battery in order to study the performance of the zinc–air battery. Results demonstrate that AgNP/rGO is an efficient and cost-effective ORR electrocatalyst for its practical application in ZABs.

Synergic Effect in a New Electrocatalyst Ni2SbTe2 for Oxygen Reduction Reaction

Pt and Pt-based materials are still the most common catalysts for oxygen reduction reaction (ORR), but it is highly desirable to develop efficient ORR electrocatalysts based on inexpensive metals. ...

Synthesis of Porous N-Rich Carbon/MXene from MXene@Polypyrrole Hybrid Nanosheets as Oxygen Reduction Reaction Electrocatalysts

Noble Metal-free catalysts attracted much attention as promising candidates for Pt-based catalyst replacement to advance applications related to oxygen reduction reaction (ORR), which is critical for large-scale renewable energy storage and conversion. Herein, this work focused on a synthesis of noble metal-free ORR electrocatalysts consisting of porous N-rich carbon/MXene, which was obtained using very conductive and reactive Ti3C2 MXene and polypyrrole (PPy) as a C and N source. The electrocatalyst exhibited excellent electrocatalytic activity and stability with an onset and a half-wave potentials equal to 0.85 and 0.71 V, respectively. Results obtained in this work demonstrate how to design efficient noble metal-free ORR electrocatalysts applicable to other chemical systems.

Universal Approach for Electronically Tuned Transition-Metal-Doped Graphitic Carbon Nitride as a Conductive Electrode Material for Highly Efficient Oxygen Reduction Reaction.

The rational design of electronically tuned transition-metal-doped conductive carbon nanostructures has emerged as a potential substitution of a platinum-group-metal (PGM)-free electrocatalyst for oxygen reduction reaction (ORR). We report here a universal strategy using a one-step thermal polymerization reaction for transition-metal-doped graphitic carbon nitride (g-C3N4) without any conductive carbon support as a highly efficient ORR electrocatalyst. X-ray absorption spectroscopy evidences the presence of Fe-Nx active sites with a possible three-coordinated Fe atom with N atoms. The as-prepared Fe-g-C3N4 with improved surface area, graphitic nature, and conductive carbon framework exhibits a superior electrochemical performance toward ORR activity in an alkaline medium. Interestingly, it displays a 0.88 V (vs reversible hydrogen electrode, RHE) half-wave potential (E1/2) with a four-electron-transfer pathway and excellent stability outperforming platinum/carbon (Pt/C) in an alkaline medium. More impressively, when the Fe-g-C3N4 catalyst is used as a cathode material in a zinc-air battery, it presents a higher peak power density (148 mW cm-2) than Pt/C (133 mW cm-2), which further established the importance of the low-cost material synthesis approach toward the development of an earth-abundant PGM-free catalyst for fuel-cell and air battery fabrication.

γ-Graphyne nanotubes as defect-free catalysts of the oxygen reduction reaction: a DFT investigation.

Graphyne materials are potential candidates to fabricate low-cost but efficient metal-free oxygen reduction reaction (ORR) electrocatalysts. However, due to the coexistence of sp and sp2 carbon atoms in graphyne, some factors playing important roles in determining the ORR activity have received little attention. In the present paper, we carried out thorough density functional theory (DFT) calculations to study the curvature effect on the ORR activity of γ-graphyne. Our results suggest that the (5, 0)-γGyNT would be an excellent metal-free ORR catalyst. Its limiting potential was computed to be 0.80 V and the corresponding active sites occupy up to 16.7% in content, much better than previously reported CACs. Moreover, it is revealed that the curvature can tune the degree of exposure of p electrons of active sites, thus tuning the ORR activity. Our findings are beneficial for further understanding catalytic behavior on graphyne related materials and we suggest a new strategy to design high performance metal-free ORR catalysts.

Upgrading the Properties of Reduced Graphene Oxide and Nitrogen-Doped Reduced Graphene Oxide Produced by Thermal Reduction toward Efficient ORR Electrocatalysts.

N-doped (NrGO) and non-doped (rGO) graphenic materials are prepared by oxidation and further thermal treatment under ammonia and inert atmospheres, respectively, of natural graphites of different particle sizes. An extensive characterization of graphene materials points out that the physical properties of synthesized materials, as well as the nitrogen species introduced, depend on the particle size of the starting graphite, the reduction atmospheres, and the temperature conditions used during the exfoliation treatment. These findings indicate that it is possible to tailor properties of non-doped and N-doped reduced graphene oxide, such as the number of layers, surface area, and nitrogen content, by using a simple strategy based on selecting adequate graphite sizes and convenient experimental conditions during thermal exfoliation. Additionally, the graphenic materials are successfully applied as electrocatalysts for the demanding oxygen reduction reaction (ORR). Nitrogen doping together with the starting graphite of smaller particle size (NrGO325-4) resulted in a more efficient ORR electrocatalyst with more positive onset potentials (Eonset = 0.82 V versus RHE), superior diffusion-limiting current density (jL, 0.26V, 1600rpm = −4.05 mA cm−2), and selectivity to the direct four-electron pathway. Moreover, all NrGOm-4 show high tolerance to methanol poisoning in comparison with the state-of-the-art ORR electrocatalyst Pt/C and good stability.

ZIF-8/PEDOT @ flexible carbon cloth electrode as highly efficient electrocatalyst for oxygen reduction reaction

Design and fabrication of highly efficient and low-cost oxygen reduction reaction (ORR) electrocatalysts is of paramount importance for practical applications. Herein, we proposed a cost-effective, metal-free catalyst based on ZIF-8 metal-organic framework nanoparticles/electro-polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film on the surface of flexible carbon cloth (CC) electrode (ZIF-8/PEDOT/CC) via a two-step procedure. For this purpose, worm-like PEDOT nanostructures were deposited on the surface of carbon fibers using a pulse electro-polymerization technique followed by facile growth of ZIF-8 polyhedra nanoparticles via a chemical bath deposition method. The ORR measurements in O2-saturated KOH electrolyte solution using the modified CC electrode demonstrated that the prepared electrode exhibits remarkable electrocatalytic activity towards ORR with 8 times increase in the cathodic current density compared to bare CC (J = 0.13–1.1 mA/cm2) along with lower overpotential due to the synergetic effects between ZIF-8 nanoparticles as particularly porous nanostructure act as electrolyte reservoirs and highly conductive PEDOT film. The Kouteckey-Levich analysis for the ZIF-8/PEDOT-modified CC electrode revealed that the oxygen reduction reaction proceeds via a nearly four-electron pathway along with superior tolerance to methanol crossover as well as enhanced stability in alkaline solution compared to the gold standard commercial Pt catalyst.

Microporous Solids En Route to Heterogeneous Electrocatalysis: The Oxygen Reduction Reaction

The recent progress and challenges in developing highly active microporous materials as heterogeneous electrocatalysts for oxygen reduction reaction (ORR) are discussed. Due to the slow kinetics of ORR, the search for novel highly stable catalysts that can outperform Pt‐based ones is a growing demand. Functional microporous materials and exceptional chemical stability are of great interest due to their unique catalytic properties. The crucial rule of porosity and catalyst design strategies are thoroughly discussed with emphasis on the influence of the degree of microporosity on the material's intrinsic catalytic activity and the current best practice for catalyst testing and activity reporting. This Review focuses on microporous materials, which are classified into crystalline as metal–organic frameworks (MOFs), covalent–organic frameworks (COFs), or amorphous porous–organic polymers (POPs) as to their recent utilization in constructing efficient ORR electrocatalysts. The fundamental challenges in obtaining stable catalysts with appreciable kinetics from non‐noble metal ions, and ways to form them utilizing microporous solids as catalyst matrices, are reviewed. The fundamental criteria for future generation ORR catalysts based on microporous solids, including stability in acidic medium, high electrical conductivity, and accessibility of the active sites within the matrix are highlighted for guidance to future works.

Fe, N-decorated three dimension porous carbonaceous matrix for highly efficient oxygen reduction reaction

Rational engineering of simple, economical and durable nonprecious metal electrocatalyst with excellent oxygen reduction reaction (ORR) activity is crucial for the electrochemical energy conversion devices, such as metal-air batteries and fuel cells. Here, we developed a highly efficient ORR electrocatalyst with rich and well-dispersed Fe-Nx active sites and iron nanocrystals decorated three dimension (3D) porous carbonaceous matrix by a rational designed carbonaceous spheres templated strategy. The fabricated electrocatalyst exhibits outstanding ORR activity with onset potential of 1.0 V and half-wave potential of 0.90 V versus reversible hydrogen electrode in alkaline media, which is much better than benchmark Pt/C. In addition, it presents particularly better performance in terms of superior stability and excellent methanol tolerance capacity. Experimental studies display that the remarkable ORR activity primarily originates from the synergetic effect of rich Fe-Nx active sites, sufficient carbon encapsulated metallic iron nanocrystals and desired meso/microporous structure. What worth to point out is that the facile synthetic technique can be extended to fabricate other low cost highly active transition metal-N-carbon scaffolds ORR electrocatalysts.

Interfacial Engineering of W2 N/WC Heterostructures Derived from Solid-State Synthesis: A Highly Efficient Trifunctional Electrocatalyst for ORR, OER, and HER.

To meet the practical demand of overall water splitting and regenerative metal-air batteries, highly efficient, low-cost, and durable electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are required to displace noble metal catalysts. In this work, a facile solid-state synthesis strategy is developed to construct the interfacial engineering of W2 N/WC heterostructures, in which abundant interfaces are formed. Under high temperature (800 °C), volatile CNx species from dicyanodiamide are trapped by WO3 nanorods, followed by simultaneous nitridation and carbonization, to form W2 N/WC heterostructure catalysts. The resultant W2 N/WC heterostructure catalysts exhibit an efficient and stable electrocatalytic performance toward the ORR, OER, and HER, including a half-wave potential of 0.81 V (ORR) and a low overpotential at 10 mA cm-2 for the OER (320 mV) and HER (148.5 mV). Furthermore, a W2 N/WC-based Zn-air battery shows outstanding high power density (172 mW cm-2 ). Density functional theory and X-ray absorption fine structure analysis computations reveal that W2 N/WC interfaces synergistically facilitate transport and separation of charge, thus accelerating the electrochemical ORR, OER, and HER. This work paves a novel avenue for constructing efficient and low-cost electrocatalysts for electrochemical energy devices.

Nitrogen and Cobalt Co-Coped Carbon Materials Derived from Biomass Chitin as High-Performance Electrocatalyst for Aluminum-Air Batteries

Development of convenient, economic electrocatalysts for oxygen reduction reaction (ORR) in alkaline medium is of great significance to practical applications of aluminum-air batteries. Herein, a biomass chitin-derived carbon material with high ORR activities has been prepared and applied as electrocatalysts in Al-air batteries. The obtained cobalt, nitrogen co-doped carbon material (CoNC) exhibits the positive onset potential 0.86 V vs. RHE (reversible hydrogen electrode) and high-limiting current density 5.94 mA cm−2. Additionally, the durability of the CoNC material in alkaline electrolyte shows better stability when compared to the commercial Pt/C catalyst. Furthermore, the Al-air battery using CoNC as an air cathode catalyst provides the power density of 32.24 mW cm−2 and remains the constant discharge voltage of 1.17 V at 20 mA cm−2. This work not only provides a facile method to synthesize low-cost and efficient ORR electrocatalysts for Al-air batteries, but also paves a new way to explore and utilize high-valued biomass materials.

An alternate aqueous phase synthesis of the Pt3Co/C catalyst towards efficient oxygen reduction reaction

AbstractCarbon supported Pt-Co alloys are among the most promising electrocatalysts towards oxygen reduction reaction (ORR) for the application in low temperature fuel cells and beyond, thus their facile and green synthesis is highly demanded. Herein we initially report an alternate aqueous phase one-pot synthesis of such catalysts (containing nominally ca. 20 wt.% Pt) based on dimethylamine borane (DMAB) reduction. The as-obtained electrocatalyst (denoted as Pt3Co/C-DMAB) is compared with the ones obtained by NaBH4 and N2H4·H2O reduction (denoted as Pt3Co/C-NaBH4 and Pt3Co/C-N2H4·H2O, respectively) as well as a commercial Pt/C, in terms of the structure and electrocatalytic property. It turns out that Pt3Co/C-DMAB exhibits the highest ORR performance among all the tested samples in an O2-saturated 0.1 mol/L HClO4, with the mass activity (specific activity) ca. 4 (6) times as large as that for Pt/C. After 10000 cycles of the accelerated degradation test, the half-wave potential for ORR on Pt3Co/C-DMAB decreases only by 4 mV, in contrast to 24 mV for that on Pt/C. Pt3Co/C-NaBH4 or Pt3Co/C-N2H4·H2O shows a specific activity comparable to that for Pt3Co/C-DMAB, but a mass activity similar to that for Pt/C. ICP-AES, TEM, XRD and XPS characterizations indicate that Pt3Co nanoparticles are well-dispersed and alloyed with a mean particle size of ca. 3.4 plusmn; 0.4 nm, contributing to the prominent electrocatalytic performance of Pt3Co/C-DMAB. This simple aqueous synthetic route may provide an alternate opportunity for developing efficient practical electrocatalysts for ORR.

Heteroatom embedded graphene-like structure anchored on porous biochar as efficient metal-free catalyst for ORR

Efficient biomass-derived carbon have large potential as alternative to metal-based catalysts for oxygen reduction reaction (ORR). This study demonstrates a feasible strategy to largely prepare enteromorpha (EP) derived biochar with N, S embedded graphene-like structure anchored, which is firstly used as efficient metal-free electrocatalyst for ORR. Omitting the selection and classification of raw material as well as further additional activation and/or modification by dopants, the preparation process was merely adjusted via pyrolysis and acid etching. The obtained catalyst with low content of N (3.80 at%), S (1.00 at%) and large surface area (778.2 m2 g−1) exhibited an onset potential of 0.95 V vs RHE in a four electron pathway, which showed superior stability and durability compared to that of commercial Pt/C catalyst. The outstanding performance of the catalyst is expected to be a potential candidate for sustainable and large-scale industrial energy conversion and storage processes in the near future.

Self-assembled copper/cobalt-containing polypyrrole hydrogels for highly efficient ORR electrocatalysts

The exploitation of high-efficiency, inexpensive, as well as durable electrocatalysts for the oxygen reduction reaction (ORR) is of vital importance for a number of emerging technologies, such as fuel cells to counter energy and environment crises. Herein, we describe a novel approach for the synthesis of conducting electrocatalysts derived from copper/cobalt-containing polypyrrole (PPy) hydrogel. This strategy relies on a pervasive supramolecular way toward controlled in situ synthesis of one-dimensional nanostructured conductive hydrogels using a reasonable dopant counter ion, which is a disc-shaped liquid crystal molecule copper phthalocyanine- 3,4′,4″,4‴-tetrasulfonic acid tetrasodium salt (CuPcTs). The formation of supramolecular crosslinked PPy hydrogel allows for efficient and homogeneous incorporation of highly active Co ion. Moreover, Co nanoparticles are also formed and doped into the carbon layer after pyrolysis, which further enhance the electrochemical activities. The prepared catalysts show outstanding electrocatalytic activity for the ORR reaction and the reaction process obviously conformed to a four-electron reduction mechanism in the alkaline electrolyte. Given the uniform nanostructures in present hydrogels, it is accredited that such strategy can offer new approach in high active nonprecious-metal-based electrocatalysts.

PANI-modified Pt/Na4Ge9O20 with low Pt loadings: Efficient bifunctional electrocatalyst for oxygen reduction and hydrogen evolution

Exploring cost-effective electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) have been a goal in the sustainable hydrogen-based society. Although abundant of alternative materials have been developed, Pt/C remains the most efficient electrocatalyst for the ORR and HER. Nevertheless, improving the stability and reducing Pt loading for Pt-based electrocatalysts are still big challenges. Herein, semiconductor crystals Na4Ge9O20 with richer topology structure was chosen as electrocatalyst support, subsequently, the conductive polymer polyaniline (PANI) was decorated on semiconductor Na4Ge9O20, low-content Pt nanoparticles (Pt NPs) with the size of 1–3 nm were then uniformly anchored on the surface of Na4Ge9O20-PANI to obtain the efficient bifunctional electrocatalyst for ORR and HER in the acidic solution. More importantly, the stability and mass activity of the obtained electrocatalyst 5 wt% Pt/Na4Ge9O20-PNAI are significantly higher than that of commercial 20 wt% Pt/C for ORR and HER. It was proposed that the PANI could not only promote the electron transfer from Na4Ge9O20 to Pt, but also stabilize the Pt NPs, thus, improving the electrocatalytic activity and stability of 5 wt% Pt/Na4Ge9O20-PNAI.

Efficient oxygen reduction activity on layered palladium phosphosulphide and its application in alkaline fuel cells

Metal chalcogenides-based electrocatalysts have received considerable attention in recent years. Herein, a layer-type ternary chalcogenide compound, PdPS is proposed as an efficient oxygen reduction reaction electrocatalyst in alkaline medium. PdPS is semiconducting that crystallizes in orthorhombic symmetry. Improvement in conductivity of PdPS using reduced graphene oxide results in excellent electrocatalytic activity. The kinetics is followed by rotating (ring) disk electrode measurements and the composite electrocatalyst is found to be stable, efficient and methanol tolerant. The catalyst is further used as cathode in anion exchange membrane fuel cell and is shown to deliver power density comparable to Pt/C catalyst. In addition, this catalyst is also capable of water oxidation from alkaline solution with favorable electrochemical parameters.

Improved Oxygen Reduction Reaction Activity of Nanostructured CoS2 through Electrochemical Tuning

Searching for efficient Pt-free oxygen reduction reaction (ORR) electrocatalysts has been actively pursued among the current electrocatalyst research community. The family of transition-metal chalc...

Facile Synthesis of Quaternary Structurally Ordered L12-Pt(Fe, Co, Ni)3 Nanoparticles with Low Content of Platinum as Efficient Oxygen Reduction Reaction Electrocatalysts.

Synthesis of electrocatalysts for oxygen reduction reaction (ORR) with not only prominent electrocatalytic performance but also a low amount of Pt is the urgent challenge in the popularization of fuel cells. In this work, through a facile synthetic strategy of spray dehydration on a solid surface and annealing process, we demonstrate the first manufacture of quaternary structurally ordered PtM3 (M = transition metal) intermetallic nanoparticles (NPs), Pt(Fe, Co, Ni)3, in order to lower the content of Pt. The atomic contents of Pt, Fe, Co, and Ni are equal and the chemical structure of Pt(Fe, Co, Ni)3 is a cubic L12-ordered structure. L12-Pt(Fe, Co, Ni)3/C electrocatalysts exhibit enhanced electrocatalytic performance toward ORR with mass activity (MA) 6.6 times higher than the commercial Pt/C and a minimal loss of 17% in MA and 1.5% loss in specific activity (SA) after 10 000 potential cycles at 0.9 V. Furthermore, the stability behavior is confirmed to be attributed to the coaction of particle sizes and the ordering effect. Compared with traditional Pt-based electrocatalysts in the stoichiometric forms of Pt3M and PtM, L12-Pt(Fe, Co, Ni)3 intermetallic NPs exhibit excellent performance and higher cost effectiveness. Moreover, this work also proposes a facile and effective synthetic strategy for manufacturing multicomponent Pt-based electrocatalysts for ORR.