Oxygen Reduction Catalysts Research Articles

Preparation of multistage microporous and mesoporous nitrogen-doped carbon nanospheres and study on electrocatalytic oxygen reduction

Non-metallic carbon-based catalysts are one of the most promising catalysts for electrocatalytic oxygen reduction (ORR). However, the controlled synthesis of the pore structures of carbon-based catalysts and the determination of catalytic sites still remains to be further explored. Based on this, two nitrogen-doped carbon-based catalysts with microporous and mesoporous structures were prepared in this paper. The two catalysts had different pore structures and nitrogen-doped species. The experimental results showed that the carbon-based catalyst (PC-NH3) rich in microporous structure and pyridine nitrogen doping had better catalytic performance, the electrocatalytic oxygen reduction performance of the catalyst was comparable to that of the platinum catalyst, and it had excellent methanol resistance and stability. This study provided important guidance for the application of porous carbon materials in oxygen reduction.

Oxygen Reduction and Hydrogen Evolution Reactions on Zigzag ReS2 Nanoribbons

Two-dimensional (2D) rhenium disulfide (ReS2) has received a lot of attention recently as a potential electrocatalyst. Since monolayer ReS2 is catalytically inactive, surface modifications are required to enhance the activity. Some of the methods adopted for this include single-atom doping, vacancy creation, creation of lower dimensional nanostructures like nanoribbons, quantum dots etc. ReS2 nanoribbons have not been as intensely explored as other transition metal dichalcogenides in electrocatalysis. The oxygen reduction and hydrogen evolution activities of two structurally distinct ReS2 nanoribbons are investigated in this work using plane wave DFT. Both type of nanoribbons investigated demonstrates enhanced catalytic activity compared to monolayer ReS2. One of the nanoribbons modelled in our studies promises good performance as a catalyst for oxygen reduction and hydrogen evolution reactions. Based on our model we conclude that the catalytic activity of ReS2 arises primarily from the edges of finite sized nanostructures. Edge activity combined with stability in acidic media and methanol tolerance make ReS2 nanoribbons a promising material for electrochemical applications.

Lignin-derived dual-doped carbon nanocomposites as low-cost electrocatalysts

Converting waste biomass into functional materials is promising to achieve the high-value utilization of low-cost and sustainable resources. Here we demonstrate a facile surface/interfacial approach to transforming biomass waste lignin to heteroatom-doped carbon-based catalysts for oxygen reduction and oxygen evolution reactions in alkaline media. The formation of dual-heteroatom incorporated carbon nanocomposites is attributed to the strong interfacial complexation in the lignin-based precursor. Compared to commercial catalyst standards, the dual-doped carbon nanocomposites show promising catalytic activities and superior long-term durability, especially for oxygen evolution reactions. The catalytic mechanisms for oxygen reduction reaction and oxygen evolution reactions are attributed to nitrogen-coordinated phosphorous and pyridinic nitrogen, respectively. The developed method is believed to facilitate the massive production of non-metal electrocatalysts from the abundant, inexpensive, and environmentally benign lignin, offering attractive renewable energy solutions.

Highly Active Porous Carbon-Supported CoNi Bimetallic Catalysts for Four-Electron Reduction of Oxygen

Great interest has been taken in oxygen reduction reaction (ORR), as a common cathode reaction in new energy sources such as fuel cells and metal–air batteries, to improve the current energy structure and develop new green energy sources. Noble metal Pt is still considered the best catalyst for this reaction. However, its disadvantages such as high cost, low selectivity, poor stability, and susceptibility to impurity poisoning severely limit its further industrial applications. Therefore, development of efficient and low-cost ORR reduction catalysts is particularly critical. M-Nx-C materials have been extensively studied to achieve a high ORR activity close to that of Pt catalysts. In this study, CoNi bimetallic alloy carbon-based oxygen reduction catalysts named CoNi-950 (Zn) were successfully synthesized, using a metal–organic framework (MOF) as a carbon precursor and a nitrogen source. The experimental results show that CoNi-950 (Zn) exhibits good ORR catalytic performance with an ultimate current density of 6.27 mA cm–2, which even exceeds that of some Pt/C catalysts with a mass loading of 20 wt % (5.92 mA cm–2). In addition, the active site of the catalyst was also identified by acid leaching and SCN– poisoning experiments, showing two sites in the form of CoNi-Nx and the CoNi alloy or its oxides in the material. Further experiments demonstrate that these two active sites have distinct ORR catalytic mechanisms, generating positive synergism in ORR. A mechanism in which O2 was catalytically reduced by CoNi-950 (Zn) in a four-electron transfer, i.e., a continuous two-step dual-electron transfer reduction process in alkaline electrolytes, is proposed.

Solvent environment engineering to synthesize Fe[sbnd]N[sbnd]C nanocubes with densely Fe-Nx sites as oxygen reduction catalysts for Zn-air battery

Zeolitic imidazole framework (ZIF)-derived iron–nitrogen-carbon (FeNC) materials are expected to be high-efficiency catalysts for oxygen reduction reaction (ORR). However, increasing the density of active sites while avoiding metal accumulation still faces significant challenges. Herein, solvent environment engineering is used to synthesize the FeNC containing dense Fe-Nx moieties by adjusting the solvent during the ZIF precursor synthesis process. Compared with methanol and water/methanol, the aqueous media can provide a more moderate Fe content for the ZIF precursor, which facilitates the construction of high-density Fe-Nx sites and prevent the appearance of iron-based nanoparticles during pyrolysis. Therefore, the FeNC(C) nanocubes synthesized in an aqueous media have the highest single atom Fe loading (0.6 at%) among the prepared samples, which presents excellent oxygen reduction properties and durability under alkaline and acidic conditions. The advantage of FeNC(C) is proven in Zn-air batteries, with outstanding performance and long-term stability.

Rational design of porous Fex-N@MOF as a highly efficient catalyst for oxygen reduction over a wide pH range

The oxygen reduction reaction (ORR) kinetics are well known to strongly rely on the activives of electrocatalysts. Herein, a Fe-N-doped porous carbon-based electrocatalyst combined with zinc (Zn) -based metal-organic frameworks (MOFs) (Fex-N@MOF) was designed and successfully fabricated via a facile process combined immersion doping and pyrolysis. By controlling the formation of Fe3C, the physical structure of porous carbon was significantly altered, and the active chemical sites of Fe species can be formed to catalyze ORR. The uniform N-doped three-dimensional interpenetrating network structure yielded a high surface area. Both Fe3C and Fe-Nx could offer an abundance of active sites and thus promoted Fe0.05-N@MOF to exhibit high ORR activity in alkaline, neutral and acid electrolytes. Fe0.05-N@MOF showed extraordinary stability and methanol tolerance under a varied pH range conditions, it could be applied as cathode electrocatalyst in different fuel cells such as Zn-air fuel cell (ZFC), microbial fuel cells (MFCs), as well as direct methanol fuel cell (DMFC). Fe0.05-N@MOF is a promising material to replace Pt-based electrocatalysts as non-precious metal catalysts.

Fe, N-Doped SrTiO3 Synthesized Using Pyrazine Carboxylic Acid-Metal Complexes: Application as an Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cell Cathodes in Acidic Media

Abstract Fe, N-doped SrTiO3 was successfully synthesized using pyrazine carboxylic acid-metal complexes as the starting materials and exhibited high onset potential of 0.8 V vs. RHE for the oxygen reduction reaction because of the formation of high-quality active sites by Fe and N doping, and electron conduction paths by carbon nanotubes.

PtRuFe/Carbon Nanotube Composites as Bifunctional Catalysts for Efficient Methanol Oxidation and Oxygen Reduction.

The design of bifunctional catalysts with high performance and low platinum for the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) is of significant implication to promote the industrialization of fuel cells. In our work, Pt/carbon nanotube (CNT), Pt3Ru/CNT, and PtRu/CNT catalysts were synthesized by plasma heat treatment, in which the pyrolysis reduction of organometallic salts and the dispersion of CNTs were achieved simultaneously, and catalytic nanoparticles with uniform particle size were anchored on the dispersed CNT surface. Later, Fe was further introduced, and PtFe/CNT, Pt3RuFe/CNT, and PtRuFe/CNT catalysts were synthesized by calcination, and the structure and electrochemical properties in both MOR and ORR of all as-synthesized catalysts were investigated. The results indicated that plasma thermal treatment has the advantage of rapidness and immediacy in the synthesis of catalysts, and the Pt/CNT, Pt3Ru/CNT, and PtRu/CNT catalysts exhibited better electrocatalytic properties than commercial platinum (JM-Pt/C) catalysts. Meanwhile, the introduction of Fe during the calcination further changed the surface electronic properties of catalytic nanoparticles and enhanced the graphitization degree of catalysts; the PtRuFe/CNT catalyst exhibited outstanding electrocatalytic properties with a mass activity of 834.3 mA mg-1 for MOR and a half-wave potential of 0.928 V in alkaline media for ORR. The combination of plasma thermal treatment and calcination puts forward a novel strategy for the optimization of catalysts, and the synthesis method based on plasma dispersion needs to be further optimized to achieve its large-scale promotion.

Tensile-Strained Platinum-Cobalt Alloy Surface on Palladium Octahedra as a Highly Durable Oxygen Reduction Catalyst.

Designing shape-controlled Pt-based core-shell nanocrystals is a prospective strategy to maximize the utilization of Pt while maintaining high activity for oxygen reduction reaction (ORR). However, the core-shell structures with ultrathin Pt shell exhibit limited electrochemical durability. Therefore, a thicker shell is proposed to successfully improve the durability of the core-shell structures by preventing the core from dissolution. Nevertheless, the deposition of Pt tends to switch to the Stranski-Krastanov (S-K) growth mode with the increase of the number of layer, resulting in the absence of a conformal morphology. Herein, we realize the deposition of three-to-five-layer epitaxial Pt-Co layers on Pd octahedral seeds by introducing tensile strain in the epitaxial layer to impede the S-K growth. The as-obtained Pd@Pt-Co octahedra with four layers exhibit enhanced mass activity (0.69 A/mgPt) and specific activity (1.00 mA/cm2) for ORR, which are 4.93 and 5 times that of the commercial Pt/C, respectively. Furthermore, it shows only 17% decay for specific activity after a 30,000-cycle durability test. This work is expected to enlighten the design and synthesis of related core-shell nanocrystals with facetted multicomponent shells, offering a promising strategy for designing cost-effective and efficient catalysts.

Design principle and synthetic approach of intermetallic Pt-M alloy oxygen reduction catalysts for fuel cells

Developing high-performance Pt-M (M = transition metal) intermetallic alloy catalysts for oxygen reduction reaction (ORR) are key to achieving large-scale applications of proton exchange membrane fuel cells (PEMFCs). It is urgent to clarify the general rules to design and prepare intermetallic Pt-M catalysts with high ORR activity and stability. In this account, the basic principles for disorder-order phase transition in terms of thermodynamics and kinetics are first introduced and our recent efforts in synthesizing fully-ordered Pt-M intermetallic nanocrystals (iNCs) with well-defined L10-ordering structures are described. Then the effective strategies for further enhancing the activity and stability of L10-Pt-M ORR catalysts for PEMFCs are exemplified. We hope that this account will provide some significant insights into the research and development of intermetallic Pt-M alloy ORR catalysts for the applications of PEMFCs and other electrochemical energy conversion technologies in the future.

Metal single-site catalyst design for electrocatalytic production of hydrogen peroxide at industrial-relevant currents

Direct hydrogen peroxide (H2O2) electrosynthesis via the two-electron oxygen reduction reaction is a sustainable alternative to the traditional energy-intensive anthraquinone technology. However, high-performance and scalable electrocatalysts with industrial-relevant production rates remain to be challenging, partially due to insufficient atomic level understanding in catalyst design. Here we utilize theoretical approaches to identify transition-metal single-site catalysts for two-electron oxygen reduction using the *OOH binding energy as a descriptor. The theoretical predictions are then used as guidance to synthesize the desired cobalt single-site catalyst with a O-modified Co-(pyrrolic N)4 configuration that can achieve industrial-relevant current densities up to 300 mA cm−2 with 96–100% Faradaic efficiencies for H2O2 production at a record rate of 11,527 mmol h−1 gcat−1. Here, we show the feasibility and versatility of metal single-site catalyst design using various commercial carbon and cobalt phthalocyanine as starting materials and the high applicability for H2O2 electrosynthesis in acidic, neutral and alkaline electrolytes.

Manipulating the spin state to activate the atomically dispersed Fe–N–C catalyst for oxygen reduction

Magnetic moment of 3dxz+ 3dyzis a good ORR activity descriptor for Fe–N–C with e1g. Medium spin Fe(iii) after NC–N doping balances O2activation and *OH desorption by tuning hybridization degree between Fe 3dxz(yz)and ORR intermediates π* orbitals.

Chemical vapor deposition towards atomically dispersed iron catalysts for efficient oxygen reduction

The Fe-SA/NC is prepared by a simple one-pot CVD pyrolysis method. This formed single-atom dispersed Fe–N4structure benefits from the spatial confinement of ZIF-8, realizing excellent oxygen reduction performance and device applications..

ZIF-L-derived autocatalytic growth of Fe, N co-doped carbon nanotubes to form a hierarchical porous structure as an efficient oxygen reduction and oxygen evolution catalyst for Zn–air batteries

The hierarchical porous Fe–N–C catalyst with self-catalytic growth of carbon nanotube coated nanoparticles exhibited satisfactory electrocatalytic performances for the reactions in charge–dischargeable Zn–air batteries.

Cu2O@Co/N-doped carbon as antibacterial catalysts for oxygen reduction in microbial fuel cells

Cu2O@Co/NC acts as an antibacterial oxygen reduction catalyst for microbial fuel cells.

Novel 2D carbon material T-graphene supported 3d transition metal single atoms as efficient oxygen reduction catalysts.

Carbon-based support anchored 3d transition metal (TM) single atom catalysts (SACs) have been widely considered as promising candidates for the oxygen reduction reaction (ORR), and their intrinsic activity is closely related to the geometric and electronic structures of the supports. T-graphene was predicted to have high conductivity and stability, so it may be also a promising support for loading SACs for electrocatalysis. Here, we systematically evaluate the ORR activity of T-graphene supported TM single atoms (TMN4-Tgra and TMC4-Tgra, TM = Sc-Zn) and their graphene supported counterparts (TMN4-Gra and TMC4-Gra). The TM(dxz)-O(px), TM(dyz)-O(py) and TM(dz2)-O(pz + s) orbital hybridizations between the active central metal and the *OH intermediate determine the ORR activity. Compared to graphene, T-graphene increases the d-band center (especially the β-spin state) of single atoms and reduces the *OH adsorption strength, which thus improves the ORR activity of the catalysts located in the left leg of the ORR activity volcano plot. Interestingly, we found that for the catalysts with different TMs anchored on the same support, the adsorption strength of oxygen intermediates increases with the increase of the d-band center of the active site, while for the catalysts with the same metal anchored on different supports, the adsorption strength of oxygen intermediates weakens with the increase of the d-band center of the active site, which can serve as a d-band center dependence law on supports and active sites for designing ORR catalysts.

Unravelling the role of iron carbide in oxygen reduction catalysts for rechargeable zinc–air batteries: a comprehensive kinetics & mechanistic study

Roles of Fe3C and Fe–Nx in N-doped Fe3C containing carbon materials as an efficient bifunctional electrocatalysts for zinc–air battery.

Bimetallic CoSn nanoparticles anchored on N-doped carbon as antibacterial oxygen reduction catalysts for microbial fuel cells.

Sluggish oxygen reduction reaction (ORR) kinetics and biofilm formation limit the power generation and stability of microbial fuel cells (MFCs). Herein, bimetallic CoSn nanoparticles anchored on ZIF-derived N-doped carbon (CoSn@NC) were designed and synthesized as bifunctional catalysts to accelerate the ORR and improve the antibacterial activity. Sn modulated the electronic structure of bimetallic CoSn by drawing electrons from Co. Electron redistribution of CoSn@NC optimized the O2 adsorption at Co sites for rapid ORR kinetics. The up-shifted d-band center of Co sites reduced the energy barrier of the rate-determining step for *O formation, resulting in efficient catalytic activity. Bimetallic CoSn nanoparticles were beneficial for the four-electron transfer process for more ˙OH species production. Sn2+ and ˙OH synergistically improved the antibacterial activity of CoSn@NC to inhibit the growth of the cathode biofilm and accelerate mass-charge transfer. CoSn@NC demonstrated superior oxygen reduction activity with a half-wave potential of 0.84 V and an onset potential of 0.90 V, respectively. The MFCs assembled with the CoSn@NC cathodic catalyst exhibited an excellent power density of 1380 mW m-2 and long-term stability for 105 h. This work provides a strategy for the design of antibacterial ORR catalysts for improved catalytic activity and long-term stability.

Gradual introduction of multiple active sites in quest of high activity metal-free oxygen reduction catalysts and exploring the synergistic effect

The multiple active sites N, defect and S active sites were introduced gradually for obtaining an efficient carbon catalyst in acidic media.

A phosphate tolerant Pt-based oxygen reduction catalyst enabled by synergistic modulation of alloying and surface modification.

Addressing phosphoric acid poisoning of platinum-based catalysts in high-temperature fuel cells still remains a strategic and synthetic problem. Here, we synthesized a Pt3Co@MoOx-NC catalyst with a Pt3Co active core and MoOx modification on the surface, which simultaneously exhibits high ORR activity and phosphate tolerance.