High-performance Electrocatalysts For Oxygen Reduction Reaction Research Articles

2D RhTe Monolayer: A highly efficient electrocatalyst for oxygen reduction reaction

Oxygen reduction reaction (ORR) electrocatalysts with excellent activity and high selectivity toward the efficient four-electron (4e) pathway are very important for the wide application of fuel cells and are worth searching vigorously. In this study, r-RhTe monolayer is identified as a good ORR electrocatalyst from three 2D RhTe configurations with low Rh-loading (i.e., r-RhTe, o-RhTe and h-RhTe) on the basis of the first-principles calculations. For the most energetically stable r-RhTe, two adjacent positively charged Te atoms on the material surface can provide an active site for oxygen dissociation. Coupled with its high stability and intrinsic conductivity, 2D r-RhTe monolayer is confirmed to possess good catalytic activity and high reaction selectivity toward ORR. Moreover, under the ligand effect caused by the substitution of Cr, Mn and Fe, the ORR catalytic activity of r-RhTe monolayer could be effectively enhanced, where very small over-potential was achieved, and even comparable to or lower than the state-of-the-art Pt (111). This shows it has considerably high ORR activity. This work is highly anticipated to provide excellent candidate materials for ORR catalysis, and the related researches based on the Rh-Te materials will provide a new way to design high-performance ORR electrocatalysts to substitute the precious metal Pt-based catalysts.

Origin of the Rarely Reported High Performance of Mn-doped Carbon-based Oxygen Reduction Catalysts.

Recent efforts to develop durable high-performance platinum-group metal (PGM)-free oxygen reduction reaction (ORR) electrocatalysts have focused on Fe- and Co-based molecular and pyrolyzed catalysts. While Mn-based catalysts have advantages of lower toxicity and higher durability, their activity has been generally poor. Nevertheless, several examples of high-performance Mn-based catalysts have been reported. Thus, it is necessary to understand why Mn-based materials much more rarely show high catalytic ORR performance and to determine the factors that can lead to the achievement of such high performance in these rare cases. We have studied the effects of the changes in the macrocycle structure, axial ligand, distance between the active sites, interactions with the dopant N atoms and the presence of an extended carbon network on the ORR catalysis of various Mn-, Fe-, and Co-based systems through the comparison of the adsorption energies of the ORR intermediates. We find that the sensitivity to the local environment changes is the largest for Mn and is the smallest for Co, with Fe between Mn and Co. Our results showed that the strong binding of OH by Mn and the strong sensitivity of the Mn to the modification of its environment necessitate a precise combination of local environment changes to achieve a high onset potential (Vonset ) in Mn-based catalysts. By contrast, the weaker binding of OH by Fe and Co and their weaker sensitivity to local environment changes lead to a wide variety of local environments with favorable catalytic activity (Vonset >0.7 V) for Co- and Fe-based systems. This explains the scarcity of reported Mn-based pyrolyzed catalysts and suggests that precise material synthesis and engineering of the active site can achieve high-performance Mn-based ORR electrocatalysts with high activity and durability.

Fe-Fe3C Functionalized Few-Layer Graphene Sheet Nanocomposites for an Efficient Electrocatalyst of the Oxygen Reduction Reaction.

Preparation of a high-efficiency, low-cost, and environmentally friendly non-precious metal catalyst for the oxygen reduction reaction (ORR) is highly desirable in fuel cells. Herein, a Fe–Fe3C-functionalized few-layer graphene sheet (Fe/Fe3C/FLG) nanocomposite was fabricated through the vacuum heat treatment technique using ferric nitrate and glucose as the precursors and exhibited a high-performance ORR electrocatalyst. Multiple characterizations confirm that the nanosized Fe particles with the Fe3C interface are uniformly distributed in the FLGs. Electrocatalytic kinetics investigation of the nanocomposite indicates that the electron transfer process is a four-electron pathway. The formation of the Fe3C interface between the Fe nanoparticles and FLGs may promote the electron transfer from the Fe to FLGs. Furthermore, the Fe/Fe3C/FLG nanocomposite not only exhibits high ORR catalytic activity but also displays desirable stability. Consequently, the obtained Fe/Fe3C/FLG nanocomposite might be a promising non-precious, cheap, and high-efficiency catalyst for fuel cells.

Iron-gelatin aerogel derivative as high-performance oxygen reduction reaction electrocatalysts in microbial fuel cells

Currently, precious based materials are known as highly efficient and widely used catalysts for oxygen reduction reaction (ORR). The expensive price and scarce resource of precious metals have stimulated researchers to explore low-cost and high-performance non-precious metal catalysts. Gelatin is a promising precursor to prepare cost-effective and high-performance catalysts because of abundant micropores and nitrogen self-doping sites after pyrolysis. Herein, we developed a new highly active ORR catalyst (G/C–Fe-2) containing Fe–N coordination sites and Fe/Fe3C nanoparticles. G/C–Fe-2 exhibited excellent ORR electrocatalytic activity (onset potential: 0.21 V, and limiting current density:7.36 mA cm−2) and high-performance in air-cathode MFCs (Output voltage: 660 mV, and maximum power density: 560 mW m−2). It is significant for synthesizing low-cost and high-activity ORR electrocatalysts through this strategy.

Electronic and Potential Synergistic Effects of Surface-Doped P-O Species on Uniform Pd Nanospheres: Breaking the Linear Scaling Relationship toward Electrochemical Oxygen Reduction.

Developing efficient oxygen reduction reaction (ORR) electrocatalysts is critical to fuel cells and metal-oxygen batteries, but also greatly hindered by the limited Pt resources and the long-standing linear scaling relationship (LSR). In this study, ∼6 nm and highly uniform Pd nanospheres (NSs) having surface-doped (SD) P-O species are synthesized and evenly anchored onto carbon blacks, which are further simply heat-treated (HT). Under alkaline conditions, Pd/SDP-O NSs/C-HT exhibits respective 8.7 (4.3)- and 5.0 (5.5)-fold enhancements in noble-metal-mass- and area-specific activity (NM-MSA and ASA) compared with the commercial Pd/C (Pt/C). It also possesses an improved electrochemical stability. Besides, its acidic ASA and NM-MSA are 2.9 and 5.1 times those of the commercial Pd/C, respectively, and reach 65.4 and 51.5% of those of the commercial Pt/C. Moreover, it also shows nearly ideal 4-electron ORR pathways under both alkaline and acidic conditions. The detailed experimental and theoretical analyses reveal the following: (1) The electronic effect induced by the P-O species can downshift the surface d-band center to weaken the intermediate adsorptions, thus preserving more surface active sites. (2) More importantly, the potential hydrogen bond between the O atom in the P-O species and the H atom in the hydrogen-containing intermediates can in turn stabilize their adsorptions, thus breaking the ORR LSR toward more efficient ORRs and 4-electron pathways. This study develops a low-cost and high-performance ORR electrocatalyst and proposes a promising strategy for breaking the ORR LSR, which may be further applied in other electrocatalysis.

Tuning Active Species in N-Doped Carbon with Fe/Fe3C Nanoparticles for Efficient Oxygen Reduction Reaction.

Transition metal-nitrogen-carbon (M-N-C) catalysts (M = Fe, Co, etc.) are the most promising substituents of Pt-based catalysts for oxygen reduction reaction (ORR). However, the insufficient active species in catalysts inevitably hamper their widespread applications. Herein, we report the regulation of the active species in the catalysts of multicomponent N-doped carbon with Fe/Fe3C nanoparticles by polydopamine (PDA) coating. It is found that the PDA is conducive to increasing the pyridinic, graphitic, and total N content in the carbon matrix. Benefiting from the chelating effects, the PDA further profits the formation of Fe-Nx structures and the implantation of Fe/Fe3C nanoparticles in the matrix during the pyrolysis. As expected, the resultant catalysts exhibit over 15 times mass activity toward ORR than nitrogen-doped carbon. Moreover, our developed catalysts show long-term stability as well as high methanol tolerance, which is superior to that of the commercial Pt/C electrode. This work provides a new avenue to explore a wider range of high-performance ORR electrocatalysts by regulating the active species.

Synergistic melamine intercalation and Zn(NO3)2 activation of N-doped porous carbon supported Fe/Fe3O4 for efficient electrocatalytic oxygen reduction.

Developing inexpensive, efficient and good stability transition metal-based oxygen reduction reaction (ORR) electrocatalysts is a research topic of great concern in the commercial application of fuel cells. Herein, with zinc nitrate as activator, iron nitrate as active component and melamine as intercalating agent and nitrogen source, an N-doped porous carbon supported Fe/Fe3O4 (Fe/Fe3O4@NC) catalyst is successfully synthesized by an impregnation–calcination method combined with freeze-drying technique. The positive onset potential (Eonset), half-wave potential (E1/2) and limiting current density (JL) of the optimal Fe/Fe3O4@NC catalyst are 1.012, 0.90 V vs. RHE and 5.87 mA cm−2, respectively. Furthermore, Fe/Fe3O4@NC catalyzes ORR mainly through a 4e− pathway, and the yield of H2O2 is less than 5%. It also manifests a robust stability after 5000 CV cycles of ADT testing, and the half-wave potential is only negatively shifted 17 mV. The structural characterization and experimental results further suggest that the outstanding ORR electrocatalytic performance of the Fe/Fe3O4@NC catalyst benefits from the synergetic effect of zinc nitrate activation and nitrogen doping, which can greatly improve the specific surface area, thus better dispersing more metal active sites. This work puts forward a simple and practicable way for preparing high-performance non-noble metal-based biomass ORR electrocatalysts.

Superior electrocatalytic ORR performance of Melaleuca Leucadendron L barks derived hierarchical porous carbon with abundant atom-scale vacancies and multiheteroatoms

Biomass feedstocks from agriculture and forestry usually possess unique isometric microstructures that are used as potential renewable precursors to synthesize hierarchically porous carbon materials for energy-conversion applications. Herein, the powders of Melaleuca leucadendron L. barks (MLBs) impregnated with a hydrogen bonded complex (HBC) were carbonized to prepare CoBN-doped porous carbon (CBNC) as oxygen reduction reaction (ORR) electrocatalysts. The microstructure, porous texture and compositions of the as-obtained CBNC samples and their intermediates were characterized by small-angle neutron scattering (SANS) and other techniques. The lamellar structure of MLBs and the HBC strategy endowed the as-obtained CBNC with a unique porous texture, large specific surface area (1041 m2 g−1) and uniformly distributed heteroatoms of Co, B and N. The introduction of Co species in the precures is beneficial to improving the formation of atomic defects. The CBNC sample obtained at the optimized conditions exhibited a half-wave potential (E1/2) of 0.83 V and a kinetic current density (jk) of 9.73 mA cm−2 as well as a robust durability and methanol tolerance in the alkaline electrolyte; its overall ORR properties were highly superior to Pt/C (jk = 8.2 mA cm−2, E1/2 = 0.82 V). This novel approach offers a feasible way towards producing high-performance ORR electrocatalysts from biomass wastes.

Impact of sp2 carbon material species on Pt nanoparticle-based electrocatalysts produced by one-pot pyrolysis methods with ionic liquids.

Pt-nanoparticle-supported graphene nanoplatelets (Pt/GNPs) and multiwalled carbon nanotube composite (Pt/MWCNTs) electrocatalysts for the oxygen reduction reaction (ORR) can be prepared using a one-pot method through the pyrolytic decomposition of the platinum precursor, platinum(ii) bis(acetylacetonate) (Pt(acac)2) in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([C4mim][Tf2N]) or N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide ([N1,1,1,3][Tf2N]) ionic liquids (ILs) with the target sp2 carbon support. In this one-pot pyrolysis method, which does not require any reagents to reduce Pt metal precursors or stabilize Pt nanoparticles, Pt nanoparticles are readily immobilized onto the sp2 surface by a thin IL layer formed at the interface, which can work as a binder. We used three types of sp2 carbon materials with different geometric shapes (graphene nanoplatelets with <3 (GNPs-3) and 18–24 layers (GNPs-20) and multiwalled carbon nanotubes (MWCNTs)) to investigate Pt nanoparticle formation and anchoring. All the electrocatalysts, especially Pt/MWCNTs, showed higher durability than the commercial catalyst owing to the combined effect of the IL binder and sp2 carbon materials. Our findings strongly suggest that the original carbon surface properties are also an important factor for creating high-performance ORR electrocatalysts.

Non-precious metal activated MoSi2N4 monolayers for high-performance OER and ORR electrocatalysts: A first-principles study

Developing high-performance electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for energy conversion and storage. Recently, a new type of two-dimensional material MoSi2N4 was successfully synthesized and received considerable attention because of novel properties and potential applications. Herein, by means of first principles calculation, the OER/ORR activities of 3d transition metal (TM) atoms embedded MoSi2N4 (TM@MSN) were investigated. The calculated results indicate that TM atoms on MoSi2N4 exhibit good electrochemical stability. On TM sites, Ti@MSN shows the highest OER activity with an overpotential of 0.48 V, whereas Cr@MSN is the most active ORR catalyst with an overpotential of 0.48 V. The Si site (Si−N1−Cu) of Cu@MSN follows the dual-site mechanism, exhibiting the same OER/ORR overpotential as that of N site (0.55/0.65 V). Interestingly, the outer N site (Zn−N1) of Zn@MSN achieves the lowest OER overpotential of 0.38 V, better than that of the state-of-the-art RuO2 catalyst. We demonstrate that 3d TM atoms not only serve as active sites themselves but also activate the host atoms to improve OER/ORR performance of MoSi2N4. Our work opens new windows of opportunity for developing novel catalysts beyond the precious metal-based electrocatalysts for efficient energy conversion and storage.

ZIF-67-derived N-doped double layer carbon cage as efficient catalyst for oxygen reduction reaction

The slow kinetic of oxygen reduction reaction (ORR) hampers the practical application of energy conversion devices, such as fuel cells, metal-air batteries. Here, an efficient ORR electrocatalyst consists of Co, Ni co-decorated nitrogen-doped double shell hollow carbon cage (Ni–Co@NHC) was fabricated by pyrolyzing Ni-doped polydopamine wrapped ZIF-67. During the preparation, polydopamine served as a protective layer can effectively prevent the aggregation of Co and Ni nanoparticles during the pyrolysis process, and at the same time forming a carbon layer to grow a double layer carbon cage. This unique hollow structure endows the catalyst with a high specific surface area as well as more exposed active sites. Also benefited from the synergistic effect between Ni and Co nanoparticles, the Ni–Co@NHC catalyst leads to an outstanding ORR performance of half-wave potential (E 1/2, 0.862 V), outperforms that of commercial Pt/C catalyst. Additionally, when Ni–Co@NHC was used in the cathode for the zinc-air battery, the cell exhibits high power density (108 mW cm−2) and high specific capacity (806 mAh g−1) at 20 mA cm−2 outperforming Pt/C. This work offers a promising design strategy for the development of high-performance ORR electrocatalysts.

Fe, B, and N Codoped Carbon Nanoribbons Derived from Heteroatom Polymers as High-Performance Oxygen Reduction Reaction Electrocatalysts for Zinc–Air Batteries

For zinc-air batteries, it is of great importance to heighten the oxygen reduction reaction (ORR) activity of cathode electrocatalysts. Herein, we synthesized carbon nanoribbons doped with Fe, B, and N as high-activity ORR electrocatalysts by a templating method. Benefiting from the melamine fiber (MF) and B doping, the as-prepared carbon nanoribbon has a high specific surface area, and the improved turnover frequency of Fe sites increases the ORR activity. The as-synthesized Fe-B-N-C electrocatalyst shows an improved half-wave potential and limited current density compared to Fe-N-C, B-N-C, and N-C. Moreover, zinc-air batteries with the Fe-B-N-C electrocatalyst exhibit a higher specific capacity and better long-term durability compared to those with commercial Pt/C. This work provides an effective strategy to synthesize noble-metal-free electrocatalysts for wide applications of zinc-air batteries.

Edge-hosted Fe-N3 sites on a multiscale porous carbon framework combining high intrinsic activity with efficient mass transport for oxygen reduction

Metal- and nitrogen-coordinated nanocarbons (M-N/Cs) represent the most promising nonprecious catalysts for the oxygen reduction reaction (ORR), but it remains challenging to simultaneously achieve high intrinsic activity, fast mass transport, and efficient utilization of active sites in a single catalyst. Herein, we design an Fe-N/C catalyst consisting of edge-hosted Fe-N3 sites dispersed on multiscale porous carbon frameworks (eFe-N3/PCF). The low coordination and edge effect of the Fe-N3 moieties endow eFe-N3/PCF with high intrinsic activity, while the enriched nanopores enable improved mass transport and atom utilization efficiency. When evaluated by a rotating disk electrode in the base, eFe-N3/PCF presents early-onset and half-wave potentials of 1.090 and 0.934 V versus the reversible hydrogen electrode, respectively. Furthermore, when employed as gas diffusion electrodes, eFe-N3/PCF displays excellent mass-transport efficiency that enables high-rate/power capabilities at practically high current densities. This work opens up opportunities for designing high-performance ORR electrocatalysts toward applications in diverse energy conversion and storage technologies.

PtCo incorporated porous carbon nanofiber as a promising oxygen reduction electrocatalyst

Designing oxygen reduction reaction (ORR) catalysts with high activity and long durability is significant for the development of proton exchange membrane fuel cells. Herein, the optimized platinum nanowires are used as templates for inducing growth of cobalt-containing metal-organic framework, deriving uniform nanofibers. After the calcination, the metal ions are transferred into the nitrogen-rich porous carbon, and wrapped by the carbon skeleton to form the PtCo bimetal incorporated nanofibers as high-performance ORR electrocatalyst. The Pt4Co@NC-900 catalyst yields high specific activity (1.37 mA cm−2) in comparison to Pt/C (0.38 mA cm−2). The mass activity (MA) of Pt4Co@NC-900 catalyst is approximately 3.8-fold higher than that of the commercial Pt/C under acidic conditions. After the accelerated durability tests, the Pt4Co@NC-900 catalyst presents only 16% loss in MA, while Pt/C catalyst retains 73.0% of the initial MA. The improved ORR performance can be ascribed to the synergistic interaction between Co and Pt.

Atomic-Scale Design of High-Performance Pt-Based Electrocatalysts for Oxygen Reduction Reaction.

Fuel cells are regarded as one of the most promising energy conversion devices because of their high energy density and zero emission. Development of high-performance Pt-based electrocatalysts for the oxygen reduction reaction (ORR) is vital to the commercial application of these fuel cell devices. Herein, we review the most significant breakthroughs in the development of high-performance Pt-based ORR electrocatalysts in the past decade. Novel and preferred nanostructures, including biaxially strained core–shell nanoplates, ultrafine jagged nanowires, nanocages with subnanometer-thick walls and nanoframes with three-dimensional surfaces, for excellent performance in ORR are emphasized. Important effects of strain, particle proximity, and surface morphology are fully discussed. The remaining changes and prospective research directions are also proposed.

Quantitative kinetic analysis on oxygen reduction reaction: A perspective

Oxygen reduction reaction (ORR) constitutes the core process of many energy storage and conversion devices including metal–air batteries and fuel cells. However, the kinetics of ORR is very sluggish and thus high-performance ORR electrocatalysts are highly regarded. Despite recent progress on minimizing the ORR half-wave potential as the current evaluation indicator, in-depth quantitative kinetic analysis on overall ORR electrocatalytic performance remains insufficiently emphasized. In this paper, a quantitative kinetic analysis method is proposed to afford decoupled kinetic information from linear sweep voltammetry profiles on the basis of the Koutecky–Levich equation. Independent parameters regarding exchange current density, electron transfer number, and electrochemical active surface area can be respectively determined following the proposed method. This quantitative kinetic analysis method is expected to promote understanding of the electrocatalytic effect and point out further optimization direction for ORR electrocatalysis.

In-situ synthesis of Co3O4 nanocrystal clusters on graphene as high-performance oxygen reduction reaction electrocatalysts

ABSTRACT The energy problem is closely related to the survival and development of human beings. Nowadays, the research of fuel cells is making rapid progress, but the bottleneck of the development of fuel cells is slow oxygen reduction reaction (ORR) of cathode. At present, it is difficult to develop a kind of oxygen reduction catalyst with high performance, low energy consumption and low pollution. Here, we synthesised Co3O4 nanocrystals loaded on a single graphene oxide layer via a convenient one-step hydrothermal method. According to the transmission electron microscopy characterisation tests, the average size of Co3O4 nanocrystals is 5 nm. Compared with the commercially available Pt/C catalyst, the obtained Co3O4/rGO catalyst demonstrates the same four-electron (4e−) oxygen reduction reaction, and the catalytic activity of ORR is significantly higher. This is due to the large surface area provided by the middle part of the composite catalyst Co3O4/rGO, which provides an effective mass transfer and electron transfer path for the catalyst.

Oxygen Reduction Reaction: MnN4 Oxygen Reduction Electrocatalyst: Operando Investigation of Active Sites and High Performance in Zinc–Air Battery (Adv. Energy Mater. 6/2021)

In article number 2002753, Lirong Zheng, Aijuan Han, Junfeng Liu and co-workers report the development of a manganese single-atomic-site catalyst anchored on porous nitrogen-doped carbon with Mn-N4 structure, which exhibits superior electrocatalytic activity and stability for the alkaline oxygen reduction reaction (ORR) and in zinc-air batteries. Furthermore, operando XAFS is applied to uncover the mechanism under realistic conditions. This work paves the way to construct high-performance ORR electrocatalysts through rational design.

Novel Co/UiO-66 metal organic framework catalyst for oxygen reduction reaction in microbial fuel cells

To improve the power generation of microbial fuel cell (MFC), the cathode is modified to increase its oxygen reduction reaction (ORR) activity by using Co/UiO-66, which derived from pyrolyzing the mixture of Co(NO3)2 as the metal precursor incorporated with NH2-UiO-66. It was found that Co/UiO-66 (MOF-900) has been developed as a high-performance electrocatalyst for ORR at a pyrolysis temperature of 900 °C. Therefore, Co/UiO-66 should be a promising oxygen reduction catalyst for application in MFCs. This study provides technical and theoretical validation for the MFC performance improvement by ORR active MOF-derived catalysts modified cathodes.

MOF-derived PtCo/Co3O4 nanocomposites in carbonaceous matrices as high-performance ORR electrocatalysts synthesized via laser ablation techniques

ZIF-67-derived carbon-based bimetallic nanocomposites with reduced Pt-loading via laser ablation synthesis in solution (LASiS) as a superior electrocatalyst for oxygen reduction reaction (ORR).