Electrocatalytic Performance For Oxygen Reduction Reaction Research Articles

Ultrafine Fe2C nanocrystals encapsulated in interconnected hollow carbon spheres as ORR electrocatalysts for Alkaline/Neutral Zn − Air batteries

The development of high − performance non − noble metal electrocatalysts for oxygen reduction reaction (ORR) superior to commercial Pt/C in both alkaline and neutral medium is critical for renewable energy technology such as metal − air battery, but remains a great challenge. Herein, hollow spherical framework structure is introduced during the solid − state reaction, enabling the active sites to exist with smaller size and more uniform dispersion. Specifically, a grape − cluster − like ORR catalyst (Fc@Fe − NHCS) is synthesized in which Fe2C nanocrystals and Fe − Nx sites are embedded in carbon layers supported by nitrogen − doped hollow carbon spheres. The resultant Fc@Fe − NHCS exhibits an ORR half − wave potential of 0.85 V in alkaline medium compared to 0.86 V for Pt/C. For neutral ORR, the half − wave potential of Fc@Fe − NHCS is 0.76 V, which is equal to that of Pt/C. Furthermore, Fc@Fe − NHCS demonstrates satisfactory peak power density and open − circuit voltage comparable to Pt/C when utilized as air cathode in self − prepared alkaline and neutral zinc − air batteries (ZABs). The co − action of the spherical framework structure with active sites of Fe2C nanocrystals and Fe − Nx sites ensures excellent ORR electrocatalytic performance, which provides a favorable electrocatalyst for various energy devices including alkaline and neutral ZABs.

New nitrogen-doped graphitic carbon nanosheets with rich structural defects and hierarchical nanopores as efficient metal-free electrocatalysts for oxygen reduction reaction in Zn-Air batteries

Carbon materials are highly promising alternative metal-free catalysts for oxygen reduction reaction (ORR), an important element reaction involved in various energy storage/conversion processes, while controllable and fine structural and morphological tunning is key for maximizing the catalytic performance. Here, we report the rational design of hierarchical porous graphitic carbon nanosheets with rich defects (d-pGCS) based on a facile two-step thermal treatment route, delivering superior catalytic ORR performance in alkaline electrolytes. The second thermal treatment is critical in creating such structural defects and nanopores. Through optimizing synthesis parameters, d-pGCS-1000 exhibits outstanding electrocatalytic ORR performance in terms of positive onset potential (0.95 V), half-wave potential (0.82 V), and limiting current density (6.02 mA cm−2). As a proof-of-concept, the obtained Zn-air battery delivers a large open-circuit voltage (1.42 V), high peak power density (182.8 mW cm−2), high specific capacity (773 mAhgZn−1), and good rate performance. Such results are comparable to or even better than the Pt/C-based Zn-air battery.

Bulky Thiolate-Protected Silver Nanocluster Ag 213 (Adm-S) 44 Cl 33 with Excellent Electrocatalytic Performance toward Oxygen Reduction

Bulky Thiolate-Protected Silver Nanocluster Ag ₂₁₃ (Adm-S) ₄₄ Cl ₃₃ with Excellent Electrocatalytic Performance toward Oxygen Reduction

Engineering the Local Coordination Environment and Density of FeN4 Sites by Mn Cooperation for Electrocatalytic Oxygen Reduction.

Single atom sites (SAS) of FeN4 are clarified as one of the most active components for the oxygen reduction reaction (ORR). Effective strategies by engineering the local coordination environment and site density of FeN4 sites are crucial to further enhance the electrocatalytic ORR performance. Herein, the integration of a second metal of Mn with Fe to construct Fe&Mn/N-C catalysts with enhanced density of FeN4 active sites and modulated electronic structure is reported. The formation of MnN4 centers modulates the local environment of FeN4 sites and reserves more FeN4 embedded in carbon substrate by forming the possible FeN4 -O-MnN4 configurations. Density functional theory calculations demonstrate that the overall energy barrier of ORR is decreased over the FeN4 -O-MnN4 moieties. Therefore, the Fe&Mn/N-C catalyst exhibits enhanced ORR performance both in alkaline and acidic solution (half-wave potentials are 0.904 and 0.781V). This work provides an effective strategy by modulating the local electronic structure and density of FeN4 active sites to improve the ORR activity and stability through Mn cooperation.

Hollow Carbon Sphere and Polyhedral Carbon Composites Supported Iron Nanoparticles as Excellent Bifunctional Electrocatalysts of Zn–Air Battery

Herein, we synthesize Fe‐based nanocatalysts supported on the composites composed of hollow carbon spheres (HCSs) and metal–organic frameworks (MOFs) by a facile pyrolysis method. The composites with different ratios of HCSs and MOFs present an interesting phenomenon: the oxygen reduction reaction (ORR) limiting current increases along with the HCSs content, while the onset potential and half‐wave potential show the highest values when the ratio between HCSs and MOFs is optimized. The composite catalysts exhibit superior ORR electrocatalytic performance than Pt/C in alkaline and neutral media. Even in the acidic media, these composite catalysts still present a close catalytic activity to Pt/C. For the oxygen evolution reaction (OER) test, the prepared Fe‐NC@NHCS‐600 shows a reduced overpotential to that of the benchmark IrO2. The rechargeable Zn‐air battery using Fe‐NC@NHCS‐600 as the catalyst of air electrode exhibits superior discharge capability with an open‐circuit voltage of 1.620 V and a maximum power density of 278.97 mW cm−2 in alkaline electrolyte, as well as an open‐circuit voltage of 1.457 V and a maximum power density of 114.96 mW cm−2 in neutral electrolyte. The battery also exhibits steady cycling stability for more than 90 and 70 h at 5 and 10 mA cm−2, respectively.

Plasma induced Fe-NX active sites to improve the oxygen reduction reaction performance

Rational design of high-efficient and low-cost catalysts as alternatives to Pt-based catalysts toward the oxygen reduction reaction (ORR) is extremely desirable but challenging. In this work, Fe@NCNT is firstly synthesized via the one-pot pyrolysis method, then Fe-NX active species are in-situ created on the prepared Fe@NCNT by a feasible “plasma inducing” strategy to synthesize the resulting catalyst (Fe@NCNT-P) for ORR. The morphology of Fe@NCNT-P is perfectly inherited by the derived carbon precursor, resulting in the core-shell structure of carbon-coated Fe and a mesoporous dominant nanostructure with a high specific surface area of 536 m2 g−1. The resultant Fe@NCNT-P catalyst exhibits remarkable ORR activity and durability, as well as outstanding performance in assembled zinc-air battery (ZAB) test with a peak power density of 240 mW cm−2. This work not only reports a novel and robust ORR catalyst, but also proposes a simple and effective strategy to improve the ORR electrocatalytic performance.

Block Copolymer Self-Assembly Guided Synthesis of Mesoporous Carbons with In-Plane Holey Pores for Efficient Oxygen Reduction Reaction.

In this paper, a simple approach, using interfacial self-assembly of block copolymers (BCPs) on self-sacrificial templates, for preparing mesoporous carbons with in-plane holey pores, including nitrogen atom-doped carbon nanosheets and nanoflowers (denoted as NHCSs and NHCFs), is reported. The approach employs sheet- or flower-like layered double hydroxide as the templates, P123 copolymer as the pore-directing agent, and m-phenylenediamine as the carbon source. The holey mesopores may shorten the mass transfer distance in the internal active sites of stacked nanosheets, while the 3D packing mode of nanosheets can reduce pore blockage caused by their tight stacking. Profiting from these structural advantages, acting as electrocatalysts for oxygen reduction reaction (ORR), both NHCSs and NHCFs show excellent catalytic performance better than that of carbon nanosheets without holey pores. Particularly, NHCFs exhibit a high half-wave-potential (0.82V) anda limiting current density (5.4mAcm-2 ), close to those of commercial Pt-C catalysts. This study provides valuable clues on building mesoporous materials with in-plane holey pores as well as on the effect of pore structure and stacking mode of 2D materials on their electrocatalytic ORR performance.

Pt nanorods oriented on Gd-doped ceria polyhedra enable superior oxygen reduction catalysis for fuel cells

Promoting the oxygen reduction reaction (ORR) performance is an urgent need to reduce the amount of Pt catalysts in fuel cells. One of the most promising strategies is interface engineering which takes advantage of the synergistic catalytic proficiencies of double or even multiple components. Herein, we synthesized the electrocatalyst that comprises Pt nanorods atomically oriented along the (111) nanofacets of Gd-doped cerium oxide polyhedra, which was much superior to commercial Pt/C catalyst for the four-electron ORR, with a 4-fold improvement of ORR intrinsic activity than Pt/C, as well as producing much less of the undesirable two-electron ORR product H2O2. It also features a remarkable stability, with negligible activity degradation in 5000-cycle test. The exposure of Pt(111) facets and the oxygen vacancy-mediated interfacial PtCe alloying facilitate O2 adsorption and dissociation together with desorption of OHad, which can account for the exceptional ORR electrocatalytic performance.

Sandwich-like superstructure of in-situ self-assembled hetero-structured carbon nanocomposite for improving electrocatalytic oxygen reduction

Developing efficient and highly low-cost electrocatalysts for oxygen reduction reaction (ORR) is highly desirable and challenging for renewable energy devices. In this work, a novel sandwich-like heterostructured nanocomposite was facilely constructed via incorporation of Co9S8 nanoclusters/Co3[Co(CN)6]2 nanocubes in N,S-doped carbon multilayers (Co9S8/Co3[Co(CN)6]2/N,S-CMLs) by a one-pot coordination-modulated pyrolysis of a mixture containing dicyandiamide, Co(NO3)2 and Evans blue at 800 °C. The control tests demonstrated critical roles of the pyrolysis temperature played on the final morphology and shape, and discussed the formation mechanism in detail. The as-prepared catalyst exhibited appealing electrocatalytic performance for ORR with a more positive onset potential (Eonset = 0.96 V vs. RHE) and half-wave potential (E1/2 = 0.87 V vs. RHE) in 0.1 M KOH electrolyte, far outperforming other home-made catalysts and commercial Pt/C. This work opens a new avenue to prepare efficient, cost-effectiveness and stable electrocatalysts in sustainable energy storage and conversion devices.

CeO2 quantum dots embedded in 3D hierarchical porous foliaceous N-doped carbon as an efficient oxygen reduction electrocatalyst for metal-air battery

The development of large-scale and highly efficiency catalysts towards oxygen reduction reaction (ORR) is of great significance for the wide application of metal–air batteries. In this work, we propose a self-sacrifice template method combined with in-situ composite technique to fabricate a novel configuration of CeO2 quantum dots embedded in hierarchical porous foliaceous N-doped carbon with both mesopores and micropores. The prepared catalyst exhibits prominent ORR electrocatalytic performance with higher half-wave potential, lower Tafel slope, and enhanced durability comparing with the commercial Pt/C catalyst. Furthermore, the Zn-air and Al–air batteries employing the prepared electrocatalysts in cathodes exhibit superior discharge performance with high open circuit voltages of 1.51 V and 1.76 V, and peak power densities of 204 and 458 mW cm−2, respectively, compared to most reported metal–air batteries. The greatly enhanced electrocatalytic performance can be ascribed to the abundant oxygen vacancies, improved redox property of Ce3+/Ce4+ as well as the three-dimensional hierarchical porous structure. This work provides a valuable chance to develop scalable quantum dot level composite catalysts in metal–air batteries.

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.

Cyanogel-Derived Synthesis of Porous PdFe Nanohydrangeas as Electrocatalysts for Oxygen Reduction Reaction.

It is important to develop cost-efficient electrocatalysts used in the oxygen reduction reaction (ORR) for widespread applications in fuel cells. Palladium (Pd) is a promising catalyst, due to its more abundant reserves and lower price than platinum (Pt), and doping an earth-abundant 3d-transition metal M into Pd to form Pd–M bimetallic alloys may not only further reduce the use of expensive Pd but also promote the electrocatalytic performance of ORR, owing to the synergistic effect between Pd and M. Here we report a cyanogel-derived synthesis of PdFe alloys with porous nanostructure via a simple coinstantaneous reduction reaction by using K2PdIICl4/K4FeII(CN)6 cyanogel as precursor. The synthesized PdFe alloys possess hydrangea-like morphology and porous nanostructure, which are beneficial to the electrochemical performance in ORR. The onset potential of the porous PdFe nanohydrangeas is determined to be 0.988 V, which is much more positive than that of commercial Pt/C catalyst (0.976 V) and Pd black catalyst (0.964 V). Resulting from the unique structural advantages and synergetic effect between bimetals, the synthesized PdFe nanohydrangeas with porous structure have outstanding electrocatalytic activity and stability for ORR, compared with the commercial Pd black and Pt/C.

Electronic Structure Regulation of Iron Phthalocyanine Induced by Anchoring on Heteroatom-Doping Carbon Sphere for Efficient Oxygen Reduction Reaction and Al-Air Battery.

Aluminum-air batteries (AABs) are deemed as a potential clean energy storage device. However, exploiting high-efficiency and stable oxygen reduction reaction (ORR) electrocatalysts in AABs is still a challenge. Iron phthalocyanine (FePc) shows a great prospect in ORR but still far from Pt-based catalysts. Here, the hybrid electrocatalysts of monolayer FePc and hollow N,S-doped carbon spheres (HNSCs) are innovatively constructed through π-π stacking to achieve high dispersion. The resulting FePc@HNSC catalyst exhibits an outstanding ORR activity, outperforming that of pristine FePc and even most Fe-based catalysts reported to date. Moreover, the AAB using FePc@HNSC catalyst not only demonstrates a superior power density than the battery with Pt/C, but also displays stable discharge voltages and excellent durability. Furthermore, the theoretical calculations confirm that the charge distribution and d-band center of the Fe atom in FePc are efficiently optimized by hybrid configuration via the introduction of N,S-doped carbon substrate. The design leads to an enriched electron density around Fe active sites and significant reduction of energy barrierfor OH* formation, which are favorable for the improvement of electrocatalytic ORR performance. This work provides a chance to expand the application of metallic macrocyclic compound electrocatalysts in various energy technologies.

Molten-Salt-Assisted Synthesis of Nitrogen-Doped Carbon Nanosheets Derived from Biomass Waste of Gingko Shells as Efficient Catalyst for Oxygen Reduction Reaction

Developing superior efficient and durable oxygen reduction reaction (ORR) catalysts is critical for high-performance fuel cells and metal–air batteries. Herein, we successfully prepared a 3D, high-level nitrogen-doped, metal-free (N–pC) electrocatalyst employing urea as a single nitrogen source, NaCl as a fully sealed nanoreactor and gingko shells, a biomass waste, as carbon precursor. Due to the high content of active nitrogen groups, large surface area (1133.8 m2 g−1), and 3D hierarchical porous network structure, the as-prepared N–pC has better ORR electrocatalytic performance than the commercial Pt/C and most metal-free carbon materials in alkaline media. Additionally, when N–pC was used as a catalyst for an air electrode, the Zn–air battery (ZAB) had higher peak power density (223 mW cm−2), larger specific-capacity (755 mAh g−1) and better rate-capability than the commercial Pt/C-based one, displaying a good application prospect in metal-air batteries.

Pyridinic-N Doped Porous Graphene Supported on Metal Substrates As the Promising Electrocatalyst for Oxygen Reduction Reaction

Nitrogen-doped carbon-based nanomaterials are promising electrocatalysts for oxygen reduction reaction (ORR) in energy conversion, but the doping type and site of nitrogen atoms are difficult to precisely control. Herein, we designed a novel porous graphene material containing only pyridinic N (PNG), exhibiting superior electrocatalytic ORR activity when it is supported on metal substrates. We have considered both Co (0001) and Ni (111) as the substrates to investigate the ORR process of PNG from density functional theory methods. Our researches have illustrated the optimal active site for ORR is the C atom next to the pyridinic N, locating at the hollow site with respect to the metal substrate. By introducing Co (0001) and Ni (111) substrates, the ORR electrocatalytic performance of PNG have been effectively enhanced with the lowest calculated overpotential of 0.41 V, which originated from the electronic coupling between the metal substrate and the C atoms of PNG. Finally, the ORR activity could be further enhanced under the tensile strain. Our study provided valuable guidance for the design of two-dimensional graphene-based heterojunction materials as efficient ORR electrocatalysts.

Self-sacrificial template synthesis of Fe, N co-doped porous carbon as efficient oxygen reduction electrocatalysts towards Zn-air battery application

Designing highly efficient non-precious based electrocatalysts for oxygen reduction reaction (ORR) is of significance for the rapid development of metal-air batteries. Herein, a hydrothermal-pyrolysis method is employed to fabricate Fe, N co-doped porous carbon materials as effective ORR electrocatalyst through adopting graphitic carbon nitride (g-C3N4) as both the self-sacrificial templates and N sources. The g-C3N4 provides a high concentration of unsaturated pyridine-type N to coordinate with iron to form Fe-N active sites. Through adjusting the Fe doping amounts, it is proved that appropriate Fe doping content is conducive to the construction of abundant defects and active sites of Fe-N. The as-prepared catalyst exhibits superior electrocatalytic ORR performance in alkaline media with half-wave potential (E1/2 = 0.82 V) and onset potential (Eonset = 0.95 V), equivalent to the commercial Pt/C catalyst. Moreover, there is almost no activity loss after 10 k continuous cyclic voltammetry cycles and methanol tolerance, indicating the excellent durability and superior methanol tolerance. Remarkably, when assembled as the cathode in a Zn-air battery, the device displays a power density of 99 mW/cm2, an open-circuit potential of 1.48 V and long-term discharge-charge cycling stability, indicating the promising potential to substitute the Pt catalyst for practical application.

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 growth of CoNi bimetal anchored on carbon nanoparticle/nanotube hybrid for boosting rechargeable Zn-air battery

Exploring highly efficient non-precious metal based catalysts for bifunctional oxygen electrode is crucial for rechargeable metal-air batteries. In this study, with MOFs as precursors, a facile coprecipitation method is designed to realize in-situ growth of the CoNi anchored carbon nanoparticle/nanotube (CoNi/N-CNN) hybrid, which can achieve the simultaneous maximum exposure of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) active centers. Benefiting from the unique structure, the CoNi/N-CNN catalyst exhibits excellent electrocatalytic performance for ORR (Eonset = 1.183 V, E1/2 = 0.819 V) and a low operating voltage of 1.718 V at 10 mA cm−2 (Ej=10) for OER. Delightfully, the home-made rechargeable Zn-air battery with CoNi/N-CNN delivers a high discharge power density up to 209 mW cm−2, and an outstanding charge–discharge cycling stability. The boosted bifunctional electrocatalytic activity can be ascribed to the strong coupling effect between Co/Ni center sites and defect-rich N-anchored carbon featured with porous and nanotube structure, which can introduce uniformly dispersed active sites, tailored electronic configuration, superb conductivity and convenient charge transfer process. The hybrid non-precious bimetal based electrocatalyst provides the possibility to develop the low-cost and high-efficient ORR/OER bifunctional electrocatalysts in rechargeable metal-air battery.

Shell-thickness-dependent Pd@PtNi core–shell nanosheets for efficient oxygen reduction reaction

Platinum-based ultrathin core–shell nanosheets catalyst with moderate shell thickness have great potential to solve the problems of highly active catalyst for oxygen reduction reaction (ORR) within proton exchange membrane fuel cells (PEMFCs). Herein, three kinds of Pd/PtNi core–shell nanosheets (Pd@PtNi NSs) catalyst under different shell thickness were developed by a synthetic strategy of depositing platinum-nickel (Pt-Ni) precursors on palladium nanosheets (Pd NSs). The ORR electrocatalytic performance of Pd@PtNi NSs–1, Pd@PtNi NSs–2 and Pd@PtNi NSs–3 catalysts were investigated using commercial Pt/C catalyst for comparison reasons. It is found that the Pd@PtNi NSs–2 catalyst with moderate shell thickness showed excellent ORR performance. Under 0.9 V (vs. reversible hydrogen electrode (RHE)), Pd@PtNi NSs–2 (1.038 A mg-1Pt+Pd) achieved mass activity (MA) 6.25 times of commercial Pt/C catalyst. Superior performance of Pd@PtNi NSs–2 was mainly attributed to: i) the ultrathin layer structure, ii) the core–shell structure, iii) the maximum coverage of Pd core, and iv) the maximum surface alloying by surface atomic diffusion.