Comparable Oxygen Reduction Reaction Performance Research Articles

Co Nanoparticles Confined in Mesoporous Mo/N Co-Doped Polyhedral Carbon Frameworks towards High-Efficiency Oxygen Reduction.

Exploiting effective non-noble metal electrocatalysts for oxygen reduction reaction (ORR) is crucial for fuel cells and metal-air batteries. Herein, we designed and fabricated Co nanoparticles confined in Mo/N co-doped polyhedral carbon frameworks (Co-NP/MNCF) derived from polyoxometalate-encapsuled metal-organic framework, which showed comparable ORR performance with commercial Pt/C and a larger diffusion-limited current density. Moreover, the Co-NP/MNCF also exhibited excellent ORR stability and methanol tolerance. These appealing performances can be attributed to the porosity regulation and heteroatom doping of metal-organic framework derived polyhedral carbon frameworks, which could be beneficial for the exposure of more active sites, the optimization of electronic structure and the mass transfer of electrolyte/electron/ion.

Ordered mesoporous carbon fiber bundles with high-density and accessible Fe-NX active sites as efficient ORR catalysts for Zn-air batteries

Fe-NX/C electrocatalysts have aroused extensive interest in accelerating sluggish oxygen reduction reaction (ORR) kinetics as potential alternatives to platinum catalysts in rechargeable Zn-air batteries (ZABs). However, the low density and poor accessibility of Fe-NX sites have severely restricted the electrocatalytic performance of Fe-NX/C. Herein, Fe, N co-doped ordered mesoporous carbon fiber bundles are prepared through a ligand-assisted strategy with nitrogen-rich 1,10-phenanthroline as space isolation agent. 1,10-Phenanthroline reveals a six-membered heterocyclic structure containing abundant nitrogen species to tightly coordinate with Fe ions, which is conducive to achieving high-density Fe-NX sites. Meanwhile, the adoption of SBA-15 as hard-templates enables the catalysts with highly ordered channels and large specific surface areas, improving the accessibility of Fe-NX sites. The optimal catalyst (PDA-Fe-900) demonstrates a positive half-wave potential of 0.84 V (vs. RHE) in alkaline solution, outperforming the commercial Pt/C (0.83 V). In addition, PDA-Fe-900 delivers comparable ORR performance to commercial Pt/C in acidic electrolyte. Impressively, when PDA-Fe-900 is employed as an air cathode, it achieves large power densities of 163.0 mW/cm2 in liquid-state ZAB and 116.6 mW/cm2 in the flexible solid-state ZAB. This work provides an efficient ligand-assisted pathway for fabricating catalysts with dense and accessible Fe-NX sites as high-performance ORR electrocatalysts for ZABs.

Heterostructural Interface in Fe3C-TiN Quantum Dots Boosts Oxygen Reduction Reaction for Al-Air Batteries.

Oxygen reduction electrocatalysts play important roles in metal-air batteries. Herein, Fe3C-TiN heterostructural quantum dots loaded on carbon nanotubes (FCTN@CNTs) are prepared as electrocatalysts for the oxygen reduction reaction (ORR) through a one-pot pyrolysis. The Fe3C-TiN quantum dots with a diameter of 2-5 nm show the unique characteristic of heterostructural interface. The as-prepared FCTN@CNTs display Pt/C comparable ORR performance (Eonset 1.06 and E1/2 0.95 V) in alkaline medium, which is ascribed to the heterostructural interface between TiN and Fe3C. Furthermore, the Al-air batteries with the FCTN@CNT catalyst display superior discharge performance, demonstrating good feasibility for practical application. This work provides an effective new method to synthesize affordable and efficient oxygen reduction reaction catalysts.

Inhibiting Surface Diffusion to Synthesize 3D Bicontinuous Nanoporous N‐Doped Carbon for Boosting Oxygen Reduction Reaction in Flexible All‐Solid‐State Al‐Air Batteries

AbstractCatalyzing oxygen reduction reaction (ORR) and accelerating oxygen diffusion are two key challenges for the requirements of the cathode catalysts in the metal‐air batteries. A promising strategy for improving both ORR performance and mass diffusion simultaneously is to build carbon‐based catalysts with ORR‐active chemical dopants and 3D interconnected porosity. Herein, a 3D nanoporous N‐doped carbon with bicontinuous porosity and interconnected open‐pore channels is reported, which is prepared by a polyaniline‐assisted template method. The polyaniline can efficiently inhibit the surface diffusion‐caused template coarsening, achieving a small pore size of 35 nm. The small porous morphology gives rise to a high N‐dopant concentration up to 7.20 at.%, which in turn exhibits a commercial Pt/C‐comparable ORR performance together with satisfied durability in alkaline media. Using these nanoporous carbon catalysts as air electrodes, an all‐solid‐state flexible Al‐air battery is assembled with the measured maximum power density reaching 130.5 mW cm−2, as compared to 106.2 mW cm−2 when the commercial Pt/C standard is used. This study provides an efficient method to synthesize 3D N‐doped carbon with bicontinuous nano‐sized pore channels for wide‐ranging applications in portable and flexible devices.

Ion‐Induced Formation of Hierarchical Porous Nitrogen‐Doped Carbon Materials with Enhanced Oxygen Reduction

AbstractNanostructured nitrogen‐doped carbon materials are considered as an appealing material to replace precious‐metal Pt‐based catalysts in fuel cells due to a high oxygen reduction reaction (ORR) activity and outstanding stability. In the present work, we developed an ion‐induced method for the fabrication of hierarchical porous nitrogen‐doped carbon materials (HPNC) using Cd‐organic complexes as sacrificial templates and precursors. During pyrolysis, a hierarchical porous structure with a high specific surface area was formed through the combination of a metal‐free ion as structure‐directing agent and the evaporation property of Cd. Benefiting from this unique structure, the resulting HPNC exhibited comparable ORR performance with commercial Pt/C, including positive onset potential of 0.96 V vs. RHE (reversible hydrogen electrode), positive half‐wave potential of 0.86 V vs. RHE, good methanol tolerance and stability. On this basis, the assembled Zn‐air battery showed high open circuit potential, power density and excellent stability.

Green algae and gelatine derived nitrogen rich carbon as an outstanding competitor to Pt loaded carbon catalysts

The development of effective catalysts for the oxygen reduction reaction (ORR) is a significant challenge in energy conversion systems, e.g., Zn–air batteries. Herein, green-algae- and gelatine-derived porous, nitrogen-rich carbons were extensively investigated as electrode materials for electrochemical catalytic reactions. These carbon-based catalysts were designed and optimized to create a metal-free catalyst via templating, carbonization, and subsequent removal of the template. The additional incorporation of graphene improved electronic conductivity and enhanced the electrochemical catalytic reaction. Porous carbons with heteroatoms were used as effective platinum-free ORR electrocatalysts for energy conversion; the presence of nitrogen in the carbon provided more active sites for ORR. Our catalyst also displayed notable durability in a rechargeable Zn–air battery energy system. More importantly, the nitrogen-containing porous carbons were found to have comparable ORR performance in alkaline media to commercially available electrocatalysts. The manuscript demonstrates that nitrogen atom insertion is an appropriate approach when aiming to eliminate noble metals from the synthesis route. N-doped carbons are competitive materials compared to reference platinum-based catalysts.

Highly active oxygen reduction reaction on Fe-nanoclustered hierarchical porous carbon derived from CO2.

This work presents a highly active electrocatalyst of CO2-derived hierarchical carbon. It retains a high surface area and enables homogeneous insertion of Fe-N-C active sites for the oxygen reduction reaction. The electrocatalyst with a highly interconnected porous structure provides oxygen reduction reaction activity with an E1/2 difference of 10 mV and a high current density equivalent to Pt/C 20 wt%.

Surface plasma-etching treatment of cobalt nanoparticles-embedded honeysuckle-like nitrogen-doped carbon nanotubes to produce high-performance catalysts for rechargeable zinc-air batteries

Developing high-performance and low-cost catalysts for oxygen reduction reaction (ORR) in metal-air batteries is challenging but necessary for their practical applications and commercialization. In this paper, a core-shell cobalt nanoparticles-embedded honeysuckle-like N-doped carbon nanotube (Co@NCNT) catalyst is synthesized through programmed carbonization with the plasma etching. The Co@NCNT displays a uniform core-shell honeysuckle-like nanostructure and exhibits comparable ORR performance to the commercial 20% Pt/C. The onset potential (Eonset) and half-wave potential (E1/2) of the Co@NCNT is 1.030 V and 0.872 V (vs. RHE), and the potential decay in E1/2 is only 9 mV after 5000 cycles accelerated durability test (ADT). Moreover, a Zinc-air battery (ZAB) with Co@NCNT cathode catalyst exhibits a peak power density of 162.5 mW cm−2 and high rate capability as well as excellent durability. The excellent performance of the Co@NCNT is mainly attributed to the synergistic effect of unique core-shell nanostructure, more defects and active sites as well as more tiny rifts in the carbon-shell induced by the plasma etching.

ZIF-8 derived nitrogen, phosphorus and sulfur tri-doped mesoporous carbon for boosting electrocatalysis to oxygen reduction in universal pH range

It is highly urgent but challenging to develop the alternative oxygen reduction reaction (ORR) catalysts to the traditional noble-metals (such as Pt). In this study, a facile and cost-efficient route is designed to construct nitrogen, phosphorus and sulfur tri-doped mesoporous carbon (NPSpC) by direct pyrolysis of ZIF-8 after pretreatment with sodium phytate solution and dodecyl mercaptan. The resultant NPSpC exhibits a large specific surface area (1641 m2/g) and excellent catalytic activity toward ORR. The values for its onset potential (0.923 V vs RHE), half wave potential (0.821 V vs RHE) and limiting diffusion current density (4.89 mA/cm2) in 0.1 M KOH are close to those of commercial Pt/C (0.945 V, 0.839 V and 5.01 mA/cm2, respectively). It also displays the superior methanol tolerance and long-time stability to Pt/C in alkaline medium. Additionally, NPSpC demonstrates the comparable ORR performance to and much better stability than the commercial Pt/C in acidic and neutral solutions. The desirable ORR performance is originated from the synergistic effects including the tri-doping of N, P and S heteroatoms, the large active surface area, the more exposed catalytic sites, well mesoporous nanostructure for sufficient accessibility of the reactants and rapid mass transfer.

COF‐Derived N,P Co‐Doped Carbon as a Metal‐Free Catalyst for Highly Efficient Oxygen Reduction Reaction

AbstractA new kind of metal‐free, porous, and N,P co‐doped carbon catalyst was prepared from a high crystalline and two dimensional (2D) covalent organic framework (COF). Remarkably, this N,P co‐doped catalyst exhibits an excellent tolerance towards methanol crossover, as well as a comparable oxygen reduction reaction performance to commercial Pt/C.

Synergy of sp-N and sp2-N codoping endows graphdiyne with comparable oxygen reduction reaction performance to Pt.

Nitrogen doped graphdiyne (NGDY) has been reported to have comparable oxygen reduction reaction (ORR) performance to Pt-based catalysts. However, the source of this enhanced ORR performance is not clearly understood. Herein, density functional theory calculations were performed to study the detailed ORR process on NGDY. The theoretically predicted overpotential (η) of GDY materials was 0.442 V, which is comparable to that of Pt-based catalysts, suggesting that GDY is a candidate for non-expensive metal-free ORR catalyst. Our results revealed that the good ORR performance of NGDY originates from the synergy of sp-N and sp2-N, which rules out the experimental proposal that sp-N doping is the dominating factor. Our results further suggest that local positive charge is not a definite descriptor to predict the ORR performance of GDY; instead ΔGO shows a better correlation with performance. Furthermore, it was revealed that the adsorption site is crucial for determining ORR performance, which should not be ignored to fully understand the catalytic activity of GDY-based materials.

Electrospun metal-organic framework nanoparticle fibers and their derived electrocatalysts for oxygen reduction reaction

The rational design of assembled metal-organic frameworks (MOFs) derived carbon materials with rapid mass transport properties and stable porous structure is highly desirable yet a great challenge to date. In this work, MOFs-derived Co/N-doped porous carbon fibers with high electrochemical performance can be prepared simply by carbonizing MOFs nanofibers, which were fabricated by the electrospinning-assisted assembly of bimetallic zeolitic imidazolate framework nanoparticles (BMZIFs) based on ZIF-8 and ZIF-67. The effects of assembly and Zn/Co ratios on the oxygen reduction reaction (ORR) performances of the electrospun fibers derivatives were systematically studied. As expected, compared to the non-electrospun samples, such doped porous carbon nanofibers exhibited excellent electrocatalytic performances without any etching or other activating processes, and the sample with the molar ratio of Zn: Co= 5:1 even showed comparable ORR performance with the commercial Pt/C catalyst under the same conditions. The high catalytic performances root in the dense assembly of MOFs within the electrospun fibers, which was beneficial to endow the derivatives with the high surface area as well as uniform N and Co doping. Besides, the one-dimensional porous structure significantly promoted the mass transfer and exposure of active sites.

Co/MnO/N-C hybrid derived from N-methyl-D-glucamine as efficient bifunctional oxygen electrocatalysts

The low oxygen reduction reaction (ORR) electrocatalytic activities of Mn-based bifunctional electrocatalysts restrict their further development in clean energy equipment. In this work, Co/MnO/N-C oxygen electrocatalyst was prepared through a simple solvothermal and subsequent annealing process by using N-Methyl-d-glucamine as nitrogen and carbon source simultaneously. Benefiting from the abundant oxygen related defect and high content of pyridinic N and graphitic N, the resultant Co/MnO/N-C hybrid presents comparable ORR performance with positive half-wave potential of 0.822 V vs. RHE, high kinetic current density of 3.81 mA cm−2 and superior stability compare with the commercial Pt/C. Besides, the as-prepared hybrid also showed efficient catalytic activity towards oxygen evolution reaction (OER) with a low overpotential of 379 mV and low Tafel slope of 101 mV dec−1. Importantly, this work presents a versatile strategy of Mn-based electrocatalyst in enhancing the ORR and OER electrocatalytic activity to the future design.

Co3O4/MnO2/Hierarchically Porous Carbon as Superior Bifunctional Electrodes for Liquid and All-Solid-State Rechargeable Zinc-Air Batteries.

The design of efficient, durable, and affordable catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is very indispensable in liquid-type and flexible all-solid-state zinc-air batteries. Herein, we present a high-performance bifunctional catalyst with cobalt and manganese oxides supported on porous carbon (Co3O4/MnO2/PQ-7). The optimized Co3O4/MnO2/PQ-7 exhibited a comparable ORR performance with commercial Pt/C and a more superior OER performance than all of the other prepared catalysts, including commercial Pt/C. When applied to practical aqueous (6.0 M KOH) zinc-air batteries, the Co3O4/MnO2/porous carbon hybrid catalysts exhibited exceptional performance, such as a maximum discharge peak power density as high as 257 mW cm-2 and the most stable charge-discharge durability over 50 h with negligible deactivation to date. More importantly, a series of flexible all-solid-state zinc-air batteries can be fabricated by the Co3O4/MnO2/porous carbon with a layer-by-layer method. The optimal catalyst (Co3O4/MnO2/PQ-7) exhibited an excellent peak power density of 45 mW cm-2. The discharge potentials almost remained unchanged for 6 h at 5 mA cm-2 and possessed a long cycle life (2.5 h@5 mA cm-2). These results make the optimized Co3O4/MnO2/PQ-7 a promising cathode candidate for both liquid-type and flexible all-solid-state zinc-air batteries.

Fe and N Co‐doped Carbons Derived from an Ionic Liquid as Active Bifunctional Oxygen Catalysts

AbstractA high‐performance electrocatalyst that could effectively catalyze the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is required in important energy conversion devices such as metal–air batteries. Herein, we report the template‐free synthesis of a Fe and N co‐doped carbon catalyst, using a novel ionic liquid as the precursor. The Fe−N−C catalyst prepared at 800 °C exhibits comparable ORR performance but significantly improved OER activity compared to the commercial Pt/C catalyst as well as good stability. We demonstrate that the excellent performance of the catalyst is caused by its high heteroatom content, large surface area, and high degree of graphitization.

A Generic Conversion Strategy: From 2D Metal Carbides (MxCy) to M‐Self‐Doped Graphene toward High‐Efficiency Energy Applications

This study first presents a subtle thermal‐chlorination strategy for a universal transformation of abundant 2D metal carbides (MxCy, e.g., Cr3C2, Mo2C, NbC, and VC) to 2D graphene and M‐self‐doped graphene (MG). The as‐obtained MG endows a transparent sheet architecture of one to four atomic layers. Simultaneously, MG with different M amounts is synthesized by tuning the chlorination parameters. Among them, the novel and representative Cr‐self‐doped graphene with optimal Cr amount (4.81 at%) demonstrates the outstanding electrochemical performance. It presents an energy density of 686 W h per kg electrode and a power density of more than 391 W per kg electrode as anode material of Li ion batteries, and four‐fold activity against the commercial iridium oxide electrode toward oxygen evolution reaction as well as a comparable oxygen reduction reaction performance to the commercial platinum catalyst. Moreover, this method is readily scalable to produce graphene and MG electrode materials on industrial levels.

A Layer-Structured Metal-Organic Framework-Derived Mesoporous Carbon for Efficient Oxygen Reduction Reaction

Developing highly active and durable electrocatalysts for the oxygen reduction reaction (ORR) is crucial to large-scale commercialization of fuel cells and metal-air batteries. Here we report a facile approach for the synthesis of nitrogen and oxygen dual-doped mesoporous layer-structured carbon electrocatalyst embedded with graphitic carbon coated cobalt nanoparticles by direct pyrolysis of a layer-structured metal-organic framework. The electrocatalyst prepared at 800 °C exhibits comparable ORR performance to Pt/C catalysts but possesses superior stability to Pt/C catalysts. This synthetic approach provides new prospects in developing sustainable carbon-based electrocatalysts for electrochemical energy conversion devices.

Use of Cobalt Polyphthalocyanine and Graphene as Precursors to Construct an Efficient Co9S8/N,S‐G Electrocatalyst for the Oxygen Electrode Reaction in Harsh Media

AbstractThe oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are fundamental reactions connected with energy conversion and/or storage devices. However, the sluggish kinetics of the ORR and OER reduce the efficiency. To address these issues, the development of efficient and robust electrode catalysts is required desperately. Herein, a new Co9S8 nanocrystal hybrid anchored on a N‐ and S‐dual‐doped graphene (Co9S8/N,S‐G) was prepared by a two‐step method, namely, a π–π assembly process of p‐phenyl‐bis(3,4‐dicyanophenyl)thioether cobalt polyphthalocyanine (PTCoPPc) and graphene oxide and a pyrolysis procedure. Electrochemical studies demonstrated that Co9S8(800)/N,S‐G exhibited a comparable ORR performance with 20 wt % Pt/C, such as an onset potential and a half‐wave potential of 0.931 and 0.811 V vs. the reversible hydrogen electrode, respectively, a limiting current density of 5.207 mA cm−2, and a good long‐term stability with a current retention of 92.6 % after 10 000 s continuous measurements. Co9S8(900)/N,S‐G displayed an excellent OER activity, which was ascribed to the presence of pyridinic N, graphitic N, and the occupation of Co−N to catalyze the ORR; and the oxygen adsorption on the surface of Co9S8(900)/N,S‐G contributed significantly to the OER activity. The approach developed here offered a new strategy to construct efficient oxygen electrode catalysts.

Rational design of graphene oxide and its hollow CoO composite for superior oxygen reduction reaction

Graphene oxide (GO) is an important derivative of graphene, fascinating the entire world with its dazzling properties and versatile performance. However, the synthesis of GO via chemical routes often results in limited control of the density of functionalities and their distribution, presenting a barrier to the spread of GO applications. We modified Hummers’ method and aimed at controlling the oxygen functionality of GO. The highest oxygen content of the modified synthetic GO (MdGO) occurs at edge regions, and the large proportion of carboxyl groups can be easily removed upon annealing. The excellent conductivity of intrinsic graphene can thus be recovered after the removal of the main functional groups. The resulting MdGO was reduced and doped with NH3, and the reduced MdGO (rMdGO) was determined to be an excellent support for oxygen reduction reaction (ORR) electrocatalysts. As a demonstration, a composite of CoO and N-rMdGO was fabricated, which exhibited highly comparable ORR performance in alkaline relative to 20 wt.% Pt/C.

Catalyst Layer Architectures with Supportless Pt Hollow Spheres for Polymer Electrolyte Fuel Cells (PEFCs)

Supportless Pt black is an attractive oxygen reduction reaction (ORR) catalyst for polymer electrolyte fuel cells (PEFCs) due to its merits such as no concern of support corrosion at high potentials and high durability against Pt dissolution at frequent potential change conditions. However, when the Pt black catalysts were fabricated as MEAs the performance is still lower than the current Pt/C catalysts and they have difficulty in reducing Pt content in the MEAs. In the present study, we have prepared sub-micron size Pt hollow spheres as an alternative catalyst layer architecture for PEFC MEAs. The big Pt spheres were employed to make 3-dimensional catalyst layer architectures and to enhance oxygen transport in catalyst layers, and hollow type Pt was made to reduce Pt content and to facilitate water management. 200 nm Pt hollow spheres with 10 nm shell thickness were prepared using carbon sphere templates. The Pt hollow spheres revealed comparable ORR performance with commercial Pt/C catalyst in a half cell test. Catalyst layer fabrication was also performed using the catalysts by optimizing the catalyst slurries and its fuel cell performance at different operating conditions and durability will be discussed based on single cell test results.