Electrocatalysts For Oxygen Reduction Reaction Research Articles

Metal-support interaction promoted multifunctional electrocatalysis on PtCo/NC with ultralow Pt loading for oxygen reduction reaction and zinc-air battery

Tri-functional PtCo/NC nanocatalysts were assembled via in-situ integration with ultralow Pt loading supported on ZIF-67 derived porous carbon material, and used as electrocatalysts for oxygen reduction reaction (ORR), ethanol oxidation reaction (EOR), hydrogen evolution reaction (HER). Detailedly, PtCo-3/NC with ultralow Pt loading (1 wt%) exhibits the halfwave potential of 0.877 V for ORR in acidic media and considerable current density for both ORR and EOR at 0.85 V, and low overpotential (η10 =10 mV) for HER. The as-assembled zinc-air batteries (ZABs) based on PtCo/NC have higher power density than Pt/C based ZABs. DFT calculation reveals the strong metal-support interactions (MSI) in PtCo/NC, which leads to the change of electronic state, redistribution of charge density and optimization of free energy, allowing it to present greater performances than Pt/C. This work highlights the possibility of using it as highly effective electrode catalysts with ultralow Pt loading in fuel cells and metal-air battery.

3D Porous Nitrogen-rich Octahedral Carbon as advanced Oxygen Reduction Reaction catalyst

A Metal-organic-frameworks (MOFs) derived 3D porous nitrogen-rich octahedral carbon (PNOC) catalyst is successfully fabricated via carbonization of MIL-101(Fe) precursor process. As-obtained PNOC combines the advantages of high surface area, well permeable pore and rich nitrogen content in one catalyst, which shows excellent catalytic activity and stability for oxygen reduction reaction (ORR). This work would offer some new insights to advanced ORR electrocatalyst material designed in fuel cells.

Engineering single-atom Fe–N active sites on hollow carbon spheres for oxygen reduction reaction

Seeking alternatives to noble metals-based electrocatalysts for oxygen reduction reaction (ORR), hollow carbon spheres (CSs) were finely tuned with stable single-atom Fe–N species through a synthesis methodology requiring only earth-abundant metal precursors. CSs with different sizes were synthesized by sol-gel polycondensation of resorcinol with formaldehyde over silica nanoparticles, followed by thermal annealing and silica etching. A catalyst screening revealed the positive impact of both the hollow core and structural defects of the CSs for ORR. Single-atom Fe–N active sites were introduced on the best performing CSs through simultaneous incorporation of iron and nitrogen precursors, and glucose. A significant enhancement in ORR activity was observed despite the small iron load introduced (0.12 wt%). ORR performance indicators, advanced characterization, and molecular simulation studies revealed nitrogen's crucial role in anchoring individual iron atoms and modulating the charge density nearby the active sites (increase of 80 mV in the half-wave potential). Adding glucose as a chelating agent enhances the metal-heteroatom coordination and subsequent dispersion of iron, accounting for an increase of 20 mV in the half-wave potential, an average of electrons transferred as high as 3.9 (at 0.4 V vs. RHE), and higher stability (99%) than that of a platinum-based (20 wt%) electrocatalyst (92%).

Microbial synthesis of N, P co-doped carbon supported PtCu catalysts for oxygen reduction reaction

Developing highly efficient and stable platinum-based electrocatalyst for oxygen reduction reaction (ORR) is critical to expediting commercialization of fuel cells. Herein, several PtCu alloy nanocatalysts supported on N, P co-doped carbon (PtCu/NPC) were prepared by microbial-sorption and carbonization-reduction. Among them, PtCu/NPC-700 °C exhibits excellent catalytic performance for ORR with a mass activity of 0.895 A mgPt−1 (@0.9 V) which is 8.29 folds of commercial Pt/C. Additionally, the ECSA and MA of PtCu/NPC-700 °C only decrease by 14.2% and 18.7% respectively, while Pt/C decreases by 35.2% and 52.8% after 10,000 cycles of ADT test. Moreover, the PtCu/NPC-700 °C catalyst emanates a maximum power density of 715 mW cm−2 and only 11.1% loss of maximum power density after 10,000 ADTs in single-cell test, indicating PtCu/NPC-700 °C also manifests higher activity and durability in actual single-cell operation than Pt/C. This research provides an easy and novel strategy for developing highly active and durable Pt-based alloy catalyst.

Hollow Porous Carbon Nanofibers with Fe–N–C Modified by Fe3O4 Nanoparticles for Enhancing Mass Transfer for Boosting the Oxygen Reduction Reaction

Designing low-cost and high-efficiency non-noble metal electrocatalysts for the oxygen reduction reaction (ORR) is critical for the development of renewable and sustainable energy devices. It is of essential importance to precisely design and rationally adjust the porous morphology and nanostructure of catalysts to improve mass transfer and the accessibility of active sites. Herein, we elaborately designed a unique hollow hierarchical porous carbon nanofiber with Fe3O4/Fe–N–C sites anchored as a high-efficiency electrocatalyst for ORR. The hollow porous carbon nanofibers (HPCNFs) were prepared via a facile convenient coaxial electrospinning technology to fabricate the hollow carbon nanofibers and through zinc nitrate-assisted pyrolysis to form a hierarchical porous structure. Benefiting from its unique hollow porous construction, facilitated mass transfer, and highly accessible active sites, the optimized Fe-HPCNFs catalyst exhibited significant ORR performance and stability, with a half-wave potential of 0.89 V outperforming the commercial catalyst (20% Pt/C). Remarkably, Zn–air batteries assembled with Fe-HPCNFs achieved excellent activity with a robust peak power density of 172 mW·cm–2 and a high specific capacity of 905.4 mAh·gZn–1. Furthermore, the ORR mechanism was investigated by density functional theory calculations, demonstrating that the synergistic effect of Fe3O4 nanoparticles and Fe–N–C active sites can effectively boost the electrocatalytic activity for ORR.

Soft‐Pyrolysis Co–N‐Implanted Polymer to Gain High‐Density Co–Nx Sites on Carbons for Efficient Oxygen Reduction in Zn–Air Batteries

A soft‐pyrolysis strategy by heating Co–N‐implanted covalent organic polymer combining on carbon nanotubes at ≤500 °C has been developed to obtain efficient Co–N–C electrocatalysts for oxygen reduction reaction (ORR). The prepared Co–N–C is highly active for ORR with a half‐wave potential of 0.91 V versus RHE in 0.1 m KOH electrolyte, superior to most of previously reported Co‐based electrocatalysts. When employing it as cathode electrocatalyst, the homemade Zn–air battery shows a peak power density of 304.2 mW cm−2, comparable to the parallel power density (250 mW cm−2) of Zn–air battery with Pt/C (20 wt%) electrocatalyst at cathode. The soft‐pyrolysis strategy not only helps to generate high density Co–Nx active sites on carbons but also facilitates the optimizing balance between active site densities, graphitization degree, and pore structure of Co–N–C catalysts. Herein, a simple and energy‐effective low‐temperature pyrolysis strategy to obtain high‐performance ORR electrocatalyst is provided.

Metal-doped imine frameworks for the oxygen reduction reaction in acidic media

The overall performance of proton exchange membrane fuel cells is limited by the sluggish kinetics of the oxygen-reduction reaction (ORR). Among the most active PGM-free ORR electrocatalysts are metal-nitrogen-carbon (M-N-C), such as Fe–N–C. The Fe–N4 ensembles in these PGM-free catalysts, present in different configurations, are proposed to be the active sites for the ORR in acid. In this work, we have synthesized a Fe/N/C catalyst via thermal treatment of a polymeric CxNy precursor obtained by the wet-polymerization of melamine (a nitrogen rich molecule) and terephthaldehyde. The materials obtained (Im-FeNC-1HT and Im-FeNC-2HT) display high ORR activity in acid electrolyte compared to other Fe–N–C catalysts prepared with precursors different than 2-methylimidazole or ZIF-8. Characterization data indicate the formation of high- and low-spin Fe-Nx ensembles, with a site density of 4.4·1019 sitesFe·g−1 estimated by electrochemical stripping of NO. The ORR activity was evaluated in a RRDE configuration in 0.1 M HClO4 and in MEA configuration in a single cell.

Ag Sputter-Deposited on MnO2-Carbon Nanotube Nanocomposites as Electrocatalysts for Oxygen Reduction Reaction in Alkaline Media

As energy demand increases, new energy conversion methods are also sought. In this study, two MnO2 and multiwalled carbon nanotube (MWCNT) composites were prepared and decorated with silver using magnetron sputtering, to evaluate their electrocatalytic activity towards the oxygen reduction reaction (ORR). Three nominal thicknesses of Ag layers were used, 5, 10 and 20 nm. The physicochemical characterisation was carried out using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, as well as X-ray photoelectron spectroscopy. The substrate materials (MnO2-MWCNT) were also investigated by X-ray diffraction analysis. The electrochemical studies of the ORR revealed that the activity and stability of the composite catalysts depend on the substrate material and the Ag layer thickness.

Glucose‐hexamethylenetetramine‐derived Co, N Co‐doped Carbon Nanoflowers with Encapsulated Co@Co3O4 as Efficient Bifunctional Oxygen Electrocatalyst for Zinc‐air Batteries

AbstractDeveloping low‐cost, eco‐friendly, and efficient bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important issue for zinc‐air batteries. In this study, HMT‐Co/G‐700 catalyst with nanoflower structure and Co, N co‐doped carbon encapsulated Co@Co3O4 nanoparticles are synthesized from D‐glucose, hexamethylenetetramine (HMT), and Co(NO3)2. HMT is presented as the complex to uniformly disperse Co@Co3O4 nanoparticles, dope nitrogen, and create the nanoflower structure. The nanoflower structure enhances high surface area to expose the active sites. The formation of Co3O4 via mild oxidation of Co surface provides oxygen vacancies to adsorb O2. HMT‐Co/G‐700 catalyst exhibits excellent ORR electrocatalytic property, i. e. high onset potential (1.03 V), high half‐wave potential (0.83 V), low Tafel slope (85.9 mV dec−1), and superior OER activity. Especially, the HMT‐Co/G‐700 catalyst assembled rechargeable zinc‐air battery present high‐power density (111.0 mW cm−2) and long cycle life at 10 mA cm−2 (576 cycles).

Co(II) Porphyrin-MWCNT Nanoconjugate as an Efficient and Durable Electrocatalyst for Oxygen Reduction Reaction.

Recently, researchers are seeking alternatives to replace Pt-based oxygen reduction reaction (ORR) catalysts used in fuel cells due to their high cost and certain stability and selectivity issues. For this purpose, we have synthesized a nanoconjugate, cobalt(II) porphyrin (5,10,15-triphenyl-20-(4-aminophenyl)porphyrinatocobalt(II), CoTPP-NH2) covalently attached to the acid-functionalized multiwalled carbon nanotubes and characterized by various techniques including UV-vis spectroscopy, FTIR, TGA, FESEM, TEM, and Raman spectroscopy. The oxygen reduction performance of the nanoconjugate is checked in basic medium. The ORR onset potential of the nanoconjugate-modified electrode is nearly the same as that of the state-of-the-art platinum-carbon electrode and stable for more than 3000 CV cycles with a 20 mV difference in the onset potential before and after the 3000 CV cycles. The above extrapolations reveal that the nanoconjugate has efficient performance for the ORR in basic medium.

Platinum nanoparticles prepared by ion implantation exhibit high durability for fuel cell applications

Proton exchange membrane fuel cells (PEMFCs) have attracted considerable attention as distributed power sources for automotive and residential applications. In PEMFCs, platinum (Pt) nanoparticles supported on carbon materials are used as electrocatalysts for oxygen reduction reactions. However, improved durability of the electrocatalysts is urgently required for commercialization purposes. We describe an ion implantation technique for the preparation of Pt nanoparticles with superior catalytic properties, suitable for fuel cell applications. The Pt nanoparticles were obtained by implanting a glassy carbon (GC) substrate with 100 keV Pt-ions, followed by electrochemical etching and a heat treatment. Electrochemical measurements of the Pt nanoparticles prepared by the proposed implantation technique demonstrated superior durability when compared to those prepared by the conventional magnetron sputtering method. We suggested that the defective structure of the GC substrate, caused by the Pt-ion implantation, has led to the improved electrochemical stability of the GC substrate and Pt-carbon support interactions, thereby enhancing the durability of our Pt nanoparticles.

Copper-cobalt bimetallic conductive metal–organic frameworks as bifunctional oxygen electrocatalyst in alkaline and neutral media

The preparation of low cost bifunctional electrocatalysts that efficiently catalyze oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is a crucial step towards realizing high-performance Zn–air batteries. Herein a bimetallic CuCo-HITP (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) conductive metal-organic frameworks (MOFs) was synthesized as a bifunctional electrocatalyst for OER and ORR through an effective and facile ammonia-assisted method. Structural characterization showed that the metal ions coordinated with HITP ligands through strong coordination bonds of M − N4 to construct a two-dimensional (2D) porous structure. The electrochemical tests demonstrated that CuCo-HITP had superior bifunctional OER and ORR electrocatalytic performance in both alkaline and neutral media. It should be attributed to the bimetallic synergistically effect, which lead to more active sites, faster charge transfer rate and improvement of the catalytic reaction kinetics.

High-efficiency oxygen electrocatalyst for Zn-air batteries on CoMn alloy encapsulated in N-doped carbon architectures

A low-cost efficient electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is urgently required for the commercialization of Zn-air batteries. Herein, CoMn nanoalloys encapsulated in nitrogen-doped hollow carbon architectures (CoMn@NHC) as dual electrocatalysts for Zn-air batteries were developed successfully. The obtained CoMn@NHC nanohybrid expresses excellent electrocatalytic performances for ORR (E1/2 = 0.87 V) and OER (Ei=10 = 1.51 V). More encouragingly, a homemade aqueous Zn-air battery using CoMn@NHC catalyst delivers a larger peak power density of 92.3 mW cm−2 and excellent stability of nearly 300 h, outperforming the commercial Pt/C + RuO2. The remarkable electrocatalytic performances are owing to the unique microstructure and the synergistic effect between CoMn alloy and N-doped carbon substrate. This study opens a new way for designing high-efficient bifunctional electrocatalysts for application in renewable energy facilities.

Three-Dimensional Fe-N-C-Supported Amorphous NiFe alloy Nanoparticles as an Efficient Bifunctional Electrocatalyst for Zn-Air Batteries

The development of highly active and durable bifunctional oxygen reduction and evolution reaction (OER/ORR) electrocatalysts is vitally important for rechargeable metal-air batteries. However, little research has been done on the development of amorphous materials as bifunctional catalysts. Here, amorphous NiFe alloy nanoparticles (a-NiFe) coupled to transition metal nitrogen-doped carbon (Fe-N-C) substrate (a-NiFe@Fe-N-C) have been produced and ducted by a simple synthesis method. It is confirmed that the a-NiFe@Fe-N-C composite has significant amorphous characteristics according to XRD, HR-TEM, and SAED characterization methods, and the amorphous structure has abundant defects caused by the disordered arrangement of atoms, which is conducive to accommodate a large mass of active sites and promote the performance of catalysts. Additionally, the large specific surface area, the interconnected multistage pore structure, and the superior electrical conductivity of the Fe-N-C substrate, as well as the synergistic effect between bimetals Ni and Fe, make a-NiFe@Fe-N-C composite electrocatalyst present superior bifunctional catalytic activity and durability. Remarkably, compared with benchmark Pt/C + IrO2, the rechargeable liquid Zinc-air battery using a-NiFe@Fe-N-C as cathode exhibits a superior power density (170 mW·cm−2), specific capacity (687.65 mAh·gZn-1) and cycling durability (100 h).

Bifunctional oxygen electrocatalysts with WN@Ni nanostructures implanted on N-doped carbon nanorods for rechargeable Zn-Air batteries

Achieving the rational design of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional noble metal-free electrocatalysts has become one of the key research areas for the application of rechargeable Zn-air batteries (ZABs), which still remains a significant challenge. Herein, an in-situ polyaniline nitriding strategy has been developed to fabricate WN-Ni heterostructured catalysts. Polyaniline serves as both the carbon source and the N species that can in situ release gas (NH3) to produce the WN phase. As-fabricated WN-Ni heterostructured catalyst exhibits excellent activity towards ORR and OER, in which the half-wave potential is 0.76 V for ORR, and the over-potential for OER is 1.68 V at 10 mA cm−2. Due to its exceptional ORR/OER activities, the assembled rechargeable ZAB obtains a high power density of 165 mW cm−2. It also exhibits outstanding stability after being subjected to a discharge-charge cycle procedure (>400 h). The remarkable activity of the WN-Ni heterostructured materials should be attributed to their hierarchical nanorod-nanoparticle structure, proper crystallinity of WN-Ni, and good charge/mass transfer ability, which effectively regulate the electron redistribution at the WN-Ni heterointerface and facilitate the charge transfer between two entities.

Noble-metal-free Co-N-C catalyst derived from cellulose-based poly(ionic liquid)s for highly efficient oxygen reduction reaction

Noble-Metal-Free nitrogen-doped carbon-based materials are promising electrocatalysts for oxygen reduction reaction (ORR), yet it remains a great challenge to construct efficient porous non-noble metal nitrogen-doped carbon (M-N-C) catalysts with uniform distribution, due to the easy aggregation of metals. Herein, we reported the synthesis and assessment of a novel and efficient noble-metal-free catalyst for oxygen reduction reaction (ORR) from pyrolysis of a cobalt-containing cellulosic poly(ionic liquid) (Co-N-C). The prepared Co-N-C catalyst possesses high surface area, hierarchical porous structure, well-dispersed Co nanoparticles and large amounts of low-coordinated Co active sites. Especially, the Co-N-C-850 sample exhibits a high ORR activity (Eonset = 0.827 V, E1/2 = 0.74 V) that can rival 20 wt% commercial Pt/C (Eonset = 0.833 V, E1/2 = 0.71 V) in alkaline media. Moreover, the Co-N-C-850 sample also shows excellent anti-methanol poisoning activity and long-term stability toward ORR compared with commercial Pt/C. Our study provides a promising avenue both for the development of non-noble M-N-C catalysts for fuel cells and the functional utilization of cellulose.

Three-dimensional porous nitrogen-doped carbon nanosheets with ultra-high surface area for high-performance oxygen reduction reaction electrocatalysts

A series of three-dimensional (3D) porous nitrogen-doped carbon nanosheets (PNCNs) have been successfully fabricated via a high-pressure carbonization followed by high-temperature thermal treatment. With the prolonging of thermal treatment time, the 3D PNCNs demonstrate several remarkable advantages for oxygen reduction reaction (ORR) electrocatalysts, including ultra-high specific surface area (more than 2100 m2/g−1), unique 3D porous structure, abundant defects, and suitable configuration of nitrogen. With these merits, the N-C-2 h based electrocatalyst exhibits outstanding ORR activities with a comparable onset potential of −40 mV (vs. Ag/AgCl), half-wave potential of −120 mV (vs. Ag/AgCl), satisfactory electron transfer number (4) and superior stability to those of commercial 20% Pt/C. The excellent electrochemical behaviors of 3D PNCNs are confirmed to be dominated by structural characteristics, which can be optimized by varying thermal treatment time. Our work offers a promising way for controllably constructing carbon-based materials with optimized ORR performance.

Biomass-Derived Bifunctional Cathode Electrocatalyst and Multiadaptive Gel Electrolyte for High-Performance Flexible Zn-Air Batteries in Wide Temperature Range.

High-efficiency and low-cost bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as well as gel electrolytes with high thermal and mechanical adaptability are required for the development of flexible batteries. Herein, abundant Setaria Viridis (SV) biomass is selected as the precursor to prepare porous N-doped carbon tubes with high specific surface area and the 900°C calcination product of SV (SV-900) shows the optimum ORR/OER activities with a small EOER -EORR of 0.734 V. Meanwhile, a new multifunctional gel electrolyte named C20E2G5 is prepared using cellulose extracted from another widely distributed biomass named flax as the skeleton, epichlorohydrin as the cross-linker and glycerol as the antifreezing agent. C20E2G5 possesses high ionic conductivity from -40 to + 60 °C, excellent tensile and compressive resistance, high adhesion, strong freezing and heat resistance. Moreover, the symmetrical cell assembled with C20E2G5 can significantly inhibit Zn dendrite growth. Finally, flexible solid-state Zn-air batteries assembled with SV-900 and C20E2G5 show high open circuit voltage, large energy density, and long-term operation stability between -40 and + 60°C. This biomass-based approach is generic and can be used for the development of diverse next-generation electrochemical energy conversion and storage devices.

Spontaneous Internal Electric Field in Heterojunction Boosts Bifunctional Oxygen Electrocatalysts for Zinc-Air Batteries: Theory, Experiment, and Application.

Heterojunctions are a promising class of materials for high-efficiency bifunctional oxygen electrocatalysts in both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the conventional theories fail to explain why many catalysts behave differently in ORR and OER, despite a reversible path (* O2 ⇋* OOH⇋* O⇋* OH). This study proposes the electron-/hole-rich catalytic center theory (e/h-CCT) to supplement the existing theories, it suggests that the Fermi level of catalysts determines the direction of electron transfer, which affects the direction of the oxidation/reduction reaction, and the density of states (DOS) near the Fermi level determines the accessibility for injecting electrons and holes. Additionally, heterojunctions with different Fermi levels form electron-/hole-rich catalytic centers near the Fermi levels to promote ORR/OER, respectively. To verify the universality of the e/h-CCT theory,this study reveals the randomly synthesized heterostructural Fe3 N-FeN0.0324 (Fex N@PC with DFT calculations and electrochemical tests. The results show that the heterostructural F3 N-FeN0.0324 facilitates the catalytic activities for ORR and OER simultaneously by forming an internal electron-/hole-rich interface. The rechargeable ZABs with Fex N@PC cathode display a high open circuit potential of 1.504 V, high power density of 223.67 mW cm-2 , high specific capacity of 766.20 mAh g-1 at 5 mA cm-2 , and excellent stability for over 300 h.

Copper nanodot-embedded nitrogen and fluorine co-doped porous carbon nanofibers as advanced electrocatalysts for rechargeable zinc-air batteries

Porous carbon-based electrocatalysts for cathodes in zinc-air batteries (ZABs) are limited by their low catalytic activity and poor electronic conductivity, making it difficult for them to be quickly commercialized. To solve these problems of ZABs, copper nanodot-embedded N, F co-doped porous carbon nanofibers (CuNDs@NFPCNFs) are prepared to enhance the electronic conductivity and catalytic activity in this study. The CuNDs@NFPCNFs exhibit excellent oxygen reduction reaction (ORR) performance based on experimental and density functional theory (DFT) simulation results. The copper nanodots (CuNDs) and N, F co-doped carbon nanofibers (NFPCNFs) synergistically enhance the electrocatalytic activity. The CuNDs in the NFPCNFs also enhance the electronic conductivity to facilitate electron transfer during the ORR. The open porous structure of the NFPCNFs promotes the fast diffusion of dissolved oxygen and the formation of abundant gas-liquid-solid interfaces, leading to enhanced ORR activity. Finally, the CuNDs@NFPCNFs show excellent ORR performance, maintaining 92.5% of the catalytic activity after a long-term ORR test of 20000 s. The CuNDs@NFPCNFs also demonstrate super stable charge-discharge cycling for over 400 h, a high specific capacity of 771.3 mAh g−1 and an excellent power density of 204.9 mW cm−2 as a cathode electrode in ZABs. This work is expected to provide reference and guidance for research on the mechanism of action of metal nanodot-enhanced carbon materials for ORR electrocatalyst design.