Diffusion-limited Current Density Research Articles

Highly stable and methanol tolerant oxygen reduction reaction electrocatalyst Co/CoO/SnO@N-C nanocubes by one-step introduction of functional components

To develop high-performance non-precious metal-based electrocatalysts for oxygen reduction reaction (ORR) is an urgent demand. We herein report an ingenious strategy to develop highly selective and competitive precious metal-free ORR electrocatalyst Co/CoO/SnO encapsulated in N-rich mesoporous carbon (CCS@NPC) nanocubes, via a simple one-step introduction of all functional components. Atomically mixed composites with significantly enhanced catalytic activity were obtained by adopting amorphous mesoporous ternary metal oxides CoSnO3 nanocubes as precursor and template. The synergistic effect of the triphase nanohybrids (Co, CoO & SnO) anchored in nitrogen-doped mesoporous carbon nanocubes promoted the catalytic reactions, owning to the anisotropic morphology, great heterojunction interfaces, and structural stability. The large-scale prepared CCS@NPC exhibited excellent electrocatalytic activity toward ORR with an admirable onset potential (1.01 V) and diffusion-limited current density (5.88 mA cm−2). The CCS@NPC showed stronger stability (20 h) and higher methanol tolerance with the concentration up to 8.0 M, compared to that of commercial Pt/C.

Heteroatom-doped hollow carbon material as an electrocatalyst for oxygen reduction reaction

The development of highly efficient and stable non-precious metal electrocatalysts is essential for the oxygen reduction reaction (ORR). In this study, a simple polymerization pyrolysis method is proposed to prepare heteroatom-doped hollow carbon nanospheres (NPSC-800) by using Fe-BDC and phosphorus-containing polymers as precursors. The unique structure allows the catalyst to show good catalytic performance (Initial potential of 0.8786 V, a half-wave potential of 0.7576 V, and a diffusion-limited current density of 4.48 mA cm-2). This research provides an effective strategy for the synthesis of heteroatom-doped carbon materials with good ORR catalytic performance.

Effect of Temperature and Cl- Concentration on the Catalytic Activity of a Stainless-Steel Oxide

Galvanic couples between high-strength, noble metal fasteners, such as those made out of titanium or stainless-steel, can cause extensive damage in aluminum alloy airframes. These galvanic couples can drive higher rates of oxidation than would be expected for general corrosion and the corrosion damage can become a stress concentration point for the nucleation of cracks. Understanding the factors that govern the catalytic activity for the oxygen reduction reaction on stainless-steel oxides is important for enabling predictions of the amount of corrosion that can occur for a given set of environmental conditions. We have focused on measurements of the diffusion limited current density for oxygen reduction on UNS S13800 stainless-steel in solutions of varying NaCl concentrations from 0.1 M to 4.6 M and air temperatures ranging from 10oC to 40oC. Estimates of the oxygen diffusion limited current were obtained from potentiodynamic polarization measurements under the various electrolyte concentrations and environmental conditions. The experimental data was then compared with calculated ilim values for the same conditions and assuming a constant diffusion layer thickness. Regression and physics-based models for the effect of environmental conditions on the experimental data have been developed and are used to estimate the effect of the electrolyte on the stainless-steel oxide.The U.S. Naval Research Laboratory sponsored this work under work unit 1L66. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Office of Naval Research, the U.S. Navy, or the U.S. government.

Enhanced oxygen reduction reaction for Zn-air battery at defective carbon fibers derived from seaweed polysaccharide

Carbon fibers with intrinsic carbon defects (D-CFs) were fabricated through heteroatoms doping and de-doping using seaweed polysaccharide as the precursor. When evaluated as oxygen reduction reaction (ORR) electrocatalyst, D-CFs display an initial potential of 0.92 V (vs. RHE) and a limiting diffusion current density of 5.38 mA·cm−2 in KOH electrolyte (0.1 M). The high peak power density of zinc-air batteries (ZABs) assembled by D-CFs is 238 mW·cm−2, that is much better than commercial Pt/C (154 mW·cm−2). In the light of density functional theory (DFT) results, enriched electrons in defects make the hybridization energy levels of active defective sites and adsorbed oxygen atoms rise to Fermi level, indicating that O2 molecules are inclined to be adsorbed onto defective carbon atoms. Therefore, abundant renewable seaweed sources, together with the excellent ORR catalytic activity, make D-CFs as the substitute of Pt/C catalyst for large-scale application of ZABs.

Engineering Active Sites of Gold-Cuprous Oxide Catalysts for Electrocatalytic Oxygen Reduction Reaction.

Understanding how the catalyst morphology influences surface sites is crucial for designing active and stable catalysts and electrocatalysts. We here report a new approach to this understanding by decorating gold (Au) nanoparticles on the surface of cuprous oxides (Cu2O) with three different shape morphologies (spheres, cubes, and petals). The Au-Cu2O particles are dispersed onto carbon nanotube (CNT) matrix with high surface area, stability, and conductivity for oxygen reduction reaction. A clear morphology-dependent enhancement of the electrocatalytic activity is revealed. Oxygenated gold species (AuO-) are found to coexist with Au0 on the cube and petal catalysts, whereas only Au0 species are present on the sphere catalyst. The AuO- species function effectively as active sites, resulting in the improved catalytic performance by changing the reaction mechanism. The enhanced catalytic performance of the petal-shaped catalyst in terms of onset potential, half-wave potential, diffusion-limited current density, and stability is closely associated with the presence of the most abundant AuO- species on its surface. Highly active AuO- species are identified on the surface of the catalysts as a result of the unique structural characteristics, which is attributed to the structural origin of high activity and stability. This insight constitutes the basis for assessing the detailed correlation between the morphology and the electrocatalytic properties of the nanocomposite catalysts, which has implications for the design of surface-active sites on metal/metal oxide electrocatalysts.

Hierarchical N-doped CNTs grafted onto MOF-derived porous carbon nanomaterials for efficient oxygen reduction

The rational design and preparation of nonprecious metal-based oxygen reduction reaction (ORR) catalysts to facilitate electron and mass transport are of great significance in oxygen-involved energy applications. Herein, a stepwise approach to synthesize a type of hierarchically porous N-doped carbon nanotubes (CNTs) grafted onto zinc-based coordination polymer derived carbon nanomaterials (M−NCNT, M = Fe/Co/Ni) is proposed. At first, an isostructural zinc-based metal–organic framework (MOF) to HKUST-1(Cu) (ZnHKUST-1) is solvothermally prepared, and then under pyrolysis to obtain MOF-derived porous carbon. After the secondary calcination, the in-situ formed N-doped CNTs are efficiently catalyzed by iron group metal-based nanoparticles (Fe/Co/Ni), which are thermally reduced by porous carbon together with additional urea. The synergistic effect between ultrahigh porosity, large surface area, suitable N-doping, high graphitization degree, and ultrafine metal particles prompts M−NCNT series to exhibit satisfactory electrocatalysis in oxygen reduction. Among them, Fe-NCNT owns the optimal ORR activity with high positive onset potential (0.987 V), half-wave potential (0.860 V) and large diffusion-limited current density (4.893 mA cm−2). Meanwhile, it shows a high current retention of 90.7% after the 24-hour stability, and the obtained Zn-air battery by Fe-NCNT with open-circuit voltage of 1.44 V owns moderate capacity and satisfying stability. The demonstrated method to prepare hierarchically porous N-doped carbon nanomaterials stemmed from MOF precursors unfolds a new route for the facile construction of efficient nanocatalysts for advanced energy applications.

Synthesis of a highly efficient bifunctional Co2P@N-doped carbon nanotubes electrocatalyst by GO-Induced assembly strategy for rechargeable Zn-air batteries

Due to the bonding force between the surface Co atom and the adsorbed intermediate are so strong that intermediate cannot desorb from Co atom, the oxygen reduction reaction of Co2P based electrocatalyst cannot satisfy the commercialized application of the Zn-air battery. In this work, a GO-induced assembly strategy was designed to construct cobalt phosphide (Co2P) nanoparticles encapsulated in N-doped carbon nanotubes (Co2P@NCNTs). The experimental results show that adding graphene oxide (GO) content has a significant impact on the formation of well-defined Co2P@NCNTs nanotubes structures and the exaltation of the graphitization degree. Benefitting from the synergistic effect between N-doped nanotubes and Co2P, the Co2P@NCNTs-15 electrocatalysts exhibited better catalytic performance, a more positive onset potential (0.90 V vs RHE) and half-wave potential (0.82 V vs RHE), maximum limiting diffusion current density (5.5 mA cm−2) and Tafel slope only 73 mV dec−1. The potential gap (ΔE) between Ej=10 of OER and ORR half-wave potential (E1/2) of Co2P@NCNTs-15 is only 0.93 V, which lower than Pt/C electrocatalyst (1.15 V). More importantly, the Co2P@NCNTs-15-based rechargeable Zn-air battery performed the highest peak power density (159.7 mW cm−2), specific capacity (792.6 mAh g−1 at 10 mA cm−2) and remarkable cycle stability. This method also offers a high yield and cost-effective synthesis strategy for preparing the other transition metal phosphide electrocatalysts.

Fe3O4-Bi2O3 nanostructures for efficient energy generation application-water oxidation under visible light irradiation

• Facile synthesis of Fe 3 O 4 -Bi 2 O 3 nanostructures for energy generation applications. • Fe 3 O 4 -Bi 2 O 3 nanostructures showed highest photocurrent density. • The lowest charge transfer resistance is achieved for Fe 3 O 4 -Bi 2 O 3 nanostructures. • Potentiodynamic of Fe 3 O 4 -Bi 2 O 3 nanostructures showed enhanced properties. Nanostructures of Fe 3 O 4 , Bi 2 O 3 , and Fe 3 O 4 -Bi 2 O 3 were synthesized by a facile coprecipitation process for energy generation applications. Various analyses are carried out to confirm the formation of the nanostructures. The prepared samples showed cube structures with optical bandgaps of 2.21, 2.50, and 2.32 eV for the Fe 3 O 4 , Bi 2 O 3 , and Fe 3 O 4 -Bi 2 O 3 nanostructures, respectively. In the X-ray photoelectron spectroscopy analysis, Fe 2+ , Fe 3+ , Bi 3+ , and Bi 5+ chemical states were observed for the Fe 3 O 4 -Bi 2 O 3 nanostructures. The lowest charge transfer resistance of 46.04 Ω and ion-conducting path resistance of 26.11 Ω were observed in electrochemical impedance spectroscopy in 0.1 M KOH for Fe 3 O 4 -Bi 2 O 3 nanostructures compared with other samples. In the potentiodynamic analysis of the Fe 3 O 4 -Bi 2 O 3 nanostructures, the enhanced Tafel slopes, exchange current density, and limiting diffusion current density under illumination associated with the Fe 3 O 4 and Bi 2 O 3 nanostructures. The maximum photocurrent density of 3.61 × 10 -4 Acm −2 was one order of magnitude higher than that of the pure Fe 3 O 4 and Bi 2 O 3 samples. Hence, the prepared Fe 3 O 4 -Bi 2 O 3 nanostructures can be utilized in energy generation applications.

MnOx anchored on N and O co-doped carbon nanotubes encapsulated with FeCo alloy as highly efficient bifunctional electrocatalyst for rechargeable Zinc–Air batteries

Currently, development of OER/ORR bifunctional electric catalysts with low cost, high catalytic activity and stability is the key step to promote the practical application of zinc-air batteries. Herein, composite catalyst with manganese oxide on N and O co-doped carbon nanotubes encapsulated with FeCo alloy ([email protected]/MnO) was prepared in situ on CFP by hydrothermal and CVD pyrolysis methods. Owing to rich CO functional group on in situ growing carbon nanotubes with 3D open structure, alloying effect of CoFe core metal embedded in carbon nanotube and the contribution of MnO supported on carbon nanotubes to ORR performance and stability, the [email protected]/MnO catalyst exhibits low overpotential of 193 mV at the current density of 10 mA/cm2 for OER, larger diffusion-limited current density of 5.75 mA/cm2 and half-wave potential (E1/2 = 0.85 V) for ORR, high specific capacity (810 mAh/gZn) and peak power density (164 mW/cm2) with the Zn-air battery and superior stability. Moreover, the peak power density of the single [email protected]/MnO-based quasi-solid state ZAB could reach 142 mW/cm2, and two quasi-solid state ZABs connected in series can power a mini fan.

Bimetal-organic framework-derived carbon nanocubes with 3D hierarchical pores as highly efficient oxygen reduction reaction electrocatalysts for microbial fuel cells

Noble metal-free and highly efficient electro-catalytic materials with hierarchically porous structures continue to be studied for the oxygen reduction reaction (ORR) in microbial fuel cells (MFCs). We report bimetal-organic framework (bi-MOF)-derived nanocubic Swiss cheese-like carbons with a novel three-dimensional hierarchically porous structure (3D Co-N-C) prepared by utilizing cetyltrimethylammonium bromide (CTAB) as a structure-directing agent to control the formation of a nanocubic skeleton, and silica spheres as a template to form a mesoporous structure. The elemental composition and chemical morphology of this material can be tuned through the Zn/Co ratio to optimize its ORR catalytic activity. The optimized 3D Co-N-C displays excellent ORR catalytic performance (half-wave potential as high as 0.754 V vs. reversible hydrogen electrode and diffusion-limiting current density of 5.576 mA cm−2) in 0.01 mol L−1 phosphate-buffered saline (PBS electrolyte), showing it can compete with the commercial 20 wt% Pt/C catalysts. The catalytic capability and long-term durability of 3D Co-N-C as an air-filled cathode electrocatalyst in an MFC device are tested, showing that the 3D CoNC-MFC can reach a high power density of 1257 mW m−2 and provide a competitive voltage during a periodic feeding operation for 192 h; these values are much higher than those of the Pt/C-MFC.

FeCo-based mesoporous carbon shells modified N-doped porous carbon spheres for oxygen reduction reaction

FeCo-based non-noble metal electrocatalysts (NNMEs) of FeCo/MCS-NPCS was fabricated by immobilization of hemin on mesoporous carbon shells modified N-doped porous carbon spheres (MCS-NPCS). The obtained FeCo/MCS-NPCS exhibits a half-wave potential (E1/2) of 0.851 ​V versus the reversible hydrogen electrode (vs. RHE) and a limited-diffusion current density (JL) of 5.45 ​mA ​cm−2. In addition, FeCo/MCS-NPCS shows comparable oxygen reduction reaction (ORR) performances to 20 ​wt% Pt/C in terms of E1/2 and JL and better electrochemical properties, including the methanol tolerance and durability in alkaline solution. Such outstanding electrochemical activities of FeCo/MCS-NPCS can be ascribed to Fe and/or Co-based nitrides and carbides as well as N-doped carbon matrixes modified with mesoporous carbon shells. This research introduces a promising path to design and synthesize highly efficient FeCo–N–C electrocatalysts towards ORR.

Hierarchical ReS 2 / nitrogen‐doped graphene hybrid nanoarchitectures for efficient oxygen reduction

The highly efficient oxygen reduction reaction (ORR) electrocatalysts are desirable for the future energy storage scenario. Herein, we report three-dimensional (3D) nanostructured electrocatalysts constructed by in situ vertical assembly of few-layer ReS2 nanosheets onto the surface of nitrogen-doped reduced graphene oxide (ReS2/NRGO). The ReS2/NRGO hybrids are featured with the fully exposed active sites, interconnected conducting channels, and facilitated charge transfer. Accordingly, the as-synthesized ReS2/NRGO hybrids achieve a relatively small Tafel slope of 71 mV dec−1 and high diffusion-limited current density of 5.58 mA cm−2, which holds potential promise for practical applications in fuel cells and metal-air batteries.

Boron and nitrogen co-doped carbon dots for boosting electrocatalytic oxygen reduction

Carbon dots (CDs) have become an emerging carbon nanomaterial for use in energy-conversion systems because of their large surface area and rapid electron transfer. Carbon dots (BN-CDs) doped with both boron and nitrogen were synthesized by a simple one-step electrochemical etching approach using low-cost petroleum coke as precursor. Compared with CDs doped with only B or N, BN-CDs showed an excellent four-electron oxygen reduction reaction (ORR) activity with a positive onset potential of 0.958 V and a large diffusion-limited current density of −4.32 mA cm−2. Furthermore, the long-term stability and methanol tolerance of BN-CDs were better than those of a commercial Pt/C catalyst. It was found by density functional theory (DFT) calculation that the co-doping of N and B promoted the adsorption of O2 molecules in the ORR process. This work provides new insight into the rational design of carbon nanomaterials and their use in energy conversion.

Embedding Fe2P nanocrystals in bayberry-like N, P-enriched carbon nanospheres as excellent oxygen reduction electrocatalyst for zinc-air battery

Transition metal phosphide/carbon composites are promising electrocatalysts for oxygen reduction reaction (ORR). Herein, we propose a facile process to fabricate a bayberry-like N, P-enriched carbon nanospheres embedded with Fe2P nanocrystals (Fe2P/NPCs). Bayberry-like polyaniline nanospheres (PANI-NS) are firstly synthesized through microemulsion template method. Then, Fe is incorporated in PANI-NS during the hydrothermal treatment. Lastly FexP nanocrystals and N, P-enriched carbonaceous carriers are obtained by pyrolyzing the hydrothermal-treated PANI-NS. The resultant FexP/NPCs exhibit a uniform particle size (~250 nm), a large specific surface area (523 m2 g−1) and a homogeneous mesoporous structure (~3.46 nm). The phase structure of FexP depends on the Fe/P (molar ratio) during hydrothermal treatment. When Fe/P is around 0.2, a preferable Fe2P phase is obtained. The Fe2P/NPCs exhibit outstanding ORR electrocatalytic activity with a half-wave potential of 0.820 V (vs. RHE) and a diffusion-limited current density of 5.58 mA cm−2, comparable with commercial Pt/C. Moreover, Fe2P/NPCs possess a good duration stability and higher methanol tolerance than commercial Pt/C. When assembled in zinc-air batteries, Fe2P/NPCs contribute to an open circuit voltage of 1.449 V, a maximum power density of 128.38 mW cm−2, and a specific capacity of 691.0 mAh g−1, superior to the commercial Pt/C-based zinc-air battery.

Rational construction of ultrafine noble metals onto carbon nanoribbons with efficient oxygen reduction in practical alkaline fuel cell

In pursuit of sustainable and eco-friendly energy output, fuel cells are well-recognized as the most promising candidates in clean energy conversion and storage technology. Noble metal-based nanomaterials have long been regarded as the most efficient electrocatalysts for the oxygen reduction reaction (ORR) in terms of activity, selectivity, and stability. Here, we propose a self-template strategy where a type of hexagonal tubular InOF-25 could be tuned by adding a different amount of surfactants. Owing to the suitable pore size, these fabricated X-CTAB@InOF-25 (X = 50–300) series are used as precursors to encapsulate a series of discrete metal complexes, including Ag(NH3)2+, AuCl4-, PdCl42-, and PtCl62-. Then, the as-prepared carbon nanoribbons doped with precious metals (M@CNR, M = Pd, Pt, Ag, Au) exhibit good performance in the electrocatalytic ORR as well as Zn-air battery due to their large surface area, rich active sites, and extremely active noble metal nanoparticles. Among them, the most optimal Pd@CNR shows an onset potential of 0.94 V vs. RHE, high diffusion-limited current density of 5.87 mA cm-2, small Tafel slope of 51.74 mV dec-1, and satisfying stability with current retention of 95.4% after 10 h. Meanwhile, these obtained M@CNR as cathode catalysts are modeled and proved by the theoretical calculation with strong oxygen adsorption for efficient ORR. In this context, the main issues, large overpotential required for ORR and fast degradation of the electrocatalysts, impair practical application, which could be relieved by the active noble metals well-protected by carbon nanomaterials from the rational design and preparation of precursors.

The Untold Tale of the ORR Polarization Curve

A rotating disk electrode (RDE) is employed to screen materials for the electrochemical oxygen reduction reaction (ORR), which is a key reaction in fuel cells and metal-air batteries. Nevertheless, even more than seven decades after the first report on RDE and the exponential growth of publications on ORR, the following questions remain unanswered: how are the ORR polarization curves related to the fuel cell polarization and power density curves, and what is hidden in the sigmoidal nature of ORR polarization curves? Here, we have made an effort to unveil various aspect of ORR polarization curves and ORR parameters such as the onset, half-wave potential, and diffusion-limited current density from the fuel cell prospective. Interestingly, we find one-to-one mapping among the matrices used to apprise the ORR and fuel cells. It is remarkable that the slope is close to unity for the fuel cell matrices and that it is projected from the ORR polarization curves. This analysis will be a great help to researchers for appraising the suitability of their designed/developed electrocatalysts targeted for fuel cells and metal-air battery applications. © 2021 American Chemical Society. All rights reserved.

Sulfur-Induced Growth of Coordination Polymer Derived-Straight Carbon Nanotubes on Carbon Nanofiber Network for Zn-Air Batteries.

Low-cost heteroatom-doped carbon nanomaterials have been widely studied for efficient oxygen reduction reaction and energy storage and conversion in metal-air batteries. A Masson pine twigs-like 3-dimensional network construction of carbon nanofibers (CNFs) with abundant straight long Co, N, and S-doped carbon nanotubes (CNTs) is developed by thermal treatment of Co-based polymer coated onto polyacrylonitrile nanofiber network together with thiourea at 900 °C, denoted as CNFT-Co9 S8 -900. It is interesting to note that the introduction of a high concentration of sulfur does not lead to the complete toxicity of catalysts, but promotes the axial growth to selectively form straight CNTs instead of curly bamboo-like CNTs. The highly graphitized in-situ grown Co, N, S-doped CNTs and the 3-dimensional N-doped CNF network provide both active catalytic sites and highly conductive paths, which are beneficial for oxygen reduction reaction (ORR). Thus, the optimal CNFT-Co9 S8 -900 performs the excellent ORR catalytic activity with a half-wave potential of 0.84 V and a diffusion-limited current density of 5.49 mA cm-2 . Furthermore, the CNFT-Co9 S8 -900-based Zn-air devices also possess a high power density of 136.9 mW cm-2 better than commercial Pt/C.

N, S-codoped porous carbon as metal-free electrocatalyst for oxygen reduction reaction

Preparing low-cost and metal-free catalysts with outstanding catalytic activity and high stability to replace noble metal catalysts is the current development trend. Herein, a facile and low-cost two-step carbonization is proposed for the preparation of N, S-codoped oxygen reduction reaction (ORR) electrocatalysts, PP350KOH800-S, from the biomass waste pomelo peel by introducing KOH and thiourea as activator. The prepared electrocatalysts have the high specific surface area and the hierarchical porous structure and exhibit excellent ORR catalytic activity with the half-wave potential of 0.87 V and the limiting diffusion current density of −7.2 mA cm−2 in alkaline media. The excellent ORR electrocatalytic activity largely depends on the large specific surface area, the porous structure, the high degree of defects, and the synergistic effect of nitrogen and sulfur atoms. The present work provides a reliable method for the preparation of cheap and effective electrocatalysts using biomass waste.

Synthesis of N-doped Co@C/CNT materials based on ZIF-67 and their electrocatalytic performance for oxygen reduction

ZIF-67/CNT materials are prepared by using in situ growth method with cobalt nitrate and 2-methylimidazole (2-MI) as raw materials, polyvinyl pyrrolidone (PVP) as complexing agents. A series of N-Co@C/CNT catalysts are prepared through heating ZIF-67/CNT in N2 atmosphere. The effects of additional proportion of CNT on the catalytic performance of N-Co@C/CNT catalysts for oxygen reduction reaction (ORR) are studied. The chemical states of the materials, micro-morphology, elemental composition, and crystalline structure are analyzed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results show that polyhedral ZIF-67 has grown on the surfaces of CNTs. After heat treatment, ZIF-67/CNT transforms to N-Co@C/CNT. The particle size of Co is 10–20 nm. N-Co@C/CNT-2.6 shows the best catalytic performance for ORR in alkaline solution with the onset potential of 0.94 V, half-wave-potential of 0.83 V, and limiting diffusion current density of 5.6 mA cm−2. The ORR on N-Co@C/CNT proceeds through a four-electron path and the yield of H2O2 is 12%, which is close to Pt/C. N-Co@C/CNT shows higher methanol-tolerant ability than Pt/C. The addition of CNT makes N-Co@C expose more active sites. CNT plays an important role in connecting different N-Co@C particles and enhancing the electron conductivity. The contents of graphitic nitrogen and pyridine nitrogen in N-Co@C/CNT-2.6 catalysts are 15.8% and 38.6%, respectively, which are higher than those in N-Co@C (7% and 34%).

Fabrication of Porous N-rich Carbon Electrocatalysts from Pyrolysis of PANI-Encapsulated CeO2 for Enhanced Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a crucial cathodic process and a technology providing renewable energy. It is essential to create ORR catalysts not containing noble metals yet still affordable and possessing high-efficiency and long-term durability. Therefore, this work developed a highly porous N-doped carbon catalyst embedded with CeO2 nanoparticles (NPs). This composite catalyst was synthesized by pyrolysis of PANI-encapsulated CeO2 NPs (CeO2/PANI) combined with in situ polymerization. The resulting catalyst exhibited an outstanding ORR performance with 0.94 and 0.81 mV onset and positive half-wave potentials, respectively, and 5.52 mA cm−2 diffusion-limited current density. The catalyst also demonstrated excellent stability. These exceptional characteristics indicate that a synergy of the N-doped carbon and CeO2 NPs provide a novel strategy of fabrication of novel ORR catalysts without using noble-metals for applications related to fuel cells and metal-air batteries.