Good Oxygen Reduction Reaction Research Articles

Heterojunction of MXenes and MN4–graphene: Machine learning to accelerate the design of bifunctional oxygen electrocatalysts

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for the development of excellent bifunctional electrocatalysts, which are key functions in clean energy production. The emphasis of this study lies in the rapid design and investigation of 153 MN4–graphene (Gra)/ MXene (M2NO) electrocatalysts for ORR/OER catalytic activity using machine learning (ML) and density functional theory (DFT). The DFT results indicated that CoN4–Gra/Ti2NO had both good ORR (0.37 V) and OER (0.30 V) overpotentials, while TiN4–Gra/M2NO and MN4–Gra/Cr2NO had high overpotentials. Our research further indicated orbital spin polarization and d-band centers far from the Fermi energy level, affecting the adsorption energy of oxygen-containing intermediates and thus reducing the catalytic activity. The ML results showed that the gradient boosting regression (GBR) model successfully predicted the overpotentials of the monofunctional catalysts RhN4–Gra/Ti2NO (ORR, 0.39 V) and RuN4–Gra/W2NO (OER, 0.45 V) as well as the overpotentials of the bifunctional catalyst RuN4–Gra/W2NO (ORR, 0.39 V; OER, 0.45 V). The symbolic regression (SR) algorithm was used to construct the overpotential descriptors without environmental variable features to accelerate the catalyst screening and shorten the trial-and-error costs from the source, providing a reliable theoretical basis for the experimental synthesis of MXene heterostructures.

Fe-doped N/S-rich carbon catalyst derived from porphyrine-ferrocene conjugated microporous polymer for bifunctional electrocatalysis and zinc-air batteries

Facile fabrication of non-noble electrocatalysis with precisely tunned active centers for oxygen reduction reaction (ORR) and zinc–air batteries (ZABs) are intriguing yet still challenging. Herein, an iron porphyrin-ferrocene conjugated microporous polymer (FeCMP) with isolated Fe centers was used as precursor to fabricate Fe-Nx electrocatalyst. Innovatively, NaSCN as both an active site protectant and a heteroatomic dopant was introduced. Subsequent carbonization at 800℃ for FeCMP mixed with NaSCN resulted in the formation of highly isolated Fe with S- and N-doped porous carbon (FeSNC800), which acts as a bifunctional catalyst with good ORR (E1/2 = 0.88 V) and OER (oxygen evolution reaction, η10 = 0.34 V) performance. The assembled Zinc-air battery possesses 118 mW cm−2 of power density and is stable over 300 cycles. This work highlights the strength of rational designed polymer precursor and heteroatom doping in controlled pyrolysis of platinum group-free electrocatalysts.

Elucidating the role of interface of Cu-Co hybrid metal oxide for oxygen reduction reaction in Zn-air batteries

Energy security and sustainable energy are becoming more crucial in the current situation. As a result, fuel cells and metal-air batteries have recently received a lot of interest. However, these devices' main drawbacks are the slowness of the oxygen reduction reaction (ORR) and the expense of the catalyst. The necessity for high-performance noble-metal-free electrocatalysts is therefore urgent. This paper describes a CuOx-Co3O4-based heterostructure with nitrogen-doped carbon support (Cu/CuOx-Co3O4/NC-700) as an effective, durable, inexpensive ORR catalyst. The catalyst exhibits good ORR activity with a half-wave potential of 0.81 V vs. RHE with a 6.5 mA cm−2 limiting current density. The observed ORR performances are comparable with benchmark Pt/C catalysts. The Zn-air battery (ZAB), utilizing the synthesized Cu/CuOx-Co3O4/NC-700 catalyst, produces a high open circuit voltage (OCV) of 1.41 V. The catalyst also exhibits a superior specific capacity of 820 mAh gZn−1 and a higher peak power density of 103 mW cm−2. Cu/CuOx-Co3O4 and NC have a strong synergistic impact and are responsible for the enhanced ORR activity. Hence, Cu/CuOx-Co3O4 heterostructures introduced oxygen vacancies, high surface area, desirable charge transfer, and unsaturated chemical bonds in the interface to create a charge redistribution. As a result, the catalytic activity has improved significantly.

First-principle calculations study of oxygen reduction electrocatalyst: Single transition metal supported on a brand-new graphitic carbon nitride (g-C7N3) substrate

Single-atom catalysts (SACs) possess promising potential as materials to catalyze oxygen reduction reaction (ORR) on account of high atomic utilization efficiency, tunable electronic structure, and exceptional catalytic performance. The ORR activities of graphite carbonitride (g-C7N3) supported 3d, 4d, and 5d transition metals are investigated. Eleven kinds of TM-C7N3 structures have been found to have good stability by computing formation energy and dissolution potential. Furthermore, density of states analysis shows a strong interaction of the metal atom and the coordination N atoms, which gives satisfactory stability of TM-C7N3. Among eleven TM-C7N3, the binding energy of reaction species on Rh-C7N3, Ni-C7N3, and Pt-C7N3 are closer to those of Pt(111), showing that they have good ORR activity. In addition, good linear relationships exist between the adsorption free energy of *OH (∆G*OH) and that of *OOH and *O, implying that ∆G*OH can be put forward as a trustworthy activity descriptor. Promisingly, the ηORR values of Rh-C7N3, Ni-C7N3, and Pt-C7N3 are 0.32, 0.38, and 0.44 V, respectively, even lower than the overpotential value of Pt(111). This suggests that these three catalysts demonstrate superior catalytic activity compared to Pt(111).

Mechanistic study of Eu single atoms occupying four vacancy centers as potential electrocatalysts for the oxygen reduction reaction.

The oxygen reduction reaction (ORR) on the oxygen electrode plays a critical role in rechargeable metal-air batteries, and the development of electrochemical energy storage and conversion technologies for the ORR is of great significance. In this study, the catalytic performance of rare earth-doped graphene (EuNxC6-x-Gra) as an electrocatalyst for the ORR was investigated. The results showed that a majority of the catalysts exhibited good ORR catalytic activity under acidic conditions, with some approaching or even surpassing commercial Pt-based catalysts (ηORR = 0.45 V). Particularly, EuN2C4-2-Gra demonstrated an ηORR of 0.38 V. It has been observed that the f-band center of Eu atoms increases with an increasing number of N atoms, and the charge distribution exhibits a "U" shape. There is a decreasing trend from N0 to N3 and an increasing trend from N4 to N6. By incorporating the proportional relationship of the adsorption free energies of reaction intermediates (ΔG*ads), a volcano diagram was constructed to rapidly assess catalytic activity. Finally, an intrinsic characteristic descriptor φ was formulated to quantitatively describe the relationship between φ and ηORR, providing a new tool for predicting and designing catalysts. This will provide guidance for the development and design of high-performance rare earth single atom catalysts.

Engineering Electronic Structure of Nitrogen‐Carbon Sites by sp3‐Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity

AbstractDevelopment of efficient and easy‐to‐prepare low‐cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn‐air batteries (ZABs). Herein, we mixed NaCl and ZIF‐8 by simple physical milling and pyrolysis to obtain a metal‐free porous electrocatalyst doped with Cl (mf‐pClNC). The mf‐pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2=0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon‐based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf‐pClNC electrocatalyst also shows state‐of‐the‐art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3‐hybridized carbon, while the sp3‐hybridized carbon and Cl together modify the electronic structure of the N‐adjacent carbons, as the active sites, while NaCl molten‐salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf‐pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm−2. Flexible quasi‐solid‐state rechargeable ZAB constructed with the mf‐pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Engineering Electronic Structure of Nitrogen-Carbon Sites by sp3 -Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity.

Development of efficient and easy-to-prepare low-cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn-air batteries (ZABs). Herein, we mixed NaCl and ZIF-8 by simple physical milling and pyrolysis to obtain a metal-free porous electrocatalyst doped with Cl (mf-pClNC). The mf-pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2 =0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon-based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf-pClNC electrocatalyst also shows state-of-the-art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3 -hybridized carbon, while the sp3 -hybridized carbon and Cl together modify the electronic structure of the N-adjacent carbons, as the active sites, while NaCl molten-salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf-pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm-2 . Flexible quasi-solid-state rechargeable ZAB constructed with the mf-pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Hybrids Composed of an Fe-Containing Wells–Dawson Polyoxometalate and Carbon Nanomaterials as Promising Electrocatalysts for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a key cathodic reaction in energy-converting systems, such as fuel cells (FCs). Thus, it is of utmost importance to develop cost-effective and efficient electrocatalysts (ECs) without noble metals to substitute the Pt-based ones. This study focuses on polyoxometalate (POM)-based ECs for ORR applications. A Wells–Dawson POM salt K7 [P2W17(FeOH2)O61].·20H2O was immobilised onto graphene flakes and multiwalled carbon nanotubes doped with nitrogen, denominated as P2W17Fe@GF_N8 and P2W17Fe@MWCNT_N8. The successful preparation of the composites was proved with various characterisation techniques, including FTIR, XPS and SEM. Both materials showed good ORR performance in an alkaline medium with similar potential onset values of ~0.84 V vs. RHE and diffusion-limiting current densities of −3.9 and −3.3 mA cm−2 for P2W17Fe@MWCNT_N8 and P2W17Fe@GF_N8, respectively. Furthermore, both composites presented low Tafel slopes (48–58 mV dec−1). Chronoamperometric tests revealed that the as-prepared nanocomposites rendered a significant improvement achieving between 90 and 94% of current retention in tolerance to methanol in comparison with Pt/C, and moderate to good long-term electrochemical stability with current retentions comprised between 68 and 88%. This work reinforces the use of POMs as important electroactive species for the preparation of alternative ORR electrocatalysts, exhibiting good activity, stability and selectivity towards the ORR in the presence of methanol.

Modulating metal-support interaction between Pt3Ni and unsaturated WOx to selectively regulate the ORR performance

Tuning strong metal-support interaction between Pt-based alloys and metal oxides is an effective strategy for modulating the performance of oxygen reduction reaction (ORR). Herein, Pt3Ni alloy anchored on WOx with different content of oxygen vacancies is synthesized, and the effect of unsaturated WOx on ORR activity/stability is revealed. Electrochemical results indicate that ORR activity is positively correlated with oxygen vacancy concentration, while durability presents the opposite trend. Density functional theory (DFT) calculation results suggest that controlling the content of oxygen vacancies can usefully adjust the charge redistribution between Pt3Ni and WOx, which can optimize the adsorption/activation of reactants, thus obtaining good ORR activity. This study uncovers the effect of unsaturated WOx on ORR performance for Pt-based alloys and provides a promising strategy to design efficient and stable ORR catalysts.

Dual-metal M-N-C (M = Mn, Co) as an effective oxygen electrocatalyst for zinc-air battery

Developing high-active and low-cost non-noble metal electrocatalysts is an efficient strategy for design of advanced rechargeable Zn-air battery (ZAB). Herein, an oxygen electrocatalyst of Prussian-blue-analogues derived MnCo dual-metal M-N-C (PBA-MnCo-N-C) is prepared using a carbonization method. The electrochemical tests show that, it owns good oxygen reduction reaction (ORR) performances with the onset potential of 0.966 V and half-wave potential of 0.859 V, almost approaching that of Pt/C catalysts. Simultaneously, a good oxygen evolution reaction (OER) activity is also obtained, with a potential of 1.844 V at 10 mA cm−2. In the practical application, as-assembled ZAB with PBA-MnCo-N-C exhibits high open circuit potential (1.48 V) and peak power density (102.25 mW cm−2), and after continuous discharge and charge for more than 160 h, the PBA-MnCo-N-C based ZAB manifests a favorable charge-discharge stability. This work provides a good reference of constructing bimetallic catalyst for high-efficiency oxygen electrocatalysis.

Nitrogen‐Enriched Porous Carbon Materials from Expanded Polystyrene Waste for Oxygen Reduction Reaction and Rechargeable Zinc–Air Battery

Transforming discardable solid waste like polystyrene (PS) foams into commercially useful applications like sustainable and eco‐friendly energy materials has attracted considerable attention. Herein, expanded PS waste is subjected to simple reactions (cross‐linking and pyrolysis) to obtain a high‐performing electrocatalyst for the oxygen reduction reaction (ORR). The optimized catalyst polystyrene‐pyrrole (PSP‐800) demonstrates good electrocatalytic ORR activity toward rechargeable zinc–air battery due to its high surface area, copious amount of micropores/mesopores, high nitrogen content, and a trace amount of Fe doping. Accordingly, PSP‐800 delivers a high onset potential (0.99 V) and a half‐wave potential of 0.88 V versus a reversible hydrogen electrode. Moreover, the rechargeable zinc–air battery using PSP‐800 as an ORR catalyst demonstrates improved stability and high‐power density (116 mW cm−2) compared to the standard Pt/C catalyst.

Metalloporphyrin doped rice husk-based biomass porous carbon materials as high performance electrocatalyst for oxygen reduction reaction in Zn-Air battery

Rice husk (RH) is one of the most abundant biomass having a unique natural structure. Herein, the highly porous rice husk carbon material (RHC) has been prepared. After loading metal (Fe, Co, Mn, Cu) complex of tetra-phenylporphyrin (TPP) and the followed calcination, a new kind of metal-nitrogen-carbon (M-N-C) electrocatalyst (MTPP/RHC) for the oxygen reduction reaction (ORR) was obtained. It was found that all prepared catalysts showed good ORR performance and the activity follows an order of Fe > Co > Mn > Cu catalyst. The best FeTPP/RHC catalyst exhibited an ORR activity with a half-wave potential of 0.88 V (Eonset = 0.96 V) and excellent long-term stability (97% retention after 30000s). In the constructed zinc-air battery, it even showed a higher specific capacity (766 mAh/g) and superior reversibility than commercial Pt/C catalysts. This work provides a new practical protocol for ORR electrocatalysts.

Enhanced oxygen reduction reaction activity and electrochemical performance of A-site deficient (La0.6Sr0.4)1-xFe0.8Ni0.2O3−δ cathode for solid oxide fuel cells

In this work, (La0.6Sr0.4)0.9Fe0.8Ni0.2O3-δ (LSFN90), a stable, highly ORR-active and cost-efficient perovskite oxide, is developed as cathode materials for solid oxide fuel cell (SOFC). The introduction of A-site deficiency results in the crystal expansion of the cubic perovskite phase and an increase in oxygen vacancy concentration at operating temperature. The LSFN90 cathode displays good oxygen reduction reaction activity and low polarization resistance values. The A-site deficiency facilitates the diffusion of oxygen ions in the electrode and accelerates the surface oxygen exchange reaction. LSFN90 is used as cathode materials for SOFC to prepare anode-supported single cells, achieving maximum power densities of 1.51, 1.27, 0.95 and 0.63 W cm−2 under wet hydrogen (3%H2O–97%H2) atmosphere at 850, 800, 750 and 700 °C, respectively. The introduction of A-site deficiency can greatly enhance the oxygen reduction reaction activity and electrochemical performance of the cathode, demonstrating that LSFN90 has significant potential as a cathode material for practical applications in solid oxide fuel cells.

The Role of Oxygen Reduction Reaction in Determining Pit Stability of FeCr Alloys

Pitting corrosion is one of the most dangerous forms of corrosion, leading to sudden catastrophic failures in engineering system. Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film. Here the ORR kinetics on conventional and high Cr content FeCr alloys made by arc-melter were investigated by experimental and computational methods. DFT calculations suggested that the overpotentials for the ORR on FeCr oxides are in the order Cr2O3 > Fe3O4 > Fe2O3 > FeCr2O4, which was experimentally confirmed on the FeCr alloys by rotating disc electrode experiments in both O2 saturated 0.1 M NaOH and 3.5 wt% NaCl. Koutecký-Levich analysis demonstrated that ORR follows a 4-electron pathway on all surfaces investigated. Moreover, the investigation of the Pourbaix diagrams of FeCr revealed that at potentials where pitting corrosion initiates the main constituents of the passive films should be a mixture of Fe2O3 and Cr2O3, rather than FeCr2O4, which is proved to be a good ORR catalyst. The results support the postulation that one role Cr additions play in the prevention of pitting corrosion is to suppress the ORR reaction.

Facile preparation and properties of high nitrogen-containing Fe/Co/N co-doped three-dimensional graphene bifunctional oxygen catalysts for zinc air battery

Fe/Co/N co-doped multi-channel interpenetrating three-dimensional graphene catalyst (FeCo–N-3D-HG) with good oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic performances is prepared by a facile method, using poly (2,5-benzimidazole) (ABPBI), iron salt, cobalt salt and nanometer CaCO3 (template). ABPBI forms a complex with iron and cobalt ions and the complex is coated on the surface of CaCO3. The pyrolysis process is carried out in an Ar gas protection, the template is removed by acid to obtain FeCo–N-3D-HG. The results show that FeCo–N-3D-HG is three-dimensional multi-layered graphene structure with multi-channels. The catalytic performance of ORR (E1/2 = 0.860 V vs RHE) is better than 20 wt% Pt/C in O2 saturated 0.1 M KOH electrolyte. The catalyst also shows similar OER performance with the RuO2 in 1 M KOH solution. The prepared zinc-air battery exhibits outstanding peak power density (261.7 mW cm−2), preeminent specific capacity (760.1 mAh g−1), and good cycle durability (150 h).

One−Step Synthesis of a Non−Precious−Metal Tris (Fe/N/F)−Doped Carbon Catalyst for Oxygen Reduction Reactions

Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (21P2-Fe1-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl3 as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst's oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials.

Highly Active Porous Carbon-Supported CoNi Bimetallic Catalysts for Four-Electron Reduction of Oxygen

Great interest has been taken in oxygen reduction reaction (ORR), as a common cathode reaction in new energy sources such as fuel cells and metal–air batteries, to improve the current energy structure and develop new green energy sources. Noble metal Pt is still considered the best catalyst for this reaction. However, its disadvantages such as high cost, low selectivity, poor stability, and susceptibility to impurity poisoning severely limit its further industrial applications. Therefore, development of efficient and low-cost ORR reduction catalysts is particularly critical. M-Nx-C materials have been extensively studied to achieve a high ORR activity close to that of Pt catalysts. In this study, CoNi bimetallic alloy carbon-based oxygen reduction catalysts named CoNi-950 (Zn) were successfully synthesized, using a metal–organic framework (MOF) as a carbon precursor and a nitrogen source. The experimental results show that CoNi-950 (Zn) exhibits good ORR catalytic performance with an ultimate current density of 6.27 mA cm–2, which even exceeds that of some Pt/C catalysts with a mass loading of 20 wt % (5.92 mA cm–2). In addition, the active site of the catalyst was also identified by acid leaching and SCN– poisoning experiments, showing two sites in the form of CoNi-Nx and the CoNi alloy or its oxides in the material. Further experiments demonstrate that these two active sites have distinct ORR catalytic mechanisms, generating positive synergism in ORR. A mechanism in which O2 was catalytically reduced by CoNi-950 (Zn) in a four-electron transfer, i.e., a continuous two-step dual-electron transfer reduction process in alkaline electrolytes, is proposed.

Supercilious Enhancement in Oxygen-Reduction Catalytic Functionalities of Cubic Perovskite Structured LaFeO3 by Co-Doping of Gd and Ce for LT-SOFCs

Low-temperature solid fuel cells (LT-SOFCs) hold remarkable promise for the cooperative corporation of small- and large-scale applications. However, the meager oxygen-reduction retort of cathode materials mires the low operating temperature conditions of SOFCs. Herein, we have developed a perovskite structured LaFeO3 by the co-doping of Gd and Ce ions, and their electrochemical properties have been studied. The developed LaFe0.8Gd0.1Ce0.1O3-δ cathode exhibits very small-area-specific-resistance and good oxygen-reduction reaction (ORR) activity at low operating temperatures of 450–500 °C. We have demonstrated a high-power density of 0.419 W-cm−2 with a LaFe0.8Gd0.1Ce0.1O3-δ cathode operating at 550 °C with H2 and atmospheric air as fuels. Moreover, LaFe0.8Gd0.1Ce0.1O3-δ exhibits high activation energy as compared to individual LaFeO3, which helps to promote ORR activity. Various spectroscopic measurements such as X-ray diffraction, SEM, EIS, UV-visible, TGA, Ramana, and photoelectron spectroscopy were employed to understand the improved ORR electrocatalytic activity of Gd and Ce co-doped LaFeO3 cathode. The results can further help to develop functional cobalt-free electro-catalysts for LT-SOFCs.

F-doped LiNi0.8Co0.15Al0.05O2-δ cathodes with enhanced ORR catalytic activity for LT-SOFCs

Developing highly effective catalysts for oxygen reduction reaction (ORR) is crucial to enable the low-temperature operation of solid oxide fuel cells (SOFCs). Recent studies have proposed a promising O2-/H+/e- conducting oxide, LiNi0.8Co0.15Al0.05O2-δ (LNCA) with good ORR catalytic activity for SOFC cathode uses. Herein, to further optimize the cathode functionality of LNCA, a fluorine anion (F-) doping strategy is applied to develop highly active LNCAF0.1 and LNCAF0.2 cathodes for Sm-doped ceria (SDC) electrolyte-based SOFCs. It is found the successful doping of F- in the oxygen site of LNCA leads to improved oxygen ionic conductivity and facilitated surface exchange and bulk diffusion of oxygen in LNCAF0.1 and LNCAF0.2, which thus gain distinctly promoted ORR catalytic activity at 450–550 °C, as confirmed by the decreased area specific resistances (ASR) and activation energy on symmetrical cells. The as-fabricated two SDC-based SOFCs with LNCAF0.1 and LNCAF0.2 cathodes exhibit peak power densities of 497 and 591 mW cm-2 at 550 °C, respectively, which are higher than that of the cell with LNCA cathode. Furthermore, the single cell with the best-performing LNCAF0.2 cathode demonstrates a good stability for 110 h at 550 °C. The present study thus provides a feasible strategy of F anion doping to promote the ORR catalytic activity of LNCA cathode for developing low-temperature SOFCs.

Ultra-Small Nanoparticles of Pd-Pt-Ni Alloy Octahedra with High Lattice Strain for Efficient Oxygen Reduction Reaction

The design and synthesis of ultra-small-sized Pt-based catalyst with specific effects for enhancing the oxygen reduction reaction (ORR) is an effective way to improve the utilization of Pt. Herein, Pt-Pd-Ni octahedra nanoparticles characterized by the ultra-small size of 4.71 nm were synthesized by a Pd seed-inducing-growth route. Initially, Pd nanocubes were synthesized under solvothermal conditions; subsequently, Pt-Ni was deposited in the Pd seed solution. The Pd seeds were oxidized into Pd2+ and combined with Pt2+ and Ni2+ in the solution and finally formed the ternary alloy small-sized octahedra. In the synthesis process of the ultra-small Pt-Pd-Ni octahedra, Pd nanocube seed played an important role. In addition, the size of the Pt-Pd-Ni octahedra could be regulated by adjusting the concentration rate of Pt-Ni. The ultra-small Pt-Pd-Ni octahedra formation by depositing Pt-Ni with a feeding ratio of 2:1 showed good ORR activity, and the high half-wave potential was 0.933 V. In addition, the Pt-Pd-Ni octahedra showed an enhanced mass activity of 0.93 A mg−1 Pt+Pd in ORR, which was 5.81 times higher than commercial Pt/C. The theoretical calculation shows that compared to Pt/C, the small-sized ternary alloy octahedra had an obvious contraction strain effect (contraction rate: 3.49%). The alloying effect affected the d-band center of the Pt negative shift. In the four-electron reaction, Pt-Pd-Ni ultra-small octahedra exhibited the lowest overpotential, resulting in the adsorption performance to become optimized. Therefore, the Pd seed-inducing-growth route provides a new idea for exploring the synthesis of small-sized nanoparticle catalysts.