Fully ordered face-centered tetragonal (fct) FePt nanoparticles (NPs) are synthesized by thermal annealing of the MgO-coated dumbbell-like FePt-Fe3O4 NPs followed by acid washing to remove MgO. These fct-FePt NPs show strong ferromagnetism with room temperature coercivity reaching 33 kOe. They serve as a robust electrocatalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 and hydrogen evolution reaction (HER) in 0.5 M H2SO4 with much enhanced activity (the most active fct-structured alloy NP catalyst ever reported) and stability (no obvious Fe loss and NP degradation after 20 000 cycles between 0.6 and 1.0 V (vs RHE)). Our work demonstrates a reliable approach to FePt NPs with much improved fct-ordering and catalytic efficiency for ORR and HER.

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Controlling nanoparticle (NP) surface strain, i.e. compression (or stretch) of surface atoms, is an important approach to tune NP surface chemistry and to optimize NP catalysis for chemical reactions. Here we show that surface Pt strain in the core/shell FePt/Pt NPs with Pt in three atomic layers can be rationally tuned via core structural transition from cubic solid solution [denoted as face centered cubic (fcc)] structure to tetragonal intermetallic [denoted as face centered tetragonal (fct)] structure. The high activity observed from the fct-FePt/Pt NPs for oxygen reduction reaction (ORR) is due to the release of the overcompressed Pt strain by the fct-FePt as suggested by quantum mechanics−molecular mechanics (QM−MM) simulations. The Pt strain effect on ORR can be further optimized when Fe in FePt is partially replaced by Cu. As a result, the fct-FeCuPt/Pt NPs become the most efficient catalyst for ORR and are nearly 10 times more active in specific activity than the commercial Pt catalyst. This structure-induced surface strain control opens up a new path to tune and optimize NP catalysis for ORR and many other chemical reactions.

There is a need to reduce the use of noble metal elementsespecially in the field of catalysis, where noble metals are ubiquitously applied. To this end, perovskite oxides, an important class of mixed oxide, have been attracting increasing attention for decades as potential replacements. Benefiting from the extraordinary tunability of their compositions and structures, perovskite oxides can be rationally tailored and equipped with targeted physical and chemical propertiesfor example, redox behavior, oxygen mobility, and ionic conductivityfor enhanced catalysis. Recently, the development of highly efficient perovskite oxide catalysts has been extensively studied. This perspective article summarizes the recent development of lanthanum-based perovskite oxides as advanced catalysts for both energy conversion applications and traditional heterogeneous reactions.

Sub-10 nm nanoparticles (NPs) of M(II)-substituted magnetite MxFe3-xO4 (MxFe1-xO•Fe2O3) (M = Mn, Fe, Co, Cu) were synthesized and studied as electrocatalysts for oxygen reduction reaction (ORR) in 0.1 M KOH solution. Loaded on commercial carbon support, these MxFe3-xO4 NPs showed the M(II)-dependent ORR catalytic activities with MnxFe3-xO4 being the most active followed by CoxFe3-xO4, CuxFe3-xO4, and Fe3O4. The ORR activity of the MnxFe3-xO4 was further tuned by controlling x and MnFe2O4 NPs were found to be as efficient as the commercial Pt in catalyzing ORR. The MnFe2O4 NPs represent a new class of highly efficient non-Pt catalyst for ORR in alkaline media.

The oxygen reduction reaction (ORR) is an important cathode reaction used in fuel cells and metal-air batteries for renewable energy applications. [1][2][3] Platinum has been studied extensively as an essential catalytic component to reduce undesired overpotentials observed in the ORR. [4] Previous computational and experimental investigations have revealed that once alloyed with first-row transition metals, such as Fe, Co, and Ni, Pt alloy thin films and nanoparticles (NPs) can show dramatic activity enhancement in ORR catalysis, [5,6] especially when the Pt-skin structure is formed on the surface of MPt. [7] This enhancement is believed to originate from the downshift of the d-band center of Pt in the alloy structure; this downshift results in a decrease of the bonding strength between Pt and the oxygenated species (often called blocking species or spectators) and an increased number of available Pt sites for oxygen adsorption. [5] Recent experiments also indicate that elongated Pt nanostructures are less subject to dissolution, Ostwald ripening, and aggregation than the Pt NPs in acidic conditions, [8][9][10][11] and that they may be robust for catalyzing the ORR with high activity and durability.Herein, we report an advanced organic-phase synthesis of thin FePt and CoPt alloy nanowires (NWs) for enhanced catalysis of the ORR. Different from the previous approach to FePt NPs [12] and FePt NWs, [13] the current synthesis through decomposition of metal pentacarbonyl and reduction of platinum acetylacetonate, [Pt(acac) 2 ], was performed in sodium oleate solution of 1-octadecene (ODE) and oleylamine (OAm). Depending on the metal carbonyl used, FePt or CoPt NWs were obtained at a high synthetic yield and with the desired control over alloy composition. Electrochemical studies showed that these NWs were active catalysts for the ORR. The specific activity and the mass activity of the 2.5 nm wide FePt NWs reached 1.53 mA cm À2 and 844 mA mg À1 Pt at 0.9 V (vs. reversible hydrogen electrode, RHE; 0.2 mA cm À2 and 110 mA mg À1 Pt at 0.95 V), while those of the benchmark Pt catalyst reached 0.32 mA cm À2 and 155 mA mg À1 Pt at 0.9 V (0.080 mA cm À2 and 35 mA mg À1 Pt at 0.95 V). The annealed 6.3 nm wide FePt NWs showed an even higher specific activity of 3.9 mA cm À2 at 0.9 V and 0.46 mA cm À2 at 0.95 V.

To further enhance the catalytic activity and durability of nanocatalysts for the oxygen reduction reaction (ORR), we synthesized a new class of 20 nm × 2 nm ternary alloy FePtM (M = Cu, Ni) nanorods (NRs) with controlled compositions. Supported on carbon support and treated with acetic acid as well as electrochemical etching, these FePtM NRs were converted into core/shell FePtM/Pt NRs. These core/shell NRs, especially FePtCu/Pt NRs, exhibited much improved ORR activity and durability. The Fe10Pt75Cu15 NRs showed a mass current densities of 1.034 A/mgPt at 512 mV vs Ag/AgCl and 0.222 A/mgPt at 557 mV vs Ag/AgCl, which are much higher than those for a commercial Pt catalyst (0.138 and 0.035 A/mgPt, respectively). Our controlled synthesis provides a general approach to core/shell NRs with enhanced catalysis for the ORR or other chemical reactions.

Using FePtAu nanoparticles (NPs) as an example, this Communication demonstrates a new structure-control strategy to tune and optimize NP catalysis. The presence of Au in FePtAu facilitates FePt structure transformation from chemically disordered face-centered cubic (fcc) structure to chemically ordered face-centered tetragonal (fct) structure, and further promotes formic acid oxidation reaction (FAOR). The fct-FePtAu NPs have mass activity as high as 2809.9 mA/mg Pt and retain 92.5% of this activity after a 13 h stability test. They become the most efficient NP catalyst ever reported for FAOR. This structure-control strategy can be extended to other multimetallic NP systems, providing a general approach to advanced NP catalysts with desired activity and durability control for practical applications.