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We report a rational method for preparation of ternary alloy (PtNiFe) nanocrystals with various shapes. PtNiFe nanocubes, polyhedrons, and octahedrons are prepared via fine-tuning the alloy compositions and surfactants, so that the crystal facet−surfactant bindings on the growth seed can be well controlled. Nanowires grow in the cylindrical template built via high concentrations of oleylamine. In the electrocatalysis examination, it appears that the oxygen reduction reaction (ORR) activities of all PtNiFe nanostructures outperform that of commercial Pt catalyst in the electrolyte of HClO 4 or H 2 SO 4 . In HClO 4 , the order of ORR activity is as follows: octahedrons ≈ nanowires > polyhedrons > nanocubes. PtNiFe nanostructures enclosed by a (111) plane, such as octahedrons and nanowires, give the highest ORR activities. Conversely, in H 2 SO 4 , the ORR activity of PtNiFe nanocubes enclosed by {100} facets is the highest among these nanostructures. The ORR activity increases in the order of nanowires ≈ octahedrons < polyhedrons, establishing a shape dependency in the ORR activity, which is valuable upon performing nanocatalysis in fuel cells.

Electrochemical reduction of CO2 to useful chemicals has been actively pursued for closing the carbon cycle and preventing further deterioration of the environment/climate. Since CO2 reduction reaction (CO2RR) at a cathode is always paired with the oxygen evolution reaction (OER) at an anode, the overall efficiency of electrical energy to chemical fuel conversion must consider the large energy barrier and sluggish kinetics of OER, especially in widely used electrolytes, such as the pH-neutral CO2-saturated 0.5 M KHCO3. OER in such electrolytes mostly relies on noble metal (Ir- and Ru-based) electrocatalysts in the anode. Here, we discover that by anodizing a metallic Ni–Fe composite foam under a harsh condition (in a low-concentration 0.1 M KHCO3 solution at 85 °C under a high-current ∼250 mA/cm2), OER on the NiFe foam is accompanied by anodic etching, and the surface layer evolves into a nickel–iron hydroxide carbonate (NiFe-HC) material composed of porous, poorly crystalline flakes of flower-like NiFe layer-double hydroxide (LDH) intercalated with carbonate anions. The resulting NiFe-HC electrode in CO2-saturated 0.5 M KHCO3 exhibited OER activity superior to IrO2, with an overpotential of 450 and 590 mV to reach 10 and 250 mA/cm2, respectively, and high stability for >120 h without decay. We paired NiFe-HC with a CO2RR catalyst of cobalt phthalocyanine/carbon nanotube (CoPc/CNT) in a CO2 electrolyzer, achieving selective cathodic conversion of CO2 to CO with >97% Faradaic efficiency and simultaneous anodic water oxidation to O2. The device showed a low cell voltage of 2.13 V and high electricity-to-chemical fuel efficiency of 59% at a current density of 10 mA/cm2.