High-entropy alloys (HEAs) have been attracting extensive research interests in designing advanced nanomaterials, while their precise control is still in the infancy stage. Herein, we have reported a well-defined PtBiPbNiCo hexagonal nanoplates (HEA HPs) as high-performance electrocatalysts. Structure analysis decodes that the HEA HP is constructed with PtBiPb medium-entropy core and PtBiNiCo high-entropy shell. Significantly, the HEA HPs can reach the specific and mass activities of 27.2 mA cm À 2 and 7.1 A mg Pt À 1 for formic acid oxidation reaction (FAOR), being the record catalyst ever achieved in Pt-based catalysts, and can realize the membrane electrode assembly (MEA) power density (321.2 mW cm À 2 ) in fuel cell. Further experimental and theoretical analyses collectively evidence that the hexagonal intermetallic core/atomic layer shell structure and multi-element synergy greatly promote the direct dehydrogenation pathway of formic acid molecule and suppress the formation of CO*.
High-entropy alloys (HEAs) have been attracting extensive research interests in designing advanced nanomaterials, while their precise control is still in the infancy stage. Herein, we have reported a well-defined PtBiPbNiCo hexagonal nanoplates (HEA HPs) as high-performance electrocatalysts. Structure analysis decodes that the HEA HP is constructed with PtBiPb medium-entropy core and PtBiNiCo high-entropy shell. Significantly, the HEA HPs can reach the specific and mass activities of 27.2 mA cm À 2 and 7.1 A mg Pt À 1 for formic acid oxidation reaction (FAOR), being the record catalyst ever achieved in Pt-based catalysts, and can realize the membrane electrode assembly (MEA) power density (321.2 mW cm À 2 ) in fuel cell. Further experimental and theoretical analyses collectively evidence that the hexagonal intermetallic core/atomic layer shell structure and multi-element synergy greatly promote the direct dehydrogenation pathway of formic acid molecule and suppress the formation of CO*.
In this work, friction stir processing (FSP) was applied to the high-strength and high-melting-point Ni-Fe-based superalloy (HT700) for the first time with negligible wear of the stir tool. Different rotation rates were chosen to investigate the effect of heat input on microstructure and tensile properties at different temperatures of friction stir processed Ni-Fe-based superalloy. The results showed that with increasing rotation rate, the percentage of high-angle grain boundaries and twin boundaries gradually decreased whereas the grain size initially increased and then remained almost constant; the difference in tensile properties of FSP samples with rotation rates of 500-700 rpm was small attributing to their similar grain size, but the maximum strength was achieved in the FSP sample with a rotation rate of 400 rpm and traverse speed of 50 mm/min due to its finest grain size. More importantly, we found that the yield strength of all FSP samples tensioned at 700 °C was enhanced clearly resulting from the reprecipitation of γ′ phase. In addition, the grain refinement mechanism of HT700 alloy during FSP was proved to be continuous dynamic recrystallization and the specific refinement process was given.
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