One-pot synthesis of Pt-Cu bimetallic nanocrystals with different structures and their enhanced electrocatalytic properties

Shape-controlled synthesis of Pt-Cu alloy nanocrystals （NCs） with unique geometries is of great importance in the rational design and deterministic synthesis of highly active electrocatalysts. Herein, Pt-Cu alloy NCs with concave octahedron （COH）, porous octahedron （POH）, yolk-shell （YSH）, and nanoflower （NOF） structures were fabricated by altering the sequential reduction kinetics in a one-pot aqueous phase. The effect of the reaction kinetics on the formation of Pt-Cu bimetallic NCs with different morphologies was analyzed quantitatively. The concentrations of glycine and metal cation are demonstrated to play a key role in the reduction of Pt（Ⅳ） and Cu（Ⅱ） ions; these significantly affected the morphology of Pt-Cu NCs. These Pt-Cu alloy NCs exhibit substantially enhanced catalytic activity and durability for methanol and formic acid oxidation compared to the commercial Pt/C catalyst. Specifically, the COH and NOF Pt-Cu NCs with more step atoms, intragranular dislocations, and protrusions showed superior electrochemical properties than those of POH and YSH Pt-Cu NCs. The structure- property relationship between the Pt-Cu NCs and their electrochemical performances was also investigated in depth.

Defect-density control of platinum-based nanoframes with high-index facets for enhanced electrochemical properties

Structure-engineered platinum-based nanoframes(NFs)at the atomic level can effectively improve the catalytic performance for fuel cells and other heterogeneous catalytic fields.We report herein,a microwave-assisted wet-chemical method for the preparation of platinum-copper-cobalt NFs with tunable defect density and architecture,which exhibit enhanced activity and durability towards the electro-oxidation reactions of methanol(MOR)and formic acid(FAOR).By altering the reduction/capping agents and thus the nucleation/growth kinetics,trimetallic platinum-copper-cobalt hexapod NFs with different density high-index facets are achieved.Especially,the rough hexapod nanoframes(rh-NFs)exhibit excellent specific activities towards MOR and FAOR,7.25 and 5.20 times higher than those of benchmark Pt/C,respectively,along with prolonged durability.The excellent activities of the rh-NFs are assigned to a synergistic effect,including high density of defects and high-index facets,suitable d-band center,and open-framework structure.This synergistic working mechanism opens up a new way for enhancing their electrocatalytic performances by increasing defect density and high-index facets in open-framework platinum-based NFs.

A logic-based controller for the mitigation of ventilation air methane in a catalytic flow reversal reactor

The control system of a catalytic flow reversal reactor （CFRR） for the mitigation of ventilation air methane was investigated. A one-dimensional heteroge- neous model with a logic-based controller was applied to simulate the CFRR. The simulation results indicated that the controller developed in this work performs well under normal conditions. Air dilution and auxiliary methane injection are effective to avoid the catalyst overheating and reaction extinction caused by prolonged rich and lean feed conditions, respectively. In contrast, the reactor is prone to lose control by adjusting the switching time solely. Air dilution exhibits the effects of two contradictory aspects on the operation of CFRR, i.e., cooling the bed and accumulating heat, though the former is in general more prominent. Lowering the reference temperature for flow reversal can decrease the bed temperature and benefit stable operation under rich methane feed condition.

PtNiCu nanowires with advantageous lattice-plane boundary for enhanced ethanol electrooxidation

It is generally accepted that the interface effect and surface electronic structure of catalysts have vital impact on catalytic properties.Understanding and tailoring the atomic arrangement of interface structure are of great importance for electrocatalysis.Herein,we proposed a simple method to synthesize etching-PtNiCu nanowires(e-PtNiCu NWs)enclosed by both(110)and(100)facets evolving from PtNiCu nanowires(PtNiCu NWs)mainly with(111)facets by selectively etching process.After acetic acid etching treatment,the e-PtNiCu NWs possess high total proportions(88.3%)of(110)and(100)facets,whereas the(111)facet is dominant in PtNiCu NWs(64%)by qualitatively and quantitatively evaluation.Combining the structure characterizations and performance tests of ethanol electrooxidation reaction(EOR),we find that the e-PtNiCu NWs display remarkably performance for EOR,which is nearly 4.5 times and 1.5 times enhancement compared with the state-of-the-art Pt/C catalyst,as well as 2.2 and 1.4 times of PtNiCu NWs,in specific activity and mass activity,respectively.The improved performance of e-PtNiCu NWs is attributed to synergistic catalytic effect between(110)and(100)facets that not only significantly decreases the onset potentials of adsorbed CO(CO_(ads))but also favors the oxidation of CO_(ads)on the surface of catalyst.Furthermore,thermodynamics and kinetic studies indicate that the synergistic effect of both(110)and(100)facets in e-PtNiCu NWs can decrease the activation energy barrier and facilitate the charge transfer during the reaction.This work provides a promising approach to construct catalysts with tunable surface electronic structure towards efficient electrocatalysis.

Interfacial synergistic effect in SnO_(2)/PtNi nanocrystals enclosed by high-index facets for high-efficiency ethylene glycol electrooxidation

Strengthening the oxide-metal interfacial synergistic interaction in nanocatalysts is identified as potential strategy to boost intrinsic activities and the availability of active sites by regulating the surface/interface environment of catalysts.Herein,the SnO_(2)/PtNi concave nanocubes(CNCs)enclosed by high-index facets(HIFs)with tunable SnO_(2)composition are successfully fabricated through combining the hydrothermal and self-assembly method.The interfacial interaction between ultrafine SnO_(2)nanoparticles and PtNi with HIFs surface structure is characterized by analytical techniques.The as-prepared 0.20%SnO_(2)/PtNi catalyst exhibits extraordinarily high catalytic performance for ethylene glycol electrooxidation(EGOR)in acidic conditions with specific activity of 3.06 mA/cm^(2),which represents 6.2-fold enhancement compared with the state-of-the-art Pt/C catalyst.Additionally,the kinetic study demonstrates that the strong interfacial interaction between SnO_(2)and PtNi not only degrades the activation energy barrier during the process of EGOR but also enhances the CO-resistance ability and long-term stability.This study provides a novel perspective to construct highly efficient and stable electrocatalysts for energy conversions.