Facile preparation of hierarchical Ni@Mn-doped NiO hybrids for efficient and durable oxygen evolution reaction

Exploring highly efficient and non-noble-metal-based electrocatalysts for oxygen evolution reaction(OER)is of great importance not only for water splitting but also for rechargeable metal-air batteries and fuel cells.Herein,we describe a simple strategy to prepare hierarchical Ni@Mn-doped Ni O hybrids using flower-like Ni-Mn layered double hydroxides(Ni Mn-LDHs)as a precursor.After calcination at 400℃for an hour under N_(2)atmosphere,the flower-like Ni Mn-LDHs transform to porous microspheres consisting of nanoparticles,in which Ni cores are encapsulated by Mn-doped NiO shells(denoted as Ni@MnNi O-400).Benefiting to this unique porous,core-shell structures and element doping,the as-prepared Ni@Mn-NiO-400 hybrid shows a low overpotential of 178 mV at the current density of 10 mA/cm^(2)and Tafel slope of 52.7 m V/dec in 1 mol/L KOH solution.More significantly,the Ni@Mn-Ni O-400 hybrid also demonstrates superior stability of 98.6%after 50 h continuously testing,much higher than pristine Ni MnLDHs and commercial IrO_(2)catalyst.In addition,theoretical simulation shows that Ni core and Mn doping greatly affect the electronic states and electronic structure of Ni O.As a result,Ni@Mn-doped Ni O hybrid possesses an optimal adsorption activity towards oxygen species than Ni O and undoped Ni@Ni O hybrid.Considering the compositional and structural flexibility of LDHs,this work may offer a simple method to prepare other non-noble metal-based electrocatalysts for OER.

Facile synthesis of hollow Ti_(3)AlC_(2)microrods in molten salts via Kirkendall effect

The microstructure and morphology of Ti_(3)AlC_(2)powders not only affect the preparation of Ti_(3)C_(2) MXene but also have a great influence on their potential applications,such as microwave absorbers,alloy additives,or catalytic supports.However,the synthesis of Ti_(3)AlC_(2)powders with desired microstructure and morphology remains a challenge.Herein,hollow Ti_(3)AlC_(2)microrods were prepared for the first time in NaCl/KCl molten salts by using titanium,aluminum,and short carbon fibers as starting materials.It was found that the short carbon fibers not only performed as carbon source but also acted as sacrificial template.Furthermore,it was revealed that TiC and Ti2AlC were initially formed on the surface of carbon fibers.The subsequent reactions between the outer Ti,Al and the inner carbon were dominated by the Kirkendall effect which gave rise to the formation of a hollow structure.Based on this mechanism,hollow Ti_(3)AlC_(2)microspheres and a series of hollow TiC,Ti_(2)AlC,and V_(2)AlC powders were also successfully fabricated.This work provides a facile route to synthesize hollow MAX phases and may give enlightenment on preparing other hollow carbide powders via the Kirkendall effect in the molten salts.