Efficient Electrocatalytic Water Oxidation by Using Amorphous Ni–Co Double Hydroxides Nanocages

Abstract

properties, e.g., mechanics and catalysis.[ 10 ] Particularly, a small but growing number of micro-and nanoscale noncrystalline materials are steadily capturing scientifi c attention, though only recently the well-characterized examples of amorphous nanomaterials have started to appear. [ 11 ] Owing to enhanced ionic conductivity as well as robust electrochemical and mechanical stability, [ 12 ] these amorphous nanomaterials have showed remarkable performance in electrochemical applications, e.g., Li-ion batteries, pseudo-capacitors, water oxidation, and sensors. [ 11b-f ] Nevertheless, it still remains as signifi cant challenges to develop the simple methods with broad applicability for synthesis of amorphous nanomaterials and study the relation between the amorphous structures and their properties.In this work, we explore, for the fi rst time to our knowledge, the feasibility of the amorphous hollow nanomaterials for effi cient electrochemical water oxidation. A unique template-engaged approach was employed here for fabrication of amorphous hollow nanomaterials. Ni-Co amorphous double hydroxides (ADHs) nanocages are chosen to demonstrate this feasibility, in view of the limited success in synthesizing cagelike structure of these materials, and emerging application of the hydroxides in water oxidation. [ 2h-j ] Furthermore, the relation between the compositions of amorphous catalysts and their OER activity is studied via both the experimental investigation and computational simulation.A two-step process was developed to synthesize the Ni-Co ADHs nanocages with well-defi ned shapes and structures. Cu 2 O nanocrystals, as the templates, were fi rst obtained via a facile wet-chemical route ( Figure S1, Supporting Information). Ni-Co ADHs nanocages were then synthesized by templating against these Cu 2 O nanocrystals at room temperature, as illustrated in Figure 1 . Briefl y, as-synthesized Cu 2 O nanocrystals are gradually removed by forming a soluble [Cu 2 (S 2 O 3 ) x ] 2−2 x complex when reacting continuously with Na 2 S 2 O 3 via a "coordinating etching" process in the synthesis solution, and then abundant amount of OH − ions are released at the etching interface. [ 11a,b ] Simultaneously, Ni 2+ and Co 2+ species can coprecipitate with these OH − ions at the etching interface to generate Ni-Co ADHs by perfectly inheriting the geometries of Cu 2 O templates and presenting cage-like nanostructures. Herein the impact of Na 2 S 2 O 3 on the precipitation of Ni 2+ and Co 2+ ions can be negligible since the interaction between Ni 2+ (Co 2+ ) ions (borderline acid) and S 2 O 3 2− ions (soft base) is not very strong on the basis of Pearson's hard and softacid-base principle. [ 11a ] The size, morphology, and structure of typical resulting nanomaterials were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM image ( Figure 2 a) shows that the products are exclusively high-quality nanocages, which inherit the geometrics The electrochemical water splitting into hydroge...

Recent Progress on Multimetal Oxide Catalysts for the Oxygen Evolution Reaction

“…Reproduced with permission. [141] Copyright 2015, Wiley-VCH. d) Synthesis process of ECT-TMOs and SEM images of each step.…”

“…Moreover, some studies have reported that the amorphous phase has advantages in terms of mechanical and electrochemical stability as the disordered structure offers structural stability. [140,141] Various amorphous single metal oxides with high efficiency (e.g., Co, [12,142] Ru, [143] Ni, [144,145] Ir, [146,147] and Mn [148,149] ) have been developed and have outperformed their crystalline counterparts. Considering the good performance of multimetal oxides in crystalline catalysts, the benefits of mixing two or more metals are also expected in amorphous catalysts.…”

Hierarchical Hollow Nanoprisms Based on Ultrathin Ni‐Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity towards Oxygen Evolution

“…[34,[36][37][38][39] Compared with the bulk solid counterparts,h ollow configurations with larger surface areas usually endow catalysts with ah igher density of surface-exposed active sites.Moreover,their large void space could effectively reduce ionic transport resistance and the ion diffusion lengths for surface reactions. [34] Very recently,afew pioneering studies have described the successful generation of hollow nanostructured (oxy)hydroxides towards water oxidation with encouraging results.…”

An Efficient and Earth‐Abundant Oxygen‐Evolving Electrocatalyst Based on Amorphous Metal Borides

“…[10] A great number of under-coordinated metal atoms, and hence abundant defects, in amorphous nanomaterial may provide more reactive sites at the catalyst surface, and as a result, facilitating the binding of hydroxyls and thus enhancing OER performance. [11] Furthermore, these amorphous nanomaterials have attracted much attention in other electrochemical applications Cost-effective and efficient oxygen-evolving electrocatalysts are urgently required for energy storage and conversion technologies.…”