Kinetically Controlled Coprecipitation for General Fast Synthesis of Sandwiched Metal Hydroxide Nanosheets/Graphene Composites toward Efficient Water Splitting

Abstract

The development of cost-effective and applicable strategies for producing efficient oxygen evolution reaction (OER) electrocatalysts is crucial to advance electrochemical water splitting. Herein, a kinetically controlled room-temperature coprecipitation is developed as a general strategy to produce a variety of sandwich-type metal hydroxide/graphene composites. Specifically, welldefined α-phase nickel cobalt hydroxide nanosheets are vertically assembled on the entire graphene surface (NiCo-HS@G) to provide plenty of accessible active sites and enable facile gas escaping. The tight contact between NiCo-HS and graphene promises effective electron transfer and remarkable durability. It is discovered that Ni doping adjusts the nanosheet morphology to augment active sites and effectively modulates the electronic structure of Co center to favor the adsorption of oxygen species. Consequently, NiCo-HS@G exhibits superior electrocatalytic activity and durability for OER with a very low overpotential of 259 mV at 10 mA cm −2 . Furthermore, a practical water electrolyzer demonstrates a small cell voltage of 1.51 V to stably achieve the current density of 10 mA cm −2 , and 1.68 V to 50 mA cm −2 . Such superior electrocatalytic performance indicates that this facile and manageable strategy with low energy consumption may open up opportunities for the cost-effective mass production of various metal hydroxides/graphene nanocomposites with desirable morphology and competing performance for diverse applications.

Surface‐Confined Fabrication of Ultrathin Nickel Cobalt‐Layered Double Hydroxide Nanosheets for High‐Performance Supercapacitors

“…Remarkably, the ultrathin NiCo‐LDH‐G nanosheets show a lower overpotential (η) of 0.337 V at the current density of 10 mA cm −2 , in comparison to that of some other common catalysts (Figure b). These electrochemical performances are comparable, and even superior to those of the Co/Ni‐based hydroxide catalysts reported recently in literature under the same electrolyte solution (0.1 m KOH or NaOH) and even 1 m KOH solution (Table S4, Supporting Information) …”

Engineering an Earth‐Abundant Element‐Based Bifunctional Electrocatalyst for Highly Efficient and Durable Overall Water Splitting

“…Surprisingly, MoS 2 /Ni 3 S 2 heterostructures functioned as a bifunctional catalyst and acquired a low cell voltage of 1.56 V at a current density of 10 mA cm −2 for overall water splitting . Emerging bimetallic structure catalysts are currently expected to further elevate catalytic properties and address the bottleneck issue these catalytic properties present . For instance, Co‐based catalysts have long been known as active catalysts, and their electrocatalytic efficiency can be improved by introducing other ions, such as Fe, Se, Cu, and Ni .…”

3D Architectures of Quaternary Co‐Ni‐S‐P/Graphene Hybrids as Highly Active and Stable Bifunctional Electrocatalysts for Overall Water Splitting

“…Highly efficient water electrolysis generally requires high-performance electrocatalysts with low overpotential, fast kinetics, and high stability. [9][10][11] Recently, transition-metal hydroxides, [7,12] phosphides, [8,[13][14][15][16] nitrides, [17,18] and chalcogenides [19][20][21][22] have been investigated as promising candidates for bifunctional electrocatalysts. [7,8] The search for earth-abundant, lowcost HER and OER electrocatalysts that are robust, have high activity and stability has triggered numerous efforts to replace noble metal-based materials.…”

“…[9][10][11] Recently, transition-metal hydroxides, [7,12] phosphides, [8,[13][14][15][16] nitrides, [17,18] and chalcogenides [19][20][21][22] have been investigated as promising candidates for bifunctional electrocatalysts. [9,12,17,19,22,34] However, the high surface energy of sheets, which are unstable, leads to the possibility of stacking with surrounding sheets through van der Waals attractions, resulting in a decrease of the active surface area. [23][24][25][26] In addition, according to recent reports, these compounds can operate as highly efficient OER electrocatalysts and could thus be utilized as bifunctional electrocatalysts.…”