Kinetically Controlled Coprecipitation for General Fast

Synthesis of Sandwiched Metal Hydroxide Nanosheets/

Graphene Composites toward Efficient Water Splitting

he 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-temper-

ature coprecipitation is developed as a general strategy to produce a variety

of sandwich-type metal hydroxide/graphene composites. Specifically, well-

defined  α -phase nickel cobalt hydroxide nanosheets are vertically assembled

on the entire graphene surface (NiCo-HS@G) to provide plenty of acces-

sible 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 manage-

able 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.

Schematic illustration of the fabrication process of NiCo-HS@G.