Electrostatically connected nanoarchitected electrocatalytic films for boosted water splitting

Active sites of two-dimensional(2D)electrocatalysts are often partially blocked owing to their inevitable stacking and hydrophobic polymeric binders in macroscale electrodes,therefore impeding their applications in efficient electrolyzers.Here,using layered double hydroxide(LDH)nanosheets as a model 2D electrocatalyst,we demonstrate that their performance toward water splitting can be boosted when they are electrostatically assembled into an organized structure pillared by hydrophilic polyelectrolytes or nanoparticles in a layer-by-layer(LbL)fashion.In particular,their mass activity on a planar electrode can be as large as 2.267 mA·μg^(-1) toward oxygen evolution reaction(OER),when NiFe-LDH nanosheets are electrostatically connected by poly(sodium 4-styrenesulfonate)(PSS),while drop-casted NiFe-LDH nanosheets only have a mass activity of 0.116 mA·μg^(-1).In addition,these homogeneous NiFe-LDH nanofilms can be easily deposited on three-dimensional(3D)surfaces with high areas,such as carbon cloths,to serve as practical electrodes with overpotentials of 328 mV at a current density of 100 mA·cm^(-2),and stability for 40 h.Furthermore,Pt nanoparticles can be LbL assembled with NiFe-LDH as bifunctional electrodes for synergistically boosted oxygen and hydrogen evolution reactions(HER),leading to successful overall water splitting powered by a 1.5 V battery.This study heralds the spatial control of 2D nanomaterials in nanoscale precision as an efficient strategy for the design of advanced electrocatalysts.

Two-step colloidal synthesis of micron-scale Bi_(2)O_(2)Se nanosheets and their electrostatic assembly for thin-film photodetectors with fast response

Recently discovered bismuth oxychalcogenide(Bi_(2) O_(2) Se) has aroused great interest due to its ultrahigh carrier mobility,tunable band gap and good environmental stability,making it a promising candidate for high-performance electronics and optoelectronics.Their synthesis by colloidal approaches represents a cost-effective alternative to well-established chemical vapor deposition methods,and the resulting electronic-grade inks are important for large-area printed or wearable electronics.However,it is still challenging to control the colloidal growth of Bi_(2) O_(2) Se nanosheets in solution in addition to their assembly into high-performance thin films.Here,we report a two-step colloidal synthesis of Bi_(2) O_(2) Se nanosheets by separating the seeding and growth steps,thereby achieving controllable production of nanosheets with a lateral size of 1.4 mm and a thickness of 10 nm at optimized reaction conditions.These Bi_(2) O_(2) Se nanosheets are electrostatically assembled into large-area thin films,from which a photodetector is fabricated with a responsivity of 6.1 A/W and a short response time of 368 ms under the 520-nm laser illumination.The device exhibits fast response to modulations as high as 100 k Hz,along with a à3 dB bandwidth of 1 kHz.This work provides an important understanding of the controlled colloidal synthesis of Bi_(2) O_(2) Se nanosheets,and demonstrates their potential applications in fast photodetectors.