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.

Fabrication of large-area and uniform semiconducting thin films of two-dimensional (2D) materials is paramount for the full exploitation of their atomic thicknesses and smooth surfaces in integrated circuits. In addition to elaborate vapor-based synthesis techniques for the wafer-scale growth of 2D films, solution-based approaches for high-quality thin films from the liquid dispersions of 2D flakes, despite underdeveloped, are alternative cost-effective tactics. Here, we present layer-by-layer (LbL) assembly as an effective approach to obtaining scalable semiconducting films of molybdenum disulfide (MoS₂) for field-effect transistors (FETs). LbL assembly is achieved by coordinating electrochemically exfoliated MoS₂ with cationic poly (diallyldimethylammonium chloride) (PDDA) through electrostatic interactions. The PDDA/MoS₂ percolating nanofilms show controlled and self-limited growth on a variety of substrates, and are easily patterned through lift-off processes. Ion gel gated FETs are fabricated on these MoS₂ nanofilms, and they show mobilities of 9.8 cm²·V^-1·s^-1, on/off ratios of 2.1 × 10⁵ with operating voltages less than 2 V. The annealing temperature in the fabrication process can be as low as 200 °C, thereby permitting the fabrication of flexible FETs on polyethylene terephthalate substrates. The LbL assembly technique holds great promise for the large-scale fabrication of flexible electronics based on solution-processed 2D semiconductors.