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.

Carboxylic acid-based metal-organic frameworks (MOFs) are normally passed for the "pre-catalysts" for oxygen evolution reaction (OER) due to the hydroxides constructed in-situ during its alkaline hydrolysis process (AHP) in lye. Whereas, it remains a mystery that they show advantageous activity over prototypical hydroxides when they are directly acted as OER catalysts. Herein, we propose for the first time that the steric hindrance effect of Nafion can induce enhanced catalytic activity of such MOFs. Different from conventional catalysts without AHP, the Nafion with 3D structure weakens the AHP of Co-MOF nanoribbons, thus forming small size and low crystallinity species (cobalt hydroxide) with more active sites. And the existence of Nafion also optimizes its electronic structure, which is confirmed by transmission electron microscopy (TEM), in-situ UV absorption spectra, in-situ Raman spectroscopy and so on. Compared with Co-MOF-K obtained by directly immersing the Co-MOF nanoribbons in 1.0 M KOH, the Co-MOF-NK obtained by AHP of Co-MOF mixed with Nafion shows better catalytic activity. Based on the above inspiration, we realized the low overpotential of 268 mV at 10 mA·cm⁻² by preparing CoFe-MOF-NK. This work provides a new understanding of the structural reconstruction of MOFs in the field of electrocatalysis.