Scalable 2D Semiconductor‐Based van der Waals Heterostructure Interface with Built‐in Electric Field for Enhanced Electrochemical Water Splitting

Electrochemical water splitting has received tremendous attention as an eco‐friendly approach to produce hydrogen. Noble metals and their oxides are commonly used as electrocatalysts to reduce activation energy barriers for hydrogen and oxygen evolution reactions in high‐performance electrodes, but their cost, scarcity, and limited stability hinder widespread adoption of electrochemical water splitting. Further advancements are therefore needed to reduce reliance on noble metals and improve the long‐term stability. Herein, solution‐processed 2D van der Waals (vdW) p–n heterostructures as an interfacial layer between catalysts and the electrode are introduced to enhance the catalytic performance. These heterostructures are formed by sequentially assembling electrochemically exfoliated black phosphorus and molybdenum disulfide nanosheets into electronic‐grade p‐ and n‐type semiconductor thin films, with the scalability extending across tens‐of‐centimeter scale areas. Benefiting from the charge distribution and built‐in electric field developed upon heterojunction formation, the vdW heterostructure interfacial layer increases both the catalytic activity and stability of commercial Pt/C and Ir/C catalysts compared to when these catalysts are directly loaded onto electrodes. Additionally, the vdW heterostructure also serves as a template for synthesizing nanostructured Pt and Ir catalysts through electrodeposition, further enhancing the catalytic performance in terms of mass activity and stability.