Back-Gated van der Waals Heterojunction Manipulates Local Charges toward Fine-Tuning Hydrogen Evolution.

Charge redistribution plays a prominent role in interpreting the intrinsic electrocatalytic mechanism. Establishing a quantitative relationship between the local charges and electrochemical performance can fundamentally update the design philosophies beyond conventional methods. We describe exertion of an external electric field in the cobalt phthalocyanine (CoPc)/MoS2 heterojunction to finely manipulate intermolecular charge transfer. The injected charges (e- ) from CoPc to MoS2 migrate to natural S vacancies and enhance Mo-H bonding. Moreover, the band gap of MoS2 and CoPc can be readily tuned by the electric field, verifying band engineering at the heterointerface. In situ photoluminescence spectra and gate-dependent electrochemical measurement reveal a linear correlation between the charge accumulation and hydrogen evolution reaction (HER) activity. This approach provides a new strategy for the design of catalysts, enabling precise regulation of the electronic configuration to improve catalytic activity.