Hydrogen evolution activity tuning via two-dimensional electron accumulation at buried interfaces

Abstract

Developing efficient earth-abundant transition metal-based electrocatalysts for the hydrogen evolution reaction (HER) is crucial for hydrogen production at scale. This paper reports that the buried electrocatalytic interfaces between Ni–Fe sulfide (NiFeS) nanosheets and TiO₂ conformal coatings (about 5 nm) achieved remarkable HER activity improvement, lowering the HER overpotential from −170 mV to −107 mV at −50 mA cm⁻² in a base. Non-HER active, permeable TiO₂ coatings grown by atomic layer deposition (ALD) achieved continuous fine-tuning of the electronic properties at the buried TiO₂/NiFeS interfaces, as a novel strategy and the main factor for electron accumulation at the interface. Core-level and valence band X-ray photoelectron spectroscopy (XPS) was used to investigate the TiO₂ electronic-structure tuning effect on the charge-transfer energetics during the HER. Their alkaline HER mechanism was elucidated by supplementing characterizations of membrane permeation, Tafel slope, and synchrotron X-ray absorption spectroscopy, which verified that the buried TiO₂/NiFeS interfaces are electrocatalytically active. This study offers a general strategy for improving the charge-transfer kinetics of an electrocatalytic system by confining catalysis at a permeable solid–solid interface. The broad applicability of permeable and tunable coatings potentially accelerates the optimization of earth-abundant catalysts to achieve high performance under operationally relevant conditions.