Enhanced photoelectrochemical nitrogen reduction to ammonia by a plasmon-active Au grating decorated with the gC3N4@MoS2 heterosystem and plasmon-active nanoparticles

Abstract

The electrochemical production of ammonia from nitrogen (so-called nitrogen reduction reaction – NRR) is one of the key tasks of modern electrochemistry. The use of photo-electrochemical approaches in the NRR allows the involvement of renewable sunlight energy and partially reduces the energy demand of the NRR process and increases its efficiency. For efficient photoelectrochemical NRR realization, a rational design of the photoelectrode used is required. In this work, we propose the design, creation, and optimization of a hybrid electrode, based on utilization of coupled 2D semiconductors and plasmonic hot spots. In our approach, the gC₃N₄@MoS₂ semiconductor (in the form of 2D flakes), with high catalytic activity towards the NRR is used as a redox-active material. For the involvement of sunlight energy, plasmon triggering is used in two modes: simple plasmonic triggering using a periodic Au grating and coupled plasmon triggering through the sandwiching of 2D gC₃N₄@MoS₂ flakes between the Au grating and different plasmon active nanoparticles (gold and silver nanoparticles with different shapes). We also carried out a series of calculations (including finite difference time domain estimation of plasmon energy distribution and density functional calculation) aimed at the estimation of the local value of plasmon energy and the NRR process under conditions of plasmon triggering. As a result of careful design and photoelectrode optimization, we were able to achieve 882.1 μg h⁻¹ mg_cat⁻¹ ammonia yield and 22.1% faradaic efficiency. The proposed photoelectrode design makes it possible to effectively use both the catalytic properties of the coupled semiconductors and the strengths of plasmon-assisted triggering.