Photoelectrochemical N₂-to-NH₃ Fixation with Recorded Yield Rate by Steering Solid-Electrolyte Interphase.

Abstract

Achieving efficiently lithium (Li)-mediated photoelectrochemical (PEC) nitrogen (N₂)-to-ammonia (NH₃) fixation at low overpotential under mild conditions remains a highly challenging task due to the complex and sluggish interfacial chemical processes. Here, we report a novel multifunctional electrolyte with ethyl 3,3,3-trifluoropropionate and sodium cation (Na⁺) to form a porous solid-electrolyte interphase (SEI) with optimizing organic/inorganic composition on the photocathode surface, leading to a rapid and stable conversion cycle of Li⁺ → Li → lithium nitride (Li₃N). As a result, the Li-mediated PEC N₂ reduction reaction system realizes a high NH₃ yield rate of ∼93 µg h^-1 cm^-2 with a high faradaic efficiency (FE) of ∼67% at 0.55 V vs. Li redox couple (vs. Li/Li⁺) under 1 sun illumination. When the light intensity is increased to 2 sun, it even achieves a record-breaking submilligram-level NH₃ yield rate, ∼109 µg h^-1 cm^-2. This work reveals a critical role of SEI for accelerating Li-Li⁺ cycle and provides a valuable guidance for building an efficient Li-mediated PEC N₂-to-NH₃ fixation at ultra-positive potential vs. Li/Li⁺.