Efficient ammonia photosynthesis from nitrate by graphene/Si Schottky junction integrated with Ni–Fe LDH catalyst

Abstract

This work presents stable and efficient photoelectrochemical (PEC) nitrate-to-ammonia conversion through the facile integration of a graphene/Si Schottky junction and earth-abundant Ni–Fe layered double hydroxide (LDH). Efficient charge separation for photogenerated carriers and large photovoltage generation can be achieved resulting from the graphene/Si Schottky junction photocathode. Through the atomic layer of graphene, the direct growth of the Ni–Fe LDH catalyst on the graphene/Si Schottky junction by electrodeposition provides excellent quality at the interfaces between the catalyst and photocathode. The Ni–Fe LDH/graphene/Si Schottky junction photocathode exhibits a promising and stable PEC conversion from nitrate to ammonia, with an optimal onset potential of 0.17 V vs. the reversible hydrogen electrode (RHE), the largest saturated photocurrent density of −31.9 mA cm⁻², and the highest faradaic efficiency of 92.5% at 0.15 V vs. RHE. Combined with the several advantages of graphene, such as inherent chemical inertness, high optical transparency, and excellent conductivity, the integration of the semiconductor LDH catalyst on the graphene/Si Schottky junction platform provides an effective strategy to achieve stable and efficient PEC nitrate-to-ammonia conversion.