As an alternative
to the high energy-intensive Haber-Bosch ammonia synthesis,
photoelectrochemical (PEC) technique has been proposed to produce ammonia from
N2 and H2O at ambient atmosphere. However, efficient and noble metal-free electrode
materials are still the key to PEC synthesis of ammonia.
A research team
led by Dr. WANG Jiahong and Prof. YU Xuefeng from the Shenzhen Institutes of
Advanced Technology (SIAT) of the Chinese Academy of Sciences proposed a black
phosphorus (BP) electrode for efficient artificial synthesis of ammonia.
The electrode was
fabricated by layer-by-layer assembly of BP nanosheets on an indium tin oxide
(ITO) substrate as the metal-free two-dimensional catalyst for the
photoelectrochemical (PEC) nitrogen reduction reaction (NRR).
The study entitled
"Photoelectrochemical Synthesis of Ammonia with Black Phosphorus" was
published in Advanced Functional Materials on April 20.
In this study, the
BP electrode exhibited highly efficient PEC NRR activity with the ammonia yield
rate of 102.4 μg·h-1 mgcat.-1, the Faradaic efficiency of 23.3% at -0.4 V and
good long-term stability, which was the best among nonmetal catalysts for synthesis
of ammonia by photocatalysis and electrocatalysis.
Moreover, the hydrogen desorption favorable surface, raised flat band, external electric field, and consumed holes improved the ammonia productivity synergistically.
The art illustration of the PEC NRR process on BP electrode. Image by WANG Jiahong.
"BP has many features that are suitable for
synthesis of ammonia," said Dr. WANG Jiahong. "It's a direct bandgap
semiconductor with high carrier mobility as well as light absorption spanning a
wide range. The weak hydrogen absorption on bare BP also can suppress the
competing hydrogen evolution reaction. The NRR catalyst library would be
expanded by the introduction of p-type two-dimensional material."