Photoelectrochemical Synthesis of Ammonia with Black Phosphorus

Abstract

Efficient production of ammonia using environmentally friendly techniques under ambient conditions is crucial to renewable energy storage and industrial applications, and catalysts with new reaction pathways are highly desirable. In this work, black phosphorus (BP) is used as a metal‐free 2D catalyst for the photoelectrochemical (PEC) nitrogen reduction reaction (NRR). The electrode is fabricated by layer‐by‐layer assembly of BP nanosheets on an indium tin oxide substrate. The PEC NRR activity in the N2 saturated aqueous electrolyte without a sacrificial agent is excellent, as exemplified by an ammonia yield rate of 102.4 µg h−1 mgcat.−1 and Faradaic efficiency of 23.3% at −0.4 V, which are the best among nonmetal catalysts for synthesis of ammonia by photocatalysis and electrocatalysis. Furthermore, the BP electrode shows excellent stability after 6 consecutive cycles. The excellent PEC catalytic properties are attributed to the light excitation enhanced electrocatalytic process and that the external bias promoted photocatalytic process improves ammonia production synergistically. The results not only demonstrate the great potential of BP in PEC catalysis, but also identify a promising technique to produce ammonia under ambient conditions using solar energy and electric energy.

Optically and Electrocatalytically Decoupled Si Photocathodes with a Porous Carbon Nitride Catalyst for Nitrogen Reduction with Over 61.8% Faradaic Efficiency

“…h) Comparison chart of FE with existing PEC NRR catalytic systems with present Au/PCN/ n + np + ‐ Si photocathode. [ 18,19,57,58 ]…”

“…Mater. 2021, 33, 2100812 [18,19,57,58] of H + ions for N 2 to NH 3 conversion as H + ions also vital for efficient NRR. [25] Tafel slope for PEC NRR under N 2 saturation was also calculated (Figure S18, Supporting Information), and the high Tafel slope of 83 mV dec −1 indicates the Volmer-Heyrovsky mechanism, which means the poor HER reaction kinetics of fabricated photocathode.…”

The development, application, and performance of black phosphorus in energy storage and conversion

“…−1 in photoelectrochemical (PEC) cell, Faradaic efficiency of 23.3% at −0.4 V, and excellent stability after 6 consecutive cycles (Figure 14j). 154 Zhu et al reported a facile strategy for the self-assembly of BP QDs on MnO2 flake via van der Waals interaction (BP QDs/MnO2). The ultrafine size of BP QDs was beneficial for the utilization of active sites, while the cooperation of graphene-like MnO2 sheet as highefficiency substrate could inhibit the BP QDs from aggregating and fulfill the robust combination.…”

Two-Dimensional Black Phosphorus Nanomaterials: Emerging Advances in Electrochemical Energy Storage Science

“…In addition, 2D BP possesses a much larger specific surface area (~ 2630 m 2 g −1 ) than graphene due to the puckered structure and increased layer distance. Therefore, 2D BP has been intensively studied and widely applied in various fields, such as ultrafast laser [ 24 ], bio-photonics [ 25 ], energy storage devices [ 26 ], optoelectronics [ 27 ], solar cell [ 28 ], and nanosensors [ 29 ].…”