Photoelectrochemical Nitrate Reduction to Ammonia on Ordered Silicon Nanowire Array Photocathodes

Hyo Eun Kim; Jeehye Kim; Eun Cheol Ra; Hemin Zhang; Youn Jeong Jang; Jae Sung Lee

doi:10.1002/anie.202204117

Photoelectrochemical Nitrate Reduction to Ammonia on Ordered Silicon Nanowire Array Photocathodes

Angew Chem Int Ed Engl. 2022 Jun 20;61(25):e202204117. doi: 10.1002/anie.202204117. Epub 2022 Apr 21.

Authors

Hyo Eun Kim¹, Jeehye Kim¹, Eun Cheol Ra¹, Hemin Zhang², Youn Jeong Jang³, Jae Sung Lee¹

Affiliations

¹ School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan, 44919, Republic of Korea.
² College of Materials Science and Engineering, Sichuan University, Chengdu, 610065, China.
³ Department of Chemical Engineering, Hanyang University, Seongdong-gu, Seoul, 04763, Republic of Korea.

PMID: 35384205
DOI: 10.1002/anie.202204117

Abstract

As a new path to "green" ammonia production, photoelectrochemical nitrate reduction reaction (PEC NO₃ RR) is investigated for the first time. An Au-decorated ordered silicon nanowire (O_SiNW) array photocathode demonstrates 95.6 % of Faradaic efficiency (FE) to ammonia at 0.2 V_RHE , which represents a more positive potential than the thermodynamic reduction potential of nitrate by utilizing photovoltage. The high FE is possible because both Si and Au surfaces are inactive for competing water reduction to hydrogen. The O_SiNW array structure is favorable to promote the PEC NO₃ RR relative to planar Si or randomly-grown Si nanowire, by enabling the uniform distribution of small Au nanoparticles as an electrocatalyst and facilitating the mass transport during the reaction. The results demonstrate the feasibility of PEC nitrate conversion to ammonia and would motivate further studies and developments.

Keywords: Ammonia Production; High Faradaic Efficiency; Ordered Silicon Nanowire Array; Photocathode; Photoelectrochemical Nitrate Reduction.