Highly Selective Ammonia Oxidation on BiVO<sub>4</sub> Photoanodes Co‐catalyzed by Trace Amounts of Copper Ions
Lei Wu, Qianqian Li, Kun Dang, Daojian Tang, Chuncheng Chen, Yuchao Zhang, Jincai Zhao
Abstract
Abstract High‐efficient photoelectrocatalytic direct ammonia oxidation reaction (AOR) conducted on semiconductor photoanodes remains a substantial challenge. Herein, we develop a strategy of simply introducing ppm levels of Cu ions (0.5–10 mg/L) into NH 3 solutions to significantly improve the AOR photocurrent of bare BiVO 4 photoanodes from 3.4 to 6.3 mA cm −2 at 1.23 V RHE , being close to the theoretical maximum photocurrent of BiVO 4 (7.5 mA cm −2 ). The surface charge‐separation efficiency has reached 90 % under a low bias of 0.8 V RHE . This AOR exhibits a high Faradaic efficiency (FE) of 93.8 % with the water oxidation reaction (WOR) being greatly suppressed. N 2 is the main AOR product with FEs of 71.1 % in aqueous solutions and FEs of 100 % in non‐aqueous solutions. Through mechanistic studies, we find that the formation of Cu−NH 3 complexes possesses preferential adsorption on BiVO 4 surfaces and efficiently competes with WOR. Meanwhile, the cooperation of BiVO 4 surface effect and Cu‐induced coordination effect activates N−H bonds and accelerates the first rate‐limiting proton‐coupled electron transfer for AOR. This simple strategy is further extended to other photoanodes and electrocatalysts.