Abstract
Ammonia is a natural pollutant in wastewater and removal technique such as ammonia electro‐oxidation is of paramount importance. The development of highly efficient and low‐costing electrocatalysts for the ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER) associated with ammonia removal is subsequently crucial. In this study, for the first time, the authors demonstrate that a perovskite oxide LaNi0.5Cu0.5O3‐δ after being annealed in Ar (LNCO55‐Ar), is an excellent non‐noble bifunctional catalyst towards both AOR and HER, making it suitable as a symmetric ammonia electrolyser (SAE) in alkaline medium. In contrast, the LNCO55 sample fired in air (LNCO55‐Air) is inactive towards AOR and shows very poor HER activity. Through combined experimental results and theoretical calculations, it is found that the superior AOR and HER activities are attributed to the increased active sites, the introduction of oxygen vacancies, the synergistic effect of B‐site cations and the different active sites in LNCO55‐Ar. At 1.23 V, the assembled SAE demonstrates ≈100% removal efficiency in 2210 ppm ammonia solution and >70% in real landfill leachate. This work opens the door for developments towards bifunctional catalysts, and also takes a profound step towards the development of low‐costing and simple device configuration for ammonia electrolysers.
Highlights
This phenomenon further emphasized that the catalytic activity of perovskites was due to the synergetic effects between nickel and copper ions, similar to those observed in NiCu bimetal and oxyhydroxies in our previous studies.[12,13]It is worth noting that perovskite oxide is much more stable than NiCu bimetal or oxyhydroxide
Cu doped lanthanum nickel perovskite (LNCO55Ar), which was prepared by a sol–gel combustion method and subsequently annealed in inert gas, has been developed as a bifunctional catalyst toward ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER)
When the LNCO55 sample was fired in air (LNCO55-Air), it was inactive toward AOR and showed very poor HER activity
Summary
The XRD patterns of LNCO73-Ar and LNCO55-Ar revealed eight diffraction peaks at 23.12°, 32.76°, 40.57°, 47.08°, 53.31°, 58.47°, 68.71°, and 78.23° corresponding to the (100), (110), (111), (200), (210), (211), (220), and (310) planes respectively These peaks conform with the LaNiO3 cubic structure (JCPDS No 04-014-0443).[38] In comparison to the two pure samples, LNO-Ar was a mixture of LaNiO3, La2CO5 (JCPDS No 00-023-0320), and NiO (JCPDS No 04-007-9781), which means it is difficult to obtain pure un-doped LaNiO3 under these conditions (Figure 1c; Figure S1, Supporting Information). When x > 0.5 in LaNi1-xCuxO3-δ, the resulting composition is no longer a pure phase, with new impure phases (La2CuO4, CuO) appearing even at increased calcining temperatures (Figure 1c; Figure S2, Supporting Information) This is consistent with the results of other reports.[41] The scanning electron microscopy (SEM) image of the as-prepared LNCO55-Ar is shown in Figure 1d and revealed to be a flake shape
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