An Efficient Symmetric Electrolyzer Based On Bifunctional Perovskite Catalyst for Ammonia Electrolysis

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 LaNi 0.5 Cu 0.5 O 3-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.

Recent advances in nanostructured heterogeneous catalysts for N-cycle electrocatalysis

“…Elnabawy et al [76] investigated AOR on eight face-centered cubic (fcc) transition metals: Au, Ag, Cu, Pt, Pd, Ni, Ir, and Rh. According to their findings, Pt(100) is the most active surface, followed by Ir(100), Pt (111), and Ir (111). In a recent review paper on NH3 production and DAFCs, the facet-sensitive electrochemical AOR on Pt surfaces is well described (Fig.…”

“…According to these reports, it is clear that Pt-, Ni-, and Cu-based materials all possess good AOR performance in practice. Tao's group [111] synthesized various amounts of Cu-doped LaNiO3, i.e., LaNi1−xCuxO3−δ (LNCO-Ar), as AOR catalysts. During electrolysis, the optimal LNCO55-Ar (Ni:Cu = 1:1) achieved a higher oxidation current than Pt/C, but it suffered from a significant current attenuation.…”

Earth‐Abundant Metal‐Based Electrocatalysts Promoted Anodic Reaction in Hybrid Water Electrolysis for Efficient Hydrogen Production: Recent Progress and Perspectives

“…[216,220] Even though Cu dopant can enhance the ammonia adsorption over NiCu-based materials, their AmOR activity will be constrained at high Cu-doping degree as a result of inactive Cu. [218,219] Therefore, an Fe-doped ternary NiCuFe oxyhydroxide was developed via electrodeposition for a better AmOR performance by Xue's group. [221] Figure 14e,f advocate that the NiCuFe oxyhydroxide prefers reaction pathway II, which the first step of adsorbing ammonia is the rate-determining step.…”

“…More recently, a perovskite LaNi 0.5 Cu 0.5 O 3‐▫ annealed in Ar (LNCO55‐Ar) was also fabricated for ammonia electrolysis, which achieved a low onset potential of 0.48 V and with rapid current increased between 0.5–0.8 V in 0.5 m KOH with 2210 ppm NH 4 Cl ( Figure 14 a,b), better than that driven by Pt/C. [ 219 ] In a chronopotentiometry test, the current density gradually decreased along with electrolysis time due to the depletion of ammonia in the electrolyte, and the removal efficiency was about 100% after operating for 100 h (Figure 14c,d). This result indicates LNCO55‐Ar is an efficient electrocatalyst for the AmOR.…”

“…Reproduced with permission. [ 219 ] Copyright 2021, Wiley‐VCH. e) Schematic illustration of the AmOR over ternary NiCuFe oxyhydroxide.…”