Rational Design of Highly Active and Stable (Bi1-xAx)2(Fe1-yBy)4O9 Mullite for Neutral- and Alkaline-Water Electrolysis

Complex oxides-based oxygen evolution reaction (OER) catalysts, such as perovskite, mullite and spinel etc. structured materials, have attracted tremendous interest due to their unique crystalline structure and surface state. However, it remains challenge to directly use them for OER because it is quite difficult to manipulate their activity and durability to satisfy the requirements of market which appreciate the cost and performance. Herein, a series of (Bi1-xAx)2(Fe1-yBy)4O9 mullite (A= La and Ca, B = Ni, Zn and Cu) were synthesized via a practical hydrothermal method that is suitable to industrialization. With the composition regulation of the A sites and B sites, the optimized (Bi1-xAx)2(Fe1-yBy)4O9 mullite (Bi2(Fe0.9Ni0.1)4O9) delivers a minimum over-potential of 421 mV and 307 mV to reach the current density 10 mA cm-2 with small Tafel slope of 68.2 mV dec-1 and 62.4 mV dec-1 in O2- saturated 1 M NaCl and 1 M KOH solution, respectively, suggesting a good OER activity in both neutral-and alkaline-conditions. Not only that, the Bi2(Fe0.9Ni0.1)4O9 shows an extraordinary cycle stability and long-term operation durability also. After 5000 times accelerate speed test (AST-LSV) and 50 h i-t measurements the Bi2(Fe0.9Ni0.1)4O9 shows only 1.50 mA cm-2(@ 10 mA cm-2) and 20.13 mA cm-2(80.26 mA cm-2 residual active) activity loss, respectively. Specially, the i-t measurement shows an increasing of current density platform ranging from 22.1 h to 29.7 h reflecting a novel self-adaptive process, which would be one of the reasons on the good durability of Bi2(Fe0.9Ni0.1)4O9. The current work paves a new avenue for precise control of the A/B-sites on surface (Bi1-xAx)2(Fe1-yBy)4O9 for high activity and durability OER electrocatalysts.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Complex oxides-based catalysts have attracted great interest due to their unique crystalline structure and surface state. However, it is challenging to use them for oxygen evolution reaction (OER) due to difficulties in manipulating their activity and durability. In this study, mullite-based catalysts were synthesized using a practical hydrothermal method. By optimizing the composition, the catalyst (Bi2(Fe0.9Ni0.1)4O9) showed excellent OER activity and durability in neutral and alkaline conditions. The results provide a new avenue for developing high-performance OER electrocatalysts by controlling the surface composition of complex oxides.