How To Teach An Old Dog New Tricks: Advancing Perovskite Via Anion Doping

Hydrogen can be easily produced through water electrolysis (2H₂O → 2H₂ + O₂), a process that makes use of electricity to break the bonds between constituent elements (i.e., hydrogen and oxygen) of water molecules and releases them in a gaseous form.

Hydrogen gas is high in energy, yet an engine that burns pure hydrogen produces almost zero pollution, unlike those powered by burning fossil fuels. Therefore, water electrolysis has long been an important research area for conversions of intermittent energy sources, such as sunlight and wind, into versatile and easily controllable forms of energy.

One of the biggest challenges that keep this process from being of large-scale application is the lack of suitable electrode materials. Pt is the state-of-the-art electrode components for catalyzing the hydrogen evolution reaction (HER), while RuO₂ is the one for the oxygen evolution reaction (OER). However, both of them suffer from the high cost, rare reserve, and poor stability. As a group of promising alternative electrode materials, perovskite oxides have been widely studied to enhance the electrode reaction rates and electrode stability in water electrolyzers. However, the current demand calls for higher activity and stability than what the state-of-the-art perovskite oxides provide. 

Typically, in the perovskite ABO₃ structure, the B-site cation is 6-fold coordinated with oxygen anions, while the A-site cation is 12-fold coordinated. Researchers in Canada and China have put forward a new way of F-anion substitution to regulate the p-blocking centers of perovskite for water splitting electrocatalysis. The researchers proposed the possible function mechanisms that are fundamentally beyond the current understandings drawn from A-/B-sites doping and can shed light on the influences of the F-anion over the catalytic performance. The F-anion doping approach is simple and universal and begins at atomic levels, so it can provide a new design guide for perovskite oxides.

The robustness of the new electrolyzer was tested under extreme conditions of high current density (~0.21 A cm^–2) and 10 M KOH, conditions that are often adopted in the commercial alkaline electrolyzers. It is seen that the new electrolyzer exhibits good electrochemical stability during this short-term test. More importantly, the amount of produced O₂ is very close to the theoretical value, and such good performance is reserved at the end of the session, reflecting a constant catalysis rate and stability under harsh conditions.

These results faithfully prove the requirements for commercial application. While there’s still more work to be done, the new research findings could help researchers design water electrolysis systems that use these types of novel materials. Next, the research team is turning its focus to stabilizing the electrode materials in order to prevent its swift degradation.

These findings are described in the article entitled Activating p-blocking centers in perovskite for efficient water splitting, recently published in the journal Chem. The work mainly describes the promising anion substitution method to regulate the lattice O activity in perovskite oxide, from a performance and design perspective. Furthermore, it discusses the fundamental concepts in electrocatalysis for the rational design of perovskite oxide through anion substitution and minutely inspects the current understanding and its impact on performance trends and future directions of perovskite electrocatalysts. This work was conducted by Dr. Bin Hua, Dr. Meng Li, and colleagues from the University of Alberta (Canada), East China University of Science and Technology (China), and Natural Resources Canada.

Reference:

1. Bin Hua, Meng Li, Wanying Pang, Weiqiang Tang, Shuangliang Zhao, Zhehui Jin, Yimin Zeng, Babak Shalchi Amirkhiz, Jing-Li Luo, Activating p-Blocking Centers in Perovskite for Efficient Water Splitting, Chem, 2018, 4, 2902-2916.