Mini Review on Active Sites in Ce-Based Electrocatalysts for Alkaline Water Splitting

Abstract

Hydrogen energy has become one of the most attractive candidates to replace traditional fossil fuels because of its lack of pollution and its high energy density. Electrocatalytic water splitting is a “green” and sustainable way to produce hydrogen but is still not sufficiently efficient at this stage. In recent years, Ce-based materials have become very popular as the electrocatalysts for water splitting primarily because of the multivalence state of Ce and easily formed oxygen vacancies readily formed in CeO2. However, until now, this interesting subject has seldom been reviewed, especially for electrocatalysts for alkaline water splitting. Herein, we outline and discuss recent progress on the active sites of Ce-based electrocatalysts for hydrogen evolution and oxygen evolution. Oxygen vacancies and interfaces between CeO2 and mixed metal components could provide optimized binding of hydrogen evolution reaction (HER) intermediates, thus promoting HER performance. For the oxygen evolution reaction (OER), Ce3+/Ce4+ redox, oxygen vacancies, and exogenous transition metals could optimize the binding of OER intermediates toward top catalytic activities. The aim of this review is to seek an overall understanding about the reaction sites in Ce-based electrocatalysts for water splitting, which may provide a guide for the future development of HER and OER Ce-based electrocatalysts toward industrial applications.

Interfacial Atom‐Substitution Engineered Transition‐Metal Hydroxide Nanofibers with High‐Valence Fe for Efficient Electrochemical Water Oxidation

“…Although the OER active sites of NiFe catalysts are controversial, it is increasingly convinced that the high‐valence transition metals, especially Fe, can optimize the OER intermediates’ free energy, thus enhancing the catalytic activity and kinetics. [ 10c , 13b , 14 , 22a ] In our NiFeV nanofiber electrocatalyst, the abundant formed high‐valence Fe via a charge transfer from Fe to V played an important role in optimizing the OER performance, and the Fe−O−V−O−Ni bridge could be recognized as the active site. [17a] …”

Aerosol-Assisted Chemical Vapor Deposition Growth of NiMoO4 Nanoflowers on Nickel Foam as Effective Electrocatalysts toward Water Oxidation

“…Ni-based electrocatalysts have attracted considerable attention since nickel is the fifth abundant element in earth having good catalytic activity for OER, and its alloys offer excellent resistant to corrosion in alkaline media. Moreover, oxo-hydroxo species of nickel­(III) such as NiOOH generated out of the anodic oxidation of Ni­(OH) 2 are highly active water oxidation electrocatalysts . Generally, the transition metal electrocatalysts show inherent slow transfer of electrons from the current collector to the catalyst, which affects their efficiency.…”

Interfacial Atom‐Substitution Engineered Transition‐Metal Hydroxide Nanofibers with High‐Valence Fe for Efficient Electrochemical Water Oxidation

“…Combining the above results, we can conclude that the interfacial atom‐substitution strategy achieves higher controllability on electronic structures of V‐doped NiFe electrocatalysts compared with the conventional one‐pot strategy. Although the OER active sites of NiFe catalysts are controversial, it is increasingly convinced that the high‐valence transition metals, especially Fe, can optimize the OER intermediates’ free energy, thus enhancing the catalytic activity and kinetics [10c, 13b, 14, 22a] . In our NiFeV nanofiber electrocatalyst, the abundant formed high‐valence Fe via a charge transfer from Fe to V played an important role in optimizing the OER performance, and the Fe−O−V−O−Ni bridge could be recognized as the active site [17a] …”