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.

The Cu/Zn ratio of the CuZn electrocatalyst is known to influence the selectivity of CO2RR, but questions remain open about how microstructure, crystal phase, and oxidation state of the metal ions change and interplay in the composition tuning process, which need to be carefully addressed for rational catalyst design. Toward this end, we designed and synthesized a series of CuZn-based aerogel materials with controlled Cu/Zn ratios and systematically investigated their effects on CO2RR catalysis. From both experimental results and theoretical calculations, we found that the introduction of Zn into Cu aerogel greatly promoted the production of CO primarily due to the unfavorable adsorption energy of *H. Surprisingly, the intake of trace Ni atoms further inhibited the H2 evolution reaction on account of the strong pinning of both *H and H2O* on the Ni sites. Therefore, the as-formed CuZn-Ni aerogel exhibited a much-improved catalytic activity and selectivity for CO generation with FE­(CO) increased to 80% from 60%. This work gives insights into the surface adsorption–desorption characteristics underlying the activity and selectivity of electrocatalysts, which is of general importance for CO2RR.

Controlling and tuning surface properties of a catalyst have always been a prime challenge for efficient hydrogen production via water splitting. Here, we report a facile method for tuning both charger transfer and sorption−desorption properties of NiFe layered double hydroxide (LDH) by intercalating a conductive polymer of polypyrrole (ppy) via an interlayer confined polymerization synthesis (ICPS) process. Ex situ characterizations and in situ electrochemical quartz-crystal microbalance with dissipation (EQCM-D) tracking experiments showed that the intercalated ppy not only improved the charge transfer property of the resulting hybrid catalyst LDH-ppy but also made it more flexible and adaptive for quick and reversible sorption−desorption of reactants and intermediates during the oxygen evolution reaction (OER) process. Consequently, the as-prepared LDH-ppy exhibited a doubled catalytic current density over the bare LDH, as visualized by in situ scanning electrochemical microscopy (SECM) at the subnanometer scale. This work sheds light on orchestrating the charge and sorbate transfer abilities of catalysts for efficient water splitting by smartly combining inorganic and organic layers.

A two-dimensional (2D) copper hybrid catalyst (Cu/CuxOF) composed of metallic Cu well dispersed on 2D F-doped CuxO nanoplates (CuxOF) is reported, which shows high catalytic activity toward the CO2RR for acetate generation.

This article reviews recent progresses in characterization techniques and material development strategies for the surface/interface engineering of energy conversion catalysts, with emphasis on surface defect engineering, surface crystalline property modulating,...