OER catalyst “surface remodeling”: basic concepts and progress!
Surface remodeling is a process in which structural changes occur on the surface of a catalyst or material. In catalytic reactions, surface remodeling can lead to changes in catalyst activity and selectivity, thus affecting reaction efficiency and product distribution. Surface remodeling usually occurs at high temperatures, high pressures, or under reaction conditions, which include processes such as adsorption, dissociation, diffusion, and recombination. These processes can lead to rearrangement of surface atoms to form new crystal structures or surface phases. The mechanism and process of surface remodeling depend on factors such as catalyst composition, morphology and reaction conditions.
Surface remodeling has important effects on catalytic reactions: first, surface remodeling can change the active site distribution and surface energy of catalysts, thus regulating the rate and selectivity of reactions. Secondly, surface reconstruction can change the interaction between catalyst and reactants, and affect the rate and energy barrier of the reaction steps such as adsorption, dissociation and diffusion. In addition, surface remodeling can modulate the stability and lifetime of catalysts. Therefore, understanding and controlling surface remodeling is crucial for designing efficient catalysts and optimizing catalytic reactions. By studying the mechanism and kinetic process of surface remodeling, the structure-activity relationship on the catalyst surface can be revealed and provide guidance for catalyst design and synthesis. In addition, the control of surface remodeling can be achieved by modulating the reaction conditions and catalyst composition to optimize the efficiency and selection of catalytic reactions!
Electrochemical water decomposition is an efficient way to produce high-purity hydrogen. However, in the anodic half-reaction, the oxygen-removal reaction (OER) requires a larger overpotential than the cathodic hydrogen-removal reaction (HER) due to the multistep proton/electron coupling, which hinders the efficient conversion of energy. Among them, noble metal catalysts such as RuO2 and IrO2 can significantly reduce the overpotential of OER, but their expensive price and scarce reserves severely limit their large-scale industrial applications.
Among the many noble metal catalyst alternatives, transition metal-based electrocatalysts have been widely studied due to their advantages of low price and abundant reserves. Among them, F in transition metal fluorides has a great electronegativity, which can push the valence state of the metal center very high, which helps to assist the catalyst surface reconstruction, formation of amorphous structure, and so on. Therefore, fluorides may be effective catalysts for OER, but there are few reports about them in the literature.
Recently, a well-crystallized NiCo bimetallic fluoride (Ni0.42Co0.58F2-G) was designed and prepared by Apping Zhao and Gongzhen Cheng at Wuhan University, and its reconstruction phenomenon during electrochemical processes was investigated. Specifically, the researchers first synthesized NiCo-based nano-array A-Ni-MeIM-Co-0.01 precursors with a large specific surface area by solid-liquid exchange method, and then converted them into NiCo bimetallic fluoride Ni0.42Co0.58F2-G with a high electrochemically active surface area by one-step gas-phase fluorination method.
Compared with the conventional liquid-phase synthesis method, the fluoride produced by the gas-phase fluorination method has higher crystallinity; meanwhile, the modulation of the electronic structure of the bimetallic center promotes efficient surface reconstruction during the electrochemical process as well as the migration of F during the reconstruction process leading to the exposure of more electrochemically active sites. This not only leads to the excellent electrochemical performance of Ni0.42Co0.58F2-G, but also ensures its electrochemical stability.
The electrochemical performance test results showed that the OER overpotential of the prepared Ni0.42Co0.58F2-G catalyst was only 313 mV at a current density of 10 mA cm-2, and the Tafel slope was 42.5 mV dec-1; moreover, the activity of the catalyst after 10,000 CV cycles still remained stable, indicating its excellent stability.
In addition, theoretical calculations showed that the construction of bimetallic centers could induce charge redistribution and generate higher valence metal sites, which could optimize the adsorption of key reaction intermediates, lower the reaction barriers, and significantly improve the OER activity. In summary, this work investigated in detail the roles of F and bimetallic centers in enhancing the OER activity of the catalysts, which is instructive for the design and preparation of highly efficient electrochemical surface reconstructed electrocatalysts.
