Salt-assisted synthesis of transition metal-based catalysts: Basic principles, recent progress in the synthetic strategy and multifunctional applications

Abstract

Transition metal-based catalysts have broad application prospects in the fields of energy and environmental science. The synthesis process with “green” and “economy” fashion, and the potential to amplify production has been pursued to meet the practical application. Common salts (NaCl and KCl etc.) are abundant in nature with good chemical stability. The salts can act as “spacers” in the solid-based salt-template method (STM) and act as liquid medium in molten salt method (MSM) to realize the designed synthesis of transition metals (TMs: Co, Mo, Ni, Fe, etc.)-based materials via special interaction of salts with reactants. The special crystal structure of the salts can induce the growth of the materials/intermediates with specific structure, realizing the better control during the synthesis. The strong polarizing force from molten salt greatly promotes the dissolution of the reactants. The liquid environment and spatial confinement effect of molten salt can make the high dispersion of the reaction process and materials. These interactions between salts and reactants are favorable to design the materials with well-defined morphology/property and enhanced performance. The (quasi) solid-based synthesis process endows the potential for amplified produce and the characteristics of easy recycling of salts give the more cost-effective synthesis process. Here, this review focuses on salt-assisted synthesis of transition metals (TMs, Co, Mo, Ni, Fe)-based materials. First, we have given the basic principles in the salt-assisted synthesis (STM and MSM). The connection and difference between two routes are summarized with an emphasis on their unique properties and contributions to the synthesis of targeted materials. Then, the recent progress in the typical TM-based materials is introduced in detail. Thirdly, we list some promising applications of the materials from these routes. The challenges and outlooks are finally proposed. This review can provide a comprehensive insight on this promising system and a guide for design of the advanced energy catalysts.