Prussian blue analogs (PBAs), the oldest artificial cyanide-based coordination polymers, possess open framework structures, large specific surface areas, uniform metal active sites, and tunable composition, showing significant perspective in electrochemical energy storage. These electrochemically active materials have also been converted to various functional metal containing nanomaterials, including carbon encapsulated metals/metal alloys, metal oxides, metal sulfides, metal phosphides, etc. originating from the multi-element compositions as well as elaborate structure design. In this paper, a comprehensive review will be presented on the recent progresses in the development of PBA frameworks and their derivatives based electrode materials and electrocatalysts for electrochemical energy storage and conversion. In particular, it will focus on the synthesis of representative nanostructures, the structure design, and figure out the correlation between nanomaterials structure and electrochemical performance. Lastly, critical scientific challenges in this research area are also discussed and perspective directions for the future research in this field are provided, in order to provide a brand new vision into the further development of novel active materials for the next-generation advanced electrochemical devices.

Prussian Blue Analogs and Their Derived Nanomaterials for Electrochemical Energy Storage and Electrocatalysis

Polypyrrole-enveloped Prussian blue nanocubes with multi-metal synergistic adsorption toward lithium polysulfides: high-performance lithium-sulfur batteries

Prussian blue analogues (PBAs) with controllable frame structures and anchored defects represent promising electrocatalysts for oxygen evolution reaction (OER) in alkaline conditions. Herein, double-shelled NiFe PBAs nanocages have been synthesized through an ion-exchange reaction between K3Fe(CN)6 and single-shelled Ni(OH)2 nanocages based on the regulation of nanoscale Kirkendall effect driven by the crystallinity difference between Ni(OH)2 and NiFe PBAs. With further mild thermal activation, carbon–nitrogen (CN) vacancies could be formed in situ in large quantities in the double-shelled NiFe PBAs nanocages. Theoretical calculation and experimental results prove that the rationally designed double-shelled NiFe PBAs nanocages with an abundance of the exposed surface have a lower energy barrier for the departure of CN groups from NiFe PBAs lattices, and thus generate CN vacancies with a concentration as high as 18.5% via a mild thermal activation strategy, which far outweigh the content of CN vacancies in the solid NiFe PBAs nanocubes. The as-prepared NiFe PBAs with abundant CN vacancies have an impressive OER activity with a low overpotential of 267 mV at 20 mA cm−2 and long-term stability with only ∼2.1% potential increase after 78 h. The opened double-shelled structure of NiFe PBAs nanocages offers highly exposed active sites and fast charge transfer kinetics. Moreover, post characterizations demonstrate the important role of CN vacancies in the suppression of Fe loss during the OER process and formation of Fe species as the active sites. This study provides an effective strategy to explore PBAs catalysts with desired nanostructures and defective multiplicity for enhanced OER catalysis.

Thermally activated carbon–nitrogen vacancies in double-shelled NiFe Prussian blue analogue nanocages for enhanced electrocatalytic oxygen evolution

The oxygen evolution reaction (OER) is of vital importance for electrochemical energy conversion technologies. The use of metal–organic framework (MOF) catalysts after postprocessing is an important method to optimize catalytic activity; however, little attention has been paid to the transformation of the electronic structure and coordinated ions under operando conditions. Here, we focus on a Prussian blue analogue (PBA) with the formula Na2Co2+[Fe2+(CN)6]·nH2O after postprocessing at a temperature of 400 °C. The catalysts exhibit a significant improvement in the OER activity with an overpotential of 254 mV against 320 mV for the initial PBA at 10 mA cm–2 in 1 M KOH. Our ex situ soft X-ray absorption spectroscopy (XAS) results demonstrate that some of the high-spin Co2+ and low-spin Fe2+ ions of PBA exhibit exchange with N and C ligands. Our fast operando hard XAS study revealed a dynamic evolution process of the transformation of ligands from N(C) in the initial Na2Co[Fe(CN)6]·nH2O to oxygen and the formation of pure low-spin Co3+ oxide and high-spin Fe3+ oxide after OER. The amorphous (Co,Fe)OOH chemical state was identified as the catalytically active state based on our operando X-ray spectroscopy results. The results of this study provide insights into a dynamic evolution process of MOFs after postprocessing and the formation of real active sites during electrocatalysis. 

In Situ Exploring of the Origin of the Enhanced Oxygen Evolution Reaction Efficiency of Metal(Co/Fe)–Organic Framework Catalysts Via Postprocessing

Electrospun prussian blue analogue derived NiCo@N-doped carbon nanofibers as efficient and highly stable electrocatalysts for neutral overall water splitting

Prussian blue analogues (PBAs) are mostly binary metallic compounds with a cubic structure, which greatly limits the structure and component of derived transition‐metal phosphides (TMPs) and affects their catalytic activities. This work focuses on regulating the morphology and composition of the PBA at the front‐end to optimize the OER performance of the derived TMP. By temperature control surfactant desorption ability, we obtain a series of ternary FeCoNi (FCN‐PBAs). With the increase of temperature, their morphologies change from truncated octahedrons to cubic octahedrons and truncated cubes, in which the Fe content basically remains unchanged and the Co/Ni ratio gradually decreased. Due to the synergistic effect among ternary TMPs, all phosphidation products (FCN‐P) exhibit better OER activities than RuO2, among which FCN‐40‐P shows the best performance. As confirmed by XPS analyses, the appropriate chemical composition enhances the oxidizabilityof TM species, promotes the chemical adsorption of OH−, and accelerates OER kinetics.

Morphology and Composition Regulation of FeCoNi Prussian Blue Analogues to Advance in the Catalytic Performances of the Derivative Ternary Transition-Metal Phosphides for OER

Manzhou Zhu

Papers

Morphology and Composition Regulation of FeCoNi Prussian Blue Analogues to Advance in the Catalytic Performances of the Derivative Ternary Transition-Metal Phosphides for OER