Functional Electrocatalysts Derived from Prussian Blue and its Analogues for Metal-Air Batteries: Progress and Prospects

Metal- air batteries holding exceptionally high energy densities have been heavily explored recently amongst the promising next generation energy suppliers. However, their development for real application is restricted mainly due to the sluggish rates of the oxygen- reduction reaction ( ORR) and oxygen- evolution reaction ( OER) in the positive electrode. Thus, searching a facile way to attain highly efficient ORR and OER electrocatalysts are highly desirable. The key factors to improve the electrochemical performance of materials are to optimize their low- dimensional feature and adjust effective compositions. Prussian blue and its analogues ( PB/ PBAs) with open framework have attracted growing attention as hopeful precursors and templates to diverse transition metal- based materials and carbon hybrids for ORR and OER. Compared to other precursors, PB/ PBAs are more feasible for large- scale application due to their easy preparation, low cost, tuneable compositions and great environmental friendliness. In this review, recent progresses in the utilization of PB/ PBA to rationally design and synthesize complex composites with controlled morphologies, sizes, and compositions for ORR, OER and metal- air batteries are described in detail. Afterwards, a brief summary of the synthetic methods to complex transition metal- based compositions with nanostructures converted from PB/ PBAs are provided. Lastly, the research challenges and possible development direction of open framework materials for metal- air batteries are outlined through analysing the merits and drawbacks of using PB/ PBAs as precursors.