Hollow Nanostructures A preferential etching method for synthesizing monocrystalline nanoframes of a Prussian blue analogue is described by M. Hu et al. in their Communication on nie.201600661" rel="references:http://dx.doi.org/10.1002/anie.201600661">page 8228 ff. The microfabricated nanoframes are active cathode materials with applicability to alkaline ion batteries.