Preparation and supercapacitive properties of 3D flower-like iron metaphosphates based on anodization of iron

•3D flower-like iron metaphosphates are prepared based on anodization of iron.•The developed synthetic route is a low-energy-consumption and cost-effective one.•Iron metaphosphates can be employed directly as an electrode for supercapacitors.•Their areal specific capacitance can reach up to 117.42 mF cm−2. Due to the high specific capacitance and wide operating potential of iron compounds, iron metaphosphates are expected to be high-performance electrode materials for supercapacitors. Herein, we propose a strategy for preparing three-dimensional (3D) flower-like iron metaphosphates on iron substrates, which includes anodization of Fe and subsequent hydrothermal treatment. The rod-like ferrous oxalate films are obtained by anodization of Fe in an oxalic acid electrolyte. Then 3D flower-like iron metaphosphates can be obtained through hydrothermal treatment of ferrous oxalate films soaked in phosphoric acid solution. The prepared 3D flower-like iron metaphosphates electrode displays a high areal capacitance of 117.4 mF cm−2, about 12.6 times higher than that of pure iron. In addition, this kind of iron metaphosphates may be further used in electrocatalysis, solar cells, and so on.