Electrochemical capacitors are facing a long-lasting challenge of obtaining metal oxide pseudocapacitive electrodes with both high mass loadings (8-10 mg cm-2) and excellent rate capability. The high-mass-loading electrodes typically contain active materials compactly stacked with thickness exceeding 1000 nm, making ions extremely challenging to diffuse throughout the thick layers rapidly. This sluggish ion diffusion undermines the excellent rate capability and ultrahigh power density – the two characteristic merits of electrochemical capacitors. This presentation will demonstrate a glucose-assisted hydrothermal method that effectively mitigates the ion-diffusion challenge. The method grows mesoporous iron oxide films on commercial carbon fibers with mass loadings approaching 10 mg cm-2 and thicknesses exceeding 1 µm. The talk will explain the mesopore-formation mechanism and highlight the pore-size controllability by the glucose concentration. This pore-size controllability enables for the first time, a systematic study on the interplay between the mesopore size and the capacitance/rate capability of the high-mass-loading iron oxide electrodes. The film with the optimal mesopore size of 3 nm exhibits the highest areal capacitance of 1502 mF cm-2 at 1 mA cm-2, and still retains 871.2 mF cm-2 at 50 mA cm-2. These performances, to the best of our knowledge, remains at the top of the reported iron-oxide-based pseudocapacitive electrodes with comparable mass loadings, and is particularly impressive for iron oxide with ultra-low ionic conductivity.

Mesoporous iron oxide pseudocapacitive electrodes with mutually high mass loadings and excellent rate capability

2019 Spring National Meeting

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