The honeycomb-structured film has advantages such as high wettability and high surface area. This structure and properties are suitable for the capacitor electrode. In this study, the electrode structure is controlled by the synthesis of MnO 2 nanoparticles using the breath figure method. The electrode performance was calculated by electrochemical measurements. As a result, the capacitance value was 100.5 F/g at 1 mV s –1 , which was improved 2.7 times as compared with that without structure control.

No abstract

We investigated the recovery of rare-earth elements from three types of Nd-Fe-B sintered magnets (Nd-mags) to study the effectiveness of the wet-mechanochemical resource recovery technique. These magnets were of different chemical compositions and were studied via the wet-mechanochemical treatment using a H2SO4-(COOH)2 mixed reaction solution. A high recovery rate (R) and high purity of rare-earth elements in the collected precipitate (P) could be achieved by optimizing the H+/RE and oxalate/RE. H+/RE is defined as the molar ratio between the H+ amount in the added H2SO4 and the rare-earth content in the Nd-mag (RE); oxalate/RE is the molar ratio between the added amount of (COOH)2 and RE values. The optimum conditions were H+/RE ∼ 5–10 and oxalate/RE ∼ 10; simultaneously, the R and P values were approximately 97 and 100 mass %, respectively. We also investigated the particle size effect on the R and P values, and the optimum treatment time was determined to be more than 1 h. Furthermore, the power consumption of the wet-mechanochemical treatment under optimal conditions was about 0.2 kWh. Thus, it was found that the wet-mechanochemical technique is an effective and eco-friendly method for recovering rare-earth elements as oxalate with high purity from a Nd-mag.