Preparation of CoS2/Nd2O3 composites and S-CNTs and their electrochemical performance in asymmetric supercapacitors

Short-duration and repetitive power fluctuations associated with train acceleration, braking, and regenerative-energy recovery require energy-storage devices with rapid response, high-rate capability, and stable cycling. Here, a CoS 2 /Nd 2 O 3 composite positive electrode prepared at a confirmed Co/Nd molar feed ratio of 2:1 and a sulfur-treated carbon-nanotube (S-CNT) negative electrode were combined in an aqueous asymmetric supercapacitor. The composite exhibited a predominantly mesoporous architecture with a Brunauer–Emmett–Teller surface area of 213.21 m 2  g −1 , while the S-CNTs retained a continuous one-dimensional conductive network and sulfur-related surface species. The CoS 2 /Nd 2 O 3 electrode delivered 1961 F g −1 at 1 A g −1 and retained 1401 F g −1 at 20 A g −1 , with 87.6% capacitance retention after 10,000 cycles. The S-CNT electrode delivered 431 F g −1 at 1 A g −1 , 28.7% above untreated CNTs under the same conditions, and retained 81.0% at 20 A g −1 . The two-electrode device retained 73.3% of its 1 A g −1 capacitance at 15 A g −1 and approximately 95.0% after 10,000 cycles. A retrospective first-order charge-balance analysis indicates that further optimization of the electrode mass ratio would be beneficial. These results support the tested material pair as a laboratory-scale platform for short-duration power buffering, while composition optimization, complete-device impedance characterization, and application-specific pulse validation would further strengthen its assessment for rail-transit applications.