Composition-dependent Charge Storage and Electrochemical Kinetics of Bi2O3/Nitrogen-doped Reduced Graphene Oxide Composite Electrodes

Understanding the relationship between electrode composition, charge-storage behavior, and electrochemical kinetics is essential for developing high-performance hybrid energy-storage materials. Herein, Bi 2 O 3 /nitrogen-doped reduced graphene oxide (N-rGO) composites with varying Bi 2 O 3 :N-rGO mass ratios (1:0.25 - 1:1) were synthesized and systematically investigated. Structural and surface analyses confirmed the coexistence of Bi 2 O 3 and N-rGO, with nitrogen functionalities predominantly consisting of pyrrolic-N, alongside graphitic-N and pyridinic-N species. Increasing the N-rGO proportion progressively enhanced the charge-storage performance, with BG100 (1:1) achieving the highest specific capacitance of approximately 823 F g -1 at 5 mV s -1 and specific discharge capacity of 442 mAh g -1 at 2.5 A g -1 . Electrochemical kinetic analysis revealed the coexistence of diffusion-controlled and surface-capacitive processes, with the capacitive contribution increasing from 18% to 49% as the scan rate increased from 5 to 100 mV s -1 . Interestingly, the highest charge-storage performance of BG100 did not correspond to the lowest fitted charge-transfer resistance, highlighting a non-monotonic relationship between N-rGO content, interfacial resistance, and charge-storage capability. Cycling measurements showed 61.7% capacity retention after 10,000 cycles, highlighting the need for further durability improvement. These findings establish a composition-dependent relationship between charge-storage performance and electrochemical kinetics in Bi 2 O 3 /N-rGO electrodes, providing insights into the design of metal oxide-carbon hybrid energy-storage materials.