Role of Shell Numbers of Multi-Shelled N-Doped Ru-Co/Co₃O₄ Graphene-Coated Nano-Spheres in Overall Water Splitting...

N-doped multi-shelled Ru-Co/Co₃O₄ graphene-coated nanospheres were synthesized from metal-organic frameworks (MOFs) using a hydrothermal method. The annealing process, conducted at temperatures of 250°C, 310°C, 380°C, 450°C, and 530°C with a heating rate of 2°C min^-1 in the presence of melamine under a nitrogen atmosphere, led to the formation of multi-shelled nanospheres. The annealing temperature played a crucial role in controlling the number of shells within the nanospheres and enhancing nitrogen incorporation into their structure. This study demonstrated that annealing at 530°C resulted in the formation of quintuple-shelled nanospheres with the highest nitrogen incorporation. The number of shells and nitrogen content emerged as key factors influencing the electrocatalytic performance of these materials in water splitting. The quintuple-shelled nanospheres demonstrated remarkable electrocatalytic efficiency, delivering the maximum current density with minimal overpotential for both hydrogen and oxygen evolution reactions (HER and OER) under acidic conditions. Conversely, reducing the number of shells led to a progressive decrease in the overall electrocatalytic performance.