Catalytic methane decomposition has been considered suitable for the green and sustainable production of high-purity H2 to help reduce greenhouse gas emissions. This research developed a copper-modified nickel-supported mesocellular silica NiCu/MS(x) catalyst synthesized at different calcination temperatures to improve the activity and stability in the CH4 decomposition reaction at 600 °C. Ni and Cu metals were loaded on a mesocellular silica (MS) support using a co-impregnation method and calcined at different temperatures (500, 600, 700, and 800 °C). The NiCu/MS(600) catalyst not only had the highest H2 yield (32.78%), which was 1.47-3.87 times higher than those of the other NiCu/MS(x) catalysts, but also showed better stability during the reaction. Calcination at 600 °C helps improve the active nickel dispersion, the reducibility of the NiCu catalyst, and the interaction of the NiCu-MS support, leading to the formation of fishbone and platelet carbon nanofibers via a tip-growth mechanism, resulting in the NiCu metals remaining active during the reaction.