High-loading, ultrafine Ni nanoparticles dispersed on porous hollow carbon nanospheres for fast (de)hydrogenation kinetics of MgH2

•A unique structural catalyst of Ni and carbon composite is developed for MgH2.•Ultrafine Ni particles are uniformly dispersed on porous hollow carbon nanospheres.•The composite with Ni loading up to 90 wt% shows highly-effective catalysis to MgH2.•The catalyzed MgH2 system shows a low peak dehydrogenation temperature of 242 °C.•A reversible capacity of 6.4 wt% achieves after 50 cycles at a moderate cyclic regime.