Methods and devices for generating power using PEM fuel cell power systems comprising a rotary bed reactor for hydrogen generation are disclosed. Hydrogen is generated by the hydrolysis of fuels such as lithium aluminum hydride and mixtures thereof. Water required for hydrolysis may be captured from the fuel cell exhaust. Water is preferably fed to the reactor in the form of a mist generated by an atomizer. An exemplary 750 We-h, 400 We PEM fuel cell power system may be characterized by a specific energy of about 550 We-h/kg and a specific power of about 290 We/kg.