An apparatus for an in-vivo power generation comprises a fuel convertor for converting glucose in a fluid to a hydrogen rich, low carbon fuel such as ethanol or methanol by the action of a bioenzyme on the glucose in the CSF. The fluid can be any one of cerebro spinal fluid, urine and glucose solution. The apparatus further comprises a biofuel cell comprising a cathode chamber and an anode chamber with a membrane assembly sandwiched between them. The membrane assembly comprises a cathode, an anode and a proton exchange membrane. The cathode is coated with an enzyme laccase, which enables extraction of oxygen when the fluid is passed through the cathode chamber. The oxygen from the cathode chamber and the hydrogen in the hydrogen rich fuel from the anode chamber diffuses through the proton exchange membrane and reacts at an ionic level to result in water and electrical power.