A portable on-demand hydrogen supplemental system is provided for producing hydrogen gas and injecting the hydrogen gas into the air intake of internal combustion engines. Hydrogen and oxygen is produced by a fuel cell from nonelectrolyte water in a nonelectrolyte water tank. The hydrogen gas is passed through a hydrogen gas collector. Nonelectrolyte water mixed with the hydrogen gas in the hydrogen gas collector is passed back thru the tank for distribution and water preservation. The system can be powered by the vehicles alternator, a stand-alone battery, waste heat or solar energy. The system utilizes an onboard diagnostic (OBD) interface in communication with the vehicle's OBD terminal, to regulate power to the system so that hydrogen production for the engine only occurs when the engine is running. The hydrogen gas is produced it is immediately consumed by the engine. No hydrogen is stored on, in or around the vehicle.