A method for onboard hydrogen production for use in fuel cells in a fuel cell electric vehicle (FCEV) is disclosed. The method comprises transferring vehicular-generated electrical energy produced by a regenerative braking system during braking and/or decent of the FCEV to one or more hydrogen electrolyzers. Water obtained from operation of one or more hydrogen fuel cells during generation of electricity from hydrogen is provided to the one or more hydrogen electrolyzers. Hydrogen is generated by means of the one or more hydrogen electrolyzers from water and the vehicular-generated electrical energy and collected in a hydrogen storage device. Heat emitted during operation of the FCEV is directed to the one or more hydrogen electrolyzers to accelerate production of hydrogen gas by the one or more hydrogen electrolyzers. A system, and a vehicle comprising a system for onboard hydrogen production for use in fuel cells in a FCEV is also disclosed.