A hydrogen fuel system for a vehicle includes a fuel tank having a fuel inlet for receiving a borohydride fuel into a fuel holding portion of an internal cavity, and a waste inlet arranged to receive the waste liquid generated by an on-board hydrogen reaction process. The waste liquid is received into a waste liquid portion of the internal cavity. An expandable divider element is positioned within the tank to keep the fuel holding portion of the internal cavity separate from the waste liquid holding portion. The waste liquid holding portion can be positioned within the internal cavity so as to allow heat from the waste liquid to preheat the fuel stored in the fuel holding portion.