The new Honda CR-V FCEV is a plug-in hybrid.
It has a 4.3kgH2 storage tank and a range of 435km. This translates into a range of 1kgH2/100km.
The 17.7kWh battery is good for 45km of battery only range.
The predominant method of producing H2 globally is Steam Methane Reforming.
The overall reaction is
CH4 + 2H2O = CO2 + 4H2
and is endothermic, meaning heat must be supplied to drive the reaction.
Doing mass balance the minimum quantity of CO2 per kgH2 produced is 5.5kgCO2/kgH2. In practice more fossil energy is needed to create the steam and sustain the reaction so the SMR is typically 8-10kgCO2 per kg H2.
This translates into 8-10kgCO2/100 km for the SMR fueled Honda FCEV neglecting the plug-in contribution to the range.
For comparison a Toyota Prius is 9.6kgCO2 / 100 km
This carbon intensity for the Honda FCEV assumes that all the H2 required to fuel the vehicle was produced from SMR. Like the electricity grid where various generation sources produce the electricity, a future H2 supply chain would be a blend of H2 production technologies many of which have a lower carbon footprint than SMR. Unlike the electricity grid which is a JIT (just in time) delivery system the H2 delivery system by definition incorporates storage. This means that a FCEV can always avail itself of a blended carbon footprint while a BEV’s carbon footprint varies with time of charge and instantaneous status of the grid.
A BEV is charged using the electricity grid. In the future a FCEV will be fueled from the natural gas grid containing a mixture of H2 and natural gas. One promising technology which can perform both the H2 separation and compression required is electrochemical Hydrogen compression.