The philosophy here is that the cell seen on the right is where electrolysis of water happens. The hydrogen is injected into the fuel stream where it is burned along with regular petrol. Allegedly, the hydrogen+petrol mixture gives higher efficiency and lower emissions compared with petrol alone. (From a conservation-of-energy standpoint, clearly putting electrolysis in the system won't gain you anything. But the claim here is that the combustion process is more efficient in the presence of hydrogen.)