The environmental impact of energy systems is increasingly scrutinized through the lens of lifecycle emissions, particularly in transportation and power generation. Comparing hydrogen combustion, fuel cells, battery-electric systems, and fossil fuels requires a well-to-wheel analysis, encompassing upstream production, distribution, and end-use emissions. Each pathway exhibits distinct carbon footprints, influenced by feedstock, energy sources, and technological efficiency.
Hydrogen combustion involves burning hydrogen in internal combustion engines or turbines, emitting only water vapor at the point of use. However, upstream emissions vary drastically depending on production methods. Steam methane reforming (SMR), the dominant method, emits 9-12 kg CO2 per kg of hydrogen due to natural gas extraction and processing. Adding carbon capture and storage (CCS) reduces this to 4-7 kg CO2/kg H2. Electrolysis, powered by renewables, can achieve near-zero emissions, but grid-powered electrolysis inherits the carbon intensity of the electricity mix. For example, using the EU average grid (approx. 230 g CO2/kWh), electrolysis emits around 12-15 kg CO2/kg H2.
Fuel cells convert hydrogen to electricity electrochemically, with higher efficiency (50-60%) than combustion (35-45%). This reduces hydrogen demand per unit of energy delivered. However, fuel cell manufacturing involves platinum-group metals, contributing to embedded emissions. Battery-electric vehicles (BEVs) exhibit zero tailpipe emissions, but their lifecycle impact depends on battery production and charging electricity. Lithium-ion battery manufacturing emits 60-100 kg CO2/kWh of capacity. Charging from renewables minimizes operational emissions, while coal-heavy grids (e.g., 800-1000 g CO2/kWh) erode the advantage.
Fossil fuels have well-documented high emissions. Gasoline combustion emits approx. 2.3 kg CO2/liter, diesel 2.7 kg CO2/liter, and natural gas 50-60 g CO2/MJ. Upstream extraction and refining add 20-30% to these figures. Coal, the most carbon-intensive, emits 90-100 g CO2/MJ.
A comparative table illustrates well-to-wheel emissions (g CO2/km) for light-duty vehicles:
Technology Production Pathway Well-to-Wheel Emissions
Hydrogen Combustion SMR (no CCS) 180-220
Hydrogen Combustion SMR + CCS 90-120
Hydrogen Combustion Renewable Electrolysis 20-40
Fuel Cell Vehicle SMR (no CCS) 120-150
Fuel Cell Vehicle Renewable Electrolysis 15-30
Battery-Electric EU Grid Mix 70-90
Battery-Electric Renewable Charging 20-40
Gasoline ICE Crude Oil Refining 240-270
Diesel ICE Crude Oil Refining 220-250
Hydrogen combustion can be environmentally preferable in specific scenarios. First, in applications requiring high-temperature heat (e.g., industrial processes, aviation), fuel cells are impractical, and hydrogen combustion offers a cleaner alternative to fossil fuels. Second, regions with abundant renewable energy can produce green hydrogen at scale, making combustion near-zero-emission. Third, retrofitting existing gas infrastructure for hydrogen reduces transition costs and avoids stranded assets.
However, hydrogen combustion faces efficiency drawbacks. Fuel cells and BEVs outperform it in energy conversion, making them preferable for most mobility applications. Additionally, hydrogen leakage—a potent indirect greenhouse gas—poses risks if not managed.
In summary, hydrogen combustion’s lifecycle emissions depend heavily on production methods. While less efficient than fuel cells or BEVs, it can decarbonize sectors where electrification is infeasible. Pairing it with green hydrogen and CCS ensures competitiveness against fossil fuels, though fuel cells remain superior where applicable. The optimal pathway hinges on local resources, infrastructure, and end-use requirements.