Life Cycle Assessment of Renewable-Based Green Hydrogen Production

Hydrogen is an energy carrier rather than a primary energy source. Its environmental performance therefore depends on the upstream energy and material system used to produce, condition and deliver it. Hydrogen can be produced from natural gas, coal, biomass, water electrolysis or combinations of these routes. Renewable-based electrolysis uses electricity generated from renewable resources to split water into hydrogen and oxygen. When renewable electricity is genuinely low-carbon and the full value chain is considered, this route can provide a substantially lower greenhouse-gas footprint than conventional fossil-based hydrogen. The fundamental electrochemical reaction is 2H¿O ¿ 2H¿ + O¿. The thermodynamic minimum electrical work is related to the Gibbs free-energy change of the reaction, while practical electrolyzers require additional energy because of activation, ohmic and mass-transfer losses. Therefore, life-cycle assessment must not treat the theoretical reaction energy as the actual electricity demand. A realistic inventory should include stack consumption, auxiliary electricity, water treatment, cooling, power electronics and operating losses.