Harnessing the enigmatic ortho-para isomeric conversion for energy-efficient and low-carbon production of liquid hydrogen

<h2>Summary</h2> Liquid hydrogen (LH₂) is considered an attractive replacement for hydrocarbon fuels, but the energy-intensive production of LH₂ hinders its uptake in industry. We find that up to 57% of energy expenditure in liquefaction comes from the exothermic conversion of the ortho-hydrogen isomer into the para-hydrogen form. Our experimental results demonstrate that full (99.6% para-hydrogen) ortho-para conversion (OPC) is impractical, leading us to consider non-ideal OPC in liquefaction simulations for the first time. We highlight that the energy and environmental costs of LH₂ are excessive if LH₂ is used before one year after liquefaction. Through tunable OPC, we reduce energy costs by 8%–13% with 83%–95% para-hydrogen compared with full OPC while still attaining loss-less LH₂ storage for 1–7 days. We demonstrate that wind-based LH₂ production leads to 20× lower CO₂ emissions than jet fuels, reducing the environmental impact of a London-New York flight (Boeing 787–9) by at least 92%.