Hydrogen-based direct reduced iron (H2-DRI) is an alternative pathway for low-carbon steel production. Yet, the lack of established process and business models defining “green steel” makes it difficult to understand what the respective H2 price has to be in order to be competitive with commercial state-of-the-art natural gas DRI. Given the importance of establishing break-even H2 prices and CO2 emission reduction potentials of H2-DRI, this study conducted techno-economic analyses of several design and operation scenarios for DRI systems. Results show that renewable H2 use in integrated DRI steel mills for both heating and the reduction of iron ore can reduce direct CO2 emissions by as much as 85%, but would require an H2 procurement cost of $1.63 per kg H2 or less. When using H2 only for iron ore reduction, economic viability is reached at an H2 procurement cost of $1.70 per kg, while achieving a CO2 emission reduction of 76% at the plant site. System design optimization strategies around excess H2 ratios in the DRI top gas and the H2 recycle pressurization can further improve performance and economics. Low H2 excess ratios are particularly attractive as they reduce pre-heating energy requirements and offer integration opportunities with static recycle ejectors if H2 is supplied at sufficiently high pressure. The potential of utilizing the electric arc furnace off-gas is shown to be much more synergistic with H2-DRI than natural gas-DRI and can increase the break-even H2 procurement cost by up to 7¢ per kg H2. Such findings are critical for setting technical performance criteria for H2 supply and storage in the iron and steel sector.

Hydrogen offers a route to storing renewable electricity and lowering greenhouse gas emissions. Metal–organic framework (MOF) adsorbents are promising candidates for hydrogen storage, but a deep understanding of their potential for large-scale, stationary back-up power applications has been lacking. Here we utilize techno-economic analysis and process modelling, which leverage molecular simulation and experimental results, to evaluate the future opportunities of MOF-stored hydrogen for back-up power applications and set critical targets for future material development. We show that with carefully designed charging–discharging patterns, MOFs coupled with electrolysers and fuel cells are economically comparable with contemporary incumbent energy-storage technologies in back-up power applications. Future research should target developing MOFs with 15 g kg−1 of recoverable hydrogen adsorbed (excess uptake) and could be manufactured for under US$10 kg−1 to make the on-site storage system a leading option for back-up power applications.

Liquid organic hydrogen carriers will likely be a key element of a future hydrogen economy by enabling the storage and transport of large quantities of hydrogen. Ethanol is a liquid organic hydrogen carrier that is readily available from biological resources, which undergoes a reversible reaction to yield hydrogen and ethyl acetate. The objective of the present study is to obtain a better understanding of the thermodynamic and environmental suitability of the ethanol–ethyl acetate cycle for hydrogen storage applications. The analysis covers three aspects: thermodynamics of the chemical reaction, energy balance of the process, and a first-order assessment of greenhouse gas emissions. Thermodynamics of the reaction are characterized by a standard Gibbs energy of reaction close to zero which allows the reaction to be shifted between hydrogenation and dehydrogenation within a moderate window of temperature and pressure conditions. The energy demand for dehydrogenation is comparatively small, resulting in an overall system efficiency of 88%. A life cycle greenhouse gas analysis over a 20-year storage system lifetime gives a carbon intensity of 7.0 kg-CO2eq/kg-H2 delivered. These results indicate that the ethanol–ethyl acetate system has considerable promise as a hydrogen carrier and should be the subject of further research.

Onsite production of gigawatt-scale wind- and solar-sourced hydrogen (H2) at industrial locations depends on the ability to store and deliver otherwise-curtailed H2 during times of power shortages. Thousands of tonnes of H2 will require storage in regions where subsurface storage is scarce, which may only be possible using liquid organic H2 carriers. We evaluate aboveground system with a focus on providing technical insights into toluene/methylcyclohexane (TOL/MCH) storage systems in locations suitable for gigawatt-scale wind- and solar-powered electrolyzer systems in the United States. Here we show that the levelized cost of storage, at a national median of US dollar $1.84/kg-H2 is spatially heterogeneous, causing minor impact on the cost of H2 supply in the Midwest, and significant impact in Central California and the Southeast. While TOL/MCH may be the cheapest aboveground bulk storage solution evaluated, upfront capital costs, modest energy efficiency, reliance on critical materials and pre-sulfided catalysts, and greenhouse gas emissions from heating are opportunities for further development.