Towards a 100 % hydrogen-driven direct reduction ironmaking future: A critical review on kinetics, bottlenecks, and research priorities

Pure hydrogen direct reduction (H2-DR) is poised to be the cornerstone technology for deep decarbonization of the iron and steel sector to attain low-carbon development in the context of emissions peak and carbon neutrality goals. Unlike conventional hydrogen-rich CO-H2 reduction, pure H2-DR presents unique thermodynamic and kinetic characteristics, alongside distinct engineering challenges. This work provides a critical review of the fundamental differences between pure H2 and CO/CO-H2 mixtures in reducing iron oxides, highlighting the endothermic nature and superior kinetics of H2 reactions. The historical development and current status of industrial projects employing 100 % H2 are systematically analyzed, with them being categorized into fluidized bed and shaft furnace routes. Furthermore, this study identifies and elaborates on the pivotal scientific bottlenecks—such as morphological evolution and sticking mechanisms—and technical hurdles—including low-grade ore adaptation and heat supply strategies—that must be overcome to realize commercial-scale pure H2-DR. Finally, a targeted research agenda aimed at accelerating the development of a sustainable and economically viable pure hydrogen ironmaking ecosystem is proposed. This review distinguishes itself by focusing exclusively on the 100 % H2 pathway, offering strategic insights for future fundamental research and process development.