Electrolysis　of　water,　especially　alkaline　water　electrolysis　(AWE),　is　the　most　promising　technology　to　produce　hydrogen　in　industry.　However,　only　4%　of　the　total　hydrogen　is　produced　in　this　way　because　the　electrode　materials　are　expensive,　inefficient,　or　unstable.　Here,　it　is　reported　that　the　large-scale　3D　printed　martensitic　steel　(AerMet100)　can　be　the　bifunctional　electrode　for　AWE　with　high　catalytic　performance,　which　may　dramatically　increase　the　green-hydrogen　percentage　in　the　market　and　provide　strategic　planning　for　energy　management.　It　is　found　that　the　martensitic　steel　by　fast　anodization　(3　min)　can　realize　ultra-high　hydrogen　and　oxygen　evolution　reactions　(HER　and　OER),　and　excellent　stability　at　high　current　densities.　Particularly,　this　electrocatalyst　shows　a　low　overpotential　of　3.18　V　and　long-term　stability　over　140　h　at　570　mA　cm(-2)　in　overall　water　splitting.　Additionally,　the　treated　large-scale　steel　can　work　well　under　a　very　high　current　up　to　20　A.　This　study　demonstrates　that　martensitic　steel　can　be　commercialized　as　a　highly　efficient　catalyst　for　industrial　hydrogen　production　in　AWE,　which　should　provide　solutions　to　the　energy　crisis　and　environmental　pollution.