Scaling up electrochemical water splitting is nowadays in high demand for hydrogen economy implementation. Tremendous eff orts over the past decade have been focused on exploring alternative catalytic materials, including a variety of earth-abundant transitionmetal-based catalysts, to replace traditional noble metals such as Pt, Ir, or Ru. Nevertheless, few eff orts have been carried out for (1) scalable catalyst synthesis on current collectors and (2) practical device design toward large-scale H2 generation. Herein, we designed a modular alkaline water-splitting electrolyzer system with scaled-up metal foam electrodes covered by low-cost NiMo alloy and Ni3 Fe oxide for efficient hydrogen evolution and oxygen evolution, respectively. An electrolyte circulation system facilitates the mass transport and thus can further boost the H2 generation particularly under large currents. As a result, the overall water-splitting performance of one-unit cell with a dimension of 10 Å~ 10 cm2 under room temperature presents an early onset voltage of 1.54 V and delivered practical currents of 20 and 55 A (9.1 and 25.0 L/h H2 generation) under 2.2 and 2.9 V without iR compensations, respectively. This demonstration could stimulate new focuses in water splitting toward more practical applications.