Morphology Control of Hydrogen Evolution Reaction Catalyst Promoting H ₂ Mass Transfer

Gas bubble accumulation during hydrogen evolution reaction (HER) hinders mass transfer and limits ampere-scale performance, making the optimization of electrode microstructures for efficient H 2 release a critical challenge. We precisely synthesized NiMo/MoO 2 -based catalysts in 1D nanorod (1D-NR), 2D nanosheet (2D-NS), and 3D nanosheet-rod complex (3D-SR) structures to identify the optimal structure for enhanced HER mass transfer. The 1D-NR with the open-channel structure and a small adhesive force exhibited the lowest bubble detachment time (200 ± 40 ms) and the lowest potential fluctuation. In an anion exchange membrane water electrolyzer, a 1D-NR-catalyzed device suppressed slug and annular flow, allowing bubble flow to predominantly occupy the central region of the channels at high current. The 1D-NR-catalyzed device achieved 1.87 A cm –2 at 1.8 V, representing 96.8% and 30.8% improvements over the 2D-NS and 3D-SR catalyzed devices, respectively. Moreover, the 1D-NR-catalyzed device showed long-term stability of 1400 h at 1 A cm –2 .