Developing efficient water splitting at high current density (>500 mA cm-2) is essential for its scalability. [1] Electrochemical water splitting is one of the most promising technological approaches for producing green hydrogen, and it plays a crucial role in achieving carbon neutrality. [2] In the meantime, additive manufacturing as a simple and facile method has attracted researchers’ interest for the past decades, and a couple of outstanding works about using 3D printing to fabricate electrodes for water-splitting have been done. [3]–[5] Here, we reported a series of monolithic 3D-printed Ni-Mo alloy electrodes for highly efficient water splitting at high current density (1500 mA cm-2) with excellent stability and bubble removal behavior, which provides a solution to scale up Ni-Mo catalysts for HER to industry use. All possible Ni-Mo metal/alloy phases were achieved by tuning the atomic composition and heat treatment procedure, and they were investigated through both experiment and simulation, and the optimal NiMo phase shows the best performance. Density functional theory (DFT) calculations elucidate that the NiMo phase has the lowest H2O dissociation energy, which further explains the exceptional performance of NiMo. In addition, the microporosity was modulated via controlled thermal treatment, indicating that the 1100 C sintered sample has excellent catalytic performance, which is attributed to the high electrochemical surface area (ECSA). Finally, the 4 different macrostructures were achieved by 3D printing, and they further improved the catalytic performance. The gyroid structure exhibits the best catalytic performance of driving 500 mA cm-2 at a low overpotential of 228 mV and 1500 mA cm-2 at 325 mV as it maximizes the efficient bubble removal from the electrode surface, which offers the great potential for high current density water splitting (shown in Figure 1).

Figure 1. (a) 3D models created from Blender. (i) woodpile structure. (ii) octet truss structure. (iii) honeycomb structure. (iv) gyroid structure. (b) SEM images of Ni-Mo electrodes with different 3D architectures. (i) woodpile structure. (ii) octet truss structure. (iii) honeycomb structure. (iv) gyroid structure. (c) HER polarization curves of different 3D architecture electrodes (53 at. % Mo) in 1M KOH solution at 1 mV s−1 with 85% iR-compensations: gyroid, octet truss, woodpile, honeycomb, and plate. (Inset: overpotential at 1500 mA cm-2) (d) Time-dependent potential curves with 85% iR-compensations for the 3D-printed Ni-Mo electrode at 10 and 50 mA cm−2. (e) Chronoamperometric measurements with 85% iR-compensation of the HER at high current densities of 1500 mA cm−2 for the 3D-printed Ni-Mo electrode.

[[1] Y. Luo, Z. Zhang, M. Chhowalla, and B. Liu, “Recent Advances in Design of Electrocatalysts for High-Current-Density Water Splitting,” Adv. Mater., vol. 34, no. 16, p. 2108133, (2022)

[2] X. Liu, M. Gong, S. Deng, T. Zhao, J. Zhang, and D. Wang, “Recent advances on metal alkoxide-based electrocatalysts for water splitting,” J. Mater. Chem. A, vol. 8, no. 20, pp. 10130–10149, (2020)

[3] S. Chang et al., “Conductivity Modulation of 3D‐Printed Shellular Electrodes through Embedding Nanocrystalline Intermetallics into Amorphous Matrix for Ultrahigh‐Current Oxygen Evolution,” Adv. Energy Mater., p. 2100968, (2021)

[4] R. A. Márquez et al., “Tailoring 3D-Printed Electrodes for Enhanced Water Splitting,” ACS Appl. Mater. Interfaces, p. acsami.2c12579, Sep. (2022)

[5] I. Sullivan et al., “ 3D Printed Nickel–Molybdenum-Based Electrocatalysts for Hydrogen Evolution at Low Overpotentials in a Flow-Through Configuration,” ACS Appl. Mater. Interfaces, vol. 13, no. 17, pp. 20260–20268, (2021)