In this work, the plating of high‐quality amorphous nickel–phosphorous coating with low resistivity of 0.45 µΩ m (298 K) on complex 3D printed polymeric structures with high uniformity is reported. Such a polymer metallization results in an effective conductivity of 4.7 × 10 4 S m −1 . This process also allows flexible structures to maintain their flexibility along with the conductivity. Octet‐truss structures with nickel–iron‐(oxo) hydroxide nanosheets electrodeposited onto further displays excellent water‐splitting performance as catalytic electrodes, i.e., in KOH ( 1 m , aq), a low oxygen evolution reaction (OER) overpotential of 197 mV at 10 mA cm −2 and Tafel slope of 51 mV dec −1 . Using this light‐weight electrode with high specific area, strength, and corrosion resistance properties, a fully functional water‐splitting system is designed and fabricated through the concentric integration of 3D printed components. A dense polymeric mesh implemented is also demonstrated as an effective separator of hydrogen and oxygen bubbles in this system.

Scaling up commercial hydrogen production by water electrolysis requires efficient oxygen evolution reaction (OER) electrodes that can deliver large current densities (more than 500 mA cm−2) at low overpotentials. Here, a highly active and conductive shell‐based cellular (Shellular) electrode is developed through a strategy of embedding nanocrystalline Ni3Nb intermetallics into an amorphous NiFe‐OOH matrix. The tailor‐made laser remelting process enables the dispersive precipitation of corrosion‐resistant nanocrystalline Ni3Nb in large numbers. After in situ electrochemical activation in the self‐developed growth‐mode‐control electrolyte, the amorphous NiFe‐OOH nanosheets and nanocrystalline Ni3Nb are formed on the as‐printed Inconel 718. The conductive atomic force microscopy (C‐AFM) studies and density functional theory (DFT) calculations elucidate that nanocrystalline Ni3Nb can simultaneously enhance the conductivity and activity of the catalyst film. Additionally, a Shellular structure inspired by nature is designed, interestingly, its specific surface area keeps constant with increases in porosity. This design can result in a large surface area and high porosity but with less material cost. Using this electrochemically activated Shellular electrode for OER, a high current density of 1500 mA cm−2 is achieved at a record‐low overpotential of 261 mV with good durability. This development may open the door for large‐scale industrial water electrolysis.

High roughness of metal structures made by selective laser melting restricted their extensive applications. A strategy of overpotential electrochemical polishing was developed for effectively smoothening three-dimensional (3D)-printed surfaces, particularly for removing sticking particles. Average surface roughness of 0.18 µm was achieved with a small thickness removed of ∼ 70 µm through a combination of overpotential and conventional electrochemical polishing. Interestingly, microlattices polished with this approach nearly doubled the specific compressive plateau stress and energy absorption over as-printed lattices. Moreover, the success with 316L stainless steel, 4130 steel and AlSi10Mg, indicates the potential of this approach for smoothening other 3D-printed metals. IMPACT STATEMENT A highly effective technology to smoothen complex and rough 3D-printed metal surfaces is developed using a novel overpotential electrochemical polishing, which can enhance mechanical and functional properties of 3D-printed metals.

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3D printing of a tailor-designed support architecture with a tunable electrochemically active surface area for improving catalyst loading contributions to catalytic activity.