Developing highly active and low-cost electrocatalysts with superior durability for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is a grand challenge to produce hydrogen by electrolysis of water. Here, we report on a facile and scalable approach to fabricate highly efficient three-dimensional (3D) bulk catalysts of core–shell nanostructures, in which few-layer NiFe layered double hydroxide (LDH) nanosheets are grown on Cu nanowire cores supported on Cu foams, toward overall water splitting. Remarkably, benefiting from the 3D hierarchical nanoarchitecture with large surface areas, fast electron transport, and open-channels for effective gas release, the resulting 3D self-standing catalysts exhibit outstanding OER activity as well as excellent HER performance in an alkaline medium. Using them as bifunctional catalysts for overall water splitting, a current density of 10 mA cm⁻² was achieved at a voltage of 1.54 V, and 100 mA cm⁻² at 1.69 V with excellent durability, which is much better than the benchmark of IrO₂(+)//Pt(−) electrodes. Our 3D core–shell electrocatalysts significantly advance the research towards large-scale practical water electrolysis.

Splitting water into hydrogen and oxygen by electrolysis using electricity from intermittent waste heat, wind, or solar energies is one of the easiest and cleanest methods for high-purity hydrogen production and an effective way to store the excess electrical power. The key dilemma for efficient large-scale production of hydrogen by splitting of water via the hydrogen and oxygen evolution reactions (HER and OER, respectively) is the high overpotential required, especially for the OER. We report an exceptionally active and durable OER catalyst yielding current densities of 500 and 1000 mA cm⁻² at overpotentials of only 259 mV and 289 mV in alkaline electrolyte, respectively, fulfilling the commercial criteria of the OER process. Together with a good HER catalyst, we have achieved the commercially required current densities of 500 and 1000 mA cm⁻² at 1.586 and 1.657 V, respectively, with very good stability, dramatically lower than any previously reported voltage. This discovery sets the stage for large-scale hydrogen production by water splitting using excess electrical power whenever and wherever available.

Electrochemical reconstruction is a powerful tool for generating highly active oxygen evolution reaction (OER) catalysts. Utilizing electrochemical reconstruction to fabricate an OER active catalyst based on a hydrogen evolution reaction (HER) catalyst enables the development of a bifunctional catalyst that possesses state-of-the-art HER and OER activity simultaneously. Here we successfully synthesized Fe-doped Ni&Ni_0.2Mo_0.8N (Fe_0.01-Ni&Ni_0.2Mo_0.8N) on Ni foam and, after rapid electrochemical reconstruction, the Fe-doped Ni&Ni_0.2Mo_0.8N compound was reconstructed into NiO co-doped with Fe and Mo (Fe_0.01&Mo-NiO). The Fe_0.01-Ni&Ni_0.2Mo_0.8N and Fe_0.01&Mo-NiO compounds were found to exhibit state-of-the-art HER and OER performance, respectively. Alkaline fresh water/seawater electrolysis was then systematically studied using the two-electrode electrolyzer Fe_0.01-Ni&Ni_0.2Mo_0.8N‖Fe_0.01&Mo-NiO. Due to the excellent seawater HER and OER activity of the individual catalysts, the electrolyzer exhibited record-high performance for seawater electrolysis, achieving a current density of 688 mA cm⁻² at 1.7 V. Further experiments under quasi-industrial conditions (6 M KOH & seawater, 60 °C) showed that the electrolyzer delivers a current density of 1000 mA cm⁻² at the extremely low voltage of 1.562 V, which is only 1.49% higher than that required for fresh water under the same conditions. Stability testing of the electrolyzer showed that it exhibits good durability over 80 h under the harsh industrial conditions. Therefore, the findings in this research promote the development of bifunctional catalysts and address the small performance differences between alkaline fresh water and seawater electrolysis under industrial conditions.