Green hydrogen production via seawater electrolysis holds a great promise for carbon-neutral energy production. However, the development of efficient and low-cost bifunctional electrocatalysts for seawater electrolysis at an industrial level remains a significant challenge. Herein, we report a facile approach based on one-dimensional (1D) cobalt carbonate hydroxide (CCH) nanoneedles (NNs) as skeleton and zeolitic imidazolate framework-67 (ZIF-67) as a sacrificial template to construct a self-supported NiCo layered double hydroxide (NiCo LDH) heterostructure nanocage (CCH@NiCo LDH) anchoring on the carbon felt (CF). The NiCo LDHs have hollow features, consisting of ultrathin layered hydroxide nanosheets. Benefiting from the structural advantages, unique carbon substrate and desirable composition, three-dimensional (3D) NiCo LDH nanocages exhibit superior performance as a bifunctional catalyst for overall seawater splitting at an industrial level and good corrosion resistance in alkaline media. In the alkaline seawater (1 M KOH + 0.5 M NaCl), it exhibits low overpotentials of 356 mV for hydrogen evolution reaction (HER) and 433 mV for oxygen evolution reaction (OER) at 400 mA·cm⁻², much better than most of reported non-noble metal catalysts. Consequently, the obtained CF electrode loading of CCH@NiCo LDH exhibits outstanding performance as anodes and cathodes for overall alkaline seawater splitting, with remarkably low cell voltages of 1.56 and 1.89 V at current densities of 10 and 400 mA·cm⁻², respectively. Moreover, the robust stability of 100 h is also demonstrated at above 200 mA·cm⁻² in alkaline seawater. Our present work demonstrates significant potential for constructing effective cost-efficient and non-noble-metal bifunctional electrocatalyst and electrode for industrial seawater splitting.

Carbon-free hydrogen as a promising clean energy source can be produced with electrocatalysts via water electrolysis. Oxygen evolution reaction (OER) as anodic reaction determines the overall efficiency of water electrolysis due to sluggish OER kinetics. Thus, it’s much desirable to explore the efficient and earth-abundant transition-metal-based OER electrocatalysts with high current density and superior stability for industrial alkaline electrolyzers. Herein, we demonstrate a significant enhancement of OER kinetics with the hybrid electrocatalyst arrays in alkaline via judiciously combining earth-abundant and ultrathin NiCo-based layered double hydroxide (NiCo LDH) nanosheets with nickel cobalt sulfides (NiCoS) with a facile metal-organic framework (MOF)-template-involved surface sulfidation process. The obtained NiCo LDH/NiCoS hybrid arrays exhibits an extremely low OER overpotential of 308 mV at 100 mA·cm⁻², 378 mV at 200 mA·cm⁻² and 472 mV at 400 mA·cm⁻² in 1 M KOH solution, respectively. A much low Tafel slope of 48 mV·dec⁻¹ can be achieved. Meanwhile, with the current density from 50 to 250 mA·cm⁻², the NiCo-LDH/NiCoS hybrid arrays can run for 25 h without any degradation. Our results demonstrate that the construction of hybrid arrays with abundant interfaces of NiCo LDH/NiCoS can facilitate OER kinetics via possible modulation of binding energy of O-containing intermediates in alkaline media. The present work would pave the way for the development of low-cost and efficient OER catalysts and industrial application of water alkaline electrolyzers.