The advancement of direct seawater electrolysis is a significant step towards sustainable hydrogen production, addressing the critical need for renewable energy sources and efficient resource utilization. However, direct seawater electrolysis has to face several challenges posed by the corrosiveness of highly concentrated chloride and the competitive chlorine evolution reaction (ClER). To overcome these issues, we designed a novel NiP₂@CoP electrocatalyst on a porous titanium microfiltration (Ti MF) membrane. The obtained bifunctional NiP₂@CoP catalyst outperforms the Pt/C and IrO₂, as evidenced by its low overpotentials of 192 and 425 mV at a current density of 500 mA·cm⁻² for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline seawater (1 M KOH + 0.5 M NaCl), respectively. Especially, only 231 and 569 mV overpotentials are required at the current density of 1500 mA·cm⁻² towards HER and OER in alkaline seawater, respectively. More importantly, no ClER was observed, demonstrating its excellent selectivity to OER. The selection of porous Ti MF membrane as an electrode substrate further enhances the performance by providing a robust structure that promotes the fast generation and release of gas bubbles. Our promising outcomes obtained with NiP₂@CoP catalysts on Ti MF support, therefore, pave the way for the commercial viability of direct seawater electrolysis technologies at industrial-level current densities.

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.

Over recent years, catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction (ORR). However, the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained. Herein Fe₃C/C and Fe₂N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15% CH₄/H₂ and pure NH₃, respectively. By acid leaching of Fe₂N/C sample, only single sites of FeN₄ species were presented, providing an ideal model for identification of catalytic functions of the single sites of FeN₄ in ORR. A correlation was conducted between the concentration of Fe^ⅡN₄ in low spin state by Mössbauer spectra and the kinetic current density at 0.8 V in alkaline media, and such a structure-performance correlation assures the catalytic roles of low spin Fe^ⅡN₄ species as highly active sites for the ORR.

Fe-based catalysts have been discovered as the best elementary metal-based heterogeneous catalysts for the ammonia synthesis in industrial application during the last century. Herein, a novel and scalable strategy is developed to prepare the K-promoted Fe/C catalyst with extremely high Fe loading (> 50 wt.%) through pyrolysis of the Fe-based metal-organic framework (MOF) xerogel. The obtained K-Fe/C catalysts exhibited superior activity and stability towards ammonia synthesis. The weight-specific reaction rate of Fe/C with K₂O as promoter can achieve 12.4 mmol·g^-1·h^-1 at 350 ℃ and 30.4 mmol·g^-1·h^-1 at 400 ℃, approximately four and two times higher than that of the commercial fused-iron catalyst (3.4 mmol·g^-1·h^-1 at 350 ℃ and 16.7 mmol·g^-1·h^-1 at 400 ℃) under the same condition, respectively. The excellent performance of K-Fe/C can be ascribed to the inherited structure derived from the metal-organic frame precursors and the promotion of potassium, which can modify the binding energy of reactant molecules on the Fe surface, transfer electrons to iron for effective activation of nitrogen, prevent agglomeration of Fe nanoparticle (NPs) and restrain side reaction of carbon matrix to methane.

Transition metal carbide (TMC) nanomaterials are promising alternatives to Pt, and are widely used as heterogeneous electrocatalysts for the electrochemical hydrogen evolution reaction (HER). In this work, a bromide-induced wet-chemistry strategy to synthesize Co₂C nanoparticles (NPs) was developed. Such NPs exhibited high electrocatalytic activity (η = 181 mV for j = -10 mA·cm^-2) and long-term stability (no obvious performance decrease after 4, 000 cycles) for the HER. This study will pave the way for the design and fabrication of TMC NPs via a wet- chemistry method, and will have significant impacts on broader areas such as nanocatalysis and energy conversion.