Developing non-precious metal-based bifunctional electrocatalysts capable for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential to achieve efficient water electrolysis for mass hydrogen production, however it remains challenging. Here, we report the synthesis of hierarchical nanorod arrays comprising core–shell structured P-doped NiMoO₄@NiFe-coordination polymer (denoted as P-NiMoO₄@NiFeCP) as bifunctional electrocatalysts for water electrolysis. Furthermore, we systematically investigate the influence of NiFeCP shell thickness on electrocatalytic activity, manifesting the presence of strong interfacial synergetic effect between P-NiMoO₄ and NiFeCP for boosting both the HER and OER. With advantageous hierarchical architectures and unique core–shell structures, optimized P-NiMoO₄@NiFeCP-7.3 (7.3 is the shell thickness in nm) requires overpotentials of merely 256 and 297 mV to yield a current density of 1000 mA·cm⁻² for the HER and OER in 1 M KOH, respectively. More importantly, it can serve as a bifunctional electrocatalyst for efficient and sustainable overall water electrolysis, delivering large current densities of 500 and 1000 mA·cm⁻² at low cell voltages of 1.804 and 1.865 V, along with high stability of over 500 h at 1000 mA·cm⁻², demonstrating the great potential of this electrocatalyst towards practical applications.

In electrocatalytic water splitting, low-cost dual-functional catalysts can not only reduce costs but also avoid cross-contamination of cathode and anode. However, the orderly aggregation of active sites for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) into a specific catalyst is very challenging. In this study, a Co/Fe₃O₄ Janus heterojunction supported on carbon fiber paper (J-CoFe-CFP) is designed and successfully synthesized. Generally, Co-Fe oxides have preferable OER activity but weak HER activity. However, in J-CoFe-CFP, due to the intense and special electronic interaction of different substances (Co and Fe₃O₄) in the Janus heterogeneous interface, a huge number of tidy high-quality HER and OER active sites are uniformly distributed on the interface simultaneously, which endows the catalyst with both excellent HER and OER performance. In HER, the overpotential @10 mA·cm⁻² (η_HER) is only 53.9 mV, and the Tafel slope is 43.7 mV·dec⁻¹. In OER, the η is 272 mV, and the Tafel slope is 50.2 mV·dec⁻¹, much lower than those of RuO₂/CFP. In the J-CoFe-CFP||J-CoFe-CFP two-electrode system, the required voltage is only 1.26 V at the beginning and 1.56 V@10 mA·cm⁻², much lower than those of RuO₂/CFP||20% Pt/C/CFP. This work provides a Janus heterojunction pathway for bifunctional water electrolysis catalysts.

Metal phosphides have shown great application potential as anode for sodium-ion batteries (NIBs) owing to high theoretical capacity, suitable operation voltage and abundant resource. Unfortunately, the application of NiP₂ anode is severely impeded by low practical capacity and fast capacity decay due to the huge volume variation and low reactivity of internal phosphorus (P) component towards Na⁺. Herein, electronic structure modulation of NiP₂ via heteroatoms doping and introducing vacancies defects to enhance Na⁺ adsorption sites and diffusion kinetics is successfully attempted. The as-synthesized three-dimensional (3D) bicontinuous carbon matrix decorated with well-dispersed fluorine (F)-doped NiP₂ nanoparticles (F-NiP₂@carbon nanosheets) delivers a high reversible capacity (585 mAh·g⁻¹ at 0.1 A·g⁻¹) and excellent long cycling stability (244 mAh·g⁻¹ over 1,000 cycles at 2 A·g⁻¹) when tested as anode in NIBs. Density functional theory (DFT) calculations reveal that F doping in NiP₂ induces the formation of P vacancies with increased Na⁺ adsorption energy and accelerates the alloying of internal P component. The F-NiP₂@carbon nanosheets//Na₃V₂(PO₄)₃ full cell is evaluated showing stable long cycling life. The heteroatoms doping-induced dual defects strategy opens up a new way of metal phosphides for sodium storage.