Ordered nanodendritic NiSe-NiS/NFF with crystalline structure for efficient overall water splitting

Developing highly efficient and durable non-precious bifunctional electrocatalysts is essential for reducing the industrial cost of electrocatalytic water splitting. Herein, an ordered nanodendritic NiSe-NiS catalyst (NiSe-NiS/NFF) is constructed by stepwise electrodeposition, where interfacial reactions convert the amorphous precursor into nanocrystalline Ni 3 SeS as the dominant crystalline phase. Such a three-dimensional dendritic architecture offers a high density of electrochemically accessible active sites, continuous pathways for electron transport, and open channels that facilitate electrolyte penetration and gas release. Consequently, NiSe-NiS/NFF requires overpotentials of 65 mV for HER and 228 mV for OER to reach 10 mA·cm −2 . For comparison, NiSe/NFF requires 83 mV for HER and 241 mV for OER, whereas NiS/NFF shows a similar HER overpotential of 60 mV but a much higher OER overpotential of 255 mV, highlighting the overall performance gain achieved by the stepwise design. Moreover, the low Tafel slopes of NiSe-NiS/NFF, 39.0 mV·dec −1 for HER and 56.6 mV·dec −1 for OER, further confirm the accelerated reaction kinetics. In a two-electrode configuration, NiSe-NiS/NFF delivers 10 mA·cm −2 at 1.53 V and maintains 96.5 % current retention over 48 h; for OER, it retains 85.8 % of the initial current density after 100 h at 100 mA·cm −2 . Under OER conditions, electrochemically driven surface reconstruction promotes the conversion of Ni 2+ to Ni 3+ , adjusts the sulfide-related S environment, and generates more NiOOH active species, thereby optimizing charge transfer and enhancing electrocatalytic activity. This study shows that stepwise electrodeposition tailors electronic states and surface reconstruction, enabling bifunctional electrocatalysts for overall water splitting.