A supramolecular-confinement pyrolysis route to ultrasmall rhodium phosphide nanoparticles as a robust electrocatalyst for hydrogen evolution in the entire pH range and seawater electrolysis

Developing efficient and durable electrocatalysts with uniform sizes for the hydrogen evolution reaction (HER) in the entire pH range and seawater is critical for scalable and sustainable hydrogen production. Herein, we report a supramolecular starch-assisted confinement-assembly-pyrolysis (SCAP) strategy for the synthesis of ultrasmall Rh2P nanoparticles with high dispersion and low loading anchored on N,P-doped porous carbon (NPC). The Rh2P/NPC composite exhibits an unprecedented HER activity with small overpotentials at 10 mA cm(-2) (40 mV in 0.5 M H2SO4 and 17 mV in 1 M KOH), as well as superior stability in both acidic and alkaline media. In addition, the Rh2P/NPC catalyst also exhibits an excellent HER performance in the entire pH range. Especially, the Rh2P/NPC catalyst shows an electrocatalytic HER activity superior to that of a 20% Pt/C catalyst in natural seawater, especially under large current densities. It only needs 160, 341 and 411 mV versus RHE to achieve current densities of 10, 100, and 300 mA cm(-2), respectively. To the best of our knowledge, this Rh2P/NPC material is the best electrocatalyst reported thus far for seawater electrolysis. Moreover, the Rh2P/NPC catalyst also shows good stability over a wide range of current densities. All these results indicate that the Rh2P/NPC catalyst can be used as a robust catalyst for hydrogen production via direct seawater electrolysis. In situ X-ray absorption spectra revealed the strong interaction between the Rh-P site and H2O during the HER catalytic process in 1 M KOH, revealing the positive role of the Rh-P site in the HER. Theoretical calculations demonstrate that the strong synergistic effects between Rh2P nanoparticles and NPC modify the electronic structure to accelerate the HER kinetics. More interestingly, the SCAP strategy not only yields a robust and pH-universal HER catalyst, but also enables a general, green, and gram-scale synthesis of other metal phosphides.