Controlled construction of Pt-Ni nanoparticles on nitrogen-doped carbon nanotubes by molten salt-assisted solid-state confinement for hydrogen evolution

Abstract

Efficient use of Pt remains a central issue in the design of alkaline hydrogen evolution catalysts. Here, Pt-Ni catalysts were constructed on nitrogen-doped carbon nanotubes by two different routes, namely conventional impregnation and molten-salt-assisted solid-state treatment. The roles of metal loading and processing method were then compared from both structural and electrochemical perspectives. The nanotube framework was retained after molten salt treatment, whereas the metal phase became more finely dispersed and showed closer contact with the support. X-ray diffraction, X-ray photoelectron spectroscopy, and microscopic observations consistently suggest that the molten-salt-treated samples contained smaller Pt-Ni particles with a more uniform distribution on the N-CNT surface. Among the catalysts investigated, Pt-Ni/N-CNTs-MS-2 gives the best overall alkaline HER performance. In 1.0 mol L-1 KOH, it requires overpotentials of 13 mV and 155 mV to reach 10 and 100 mA cm-2, respectively. It also shows a Tafel slope of 57.32 mV dec-1, a charge transfer resistance of 47.24 Ω, and a double layer capacitance of 14.05 mF cm-2, together with stable operation for about 25 h. These results show that combining an appropriate metal loading with molten salt assisted confinement is an effective way to regulate nanoparticle dispersion, improve interfacial charge transport, and enhance the alkaline hydrogen evolution performance of Pt-Ni/N-CNTs catalysts.