Ni_xRh_1−xbimetallic alloy nanofibers as a pH-universal electrocatalyst for the hydrogen evolution reaction: The synthetic strategy and fascinating electroactivity

Ni_xRh_1-xalloy nanofibers were synthesized by the thermal reduction of single-phase spinel NiRh₂O₄nanofibers under a hydrogen gas flow. First, single-phase NiRh₂O₄nanofibers were preparedviacalcination preceded by electrospinning. The synthetic conditions including the metal precursor ratio in electrospinning solution and calcination temperature were finely optimized to produce single-phase NiRh₂O₄. Then, the thermal treatment at a temperature ≥200 °C under a H₂gas flow converted NiRh₂O₄to Ni_xRh_1-xalloy nanofibers. Their electrocatalytic activity for the hydrogen evolution reaction (HER) was examined with voltammetry in alkaline, neutral and acidic media. Ni_xRh_1-xalloy nanofibers showed the lowest overpotentials at −10 mA cm⁻²and the smallest Tafel slopes in all media, indicating a HER activity superior to those of commercial Pt, pure Rh metal, and Rh-/Ni-based electrocatalysts found in the literature. The reason for the superb activity of Ni_xRh_1-xalloys is ascribed to the synergistic effect of the facilitated hydrogen adsorption on alloyed Rh and Ni atoms and the enlarged electroactive areas from the porous uneven nanofiber structure. Considering that only a few pH-universal HER catalysts have been reported, Ni_xRh_1-xalloy nanofibers, where expensive Rh is diluted with cheap Ni, present excellent feasibility as a practical and cost-effective HER catalyst.