Boosted Electron-Transfer Kinetics of Hydrogen Evolution Reaction at Bimetallic RhCo Alloy Nanotubes in Acidic Solution

RhCo alloy nanotubes were synthesized via the reduction of single-phase Co₂RhO₄ nanotubes. The reduction was conducted by thermal annealing of the Co₂RhO₄ nanotubes under hydrogen gas flow. The crystallinity of the prepared RhCo alloy nanotubes depended on the reduction temperature: amorphous phase (200 °C reduction) and the crystalline phase (300 °C reduction). The hydrogen evolution reaction (HER) on RhCo alloys was investigated with voltammetry in 1.0 M HClO₄ solution. Amorphous RhCo alloys provided lower overpotential than the crystalline counterpart despite their similar morphology and composition. Of great interest, amorphous RhCo alloy nanotubes exhibited an outstanding HER electroactivity verified with a low overpotential at -10 mA cm^-2 (-22 mV) and a small Tafel slope (-24.1 mV dec^-1), outperforming commercial Pt, pure Rh metal, and the other previously reported Rh-based catalysts. This excellent HER activity of amorphous RhCo nanotubes was attributed to the amorphous structure having a large electrochemical surface area and maximized Rh-Co interfaces in the alloy facilitating HER. Active but expensive Rh alloyed with less active but cheap Co was successfully demonstrated as a potential cost-effective HER catalyst.