Rhenium oxide/sulfide binary phase flakes decorated on nanofiber support for enhanced activation of electrochemical conversion reactions

Because of their versatile application potential, such as fuel cells and water electrolysis, boosting electrochemical half-cell reactions has been highlighted to realize energy conversion systems. However, sluggish multi-charge transfer reactions lower the energy efficiency for cell operation. Tailoring hierarchical catalyst nanostructures comprising heterogeneous crystalline phases allows for the improvement of limited activities and reaction performance. This study examines the controllable synthesis of heterogeneous rhenium oxide (ReO_x) and rhenium sulfide (ReS₂) nanoflakes vertically aligned on carbon nanofibers (CNFs) by thermal chemical vapor deposition (CVD). Their potential application as electrocatalysts in various electrochemical half-cell reactions for fuel cells and water electrolysis is elucidated. The phase portion of oxide and sulfide in the ReO_x/ReS₂ nanoflake-decorated CNF catalyst can be thermally tuned from an oxide-rich phase to a sulfide-rich phase, thereby optimizing the catalytic activities for hydrogen evolution (E_onset: −0.24 V) and oxygen reduction reactions (E_onset: 0.778 V, number of electron: 3.8), which is comparable to the performance of commercial Pt/C catalysts. The morphological and structural evolution mechanism of the ReO_x/ReS₂ nanoflake-decorated CNF catalyst materials is investigated using diverse material characterizations. This study suggests a synthetic method for temperature-dependent heterogeneous phase control of non-precious-metal-based hierarchical materials and offers a basis for developing efficient catalyst alternatives for application to sustainable energy conversion and storage systems.