Au-Ru alloy nanofibers as a highly stable and active bifunctional electrocatalyst for acidic water splitting

Bimetallic AuRu alloy nanofibers (NFs) with Au:Ru atomic ratios of 7.5:92.5 are constructed and characterized as a bifunctional electrocatalyst for electrochemical overall water splitting (OWS) of both oxygen (OER) and hydrogen evolution reaction (HER). First, composite NFs consisting of RuO2 fibrous mainframes adorned with tiny Au nanoparticles are synthesized by electrospinning and calcination. The following heat treatment of these composite NFs under H2 gas flowing induces the reduction of RuO(2 )mainframes to metallic Ru within which Au atoms are dispersed to form homogeneous AuRu alloy NFs regardless of their immiscibility. The OWS activities of prepared AuRu alloy NFs are investigated in 0.5 M H2SO4 aqueous solution; and compared to those of RuO2, Ru, Au, and commercial catalysts, M/C (20 wt% metal loading on Vulcan XC-72 with M = Pt, Ru and Ir). In particular, AuRu alloy NFs show outstanding activity for OER: the lowest overpotential at 10 mA cm-2 and the smallest Tafel slope among the tested catalysts. Of great importance, AuRu alloy NFs also present an excellent long-term stability in a sharp contrast to easily deteriorated Ru-based catalysts (e.g., Ru NFs and Ru/C). AuRu alloy NFs also exhibit good HER activity and stability better than most of tested materials. In a two-electrode system, AuRu NFs divide divide AuRu NFs is confirmed to have a lower overpotential for OWS than Ir/C divide divide Pt/C, a commercial standard. The OWS performance of AuRu alloy NFs is superior to those of Ru-based bifunctional catalysts found in the literature. HER at AuRu alloy is further studied with density functional theory calculation. The current study reveals Ru alloyed with a small amount of Au having a robust nanofibrous morphology improves the electroactivity and stability for both OER and HER in acidic environments. Given that stable bifunctional catalysts for acidic water splitting have been rarely reported, AuRu alloy NFs exhibit an outstanding feasibility as a practical electrocatalyst for overall water splitting with the high activity and stability.