Electrochemical hydrogen evolution reaction (HER) has been considered as a promising way to achieve clean hydrogen generation. Nevertheless, up to now, platinum (Pt) based electrocatalysts remain as benchmark electrocatalysts for HER. The development of HER is seriously limited due to the high cost and scarcities of Pt. Thus, more efficient electrocatalyst with lower cost is highly desired for HER. Metal phosphides have been considered as promising electrocatalysts for HER due to their facile synthesis and low-cost. It is noteworthy that ruthenium (Ru) is much richer in nature and its price is much lower than that of Pt, though Ru is a noble metal. Thus, introducing Ru into metal phosphides is a reasonable design for achieving efficient and low-cost electrocatalyst for HER. In this work, a series of FexRu1-x-P nano-composites were prepared via a two-step procedure. Briefly, the precursor FexRu1-x was synthesized in aqueous solution using hexadecyl trimethyl ammonium bromide (CTAB) as soft template and NaBH4 as reducing agent. Then, FexRu1-x-P was prepared by low-temperature (350℃) phosphidation of FexRu1-x-P nanosheets using NaH2PO2 as a phosphorus source under N2/H2(5%) atmosphere. The morphologies, structures and compositions of the as-prepared FexRu1-x and FexRu1-x-P nano-composites were characterized using scan electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), etc. Physical characterizations revealed that FexRu1-x and FexRu1-x-P with x>0.2 displayed ultrathin nanosheet morphyology. When Fe content further reduced, the FexRu1-x and FexRu1-x-P were nanoparticles. XRD results demonstrated that no obvious XRD peak was observed for Fe0.9Ru0.1-P in the range of 2θ=30°-80°, indicating that they are amorphous in nature. With the increasing of Ru content, a broad peak at 2θ=44° was observed, corresponding to the (101) plane of Ru or FeRu. Nevertheless, broad XRD peak again indicated the poor crystallinity of FexRu1-x-P. The HER catalytic activities of FexRu1-x-P were evaluated using linear sweep voltammetry (LSV) in acidic media. The results suggested that FexRu1-x-P nano-composites displayed better HER catalytic activities than the similarly prepared Fe- P and Ru-P nanomaterials. Among them, Fe0.3Ru0.7-P exhibited the best HER catalytic activity with a low overpotential (η10) of 31 mVat 10 mA/cm2 and small Tafel slope of 37.98 mV/dec, which are even comparable to those (η10 of 28 mVand Tafel slope of 26.88 mV/dec) of the commercial Pt/C. Furthermore, to better understand the good catalytic performance of Fe0.3Ru0.7-P, XPS studies were performed to investigate its compositions. The results demonstrated that the Fe0.3Ru0.7-P contains Ru0, Fe-P, Ru-P species which are all HER active, as well as the HER inactive species of iron phosphate. These XPS results thus indicated that the phosphidation of FexRu1-x at low-temperature is incomplete. With the increasing of the Fe content in precursor, the content of HER inactive iron phosphate in FexRu1-x-P is increasing as well, which may account for the inferior catalytic activity of FexRu1-x-P with x>0.3. In summary, we prepared a series of FexRu1-x-P nanostructures via a two-step procedure. Electrochemical characterizations revealed that among this series Fe0.3Ru0.7-P exhibited the best HER activity with a low overpotential (η10) of 31 mVat 10 mA/cm2 and small Tafel slope of 37.98 mV/dec, which are even comparable to those of the commercial Pt/C. Physical characterizations revealed that Fe0.3Ru0.7-P shows nanosheet morphology and is nearly amorphous in nature. XPS results suggested that Fe0.3Ru0.7-P contains a variety of HER active species including Ru0, Fe-P and Ru-P which all contribute to their HER performance. © 2019, Science Press. All right reserved.
