Bi-functional RuO 2 /Co 3 O 4 Core/Shell Nanofibers as a Multi-component One-Dimensional Water Oxidation Catalyst

Transcription

1 This journal is The Royal Society of Chemistry Supporting Information Bi-functional RuO /Co O Core/Shell Nanofibers as a Multi-component One-Dimensional Water Oxidation Catalyst Jong Wan Ko, Won-Hee Ryu, Il-Doo Kim*, Chan Beum Park* Experimental Details Materials: Cobalt (II) acetate tetrahydrate [CH (COO) Co H O], ruthenium (III) chloride (RuCl ), polyvinylpyrrolidone (PVP, Mw =,00,000), N,Ndimethylformamide, sodium tetraborate decahydrate (Na B O 7 0H O), tris (, -bipyridyl) dichlororuthenium(ii) hexahydrate ([Ru(bpy) ]Cl H O), Co O (particle size <0 nm), and sodium persulfate (Na S O 8 ) were purchased from Sigma-Aldrich (St. Louis, USA) and all chemicals were used without further purification. Synthesis of Co O, RuO and RuO /Co O NFs: To prepare the metal precursor solution, (CH COO) Co H O and RuCl with a different atomic ratio of Ru/Co (total precursor weight of g) were dissolved in 7. g of N,N-dimethylformamide and continuously stirred at room temperature for h. Then, g of PVP was dissolved and stirred in the precursor solution for h. For the RuO /Co O NFs, the value 8 : was selected as the ratio of Ru : Co. A feeding rate was controlled at 0. ml h - during electrospinning and a stainless steel foil as a collector was vertically positioned cm away from the syringe needle ( gauge) under a constant potential of 0 kv to collect as-spun sole Co or sole Ru or Ru/Co precursor/pvp NFs. The obtained as-spun NFs were calcined at 00 C for h in air atmosphere. Characterization of synthesized Co O, RuO and RuO /Co O NFs: The morphologies of the prepared samples were observed using an XL0SFEG scanning electron microscopy (PHILIPS, USA) and a Tecnai F0 S-Twin transmission electron microscope (FEI Company,

2 This journal is The Royal Society of Chemistry USA). The element distribution was investigated using EDS mapping. The crystalline phase of the samples was analyzed using a D/MAX-RC X-ray diffractometer (RIGAKU Co., Japan) and a MultiLab 000 X-ray photoelectron spectroscopy (Thermo scientific, UK). The surface area of the samples were measured using Brunauer-Emmett-Teller (BET) method with a Tristar II 00 surface area analyzer (Micromeritics, USA). Catalytic oxygen evolution: Photochemical water oxidation experiments were conducted in 0 ml vials containing 0 ml of sodium borate buffer (80 mm, ph 8.0) with mg Na S O 8, mg [Ru(bpy) ]Cl H O, and 0 mg of Co O nanoparticles, Co O, RuO, and RuO /Co O NFs. Photochemical oxygen evolution was continuously monitored using a custom-made oxygen analysis system. The reaction solution was irradiated using a xenon lamp (0 W) with a 0 nm cut-off filter and purged with N (99.999%) gas as a carrier gas. The oxygen concentration of the carrier gas was monitored using a series 00 Trace Oxygen Transmitter (Alpha Omega Instruments Co., USA). Electrochemical measurements: Cyclic voltammetry (CV) was performed using a WMPG000 potensitostat/galvanostat (WonATech, Korea) with Co O, RuO, and RuO /Co O NFs-Nafion solution ( mg in 00 μl) deposited on a glassy carbon electrode as a working electrode, a platinum wire as a counter electrode, and an Ag/AgCl reference electrode in a sodium borate buffer solution (80 mm, ph 8.0) at room temperature with a scan rate of 00 mv s -. Catalytic activity measurements: The catalytic activity of Co O, RuO, and RuO /Co O NFs + in photochemical water oxidation with Ru(bpy) was estimated by monitoring the decay of Ru(bpy) +. A phosphate buffer solution (90 μl, 00 mm, ph.) containing Na S O 8 ( + mm) and Ru(bpy) ( mm) in a ml quartz cuvette (with a path length of cm) was + irradiated by a xenon lamp to produce photo-induced Ru(bpy) for seconds. To the prepared reaction solution, 0 μl of phosphate buffer solution (00 mm, ph.) containing

3 This journal is The Royal Society of Chemistry 0 Co O, RuO, and RuO /Co O NFs ( mg in 0 ml) was added. Then, the decrease in UV + absorbance intensity of the reaction solution at 70 nm attributable to Ru(bpy) was monitored during catalytic water oxidation by Co O, RuO, and RuO /Co O NFs using a UV-visible spectrophotometer (Jasco Inc., Japan) in the time course mode.

4 This journal is The Royal Society of Chemistry 0 Fig. S SEM images of (a, b) the as-spun NFs of Co precursor with PVP, (c) the as-spun NFs of Ru precursor with PVP, and (d) the as-spun NFs of Ru/Co ( : 8) precursor with PVP prepared by electrospinning.

5 This journal is The Royal Society of Chemistry 0 Fig. S X-ray diffraction patterns of electrospun Co O, RuO and RuO /Co O NFs calcined at 00 C for h. For reference, standard X-ray diffraction data (JCPDS) of Co O and RuO were also indexed.

6 This journal is The Royal Society of Chemistry 0 7 Fig. S XPS spectra of Co O NFs in the wide range from 0 to 0 ev. (a) the XPS scan of Co O NFs indicating two compositional elements (i.e., Co, and O); (b) the XPS spectra of Co O NFs in magnified scale exhibiting Co p / and Co p / peaks; (c) the XPS scan of RuO NFs showing Ru and O elements; and (d) Ru d spectrum of RuO NF confirming the existence of Ru + ions in the synthesized NF.

7 This journal is The Royal Society of Chemistry 0 Fig. S STEM image of the RuO /Co O NF; element map of (a) as-synthesized NF (b) purple (cobalt); and (c) green (ruthenium) 7

8 This journal is The Royal Society of Chemistry 0 Fig. S (a) The XPS scan of RuO /Co O NFs indicating three compositional elements (i.e., Co, Ru, and O) in the wide range from 0 to 0 ev; (b) the XPS spectra of RuO /Co O at a magnified scale exhibiting Co p / and Co p / peaks; and (c) the Ru p spectrum of RuO /Co O confirming the existence of Ru + ions in the composite. 8

9 This journal is The Royal Society of Chemistry 0 Fig. S Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) curves of (a) cobalt acetate precursor/pvp fibers and (b) cobalt acetate and ruthenium chloride precursor/pvp composite fibers. (c) ruthenium chloride precursor/pvp fibers. 9

10 This journal is The Royal Society of Chemistry 0 7 Fig. S7 The absorbance spectra of [Ru(bpy) ]Cl H O solution ( mm) containing Na S O 8 ( mm) in an 80 mm NaB (ph 8.0) buffer (a) before and (b) after visible light irradiation (> 0 nm). The absorption peaks at approximately 0 nm and 70 nm correspond to Ru(bpy) + and Ru(bpy) +, respectively. After visible light irradiation, the absorption peak + + corresponding to Ru(bpy) increased because of photo-induced oxidation of Ru(bpy) + whereas the absorption peak of Ru(bpy) decreased. 0