9-octyl-2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole (M1), 5-bromo-1,10-phenanthroline (M2), toluene, K2CO3, NaH2PO4·2H2O, tetrabutylammonium fluoride (NBu4F), Pd[P(C5H5)3]4, Na2HPO4·12H2O, Cu(ClO4)2·6H2O, and isopropanol were all analytical reagent (AR) grade and were obtained from Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China) Pt/C (20% Pt content) and nafion (5% content) were obtained from Shanghai Geshi Energy Technology Co., Ltd. (Shanghai, China), and ultrapure water was used without any disposal. Pure grade O2 and N2 were used to saturate the electrode test solutions.
3.2. Synthesis of OCBP and Cu-SOCBP
M1 (2.034 g, 4 mM), M2 (1.950 g, 8 mM), Pd[P(C5
(0.37g, 0.32 mM), and NBu4
F (0.015 g) were added to a mixture medium consisting of toluene (90 mL) and Na2
(60 mL, 2 M), which were combined in a round-bottom flask. This flask was maintained at 120 °C under an argon atmosphere and stirred magnetically. The solvent and water were distilled under vacuum to obtain the solid crude product. The crude product was redissolved in chloroform and rinsed with water three times [39
]. Excess solvents were removed via distillation to concentrate the organic phase, which was then subjected to silica gel column chromatography, and the solvent mixture of dichloromethane/n
-hexane (2:1, v
) was used as the elution solvent. Finally, the product was obtained as a white solid (OCBP) with a yield of 65%. The 1
H nuclear magnetic resonance (1
H NMR) (400 MHz, cdcl3
) and 13
C NMR (101 MHz, cdcl3
) spectra of OCBP are shown in Figure 11
1H NMR (400 MHz, cdcl3) δ 9.24 (dt, J = 4.1, 1.5 Hz, 4H), 8.43 (dd, J = 8.4, 1.6 Hz, 1H), 8.38–8.29 (m, 1H), 7.91 (s, 2H), 7.69 (dd, J = 8.0, 4.3 Hz, 2H), 7.61 (dd, J = 8.4, 4.2 Hz, 4H), 7.46 (dd, J = 7.9, 1.2 Hz, 2H), 4.39 (t, J = 7.0 Hz, 2H), 1.94 (dd, J = 13.3, 5.9 Hz, 4H), 1.48–1.36 (m, 1H), 1.34–1.11 (m, 2H), 0.78 (t, J = 6.8 Hz, 3H).
13C NMR (101 MHz, cdcl3) δ 150.12 (d, J = 18.2 Hz), 146.36 (s), 145.69 (s), 141.00 (s), 139.64 (s), 136.70 (s), 135.93 (s), 134.77 (s), 128.26 (s), 128.05 (s), 126.69 (s), 123.37 (s), 122.80 (s), 122.17 (s), 121.37 (s), 120.46 (s), 110.26 (s), 77.34 (s), 77.02 (s), 76.70 (s), 43.26 (s), 31.64 (s), 29.43–28.77 (m), 27.34 (s), 22.50 (s), 13.96 (s).
Also, Figure 12
shows the IR spectrum of OCBP. Assignment of the vibrational bands is as follows [40
]: the peak at 3030 cm−1
corresponds to aromatic C–H stretching, and the peaks between 2922 and 2851 cm−1
correspond to C–H stretching of aliphatic side chains. Bands at 1596–1478 cm−1
and 1325 cm−1
are ascribed to the stretching vibrations of the C=N bond (phenanthroline ring) and the C–N bond (carbazole ring), respectively, and this is direct evidence for the linkage of the phenanthroline and carbazole ring. The bands in the region of 1478–1419 cm−1
are assigned to the C=C skeleton vibration of the benzene ring. In addition, the peak at 1325 cm−1
corresponds to the stretching vibration of the C–N bond in the phen ring, and the strong peak at 741 cm−1
corresponds to the out-of-plane bending vibration of the C–H bond on the phen ring. The peak at 805 cm−1
is attributed to the out-of-plane bending vibration of the adjacent C–H hydrogen atoms on the carbazole ring. In all, the data of the Infrared spectroscopy (IR) further confirm the successful synthesis of the desired OCBP compound.
To prepare Cu-SOCBP, the monomer OCBP (3.8148 mg, 0.006 mmol) was dissolved in 1 mL of acetonitrile under a nitrogen atmosphere. Copper(II) perchlorate hexahydrate (2.22 mg, 0.006 mmol) was then dissolved in 1 mL of acetonitrile and added dropwise into the above OCBP solution. The resulting green solution was the solution of Cu-SOCBP. The weight-average molecular weight of Cu-SOCBP was as high as Mw
= 6.5 × 106
Da, which might be an indication of the formation of the supramolecule complexes (See Supplementary Materials
about the test method). The synthetic routes for monomers OCBP and Cu-SOCBP are shown in Scheme 1
3.4. Physical Characterization and Electrochemical Studies
H NMR and 13
C NMR spectra of OCBP were recorded in CDCl3
at 400 MHz using a Varian AMX 400 spectrometer (Varian Inc., Santa Clara, CA, USA), and tetramethylsilane was used as the internal standard. Fourier transform infrared (FT-IR) spectra were recorded using a Nicolet 170 SX FTIR spectrometer (Thermo Fisher Scientific Inc., Waltham, MA, USA) with samples embedded in KBr pellets. To gain information on the microstructures of the catalyst, the catalyst was uniformly dispersed on the surface of Indium tin oxide (ITO)-coated glass, and scanning electron microscopy (SEM) was recorded using a ZEISS scanning electron microscope(SEM, Carl Zeiss Ltd., Oberkochen, Germany). X-ray photoelectron spectroscopy (XPS, ESCALAB 250 Xi, Thermo Fisher Scientific Inc., Waltham, MA, USA) was used to analyze the elemental compositions of the samples and the valence states of those elements. Electrochemical measurements were all taken using a computer-controlled Autolab potentiostat/galvanostat (PGSTAT302N, Metrohm Autolab, The Netherlands). A standard three-electrode electrochemical system was used, in which a GC electrode (diameter, 5 mm) or RRDE (outer diameter 7.92 mm, inner diameter 6.25 mm) was used as the working electrode, an Ag/AgCl (saturated potassium chloride) (0.197 V + 0.0591 × pH vs. reversible hydrogen electrode (RHE) at 25 °C) electrode was used as the reference electrode, and a platinum electrode was used as the counter electrode [41
]. The testing medium used as the electrolyte was 0.1 M phosphate buffer solution (PBS), and as required by the tests, the electrolyte medium was saturated with oxygen or nitrogen gas, which was provided by a gas supply device alongside the electrochemical testing system. The XRD spectra were measured by a XD-3 Purkinje diffractometer (Beijing Purkinje General Instrument Co. Ltd., Beijing, China), employing monochromatized Cu Ka1
radiation, and the scan rate was 4°/min over the range of 2θ
= 10–60°. The physisorption test was conducted on a TriStar II 3020 specific surface and pore analyzer.