Investigation of spectroelectrochemical and electrocatalytic behavior of a new water soluble cobalt(II)phthalocyanine

Yeni, suda çözünür kobalt(II)ftalosiyaninin spektroelektrokimyasal ve elektrokatalitik davranışlarının incelenmesi

Abstract

A New, water-soluble cobalt phthalocyanine, NhtCoPc, where Nht indicates 1-naphthoxy-4- sulfonic acid sodium salt, was synthesized and its electro-spectroelectrochemical and electrocatalytic behavior towards oxygen reduction reaction were investigated in details. NhtCoPc was prepared by a reaction of NhtH2Pc and anhydrous cobalt acetate in 25 ml of methanol for 48 h under nitrogen atmosphere at refluxed tempreature. The crude product was purified by column chromatography (silica gel, MeOH-CH2Cl2, 10:1). The complexation reaction was monitored with the UV-vis spectral changes of NhtH2Pc in methanol solution. The reaction was completed when the main Q-band was observed in maximum intensity. The green color of solution was changed into blue color during complexation reaction. The column chromatography with methanol/dichloromethane (10:1) of eluent on silica gel was employed to obtain pure product. The blue product was soluble in water, methanol, and DMSO due to the introduction of the naphthoxy-sulfonic acid sodium salt having hydrophilic character on the peripheral position of phthalocyanine ring. The desired compound, which is substituted by four naphthoxysulfonic acid sodium salt groups on the periphery of each phthalocyanine is isolated as a mixture of isomers, all of which appear to have the same electrochemical properties. Elemental analysis and spectroscopic data (IR and UV–vis) confirmed the assigned structure for NhtCoPc. The formation of the NhtCoPc was confirmed by the disappearance of the characteristic NH stretching absorption of the inner core of the metal-free phthalocyanine. The complex also exhibited the characteristic absorption bands at 1275 (Ar–O–Ar), and 1183 cm−1 (O–S–O) as expected. 1H NMR spectrum of NhtCoPc could not be taken due to paramagnetic nature of the complex. The electrochemical studies showed that the cobalt complex exhibited two reversible one-electron reductions with the corresponding anodic wave and an irreversible oxidation reaction in DMSO solution. These two reduction and one oxidation processes were assigned to Co(1+)Pc(2- )/Co(2+)Pc(2-), Co(+)Pc(3-)/Co(+)Pc(2-), and Co(3+)Pc(2-)/Co(2+)Pc(2-) couples, respectively. The electrode processes were found to be diffusion controlled as demonstrated by the linearity of a plot of peak current versus square root of scan rate for scan rate ranging from 0.010 to 0.50 V.s-1. The controlled potential coulometric (CPC) study indi- cated that the number of electrons transferred for electrochemical reactions of the complex was one for each oxidation and reduction processes. The spectroelectrochemical behavior of NhtCoPc was investigated using an in situ spectroelectrochemical technique including chronoamperometry and UV-vis spectroscopy in DMSO solution containing 0.2M TBAP. The UV-vis spectral changes for the reduced and oxidized species of NhtCoPc were obtained in a thin-layer cell during applied potentials. The welldefined UV–vis spectra of the monanionic species [NhtCo(+)Pc(2-)]-, the di-anionic species [NhtCo(+)Pc(3-)]2-, and the mono-cationic species [NhtCo(3+)Pc(2-)]+, were obtained by the applied potentials (E app = -0.60 V, E app = -1.40 V, and Eapp = 0.70 V respectively) in a thin-layer cell. NhtCoPc was incorporated into the conductive polyaniline, PAni films as a dopant-anion during elektro- polymerization in acidic medium, and thus the Pt/PAni-NhtCoPc modified electrode. formed. This modified electrode was characterized by scanning electron microscopy, SEM, as well. Addition of NhtCoPc to the polymerization solution, caused great change on the morphology of the obtained modified film and increased the redoxactivity of the modified PAni-NhtCoPc film compared to those of Pt/PAni and bare platinum electrodes towards oxygen reduction in the same experimental conditions. The enhancement in the activity for oxygen reduction reaction was attributed to the different theories: (i) the catalytic activity was probably depend on the amount of macro-cyclic catalyst, (ii) the functionalization of the macrocyle ring of phthalocyanine, (iii) the PAni-CoPc structure favoring the formation of dimmers and (iv) the good molecular dispersion of NhtCoPc in polyaniline. In our system, the PAni film modified by cobalt phthalocyanine having naphthoxy-sulfonated groups on the macrocycle core of phthalocyanine favoring the formation of dimers which improve the disordered growth of aggregates leads to a rougher electrode surface as seen from the SEM image of the PAni-CoPc film. This structure results in to enhance the activity for oxygen reduction reaction. Stability of modified electrodes was proved after five cycles.

Özet

Yeni, suda çözünen 2(3),9(10),16(17),23(24)-tetrakis [4-(1-naftoksi-4-sulfonik asit sodyum)] kobalt( II)ftalosiyanin, NhtCoPc (Nht burada 1-naftoksi-4-sulfonik asit sodyum tuzu), sentezlendi, elementel analiz yöntemi, spektroskopik yöntemlerle (IR ve UV–vis) karakterize edilerek ve elektrokimyasal, spektroelektrokimyasal ve moleküler oksijenin indirgenmesine yönelik elektro-katalitik davranışları detaylı bir şekilde incelendi. Kompleksleşme reaksiyonu metanol ortamında 2(3),9(10),16(17),23(24)- tetrakis [4-(1-naftoksi-4-sulfonik asit sodyum)] ftalosiyanin, NhtH2Pc’nin UV-vis spektrum değişikliklerine göre takip edildi. Q bandının maksimum şiddette olduğu anda reaksiyon tamamlandı. Elektrokimyasal çalışmalardan şu sonuçlar çıkarılmıştır: DMSO çözeltisinde kobalt(II) kompleksi anodik dalgaya karşılık gelen bir elektronlu iki tersinir indirgenme reaksiyonu ve bir tersinir olmayan yükseltgenme reaksiyonu sergilemiştir. Gerçekleşen indirgenme reaksiyonları ve yükseltgenme reaksiyonu, Co(1+)Pc(2-)/Co(+2)Pc(2-), Co(+)Pc(3-)/Co(+)Pc(2-),ve Co(3+)Pc(2-) /Co(+2)Pc(2-) çiftlerine sırası ile karşılık gelir. İnce-tabaka hücrede sırası ile E appl = -0.60 V, $E_ {appl}$ = -1.40 V ve $E_ {appl}$ = 0.70 V potansiyelleri uygulanarak tek-anyonik [NhtCo(+)Pc(2-)]-, çift-anyonik [NhtCo(+)Pc(3-)$]^{2-}$- ve tek-katyonik türlerin [NhtCo(3+)Pc(2-)]+ iyi tanımlanmış UV-vis spektrumları elde edildi. NhtCoPc asidik ortamda elektropolimerizasyon sırasında dopant(eklenen) anyon olarak iletken polianilin ağ içine dahil edildi. Böylelikle modifiye Pt/PAni-NhtCoPc elektrot hazırlandı. Modifiye edilmiş elektrot SEM (elektron mikroskopu ile) karakterize edildi. NhtCoPc’ninpolimerizas-yon ortamına ilavesi ile elde edilen filmin morfolojisi önemli ölçüde değiştiği ve oluşan PAni-NhtCoPc filmin oksijen indirgenmesine yönelik redoks aktivitesinin yalnız platin ya da Pt/PAni elektrodlara kıyasla aynı deney koşullarında arttığı görüldü.