Surface and electrochemical characterisation of aryl film and nanocomposite material modified carbon and metal-based electrodes
Date
2019-07-08
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Abstract
Käesoleva doktoritöö eesmärk oli valmistada ja uurida arüülkiledega modifitseeritud süsinik- ja metallelektroodide ning mitteväärismetallidel põhinevate katalüsaatormaterjalide pinna- ja elektrokeemilisi omadusi. Valmistatud elektroodide pinda iseloomustati erinevate füüsikaliste ja elektrokeemiliste meetoditega (röntgenfotoelektronspektroskoopia (XPS), aatomjõumikroskoopia (AFM), tsükliline voltamperomeetria ja pöörleva ketaselektroodi meetod (RDE)). Doktoritöö esimene ja teine osa kirjeldavad süsinik- ja metallelektroodide spontaanset ja ka elektrokeemilist modifitseerimist 9,10-antrakinooni (AQ) ja 4-nitrofenüülrühmadega (NP) diasooniumisoolade redutseerumise meetodil. Elektrokeemiliseks modifitseerimiseks kasutati nii „tavalist“, redokspookimise kui ka esmakordselt redokspookimise ja RDE kombineeritud meetodit. XPS ja AFM analüüsil tehti kindlaks arüülrühmade olemasolu elektroodidel ning lisaks uuriti nende mõju hapniku redutseerumisreaktsioonile ja elektroodi pinna blokeerumist arüülkile tõttu Fe(CN)63/4 redokspaari suhtes. Tehti kindlaks, et paksemate ja suurema elektroaktiivsete arüülrühmade hulgaga kilede valmistamiseks oli kõige sobivam redokspookimise ja RDE kombineeritud meetod. Antud meetodit kasutades valmistati suurima teadaoleva elektroaktiivsete AQ rühmade pindkontsentratsiooniga modifitseeritud klaassüsinik, Au ja Cu elektroodid ning samuti kõige paksem arüülkile käesolevas doktoritöös (47 nm), mis saadi NP kilega Cu elektroodi korral. Doktoritöö viimases osas uuriti elektrokedratud polümeeridel põhinevaid süsiniknanotorudega komposiitmaterjale ja ränioksükarbiidil põhinevaid materjale eesmärgiga kasutada neid mitteväärismetallkatalüsaatoritena hapniku redutseerumisreaktsioonil. Kõige aktiivsem katalüsaatormaterjal saadi ränioksükarbiidil põhinevate materjalide puhul, mis sisaldas siirdemetalli (Co) ja lämmastikku. Sellel katalüsaatoril toimus hapniku redutseerumine 4-elektronilise protsessina, mis on oluline kütuseelemendis rakendamise seisukohalt. Antud katalüsaatormaterjali hapniku redutseerumise aktiivsuse olulisimaks põhjuseks leiti olevat materjali struktuuri pürolüüsi käigus viidud aktiivsed lämmastikurühmad ja siirdemetall
The aim of the present PhD thesis was to prepare and characterise the aryl film modified carbon and metal electrodes and in addition, the nonprecious metal (NPM) catalysts. The surface of the prepared electrodes was investigated by several physical and electrochemical methods (e.g. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), cyclic voltammetry and the rotating disc electrode (RDE) method). The first and the second part of the PhD thesis describe the spontaneous and electrochemical modification of carbon and metal electrodes with 9,10-anthraquinone (AQ) and 4-nitrophenyl (NP) groups using the aryldiazonium salt reduction method. For the electrochemical functionalisation, the “normal” electrografting, redox grafting (RG) and the RG and RDE combined methods were used. The presence of the aryl groups on the electrodes was ascertained by the XPS and AFM experiments. Additionally, the influence of the aryl film on the oxygen reduction reaction (ORR) activity and towards the Fe(CN)63/4 redox probe was studied. It was found that for the preparation of thicker films with higher amount of electroactive aryl groups, the RG and RDE combined method was beneficial. Via latter method, the highest known amount of electroactive AQ groups was obtained in the aryl films on glassy carbon, Au and Cu electrodes and also, the thickest film of 47 nm was prepared by this method in case of NP film modified Cu electrode. In the last part of the PhD thesis, the ORR was studied on polymer based carbon nanotube containing composites and on the siliconoxycarbide based materials for the application as NPM catalysts. The highest ORR activity was obtained in case of transition metal (Co) and nitrogen containing siliconoxycarbide material. On the latter catalyst material the ORR proceeds via 4-electron pathway that is crucial for the fuel cell applications. The high ORR performance of the latter catalyst was attributed to the introduction of N-functionalities and transition metal into the material during the pyrolysis.
The aim of the present PhD thesis was to prepare and characterise the aryl film modified carbon and metal electrodes and in addition, the nonprecious metal (NPM) catalysts. The surface of the prepared electrodes was investigated by several physical and electrochemical methods (e.g. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), cyclic voltammetry and the rotating disc electrode (RDE) method). The first and the second part of the PhD thesis describe the spontaneous and electrochemical modification of carbon and metal electrodes with 9,10-anthraquinone (AQ) and 4-nitrophenyl (NP) groups using the aryldiazonium salt reduction method. For the electrochemical functionalisation, the “normal” electrografting, redox grafting (RG) and the RG and RDE combined methods were used. The presence of the aryl groups on the electrodes was ascertained by the XPS and AFM experiments. Additionally, the influence of the aryl film on the oxygen reduction reaction (ORR) activity and towards the Fe(CN)63/4 redox probe was studied. It was found that for the preparation of thicker films with higher amount of electroactive aryl groups, the RG and RDE combined method was beneficial. Via latter method, the highest known amount of electroactive AQ groups was obtained in the aryl films on glassy carbon, Au and Cu electrodes and also, the thickest film of 47 nm was prepared by this method in case of NP film modified Cu electrode. In the last part of the PhD thesis, the ORR was studied on polymer based carbon nanotube containing composites and on the siliconoxycarbide based materials for the application as NPM catalysts. The highest ORR activity was obtained in case of transition metal (Co) and nitrogen containing siliconoxycarbide material. On the latter catalyst material the ORR proceeds via 4-electron pathway that is crucial for the fuel cell applications. The high ORR performance of the latter catalyst was attributed to the introduction of N-functionalities and transition metal into the material during the pyrolysis.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
süsinikelektroodid, metallelektroodid, süsiniknanotorud, komposiitmaterjalid, hapnik, elektrokeemiline reduktsioon