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Conducting, functional polymers from bio-organic molecules for catalysis / submitted by DI. Halime Coskun Aljabour
AuthorCoskun Aljabour, Halime
CensorSariciftci, Niyazi Serdar ; Paulik, Christian
Thesis advisorSariciftci, Niyazi Serdar
PublishedLinz, 2018
Description98 Blätter : Illustrationen
Institutional NoteUniversität Linz, Dissertation, 2018
In Zusammenarbeit mit dem Institut für Physikalische Chemie
Document typeDissertation (PhD)
Keywords (DE)leitfähige, funktionelle Polymere / Katalyse
Keywords (EN)conducting, functional polymers / catalysis
URNurn:nbn:at:at-ubl:1-25872 Persistent Identifier (URN)
 The work is publicly available
Conducting, functional polymers from bio-organic molecules for catalysis [5.67 mb]
Abstract (English)

The utilization of bio-inspired, polymer-based materials in the field of catalysis can help to resolve relevant energy questions in the 21th century. This work is dedicated to the design and engineering of electrocatalysts for carbon dioxide reduction reaction (CO2RR) and hydrogen evolution reaction (HER) using bio-derived, hydrogen-bonded systems, that exhibit heterogenous catalytic activity. These will be important as sustainable systems, which are shown here to exhibit tremendous performance. In light of todays dependence on expensive and rare noble metals, it is of outmost interest to develop alternative polymeric and non-metallic contenders, which will replace metals and thus increase the catalyst material pool and the catalyst versatility. The here demonstrated electrocatalytic polymers are low-cost and bio-inspired, have low environmental impact and at the same time offer similar stability as noble metals but also tunable physical-electronic properties. Combined with their bio-compatibility they will be a future emerging material class in the field of electrocatalysis. The focus of this thesis has been to generate polymers with superior catalytic activity and therefore their electronic properties have been improved, in particular their intrinsically low capability to transport electrons. In their initial state, most biopolymers are insulators. In this work, a novel synthesis path is shown to create doped conductive biopolymers with excellent catalytic activity and long-term stability. The synthesis of two conductive and electrocatalytic biopolymers is presented: these are first polydopamine (PDA) as a derivative of the naturally occurring pigment eumelanin, and, second, polyguanine (PG), a purine base and component of the desoxyribonucleic acid (DNA), which adopted an emeraldine-related structure. Both biopolymers have been applied as electrocatalysts for CO2RR and/or HER. The synthesis pathway from the monomers to the conductive and functional biopolymers is described using a facile one-step oxidative chemical vapor deposition (o-CVD) technique. This has been the crucial effort to unit polymerization and doping leading to the desired electrically conductive biopolymers in a single step reaction without compromising on the organic functionality remaining unchanged on the polymer backbone. Besides replacing the metal catalysts by organic units, the main motivation in this work was to mimic natural phenomena by using artificial biopolymers. Therefore, polydopamine was firstly applied as an electrocatalyst for CO2RR to convert the anthropogenic carbon dioxide emissions into useful chemical feedstock. The catalytic effect driven by hydrogen-bonded functional motifs resulted in significant electrocatalytic performance with almost > 90 % Faraday efficiency and a geometric current density of 18 mA cm-2 at 210 mV overpotential. Besides the CO2 reduction productions leading to CO and formate, hydrogen was also produced as a side-product at neutral pH. This result gave the hint, that hydrogen could be evolved by the PDA catalyst, when the polymer is further re-designed. In the next approach, such structurally modified PDA was applied in HER in an acidic medium showing excellent HER performance with a Tafel slope of 80 mV dec-1 and an overpotential of -190 mV vs. reversible hydrogen electrode (RHE) at 10 mA cm-2 and stable catalytic activity demonstrated by an initial 168 hours electrolysis. More important, scaled continuous-flow electrolysis was exhibited, producing 1 L of molecular hydrogen within less than 9 hours using 2.3 mg of biopolymer electrocatalyst. In order to confirm the proof-of-principle of catalytic activity in biopolymers containing organic themes, an alternative concept was sought: polyguanine (PG) is synthesized similarly to PDA and utilized it as HER electrocatalyst. Its ability to bind protons similar to the emeraldine form of polyaniline led to a signficiant HER activity with a Tafel slope as low as 80 mV dec-1 at an overpotential of -290 mV vs. RHE at 10 mA cm-2 and 80 hours of continuous electrolysis. The idea of employing biopolymers in various heterogenous electrocatalytic applications reveals that these emerging materials will be promising candidates for future sustainable energy conversion catalysts.

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