Sinteza in karakterizacija z dušikom dopiranega termično obdelanega grafen oksida

Skočir, Žiga (author), Genorio, Boštjan (mentor)

Uporaba fosilnih goriv, kot primarnega vira energije, je v zadnjih desetletjih močno vplivala na povečanje koncentracije CO2 v ozračju. Globalno segrevanje tako postaja vedno večja nevarnost. Eden izmed alternativnih virov goriv je vodik, ki se uporablja kot gorivo v gorivnih celicah, kjer poteka reakcija med vodikom in kisikom, ki reagirata do vode. Glavna prednost gorivnih celic je, da ne proizvajajo CO2. Njihova glavna slabost pa je cena, ki izvira predvsem iz cene katalizatorja. Trenutno se v gorivnih celicah za katalizator uporablja platino, ki je zelo draga saj je na zemlji ni v izobilju. Zaradi tega se v zadnjih letih išče cenovno bolj ugodno alternativo platine, ki bo imela primerljive elektrokatalitske lastnosti kot platina. Grafen in njegove modifikacije trenutno izkazujejo dober potencial za zamenjavo platinskega katalizatorja, še posebno dobre lastnosti ima z dušikom dopiran grafen (N-grafen). V sklopu raziskave smo razvili in postavili nov sistem za sintezo N-grafena, kjer sinteza poteče v nekaj minutah. Vzorce sem sintetiziral iz štirih različnih začetnih prekurzorjev, in sicer uporabljena sta bila dva različna tipa grafita (KS44 in KS6L) in dva različna tipa več stenskih ogljikovih nanocevk (C-grade in M-grade). Vzorci so bili predhodno oksidirani z izboljšano Hummers metodo do grafen oksida in grafen oksidnih nanotrakov. Te oksidirane vzorce sem nato dopiral s pirolizo v NH3 atmosferi pri temperaturah 800°C, 1000°C in 1200°C. Tako pripravljene vzorce sem primerjal z nedopiranimi vzorci, ki so bili pripravljeni s pirolizo v dušikovi atmosferi. Nova sinteza se je izkazala za uspešno. S hitrejšim segrevanjem smo pridobili vzorce z višjo specifično površino in deležem dušika. Vsi vzorci so zaradi novega pristopa izražali boljše elektrokatalitske lastnosti. Elektrokatalitske lastnosti vzorcev sem primerjal tako v kislem kot alkalnem mediju. Vsi vzorci so imeli boljšo stabilnost in aktivnost na reakcijo redukcije kisika (ORR) v alkalnem mediju. Medtem pa so imeli vzorci boljšo selektivnost na 4-elektronski način redukcije kisika v kislem mediju. Vzorec z najboljšimi elektrokatalitskimi lastnosti je bil v obeh medijih dopiran vzorec sintetiziran iz M-grade tipa več stenskih ogljikovih nanocevk.

• Language: Slovenian
• Keywords: elektrokatalizator, gorivne celice, N-dopiran grafen, reakcija redukcije kisika (ORR)
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2022
• PID: 20.500.12556/RUL-136672
• COBISS.SI-ID: 108503555
• Publication date in RUL: 13.05.2022

Secondary language

• Language: English
• Title: Synthesis and characterization of thermally treated nitrogen doped graphene oxide

Abstract

The use of fossil fuels as a primary energy source has had a strong impact on increased concentration levels of CO2 in the atmosphere in recent decades. However, global warming is increasingly becoming a major threat. One of the alternative sources of fossil fuels is hydrogen, which is used as a fuel in fuel cells. Here, energy is obtained by converting chemical energy into electricity. In a fuel cell, a reaction takes place between hydrogen and oxygen, which reacts to water. The main advantage of fuel cells is that they do not produce CO2. Their main disadvantage, however, is the price, which stems mainly from the price of the catalyst. Currently, platinum is used as a catalyst in fuel cells, which is very expensive as it is not abundant on Earth. As a result, a more cost-effective alternative to platinum, which will have comparable electrocatalytic properties to platinum, has been sought in recent years. Graphene and its modifications currently show good potential for platinum catalyst replacement, especially nitrogen-doped graphene (N-graphene). As part of my research, we developed and set up a new N-graphene synthesis system where the synthesis takes place in just a few minutes. I synthesized the samples from four different initial precursors, namely, two different types of graphite (KS44 and KS6L) and two different types of multi-walled carbon nanotubes (C-grade and M-grade) were used. The samples were pre-oxidized by the improved Hummers method to graphene oxide and graphene oxide nanoribbons. The oxidized samples were then doped by pyrolysis in an NH3 atmosphere at temperatures 800°C, 1000°C and 1200°C. I compared these samples with undoped samples prepared by pyrolysis under a nitrogen atmosphere. The new synthesis proved to be successful, with faster heating we obtained samples with a higher specific surface area and nitrogen content. All samples exhibited better electro-catalytic properties due to the new synthesis. I compared the electro-catalytic properties of the samples in acidic and alkaline media. All samples had better stability and activity for ORR in alkaline medium. Meanwhile, the samples had better selectivity for 4-electron pathway ORR in acidic medium. The sample with the best electrocatalytic properties was the doped sample synthesized from the M-grade type of multi-walled carbon nanotubes in both media.

• Keywords: electro-catalysis, fuel cells, N-graphene, oxygen reduction reaction (ORR)