Max-Planck-Institut für Kolloid-und Grenzflächenforschung Chemical Functionalization of Porous Carbon-based Materials to Enable Novel Modes for Efficient Electrochemical N2 fixation Dissertation zur Erlangung des akademischen Grades Doktor der Naturwissenschaften (Dr. rer. nat.) in der Wissenschaftsdisziplin „Kolloidchemie“ eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Potsdam von Qing Qin geboren am 09.10.1993 in Anhui, China Potsdam-Golm, im September 2019 1 Acknowledgement Although words alone are not enough to give the appropriate gratitude to all people whom stood beside me and supported me during my PhD studies, I would like to express my most sincere acknowledgement to the efforts of these people. Firstly, I want to express my deep acknowledgement to my great supervisor Dr. Martin Oschatz, the group leader in our carbon group and as well as a professor in replacement at Potsdam University. I really enjoyed the discussions with him about science, which nurtured my passion for carbon and encouraged me to embark on the path of academic area. I am sincerely thankful to his efforts, suggestions, and support towards my research topics and revision of my papers and thesis. If not for his motivation, dedication and energy, this study and many others not covered in this thesis would undoubtedly never achieve fruition. Beyond science, two important things that he taught me in the life are to be strong and patient. Thanks, Martin! I always feel privileged to be his PhD student. Thanks to Prof. Dr. Yan Lu in Helmholtz-Center Berlin for Materials and Energy for being my second supervisor, discussing about my research topic, and reviewing this thesis. Great thanks to the group members in my carbon group. Many thanks to Runyu, who is the first friend I made in MPI, and he helped me a lot not only in the life, but also in the experiment. Great thanks to Milena for helping me a lot when I first came to this unknown country, listening to my complains, sharing my happiness, and telling me more about Germen culture and rules. Great thanks to Ipek, a lovely girl who always looks happy, for the help and valuable friendship. Great thanks to Ralf for the 2 Raman and gas adsorption measurement. Many thanks to Konstantin, Feili, Sandy and Sol as well. It is really my great honor to meet and make friends with them. I love my carbon group! I would like to show thanks to my good friend and collaborator of Dr. Yun Zhao from the Leibniz Institute for Catalysis, who helped me to do the DFT calculations and discuss the results with me. Also many thanks to Dr. Haijun Jiao, as he provided many useful suggestions for paper polishing and improvements of DFT calculations. Besides, I want to thank Max Schmallegger in Graz University of Technology for the EPR measurements and discussion of the results. Great thanks to Jianrui, who can always share my happiness or sadness. Because of you, my life becomes more colorful and is thus full of fun. Many thanks to Qian, my good friend and my sister in MPI. She is also an excellent hair dresser. Thanks for the warm accompany and haircut. I am very grateful to Ines and Ursula for the lab organization, which provides a clean and convenient environment for the research work. Great thanks to Tobias for measuring TEM, patiently discussing my projects, and teaching me a lot of knowledge about TEM. Many thanks to Antje for the TGA and elemental analysis, Johannes for XPS measurements, Heike and Rona for the SEM and TEM measurements, Elinor and Ursula for the electrospinning. Thanks to Sasha, Clemens and Ryan for giving me the access to the facilities in their labs. Many thanks to my friends and very nice colleagues (Nieves, Jose, Marius, Lana, Paolo, Jin, Barius, Zhihong, etc.) in MPI, especially the meal pals (Guigang, Kai, Shaowen, Ang, Shuangyan, etc.) to Potsdam University every day, who have contributed to make my life here a great and memorable experience. 3 I would like to thank my idol, Bibi Zhou, who is a famous singer in China. I have loved her for 14 years since 2005. Daily life is always so trivial, but her figure fills up every stage of my youth. What is an idol and what does an idol mean? Everyone may have his or her own answer. For me, Bibi is my life mentor and source of positive energy. Her good personalities and attitudes towards life and dream have a deep influence on me. She is like the brightest star in my world to guide me to search for the light and hope. Every time I felt sad, lonely or stressed, her music and smile made me feel much better. The long distance between Germany and China, as well as the high workload made it impossible to attend most of her fans meeting activities and concerts. But on 11th November in 2018, she came to Germany. That had to be the most valuable gift and surprise for me. So life is wonderful, right? Thank you, Bibi, for warming my whole life. Special thanks to my beloved and dear parents for their encouragement, accompany, patience and love. Although they cannot speak English and have no idea about my research, they try their best to support and encourage me to do what I want, and make me never feel alone. Many thanks to my grandparents, aunts, uncles, cousins and so on for all their love and help. The support of my good friends in China (Zhu, Meimei, Id, Xiaojing, Liting, Yu, Lu, Ling, Wuyong, Lei, Bei, Shuqi, etc.) also makes my life funnier, meaningful, and easier to keep on moving forward. Deep thanks to Liuliu for the always warm accompany and sharing of all my emotions. I thank my committee members and reviewers for their valuable suggestions and time. 4 Deep thanks to the Max Planck Institute of Colloids and Interfaces and the Excellence Cluster “UniSysCat” for funding my research projects and travel expenses for the different conferences. Great thanks to everyone I have met along the way. Thanks for all the love and injury in my life. Finally, I would like to acknowledge my senior supervisor of Prof. Dr. Dr. h. c. Markus Antonietti, the director of the Colloid Chemistry Department of the Max Planck Institute of Colloids and Interfaces, for providing me the precious opportunity to pursue my doctorate here and acting as a role model for me not only in academics but also in life. I really enjoy the discussion with him, and his profound knowledge and patient guidance can always enlighten me. His good suggestions can also lead me to a more deep and systematic study of my research topics. With his encouragement, I finally make a plan for my future and I will try my best to achieve all my goals. I hope to be an excellent QQ, and to be one of his best PhD students. 5 Table of Contents 1. Motivation ............................................................................................................................. 9 2. Background and outline ..................................................................................................... 13 2.1. An overview over carbon and carbon nanomaterials .............................................. 13 2.2. An overview over porous amorphous carbon materials .......................................... 14 2.2.1. Synthesis of porous carbon materials ................................................................. 15 2.2.2. Functionalization of porous carbon materials ................................................... 18 2.3. Brief introduction of NH3 synthesis ........................................................................... 20 2.3.1. Haber-Bosch process ............................................................................................ 21 2.3.2. Biological process .................................................................................................. 23 2.3.3. Photochemical N2 fixation .................................................................................... 24 2.3.4. Electrochemical N2 fixation .................................................................................. 25 2.4. Main challenges for electrochemical N2 fixation ...................................................... 29 2.4.1. Selectivity, activity and stability .......................................................................... 29 2.4.2. Reaction mechanism ............................................................................................. 30 2.5. Outline .......................................................................................................................... 31 3. Enhanced electrocatalytic N2 reduction via partial anion substitution in titanium oxide- carbon composites .................................................................................................................. 33 3.1. Synthesis and characterization of M-Ts .................................................................... 35 3.2. Experimental studies of NRR active sites in M-Ts ................................................... 47 3.3. Mechanism studies through DFT calculations (in collaboration with Dr. Yun Zhao and Dr Haijun Jiao) ............................................................................................................ 59 4. Single-site gold catalysts on hierarchical N-doped porous noble carbon for enhanced electrochemical reduction of nitrogen .................................................................................. 65 4.1. Synthesis and characterization of AuSAs-NDPCs .................................................... 66 4.2. Influence of Au single sites on the NRR performance ............................................. 72 6