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Carbon based Artificial Leaf for SOLar fuel production

Periodic Reporting for period 1 - CALSOL (Carbon based Artificial Leaf for SOLar fuel production)

Reporting period: 2018-10-01 to 2020-09-30

The newly formed European Commission accommodated the United Nations Sustainable Development Goals 7 (affordable and clean energy) and 13 (climate action) into what is now referred to as the European Green Deal with the chief-aim of being the world’s first climate-neutral continent by 2050. Before the European Green Deal, the goals for 2020 were: (1) to cut greenhouse gasses by 20% (from the 1990 levels), (2) increase the share of renewables to a total of 20% and (3) improve the energy efficiency by 20% which were challenging to achieve. However, the current 2030 action plan is planning: (1) to further cut the greenhouse gasses by 40% (from the 1990 levels), (2) raise the share of renewables to 32% and (3) enhance the energy efficiency by 32.5%. Such ambitious goals can be met only by technologies that make use of renewable energy. Sun driven electrochemical reactions, such as (1) photocatalytic environmental remediation, (2) photoelectrochemical water splitting to generate hydrogen fuel and (3) photoelectrochemical carbon dioxide reduction to produce chemical feedstocks, will have the utmost importance in achieving sustainability. The electron-hole pair generated by illuminated semiconductors are the key in unlocking the full potential of photoelectrochemistry. Further on, the attention was focused on finding cheap and abundant materials such as polymeric carbon nitride which has been in the spotlight for more than a decade. In this respect, the action at-hand aimed at:
1. Designing a new carbon nitride with a suitable electron band structure
2. Explore multi-site carbon dioxide reaction reaction at metal/carbon nitride composites
Two different carbon nitride synthesis routes were tried in the action at-hand: (1) the traditional thermal polycondensation route and (2) a plasma polymerization route. The traditional route is firstly discussed which is based on the manuscript in submission to ACS Catalysis. Then, the discussion is moved towards the plasma polymerized carbon nitride. The last part of this section discusses the preparation of metal catalysts and the metal/carbon nitride assembly.

The results were exploited by the ER in 1 national project application, 1 Romanian-Norwegian application and 1 H2020-Twinning. Such a network will generate new ideas and expand the knowledge in CRR until a critical mass is reached to influence policymakers.
There were 2 main contributions to the state of the art (SoA). Firstly, the product of thermal polycondensation of melamine has been shown irrefutably that is not graphitic carbon nitride. The results of this action showed that the melon structure is more accurate than C3N4, however, melon is not the ideal structure. It has been concluded that the result of thermal polycondensation of melamine is a defective melon structure which was shown to degrade considerably during photoelectrochemical experiments which was the reason for looking into new synthesis routes. Secondly, the importance of photoelectrode stability is emphasized in Figure 9 which shows the dependence of the flatband potential as a function of pH. The flatband potential can be determined from the Mott-Schottky plots which can be equivalated to the conduction band in the case of carbon nitride. Figure 9 clearly shows that the flatband potential decreases from approx. -1.5 V vs. Ag/AgCl to -1.8 vs. Ag/AgCl. This pH dependence means that the electron band structure of carbon nitrides is continuously changing and a change in the bandgap is expected after prolonged use.